On Tue, Dec 12, 2023 at 1:05 PM Naveen Yerramneni
<[email protected]> wrote:
>
>     This patch contains changes to enable DHCP Relay Agent support for 
> overlay subnets.
>
>     USE CASE:
>     ----------
>       - Enable IP address assignment for overlay subnets from the centralized 
> DHCP server present in the underlay network.
>
>     PREREQUISITES
>     --------------
>       - Logical Router Port IP should be assigned (statically) from the same 
> overlay subnet which is managed by DHCP server.
>       - LRP IP is used for GIADRR field when relaying the DHCP packets and 
> also same IP needs to be configured as default gateway for the overlay subnet.
>       - Overlay subnets managed by external DHCP server are expected to be 
> directly reachable from the underlay network.
>
>     EXPECTED PACKET FLOW:
>     ----------------------
>     Following is the expected packet flow inorder to support DHCP rleay 
> functionality in OVN.
>       1. DHCP client originates DHCP discovery (broadcast).
>       2. DHCP relay (running on the OVN) receives the broadcast and forwards 
> the packet to the DHCP server by converting it to unicast. While forwarding 
> the packet, it updates the GIADDR in DHCP header to its
>          interface IP on which DHCP packet is received.
>       3. DHCP server uses GIADDR field to decide the IP address pool from 
> which IP has to be assigned and DHCP offer is sent to the same IP (GIADDR).
>       4. DHCP relay agent forwards the offer to the client, it resets the 
> GIADDR field when forwarding the offer to the client.
>       5. DHCP client sends DHCP request (broadcast) packet.
>       6. DHCP relay (running on the OVN) receives the broadcast and forwards 
> the packet to the DHCP server by converting it to unicast. While forwarding 
> the packet, it updates the GIADDR in DHCP header to its
>          interface IP on which DHCP packet is received.
>       7. DHCP Server sends the ACK packet.
>       8. DHCP relay agent forwards the ACK packet to the client, it resets 
> the GIADDR field when forwarding the ACK to the client.
>       9. All the future renew/release packets are directly exchanged between 
> DHCP client and DHCP server.
>
>     OVN DHCP RELAY PACKET FLOW:
>     ----------------------------
>     To add DHCP Relay support on OVN, we need to replicate all the behavior 
> described above using distributed logical switch and logical router.
>     At, highlevel packet flow is distributed among Logical Switch and Logical 
> Router on source node (where VM is deployed) and redirect chassis(RC) node.
>       1. Request packet gets processed on the source node where VM is 
> deployed and relays the packet to DHCP server.
>       2. Response packet is first processed on RC node (which first recieves 
> the packet from underlay network). RC node forwards the packet to the right 
> node by filling in the dest MAC and IP.
>
>     OVN Packet flow with DHCP relay is explained below.
>       1. DHCP client (VM) sends the DHCP discover packet (broadcast).
>       2. Logical switch converts the packet to L2 unicast by setting the 
> destination MAC to LRP's MAC
>       3. Logical Router receives the packet and redirects it to the OVN 
> controller.
>       4. OVN controller updates the required information(GIADDR) in the DHCP 
> payload after doing the required checks. If any check fails, packet is 
> dropped.
>       5. Logical Router converts the packet to L3 unicast and forwards it to 
> the server. This packets gets routed like any other packet (via RC node).
>       6. Server replies with DHCP offer.
>       7. RC node processes the DHCP offer and forwards it to the OVN 
> controller.
>       8. OVN controller does sanity checks and  updates the destination MAC 
> (available in DHCP header), destination IP (available in DHCP header), resets 
> GIADDR  and reinjects the packet to datapath.
>          If any check fails, packet is dropped.
>       9. Logical router updates the source IP and port and forwards the 
> packet to logical switch.
>       10. Logical switch delivers the packet to the DHCP client.
>       11. Similar steps are performed for Request and Ack packets.
>       12. All the future renew/release packets are directly exchanged between 
> DHCP client and DHCP server
>
>     NEW OVN ACTIONS
>     ---------------
>
>       1. dhcp_relay_req(<relay-ip>, <server-ip>)
>           - This action executes on the source node on which the DHCP request 
> originated.
>           - This action relays the DHCP request coming from client to the 
> server. Relay-ip is used to update GIADDR in the DHCP header.
>       2. dhcp_relay_resp_fwd(<relay-ip>, <server-ip>)
>           - This action executes on the first node (RC node) which processes 
> the DHCP response from the server.
>           - This action updates  the destination MAC and destination IP so 
> that the response can be forwarded to the appropriate node from which request 
> was originated.
>           - Relay-ip, server-ip are used to validate GIADDR and SERVER ID in 
> the DHCP payload.
>
>     FLOWS
>     -----
>     Following are the flows required for one overlay subnet.
>
>       1. table=27(ls_in_l2_lkup      ), priority=100  , match=(inport == 
> <vm_port> && eth.src == <vm_mac> && ip4.src == 0.0.0.0 && ip4.dst == 
> 255.255.255.255 && udp.src == 68 && udp.dst == 67), 
> action=(eth.dst=<lrp_mac>;outport=<lrp-port>;next;/* DHCP_RELAY_REQ */)
>       2. table=3 (lr_in_ip_input     ), priority=110  , match=(inport == 
> <lrp_port> && ip4.src == 0.0.0.0 && ip4.dst == 255.255.255.255 && udp.src == 
> 68 && udp.dst == 67), 
> action=(dhcp_relay_req(<lrp_ip>,<dhcp_server_ip>);ip4.src=<lrp_ip>;ip4.dst=<dhcp_server_ip>;udp.src=67;next;
>  /* DHCP_RELAY_REQ */)
>       3. table=3 (lr_in_ip_input     ), priority=110  , match=(ip4.src == 
> <dhcp_server_ip> && ip4.dst ==<lrp_ip> && udp.src == 67 && udp.dst == 67), 
> action=(next;/* DHCP_RELAY_RESP */)
>       4. table=17(lr_in_dhcp_relay_resp_fwd), priority=110  , match=(ip4.src 
> == <dhcp_server_ip> && ip4.dst == <lrp_ip> && udp.src == 67 && udp.dst == 
> 67), 
> action=(dhcp_relay_resp_fwd(<lrp_ip>,<dhcp_server_ip>);ip4.src=<lrp_ip>;udp.dst=68;outport=<lrp_port>;output;
>  /* DHCP_RELAY_RESP */)
>
>     NEW PIPELINE STAGES
>     -------------------
>     Following stage is added for DHCP relay feature. Some of the flows are 
> fitted into the existing pipeline tages.
>       1. lr_in_dhcp_relay_resp_fwd
>           - Forward teh DHCP response to the appropriate node
>
>     NB SCHEMA CHANGES
>     ----------------
>       1. New DHCP_Relay table
>           "DHCP_Relay": {
>                 "columns": {
>             "name": {"type": "string"},
>                     "servers": {"type": {"key": "string",
>                                            "min": 0,
>                                            "max": 1}},
>                     "external_ids": {
>                         "type": {"key": "string", "value": "string",
>                                 "min": 0, "max": "unlimited"}}},
>                 "isRoot": true},
>       2. New column to Logical_Router_Port table
>           "dhcp_relay": {"type": {"key": {"type": "uuid",
>                                 "refTable": "DHCP_Relay",
>                                 "refType": "weak"},
>                                 "min": 0,
>                                 "max": 1}},
>       3. New column to Logical_Switch_table
>           "dhcp_relay_port": {"type": {"key": {"type": "uuid",
>                                         "refTable": "Logical_Router_Port",
>                                         "refType": "weak"},
>                                          "min": 0,
>                                          "max": 1}}},
>
>     Commands to enable the feature:
>     ------------------------------
>       - ovn-nbctl create DHCP_Relay servers=<ip>
>       - ovn-nbctl set Logical_Router_port <lrp_uuid> 
> dhcp_relay=<dhcp_relay_uuid>
>       - ovn-nbctl set Logical_Switch <ls_uuid> dhcp_relay_port=<lrp_uuid>
>
>     Example:
>     -------
>      ovn-nbctl ls-add sw1
>      ovn-nbctl lsp-add sw1 sw1-port1
>      ovn-nbctl lsp-set-addresses sw1-port1 <MAC> #Only MAC address has to be 
> specified when logical ports are created.
>      ovn-nbctl lr-add lr1
>      ovn-nbctl lrp-add lr1 lr1-port1 <MAC> <GATEWAY_IP/Prefix> #GATEWAY IP is 
> set in GIADDR field when relaying the DHCP requests to server.
>      ovn-nbctl lsp-add sw1 lr1-attachment
>      ovn-nbctl lsp-set-type lr1-attachment router
>      ovn-nbctl lsp-set-addresses lr1-attachment <MAC>
>      ovn-nbctl lsp-set-options lr1-attachment router-port=lr1-port1
>      ovn-nbctl create DHCP_Relay servers=<DHCP_SERVER_IP>
>      ovn-nbctl set Logical_Router_port <lrp_uuid> dhcp_relay=<relay_uuid>
>      ovn-nbctl set Logical_Switch <ls_uuid> dhcp_relay_port=<lrp_uuid>
>
>     Limitations:
>     ------------
>       - All OVN features that needs IP address to be configured on logical 
> port (like proxy arp, etc) will not be supported for overlay subnets on which 
> DHCP relay is enabled.
>
>     References:
>     ----------
>       - rfc1541, rfc1542, rfc2131
>
> Signed-off-by: Naveen Yerramneni <[email protected]>
> Co-authored-by: Huzaifa Calcuttawala <[email protected]>
> Signed-off-by: Huzaifa Calcuttawala <[email protected]>
> CC: Mary Manohar <[email protected]>

Hi Naveen,

Thanks for the patch.  Sorry for the delayed response.

I've a few comments.

1.  Regarding the newly added Table - DHCP_Relay in NB DB and the
newly added columns in Logical_Switch and
    Logical_Router table.

    I don't think there is a need to add the new table DHCP_Relay
since it only stores the dhcp relay agent server ip.
    Also it could complicate the northd incremental processing.

    If for example we have below logical switches and router

    ovn-nbctl lr-add R1
    ovn-nbctl ls-add sw0
    ovn-nbctl ls-add sw1
    ovn-nbctl ls-add sw-ext
    ovn-nbctl lrp-add R1 rp-sw0 00:00:01:01:02:03 192.168.1.1/24
    ovn-nbctl lrp-add R1 rp-sw1 00:00:03:01:02:03 192.168.2.1/24
    ovn-nbctl lrp-add R1 rp-ext 00:00:02:01:02:03 172.16.1.254/24

    ovn-nbctl lsp-add sw0 sw0-rp -- set Logical_Switch_Port sw0-rp \
    type=router options:router-port=rp-sw0 \
    -- lsp-set-addresses sw0-rp router

    ovn-nbctl lsp-add sw1 sw1-rp -- set Logical_Switch_Port sw1-rp \
    type=router options:router-port=rp-sw1 \
    -- lsp-set-addresses sw1-rp router

    I'd suggest doing something like below to enable this feature.

    ovn-nbctl set Logical_Switch_Port sw0-rp options:dhcp_relay=true
    ovn-nbctl set Logical_Switch_Port sw1-rp options:dhcp_relay=true

    (Make sure that only one logical switch port of type router can
have this flag - dhcp_relay set
     for a given logical switch and document this limitation.)

    ovn-nbctl set Logical_Router_port rp-sw0 options:dhcp_relay_ip=172.16.1.1
    ovn-nbctl set Logical_Router_port rp-sw1 options:dhcp_relay_ip=172.16.1.1

    Let me know if there are any limitations with this.

2.  Regarding the newly added actions - dhcp_relay_req() and
dhcp_relay_resp_fwd().
     Both of these actions are encoded as OVS controller action with
pause enabled.
     Which means ovs-vswitchd has to freeze the flow translation and
resume the flow translation
     once the ovn-controller resumes it.  But the functions
pinctrl_handle_dhcp_relay_req()
     and pinctrl_handle_dhcp_relay_resp_fwd() do not resume the packet
if the packet
     has some errors.  This is wrong.  Otherwise vswitchd will never thaw the
     frozen translation.

     You can see the existing OVN actions - put_dhcp_opts() and few others which
     use controller action with pause.  In such actions, the result of
these actions
     are stored in a register bit (i.e if put_dhcp_opts() was successful or not)
     and in the next stage we take a decision based on the result.

     For the action dhcp_relay_req(relay_ip, server_ip),  I don't
think you should use the pause flag.
     Also in this action the argument server_ip is never used in the
function pinctrl_handle_dhcp_relay_req()
     other than to just log.

     I'd suggest you do something like this:

    table=3 (lr_in_ip_input     ), priority=110  , match=(inport ==
"lrp1" && ip4.src == 0.0.0.0 && ip4.dst == 255.255.255.255 && udp.src
== 68 && udp.dst == 67),
    action=(dhcp_relay_req { ip4.src = 192.168.1.1; ip4.dst =
172.16.1.1; udp.src = 67; dhcp_header.giaddr = <relay_ip>;
next(pipeline=ingress,table=S_ROUTER_IN_UNSNAT);  /* DHCP_RELAY_REQ */
}

    dhcp_relay_req action would get translated into a controller
action with pause=false and all the inner actions of this are encoded
as
    normal actions and stored in the userdata of controller action.
Please see icmp4_error {} as an example.
    Add a new OVN field 'dhcp_header.giaddr' which gets translated as
controller action with pause flag set.
    Please see the existing OVN field - icmp4.frag_mtu as an example
and see this commit for reference [1]
    When encoding this new OVN field, store the relay_ip in the
userdata buffer and in pinctrl.c
    get the relay_ip value and store it in the dhcp header field.


    For the action dhcp_relay_resp_fwd,  I'd suggest something like below:

      table=17 (lr_in_dhcp_relay_resp_chk), priority=110  ,
match=(ip4.src == 172.16.1.1 && ip4.dst == 192.168.1.1 && udp.src ==
67 && udp.dst == 67),
      action=(reg0[0] = dhcp_relay_resp_chk(dhcp_header.giaddr ==
<relay_ip>); next;)
      table=17 (lr_in_dhcp_relay_resp), priority=110  , match=(ip4.src
== 172.16.1.1 && ip4.dst == 192.168.1.1 && udp.src == 67 && udp.dst ==
67 && reg0[0] == 1),
      action=(ip4.src = 192.168.1.1; udp.dst = 68; outport = "lrp1";
output; /* DHCP_RELAY_RESP */)

       I used reg0[0] as an example.  You may need to check the free
register bit and use it.

      You need to encode dhcp_relay_resp_chk as controller action with
pause=true, and store the relay_ip in the userdata buffer.
      And in pinctrl.c  check that  'dhcp_header.giaddr == relay_ip'
or not.  If so, set the result register bit to 1, else to 0.

   Let me know if you've any questions.

3.  The newly added functions in pinctrl.c have a lot of repetitive
code and it is very much similar to existing
pinctrl_handle_put_dhcp_opts()
    Please see if the duplicate code can be avoided.

[1] - 
https://github.com/ovn-org/ovn/commit/3d9fec3fd5992e1201b4d4fdf43f1f397e8d5ea1

Thanks
Numan

> ---
>  controller/pinctrl.c  | 441 ++++++++++++++++++++++++++++++++++++++++++
>  include/ovn/actions.h |  26 +++
>  lib/actions.c         | 117 +++++++++++
>  lib/ovn-l7.h          |   1 +
>  northd/northd.c       | 177 ++++++++++++++++-
>  ovn-nb.ovsschema      |  25 ++-
>  ovn-nb.xml            |  28 +++
>  tests/atlocal.in      |   3 +
>  tests/ovn-northd.at   |  41 +++-
>  tests/ovn.at          |  12 +-
>  tests/system-ovn.at   | 150 ++++++++++++++
>  utilities/ovn-trace.c |  28 +++
>  12 files changed, 1032 insertions(+), 17 deletions(-)
>
> diff --git a/controller/pinctrl.c b/controller/pinctrl.c
> index 5a35d56f6..45240f01d 100644
> --- a/controller/pinctrl.c
> +++ b/controller/pinctrl.c
> @@ -1897,6 +1897,437 @@ is_dhcp_flags_broadcast(ovs_be16 flags)
>      return flags & htons(DHCP_BROADCAST_FLAG);
>  }
>
> +static const char *dhcp_msg_str[] = {
> +[0] = "INVALID",
> +[DHCP_MSG_DISCOVER] = "DISCOVER",
> +[DHCP_MSG_OFFER] = "OFFER",
> +[DHCP_MSG_REQUEST] = "REQUEST",
> +[OVN_DHCP_MSG_DECLINE] = "DECLINE",
> +[DHCP_MSG_ACK] = "ACK",
> +[DHCP_MSG_NAK] = "NAK",
> +[OVN_DHCP_MSG_RELEASE] = "RELEASE",
> +[OVN_DHCP_MSG_INFORM] = "INFORM"
> +};
> +
> +static bool
> +dhcp_relay_is_msg_type_supported(uint8_t msg_type)
> +{
> +    return (msg_type >= DHCP_MSG_DISCOVER && msg_type <= 
> OVN_DHCP_MSG_RELEASE);
> +}
> +
> +static const char *dhcp_msg_str_get(uint8_t msg_type)
> +{
> +    if (!dhcp_relay_is_msg_type_supported(msg_type)) {
> +        return "INVALID";
> +    }
> +    return dhcp_msg_str[msg_type];
> +}
> +
> +/* Called with in the pinctrl_handler thread context. */
> +static void
> +pinctrl_handle_dhcp_relay_req(
> +    struct rconn *swconn,
> +    struct dp_packet *pkt_in, struct ofputil_packet_in *pin,
> +    struct ofpbuf *userdata,
> +    struct ofpbuf *continuation)
> +{
> +    enum ofp_version version = rconn_get_version(swconn);
> +    enum ofputil_protocol proto = ofputil_protocol_from_ofp_version(version);
> +    struct dp_packet *pkt_out_ptr = NULL;
> +
> +    /* Parse relay IP and server IP. */
> +    ovs_be32 *relay_ip = ofpbuf_try_pull(userdata, sizeof *relay_ip);
> +    ovs_be32 *server_ip = ofpbuf_try_pull(userdata, sizeof *server_ip);
> +    if (!relay_ip || !server_ip) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: relay ip or server ip "
> +                  "not present in the userdata");
> +        return;
> +    }
> +
> +    /* Validate the DHCP request packet.
> +     * Format of the DHCP packet is
> +     * 
> ------------------------------------------------------------------------
> +     *| UDP HEADER  | DHCP HEADER  | 4 Byte DHCP Cookie | DHCP OPTIONS(var 
> len)|
> +     * 
> ------------------------------------------------------------------------
> +     */
> +
> +    size_t in_l4_size = dp_packet_l4_size(pkt_in);
> +    const char *end = (char *) dp_packet_l4(pkt_in) + in_l4_size;
> +    const char *in_dhcp_ptr = dp_packet_get_udp_payload(pkt_in);
> +    if (!in_dhcp_ptr) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: invalid or incomplete "
> +                  "DHCP packet received");
> +        return;
> +    }
> +
> +    const struct dhcp_header *in_dhcp_data
> +        = (const struct dhcp_header *) in_dhcp_ptr;
> +    in_dhcp_ptr += sizeof *in_dhcp_data;
> +    if (in_dhcp_ptr > end) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: invalid or incomplete "
> +                "DHCP packet received, bad data length");
> +        return;
> +    }
> +    if (in_dhcp_data->op != DHCP_OP_REQUEST) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: invalid opcode in the "
> +                "DHCP packet: %d", in_dhcp_data->op);
> +        return;
> +    }
> +
> +    /* DHCP options follow the DHCP header. The first 4 bytes of the DHCP
> +     * options is the DHCP magic cookie followed by the actual DHCP options.
> +     */
> +    ovs_be32 magic_cookie = htonl(DHCP_MAGIC_COOKIE);
> +    if (in_dhcp_ptr + sizeof magic_cookie > end ||
> +        get_unaligned_be32((const void *) in_dhcp_ptr) != magic_cookie) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: magic cookie not present "
> +                "in the packet");
> +        return;
> +    }
> +
> +    if (in_dhcp_data->giaddr) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: giaddr is already set");
> +        return;
> +    }
> +
> +    if (in_dhcp_data->htype != 0x1) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: packet is recieved with "
> +                "unsupported hardware type");
> +        return;
> +    }
> +
> +    ovs_be32 *server_id_ptr = NULL;
> +    const uint8_t *in_dhcp_msg_type = NULL;
> +
> +    in_dhcp_ptr += sizeof magic_cookie;
> +    ovs_be32 request_ip = in_dhcp_data->ciaddr;
> +    while (in_dhcp_ptr < end) {
> +        const struct dhcp_opt_header *in_dhcp_opt =
> +            (const struct dhcp_opt_header *) in_dhcp_ptr;
> +        if (in_dhcp_opt->code == DHCP_OPT_END) {
> +            break;
> +        }
> +        if (in_dhcp_opt->code == DHCP_OPT_PAD) {
> +            in_dhcp_ptr += 1;
> +            continue;
> +        }
> +        in_dhcp_ptr += sizeof *in_dhcp_opt;
> +        if (in_dhcp_ptr > end) {
> +            break;
> +        }
> +        in_dhcp_ptr += in_dhcp_opt->len;
> +        if (in_dhcp_ptr > end) {
> +            break;
> +        }
> +
> +        switch (in_dhcp_opt->code) {
> +        case DHCP_OPT_MSG_TYPE:
> +            if (in_dhcp_opt->len == 1) {
> +                in_dhcp_msg_type = DHCP_OPT_PAYLOAD(in_dhcp_opt);
> +            }
> +            break;
> +        case DHCP_OPT_REQ_IP:
> +            if (in_dhcp_opt->len == 4) {
> +                request_ip = 
> get_unaligned_be32(DHCP_OPT_PAYLOAD(in_dhcp_opt));
> +            }
> +            break;
> +        /* Server Identifier */
> +        case OVN_DHCP_OPT_CODE_SERVER_ID:
> +            if (in_dhcp_opt->len == 4) {
> +                server_id_ptr = DHCP_OPT_PAYLOAD(in_dhcp_opt);
> +            }
> +            break;
> +        default:
> +            break;
> +        }
> +    }
> +
> +    /* Check whether the DHCP Message Type (opt 53) is present or not */
> +    if (!in_dhcp_msg_type) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_REQ: missing message type");
> +        return;
> +    }
> +
> +    /* Relay the DHCP request packet */
> +    uint16_t new_l4_size = in_l4_size;
> +    size_t new_packet_size = pkt_in->l4_ofs + new_l4_size;
> +
> +    struct dp_packet pkt_out;
> +    dp_packet_init(&pkt_out, new_packet_size);
> +    dp_packet_clear(&pkt_out);
> +    dp_packet_prealloc_tailroom(&pkt_out, new_packet_size);
> +    pkt_out_ptr = &pkt_out;
> +
> +    /* Copy the L2 and L3 headers from the pkt_in as they would remain same*/
> +    dp_packet_put(
> +        &pkt_out, dp_packet_pull(pkt_in, pkt_in->l4_ofs), pkt_in->l4_ofs);
> +
> +    pkt_out.l2_5_ofs = pkt_in->l2_5_ofs;
> +    pkt_out.l2_pad_size = pkt_in->l2_pad_size;
> +    pkt_out.l3_ofs = pkt_in->l3_ofs;
> +    pkt_out.l4_ofs = pkt_in->l4_ofs;
> +
> +    struct ip_header *out_ip = dp_packet_l3(&pkt_out);
> +
> +    struct udp_header *udp = dp_packet_put(
> +        &pkt_out, dp_packet_pull(pkt_in, UDP_HEADER_LEN), UDP_HEADER_LEN);
> +
> +    struct dhcp_header *dhcp_data = dp_packet_put(&pkt_out,
> +        dp_packet_pull(pkt_in, new_l4_size - UDP_HEADER_LEN),
> +        new_l4_size - UDP_HEADER_LEN);
> +    dhcp_data->giaddr = *relay_ip;
> +    if (udp->udp_csum) {
> +        udp->udp_csum = recalc_csum32(udp->udp_csum,
> +            0, dhcp_data->giaddr);
> +    }
> +    pin->packet = dp_packet_data(&pkt_out);
> +    pin->packet_len = dp_packet_size(&pkt_out);
> +
> +    /* Log the DHCP message. */
> +    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(20, 40);
> +    const struct eth_header *l2 = dp_packet_eth(&pkt_out);
> +    VLOG_INFO_RL(&rl, "DHCP_RELAY_REQ:: MSG_TYPE:%s MAC:"ETH_ADDR_FMT
> +                " XID:%u"
> +                " REQ_IP:"IP_FMT
> +                " GIADDR:"IP_FMT
> +                " SERVER_ADDR:"IP_FMT,
> +                dhcp_msg_str_get(*in_dhcp_msg_type),
> +                ETH_ADDR_BYTES_ARGS(dhcp_data->chaddr), 
> ntohl(dhcp_data->xid),
> +                IP_ARGS(request_ip), IP_ARGS(dhcp_data->giaddr),
> +                IP_ARGS(*server_ip));
> +    queue_msg(swconn, ofputil_encode_resume(pin, continuation, proto));
> +    if (pkt_out_ptr) {
> +        dp_packet_uninit(pkt_out_ptr);
> +    }
> +}
> +
> +/* Called with in the pinctrl_handler thread context. */
> +static void
> +pinctrl_handle_dhcp_relay_resp_fwd(
> +    struct rconn *swconn,
> +    struct dp_packet *pkt_in, struct ofputil_packet_in *pin,
> +    struct ofpbuf *userdata,
> +    struct ofpbuf *continuation)
> +{
> +    enum ofp_version version = rconn_get_version(swconn);
> +    enum ofputil_protocol proto = ofputil_protocol_from_ofp_version(version);
> +    struct dp_packet *pkt_out_ptr = NULL;
> +
> +    /* Parse relay IP and server IP. */
> +    ovs_be32 *relay_ip = ofpbuf_try_pull(userdata, sizeof *relay_ip);
> +    ovs_be32 *server_ip = ofpbuf_try_pull(userdata, sizeof *server_ip);
> +    if (!relay_ip || !server_ip) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP: relay ip or server ip "
> +                "not present in the userdata");
> +        return;
> +    }
> +
> +    /* Validate the DHCP request packet.
> +     * Format of the DHCP packet is
> +     * 
> ------------------------------------------------------------------------
> +     *| UDP HEADER  | DHCP HEADER  | 4 Byte DHCP Cookie | DHCP OPTIONS(var 
> len)|
> +     * 
> ------------------------------------------------------------------------
> +     */
> +
> +    size_t in_l4_size = dp_packet_l4_size(pkt_in);
> +    const char *end = (char *) dp_packet_l4(pkt_in) + in_l4_size;
> +    const char *in_dhcp_ptr = dp_packet_get_udp_payload(pkt_in);
> +    if (!in_dhcp_ptr) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP_FWD: invalid or incomplete "
> +                "packet received");
> +        return;
> +    }
> +
> +    const struct dhcp_header *in_dhcp_data
> +        = (const struct dhcp_header *) in_dhcp_ptr;
> +    in_dhcp_ptr += sizeof *in_dhcp_data;
> +    if (in_dhcp_ptr > end) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP_FWD: invalid or incomplete "
> +                    "packet received, bad data length");
> +        return;
> +    }
> +    if (in_dhcp_data->op != DHCP_OP_REPLY) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP_FWD: invalid opcode "
> +                "in the packet: %d", in_dhcp_data->op);
> +        return;
> +    }
> +
> +    /* DHCP options follow the DHCP header. The first 4 bytes of the DHCP
> +     * options is the DHCP magic cookie followed by the actual DHCP options.
> +     */
> +    ovs_be32 magic_cookie = htonl(DHCP_MAGIC_COOKIE);
> +    if (in_dhcp_ptr + sizeof magic_cookie > end ||
> +        get_unaligned_be32((const void *) in_dhcp_ptr) != magic_cookie) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP_FWD: magic cookie not present "
> +                "in the packet");
> +        return;
> +    }
> +
> +    if (!in_dhcp_data->giaddr) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP_FWD: giaddr is "
> +                    "not set in request");
> +        return;
> +    }
> +    ovs_be32 giaddr = in_dhcp_data->giaddr;
> +
> +    ovs_be32 *server_id_ptr = NULL;
> +    ovs_be32 lease_time = 0;
> +    const uint8_t *in_dhcp_msg_type = NULL;
> +
> +    in_dhcp_ptr += sizeof magic_cookie;
> +    while (in_dhcp_ptr < end) {
> +        const struct dhcp_opt_header *in_dhcp_opt =
> +            (const struct dhcp_opt_header *) in_dhcp_ptr;
> +        if (in_dhcp_opt->code == DHCP_OPT_END) {
> +            break;
> +        }
> +        if (in_dhcp_opt->code == DHCP_OPT_PAD) {
> +            in_dhcp_ptr += 1;
> +            continue;
> +        }
> +        in_dhcp_ptr += sizeof *in_dhcp_opt;
> +        if (in_dhcp_ptr > end) {
> +            break;
> +        }
> +        in_dhcp_ptr += in_dhcp_opt->len;
> +        if (in_dhcp_ptr > end) {
> +            break;
> +        }
> +
> +        switch (in_dhcp_opt->code) {
> +        case DHCP_OPT_MSG_TYPE:
> +            if (in_dhcp_opt->len == 1) {
> +                in_dhcp_msg_type = DHCP_OPT_PAYLOAD(in_dhcp_opt);
> +            }
> +            break;
> +        /* Server Identifier */
> +        case OVN_DHCP_OPT_CODE_SERVER_ID:
> +            if (in_dhcp_opt->len == 4) {
> +                server_id_ptr = DHCP_OPT_PAYLOAD(in_dhcp_opt);
> +            }
> +            break;
> +        case OVN_DHCP_OPT_CODE_LEASE_TIME:
> +            if (in_dhcp_opt->len == 4) {
> +                lease_time = 
> get_unaligned_be32(DHCP_OPT_PAYLOAD(in_dhcp_opt));
> +            }
> +            break;
> +        default:
> +            break;
> +        }
> +    }
> +
> +    /* Check whether the DHCP Message Type (opt 53) is present or not */
> +    if (!in_dhcp_msg_type) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP: missing message type");
> +        return;
> +    }
> +
> +    if (!server_id_ptr) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP: missing server identifier");
> +        return;
> +    }
> +
> +    if (*server_id_ptr != *server_ip) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP: server identifier mismatch");
> +        return;
> +    }
> +
> +    if (giaddr != *relay_ip) {
> +        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> +        VLOG_WARN_RL(&rl, "DHCP_RELAY_RESP: giaddr mismatch");
> +        return;
> +    }
> +
> +
> +    /* Update destination MAC & IP so that the packet is forward to the
> +     * right destination node.
> +     */
> +    uint16_t new_l4_size = in_l4_size;
> +    size_t new_packet_size = pkt_in->l4_ofs + new_l4_size;
> +
> +    struct dp_packet pkt_out;
> +    dp_packet_init(&pkt_out, new_packet_size);
> +    dp_packet_clear(&pkt_out);
> +    dp_packet_prealloc_tailroom(&pkt_out, new_packet_size);
> +    pkt_out_ptr = &pkt_out;
> +
> +    /* Copy the L2 and L3 headers from the pkt_in as they would remain same*/
> +    struct eth_header *eth = dp_packet_put(
> +        &pkt_out, dp_packet_pull(pkt_in, pkt_in->l4_ofs), pkt_in->l4_ofs);
> +
> +    pkt_out.l2_5_ofs = pkt_in->l2_5_ofs;
> +    pkt_out.l2_pad_size = pkt_in->l2_pad_size;
> +    pkt_out.l3_ofs = pkt_in->l3_ofs;
> +    pkt_out.l4_ofs = pkt_in->l4_ofs;
> +
> +    struct udp_header *udp = dp_packet_put(
> +        &pkt_out, dp_packet_pull(pkt_in, UDP_HEADER_LEN), UDP_HEADER_LEN);
> +
> +    struct dhcp_header *dhcp_data = dp_packet_put(
> +        &pkt_out, dp_packet_pull(pkt_in, new_l4_size - UDP_HEADER_LEN),
> +        new_l4_size - UDP_HEADER_LEN);
> +    memcpy(&eth->eth_dst, dhcp_data->chaddr, sizeof(eth->eth_dst));
> +
> +    /* Send a broadcast IP frame when BROADCAST flag is set. */
> +    struct ip_header *out_ip = dp_packet_l3(&pkt_out);
> +    ovs_be32 ip_dst;
> +    ovs_be32 ip_dst_orig = get_16aligned_be32(&out_ip->ip_dst);
> +    if (!is_dhcp_flags_broadcast(dhcp_data->flags)) {
> +        ip_dst = dhcp_data->yiaddr;
> +    } else {
> +        ip_dst = htonl(0xffffffff);
> +    }
> +    put_16aligned_be32(&out_ip->ip_dst, ip_dst);
> +    out_ip->ip_csum = recalc_csum32(out_ip->ip_csum,
> +              ip_dst_orig, ip_dst);
> +    if (udp->udp_csum) {
> +        udp->udp_csum = recalc_csum32(udp->udp_csum,
> +            ip_dst_orig, ip_dst);
> +    }
> +    /* Reset giaddr */
> +    dhcp_data->giaddr = htonl(0x0);
> +    if (udp->udp_csum) {
> +        udp->udp_csum = recalc_csum32(udp->udp_csum,
> +            giaddr, 0);
> +    }
> +    pin->packet = dp_packet_data(&pkt_out);
> +    pin->packet_len = dp_packet_size(&pkt_out);
> +
> +    /* Log the DHCP message. */
> +    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(20, 40);
> +    const struct eth_header *l2 = dp_packet_eth(&pkt_out);
> +    VLOG_INFO_RL(&rl, "DHCP_RELAY_RESP_FWD:: MSG_TYPE:%s MAC:"ETH_ADDR_FMT
> +             " XID:%u"
> +             " YIADDR:"IP_FMT
> +             " GIADDR:"IP_FMT
> +             " SERVER_ADDR:"IP_FMT,
> +             dhcp_msg_str_get(*in_dhcp_msg_type),
> +             ETH_ADDR_BYTES_ARGS(dhcp_data->chaddr), ntohl(dhcp_data->xid),
> +             IP_ARGS(dhcp_data->yiaddr),
> +             IP_ARGS(giaddr), IP_ARGS(*server_id_ptr));
> +    queue_msg(swconn, ofputil_encode_resume(pin, continuation, proto));
> +    if (pkt_out_ptr) {
> +        dp_packet_uninit(pkt_out_ptr);
> +    }
> +}
> +
>  /* Called with in the pinctrl_handler thread context. */
>  static void
>  pinctrl_handle_put_dhcp_opts(
> @@ -3203,6 +3634,16 @@ process_packet_in(struct rconn *swconn, const struct 
> ofp_header *msg)
>          ovs_mutex_unlock(&pinctrl_mutex);
>          break;
>
> +    case ACTION_OPCODE_DHCP_RELAY_REQ:
> +        pinctrl_handle_dhcp_relay_req(swconn, &packet, &pin,
> +                                     &userdata, &continuation);
> +        break;
> +
> +    case ACTION_OPCODE_DHCP_RELAY_RESP_FWD:
> +        pinctrl_handle_dhcp_relay_resp_fwd(swconn, &packet, &pin,
> +                                     &userdata, &continuation);
> +        break;
> +
>      case ACTION_OPCODE_PUT_DHCP_OPTS:
>          pinctrl_handle_put_dhcp_opts(swconn, &packet, &pin, &headers,
>                                       &userdata, &continuation);
> diff --git a/include/ovn/actions.h b/include/ovn/actions.h
> index 49cfe0624..47d41b90f 100644
> --- a/include/ovn/actions.h
> +++ b/include/ovn/actions.h
> @@ -95,6 +95,8 @@ struct collector_set_ids;
>      OVNACT(LOOKUP_ND_IP,      ovnact_lookup_mac_bind_ip) \
>      OVNACT(PUT_DHCPV4_OPTS,   ovnact_put_opts)        \
>      OVNACT(PUT_DHCPV6_OPTS,   ovnact_put_opts)        \
> +    OVNACT(DHCPV4_RELAY_REQ,  ovnact_dhcp_relay)      \
> +    OVNACT(DHCPV4_RELAY_RESP_FWD, ovnact_dhcp_relay)      \
>      OVNACT(SET_QUEUE,         ovnact_set_queue)       \
>      OVNACT(DNS_LOOKUP,        ovnact_result)          \
>      OVNACT(LOG,               ovnact_log)             \
> @@ -387,6 +389,14 @@ struct ovnact_put_opts {
>      size_t n_options;
>  };
>
> +/* OVNACT_DHCP_RELAY. */
> +struct ovnact_dhcp_relay {
> +    struct ovnact ovnact;
> +    int family;
> +    ovs_be32 relay_ipv4;
> +    ovs_be32 server_ipv4;
> +};
> +
>  /* Valid arguments to SET_QUEUE action.
>   *
>   * QDISC_MIN_QUEUE_ID is the default queue, so user-defined queues should
> @@ -750,6 +760,22 @@ enum action_opcode {
>
>      /* multicast group split buffer action. */
>      ACTION_OPCODE_MG_SPLIT_BUF,
> +
> +    /* "dhcp_relay_req(relay_ip, server_ip)".
> +     *
> +     * Arguments follow the action_header, in this format:
> +     *   - The 32-bit DHCP relay IP.
> +     *   - The 32-bit DHCP server IP.
> +     */
> +    ACTION_OPCODE_DHCP_RELAY_REQ,
> +
> +    /* "dhcp_relay_resp_fwd(relay_ip, server_ip)".
> +     *
> +     * Arguments follow the action_header, in this format:
> +     *   - The 32-bit DHCP relay IP.
> +     *   - The 32-bit DHCP server IP.
> +     */
> +    ACTION_OPCODE_DHCP_RELAY_RESP_FWD,
>  };
>
>  /* Header. */
> diff --git a/lib/actions.c b/lib/actions.c
> index a73fe1a1e..69df428c6 100644
> --- a/lib/actions.c
> +++ b/lib/actions.c
> @@ -2629,6 +2629,118 @@ ovnact_controller_event_free(struct 
> ovnact_controller_event *event)
>      free_gen_options(event->options, event->n_options);
>  }
>
> +static void
> +format_DHCPV4_RELAY_REQ(const struct ovnact_dhcp_relay *dhcp_relay,
> +                struct ds *s)
> +{
> +    ds_put_format(s, "dhcp_relay_req("IP_FMT","IP_FMT");",
> +                  IP_ARGS(dhcp_relay->relay_ipv4),
> +                  IP_ARGS(dhcp_relay->server_ipv4));
> +}
> +
> +static void
> +parse_dhcp_relay_req(struct action_context *ctx,
> +               struct ovnact_dhcp_relay *dhcp_relay)
> +{
> +    /* Skip dhcp_relay_req( */
> +    lexer_force_match(ctx->lexer, LEX_T_LPAREN);
> +
> +    /* Parse relay ip and server ip. */
> +    if (ctx->lexer->token.format == LEX_F_IPV4) {
> +        dhcp_relay->family = AF_INET;
> +        dhcp_relay->relay_ipv4 = ctx->lexer->token.value.ipv4;
> +        lexer_get(ctx->lexer);
> +        lexer_match(ctx->lexer, LEX_T_COMMA);
> +        if (ctx->lexer->token.format == LEX_F_IPV4) {
> +            dhcp_relay->family = AF_INET;
> +            dhcp_relay->server_ipv4 = ctx->lexer->token.value.ipv4;
> +            lexer_get(ctx->lexer);
> +        } else {
> +            lexer_syntax_error(ctx->lexer, "expecting IPv4 dhcp server ip");
> +            return;
> +        }
> +    } else {
> +          lexer_syntax_error(ctx->lexer, "expecting IPv4 dhcp relay "
> +                          "and server ips");
> +          return;
> +    }
> +    lexer_force_match(ctx->lexer, LEX_T_RPAREN);
> +}
> +
> +static void
> +encode_DHCPV4_RELAY_REQ(const struct ovnact_dhcp_relay *dhcp_relay,
> +                    const struct ovnact_encode_params *ep,
> +                    struct ofpbuf *ofpacts)
> +{
> +    size_t oc_offset = 
> encode_start_controller_op(ACTION_OPCODE_DHCP_RELAY_REQ,
> +                                                  true, ep->ctrl_meter_id,
> +                                                  ofpacts);
> +    ofpbuf_put(ofpacts, &dhcp_relay->relay_ipv4,
> +            sizeof(dhcp_relay->relay_ipv4));
> +    ofpbuf_put(ofpacts, &dhcp_relay->server_ipv4,
> +            sizeof(dhcp_relay->server_ipv4));
> +    encode_finish_controller_op(oc_offset, ofpacts);
> +}
> +
> +static void
> +format_DHCPV4_RELAY_RESP_FWD(const struct ovnact_dhcp_relay *dhcp_relay,
> +                    struct ds *s)
> +{
> +    ds_put_format(s, "dhcp_relay_resp("IP_FMT","IP_FMT");",
> +                  IP_ARGS(dhcp_relay->relay_ipv4),
> +                  IP_ARGS(dhcp_relay->server_ipv4));
> +}
> +
> +static void
> +parse_dhcp_relay_resp_fwd(struct action_context *ctx,
> +               struct ovnact_dhcp_relay *dhcp_relay)
> +{
> +    /* Skip dhcp_relay_resp( */
> +    lexer_force_match(ctx->lexer, LEX_T_LPAREN);
> +
> +    /* Parse relay ip and server ip. */
> +    if (ctx->lexer->token.format == LEX_F_IPV4) {
> +        dhcp_relay->family = AF_INET;
> +        dhcp_relay->relay_ipv4 = ctx->lexer->token.value.ipv4;
> +        lexer_get(ctx->lexer);
> +        lexer_match(ctx->lexer, LEX_T_COMMA);
> +        if (ctx->lexer->token.format == LEX_F_IPV4) {
> +            dhcp_relay->family = AF_INET;
> +            dhcp_relay->server_ipv4 = ctx->lexer->token.value.ipv4;
> +            lexer_get(ctx->lexer);
> +        } else {
> +            lexer_syntax_error(ctx->lexer, "expecting IPv4 dhcp server ip");
> +            return;
> +        }
> +    } else {
> +          lexer_syntax_error(ctx->lexer, "expecting IPv4 dhcp relay and "
> +                          "server ips");
> +          return;
> +    }
> +    lexer_force_match(ctx->lexer, LEX_T_RPAREN);
> +}
> +
> +static void
> +encode_DHCPV4_RELAY_RESP_FWD(const struct ovnact_dhcp_relay *dhcp_relay,
> +                    const struct ovnact_encode_params *ep,
> +                    struct ofpbuf *ofpacts)
> +{
> +    size_t oc_offset = encode_start_controller_op(
> +                                ACTION_OPCODE_DHCP_RELAY_RESP_FWD,
> +                                true, ep->ctrl_meter_id,
> +                                ofpacts);
> +    ofpbuf_put(ofpacts, &dhcp_relay->relay_ipv4,
> +                  sizeof(dhcp_relay->relay_ipv4));
> +    ofpbuf_put(ofpacts, &dhcp_relay->server_ipv4,
> +                  sizeof(dhcp_relay->server_ipv4));
> +    encode_finish_controller_op(oc_offset, ofpacts);
> +}
> +
> +static void ovnact_dhcp_relay_free(
> +          struct ovnact_dhcp_relay *dhcp_relay OVS_UNUSED)
> +{
> +}
> +
>  static void
>  parse_put_opts(struct action_context *ctx, const struct expr_field *dst,
>                 struct ovnact_put_opts *po, const struct hmap *gen_opts,
> @@ -5451,6 +5563,11 @@ parse_action(struct action_context *ctx)
>          parse_sample(ctx);
>      } else if (lexer_match_id(ctx->lexer, "mac_cache_use")) {
>          ovnact_put_MAC_CACHE_USE(ctx->ovnacts);
> +    } else if (lexer_match_id(ctx->lexer, "dhcp_relay_req")) {
> +        parse_dhcp_relay_req(ctx, ovnact_put_DHCPV4_RELAY_REQ(ctx->ovnacts));
> +    } else if (lexer_match_id(ctx->lexer, "dhcp_relay_resp_fwd")) {
> +        parse_dhcp_relay_resp_fwd(ctx,
> +              ovnact_put_DHCPV4_RELAY_RESP_FWD(ctx->ovnacts));
>      } else {
>          lexer_syntax_error(ctx->lexer, "expecting action");
>      }
> diff --git a/lib/ovn-l7.h b/lib/ovn-l7.h
> index ad514a922..e08581123 100644
> --- a/lib/ovn-l7.h
> +++ b/lib/ovn-l7.h
> @@ -69,6 +69,7 @@ struct gen_opts_map {
>   */
>  #define OVN_DHCP_OPT_CODE_NETMASK      1
>  #define OVN_DHCP_OPT_CODE_LEASE_TIME   51
> +#define OVN_DHCP_OPT_CODE_SERVER_ID    54
>  #define OVN_DHCP_OPT_CODE_T1           58
>  #define OVN_DHCP_OPT_CODE_T2           59
>
> diff --git a/northd/northd.c b/northd/northd.c
> index 07dffb15a..7ac831fae 100644
> --- a/northd/northd.c
> +++ b/northd/northd.c
> @@ -181,11 +181,13 @@ enum ovn_stage {
>      PIPELINE_STAGE(ROUTER, IN,  IP_ROUTING_ECMP, 14, 
> "lr_in_ip_routing_ecmp") \
>      PIPELINE_STAGE(ROUTER, IN,  POLICY,          15, "lr_in_policy")         
>  \
>      PIPELINE_STAGE(ROUTER, IN,  POLICY_ECMP,     16, "lr_in_policy_ecmp")    
>  \
> -    PIPELINE_STAGE(ROUTER, IN,  ARP_RESOLVE,     17, "lr_in_arp_resolve")    
>  \
> -    PIPELINE_STAGE(ROUTER, IN,  CHK_PKT_LEN,     18, "lr_in_chk_pkt_len")    
>  \
> -    PIPELINE_STAGE(ROUTER, IN,  LARGER_PKTS,     19, "lr_in_larger_pkts")    
>  \
> -    PIPELINE_STAGE(ROUTER, IN,  GW_REDIRECT,     20, "lr_in_gw_redirect")    
>  \
> -    PIPELINE_STAGE(ROUTER, IN,  ARP_REQUEST,     21, "lr_in_arp_request")    
>  \
> +    PIPELINE_STAGE(ROUTER, IN,  DHCP_RELAY_RESP_FWD, 17,                     
>  \
> +                  "lr_in_dhcp_relay_resp_fwd")                               
>  \
> +    PIPELINE_STAGE(ROUTER, IN,  ARP_RESOLVE,     18, "lr_in_arp_resolve")    
>  \
> +    PIPELINE_STAGE(ROUTER, IN,  CHK_PKT_LEN,     19, "lr_in_chk_pkt_len")    
>  \
> +    PIPELINE_STAGE(ROUTER, IN,  LARGER_PKTS,     20, "lr_in_larger_pkts")    
>  \
> +    PIPELINE_STAGE(ROUTER, IN,  GW_REDIRECT,     21, "lr_in_gw_redirect")    
>  \
> +    PIPELINE_STAGE(ROUTER, IN,  ARP_REQUEST,     22, "lr_in_arp_request")    
>  \
>                                                                        \
>      /* Logical router egress stages. */                               \
>      PIPELINE_STAGE(ROUTER, OUT, CHECK_DNAT_LOCAL,   0,                       
> \
> @@ -9610,6 +9612,80 @@ build_dhcpv6_options_flows(struct ovn_port *op,
>      ds_destroy(&match);
>  }
>
> +static void
> +build_lswitch_dhcp_relay_flows(struct ovn_port *op,
> +                           const struct hmap *lr_ports,
> +                           const struct hmap *lflows,
> +                           const struct shash *meter_groups OVS_UNUSED)
> +{
> +    if (op->nbrp || !op->nbsp) {
> +        return;
> +    }
> +    /* consider only ports attached to VMs */
> +    if (strcmp(op->nbsp->type, "")) {
> +        return;
> +    }
> +
> +    if (!op->od || !op->od->n_router_ports ||
> +        !op->od->nbs || !op->od->nbs->dhcp_relay_port) {
> +        return;
> +    }
> +
> +    struct ds match = DS_EMPTY_INITIALIZER;
> +    struct ds action = DS_EMPTY_INITIALIZER;
> +    struct nbrec_logical_router_port *lrp = op->od->nbs->dhcp_relay_port;
> +    struct ovn_port *rp = ovn_port_find(lr_ports, lrp->name);
> +
> +    if (!rp || !rp->nbrp || !rp->nbrp->dhcp_relay) {
> +        return;
> +    }
> +
> +    struct ovn_port *sp = NULL;
> +    struct nbrec_dhcp_relay *dhcp_relay = rp->nbrp->dhcp_relay;
> +
> +    for (int i = 0; i < op->od->n_router_ports; i++) {
> +        struct ovn_port *sp_tmp = op->od->router_ports[i];
> +        if (sp_tmp->peer == rp) {
> +            sp = sp_tmp;
> +            break;
> +        }
> +    }
> +    if (!sp) {
> +      return;
> +    }
> +
> +    char *server_ip_str = NULL;
> +    uint16_t port;
> +    int addr_family;
> +    struct in6_addr server_ip;
> +
> +    if (!ip_address_and_port_from_lb_key(dhcp_relay->servers, &server_ip_str,
> +                                         &server_ip, &port, &addr_family)) {
> +        return;
> +    }
> +
> +    if (server_ip_str == NULL) {
> +        return;
> +    }
> +
> +    ds_put_format(
> +        &match, "inport == %s && eth.src == %s && "
> +        "ip4.src == 0.0.0.0 && ip4.dst == 255.255.255.255 && "
> +        "udp.src == 68 && udp.dst == 67",
> +        op->json_key, op->lsp_addrs[0].ea_s);
> +    ds_put_format(&action,
> +                  "eth.dst=%s;outport=%s;next;/* DHCP_RELAY_REQ */",
> +                  rp->lrp_networks.ea_s,sp->json_key);
> +    ovn_lflow_add_with_hint__(lflows, op->od,
> +                              S_SWITCH_IN_L2_LKUP, 100,
> +                              ds_cstr(&match),
> +                              ds_cstr(&action),
> +                              op->key,
> +                              NULL,
> +                              &lrp->header_);
> +    free(server_ip_str);
> +}
> +
>  static void
>  build_drop_arp_nd_flows_for_unbound_router_ports(struct ovn_port *op,
>                                                   const struct ovn_port *port,
> @@ -10181,6 +10257,13 @@ build_lswitch_dhcp_options_and_response(struct 
> ovn_port *op,
>          return;
>      }
>
> +    if (op->od && op->od->nbs
> +        && op->od->nbs->dhcp_relay_port) {
> +        /* Don't add the DHCP server flows if DHCP Relay is enabled on the
> +         * logical switch. */
> +        return;
> +    }
> +
>      bool is_external = lsp_is_external(op->nbsp);
>      if (is_external && (!op->od->n_localnet_ports ||
>                          !op->nbsp->ha_chassis_group)) {
> @@ -14458,6 +14541,86 @@ build_dhcpv6_reply_flows_for_lrouter_port(
>      }
>  }
>
> +static void
> +build_dhcp_relay_flows_for_lrouter_port(
> +        struct ovn_port *op, struct hmap *lflows,
> +        struct ds *match)
> +{
> +    if (!op->nbrp || !op->nbrp->dhcp_relay) {
> +        return;
> +    }
> +    struct nbrec_dhcp_relay *dhcp_relay = op->nbrp->dhcp_relay;
> +    if (!dhcp_relay->servers) {
> +        return;
> +    }
> +
> +    int addr_family;
> +    /* currently not supporting custom port */
> +    uint16_t port;
> +    char *server_ip_str = NULL;
> +    struct in6_addr server_ip;
> +
> +    if (!ip_address_and_port_from_lb_key(dhcp_relay->servers, &server_ip_str,
> +                                         &server_ip, &port, &addr_family)) {
> +        return;
> +    }
> +
> +    if (server_ip_str == NULL) {
> +        return;
> +    }
> +
> +    struct ds dhcp_action = DS_EMPTY_INITIALIZER;
> +    ds_clear(match);
> +    ds_put_format(
> +        match, "inport == %s && "
> +        "ip4.src == 0.0.0.0 && ip4.dst == 255.255.255.255 && "
> +        "udp.src == 68 && udp.dst == 67",
> +        op->json_key);
> +    ds_put_format(&dhcp_action,
> +                "dhcp_relay_req(%s,%s);"
> +                "ip4.src=%s;ip4.dst=%s;udp.src=67;next; /* DHCP_RELAY_REQ 
> */",
> +                op->lrp_networks.ipv4_addrs[0].addr_s, server_ip_str,
> +                op->lrp_networks.ipv4_addrs[0].addr_s, server_ip_str);
> +
> +    ovn_lflow_add_with_hint(lflows, op->od, S_ROUTER_IN_IP_INPUT, 110,
> +                            ds_cstr(match), ds_cstr(&dhcp_action),
> +                            &op->nbrp->header_);
> +
> +    ds_clear(match);
> +    ds_clear(&dhcp_action);
> +
> +    ds_put_format(
> +        match, "ip4.src == %s && ip4.dst == %s && "
> +        "udp.src == 67 && udp.dst == 67",
> +        server_ip_str, op->lrp_networks.ipv4_addrs[0].addr_s);
> +    ds_put_format(&dhcp_action, "next;/* DHCP_RELAY_RESP */");
> +    ovn_lflow_add_with_hint(lflows, op->od, S_ROUTER_IN_IP_INPUT, 110,
> +                            ds_cstr(match), ds_cstr(&dhcp_action),
> +                            &op->nbrp->header_);
> +
> +    ds_clear(match);
> +    ds_clear(&dhcp_action);
> +
> +    ds_put_format(
> +        match, "ip4.src == %s && ip4.dst == %s && "
> +        "udp.src == 67 && udp.dst == 67",
> +        server_ip_str, op->lrp_networks.ipv4_addrs[0].addr_s);
> +    ds_put_format(&dhcp_action,
> +          "dhcp_relay_resp_fwd(%s,%s);ip4.src=%s;udp.dst=68;"
> +          "outport=%s;output; /* DHCP_RELAY_RESP */",
> +          op->lrp_networks.ipv4_addrs[0].addr_s, server_ip_str,
> +          op->lrp_networks.ipv4_addrs[0].addr_s, op->json_key);
> +    ovn_lflow_add_with_hint(lflows, op->od, S_ROUTER_IN_DHCP_RELAY_RESP_FWD,
> +                            110,
> +                            ds_cstr(match), ds_cstr(&dhcp_action),
> +                            &op->nbrp->header_);
> +
> +    ds_clear(match);
> +    ds_clear(&dhcp_action);
> +
> +    free(server_ip_str);
> +}
> +
>  static void
>  build_ipv6_input_flows_for_lrouter_port(
>          struct ovn_port *op, struct hmap *lflows,
> @@ -15673,6 +15836,8 @@ build_lrouter_nat_defrag_and_lb(struct ovn_datapath 
> *od, struct hmap *lflows,
>      ovn_lflow_add(lflows, od, S_ROUTER_OUT_POST_SNAT, 0, "1", "next;");
>      ovn_lflow_add(lflows, od, S_ROUTER_OUT_EGR_LOOP, 0, "1", "next;");
>      ovn_lflow_add(lflows, od, S_ROUTER_IN_ECMP_STATEFUL, 0, "1", "next;");
> +    ovn_lflow_add(lflows, od, S_ROUTER_IN_DHCP_RELAY_RESP_FWD, 0, "1",
> +                  "next;");
>
>      const char *ct_flag_reg = features->ct_no_masked_label
>                                ? "ct_mark"
> @@ -16154,6 +16319,7 @@ build_lswitch_and_lrouter_iterate_by_lsp(struct 
> ovn_port *op,
>      build_lswitch_dhcp_options_and_response(op, lflows, meter_groups);
>      build_lswitch_external_port(op, lflows);
>      build_lswitch_ip_unicast_lookup(op, lflows, actions, match);
> +    build_lswitch_dhcp_relay_flows(op, lr_ports, lflows, meter_groups);
>
>      /* Build Logical Router Flows. */
>      build_ip_routing_flows_for_router_type_lsp(op, lr_ports, lflows);
> @@ -16183,6 +16349,7 @@ build_lswitch_and_lrouter_iterate_by_lrp(struct 
> ovn_port *op,
>      build_egress_delivery_flows_for_lrouter_port(op, lsi->lflows, 
> &lsi->match,
>                                                   &lsi->actions);
>      build_dhcpv6_reply_flows_for_lrouter_port(op, lsi->lflows, &lsi->match);
> +    build_dhcp_relay_flows_for_lrouter_port(op, lsi->lflows, &lsi->match);
>      build_ipv6_input_flows_for_lrouter_port(op, lsi->lflows,
>                                              &lsi->match, &lsi->actions,
>                                              lsi->meter_groups);
> diff --git a/ovn-nb.ovsschema b/ovn-nb.ovsschema
> index b2e0993e0..6863d52cd 100644
> --- a/ovn-nb.ovsschema
> +++ b/ovn-nb.ovsschema
> @@ -1,7 +1,7 @@
>  {
>      "name": "OVN_Northbound",
> -    "version": "7.2.0",
> -    "cksum": "1069338687 34162",
> +    "version": "7.3.0",
> +    "cksum": "2325497400 35185",
>      "tables": {
>          "NB_Global": {
>              "columns": {
> @@ -89,7 +89,12 @@
>                      "type": {"key": {"type": "uuid",
>                                       "refTable": "Forwarding_Group",
>                                       "refType": "strong"},
> -                                     "min": 0, "max": "unlimited"}}},
> +                                     "min": 0, "max": "unlimited"}},
> +                "dhcp_relay_port": {"type": {"key": {"type": "uuid",
> +                                            "refTable": 
> "Logical_Router_Port",
> +                                            "refType": "weak"},
> +                                            "min": 0,
> +                                            "max": 1}}},
>              "isRoot": true},
>          "Logical_Switch_Port": {
>              "columns": {
> @@ -436,6 +441,11 @@
>                  "ipv6_prefix": {"type": {"key": "string",
>                                        "min": 0,
>                                        "max": "unlimited"}},
> +                "dhcp_relay": {"type": {"key": {"type": "uuid",
> +                                            "refTable": "DHCP_Relay",
> +                                            "refType": "weak"},
> +                                            "min": 0,
> +                                            "max": 1}},
>                  "external_ids": {
>                      "type": {"key": "string", "value": "string",
>                               "min": 0, "max": "unlimited"}},
> @@ -529,6 +539,15 @@
>                      "type": {"key": "string", "value": "string",
>                               "min": 0, "max": "unlimited"}}},
>              "isRoot": true},
> +        "DHCP_Relay": {
> +            "columns": {
> +                "servers": {"type": {"key": "string",
> +                                       "min": 0,
> +                                       "max": 1}},
> +                "external_ids": {
> +                    "type": {"key": "string", "value": "string",
> +                             "min": 0, "max": "unlimited"}}},
> +            "isRoot": true},
>          "Connection": {
>              "columns": {
>                  "target": {"type": "string"},
> diff --git a/ovn-nb.xml b/ovn-nb.xml
> index fcb1c6ecc..dc20892e1 100644
> --- a/ovn-nb.xml
> +++ b/ovn-nb.xml
> @@ -608,6 +608,11 @@
>        Please see the <ref table="DNS"/> table.
>      </column>
>
> +    <column name="dhcp_relay_port">
> +      This column defines the <ref table="Logical_Router_Port"/> on which
> +      DHCP relay is enabled.
> +    </column>
> +
>      <column name="forwarding_groups">
>        Groups a set of logical port endpoints for traffic going out of the
>        logical switch.
> @@ -2980,6 +2985,11 @@ or
>        port has all ingress and egress traffic dropped.
>      </column>
>
> +    <column name="dhcp_relay">
> +      This column is used to enabled DHCP Relay. Please refer
> +      to <ref table="DHCP_Relay"/> table.
> +    </column>
> +
>      <group title="Distributed Gateway Ports">
>        <p>
>          Gateways, as documented under <code>Gateways</code> in the OVN
> @@ -4286,6 +4296,24 @@ or
>      </group>
>    </table>
>
> +  <table name="DHCP_Relay" title="DHCP Relay">
> +    <p>
> +      OVN implements native DHCPv4 relay support which caters to the common
> +      use case of relaying the DHCP requests to external DHCP server.
> +    </p>
> +
> +    <column name="servers">
> +      <p>
> +        The DHCPv4 server IP address.
> +      </p>
> +    </column>
> +    <group title="Common Columns">
> +      <column name="external_ids">
> +        See <em>External IDs</em> at the beginning of this document.
> +      </column>
> +    </group>
> +  </table>
> +
>    <table name="Connection" title="OVSDB client connections.">
>      <p>
>        Configuration for a database connection to an Open vSwitch database
> diff --git a/tests/atlocal.in b/tests/atlocal.in
> index 63d891b89..32d1c374e 100644
> --- a/tests/atlocal.in
> +++ b/tests/atlocal.in
> @@ -187,6 +187,9 @@ fi
>  # Set HAVE_DHCPD
>  find_command dhcpd
>
> +# Set HAVE_DHCLIENT
> +find_command dhclient
> +
>  # Set HAVE_BFDD_BEACON
>  find_command bfdd-beacon
>
> diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at
> index 19e4f1263..4d8c9ff26 100644
> --- a/tests/ovn-northd.at
> +++ b/tests/ovn-northd.at
> @@ -8786,9 +8786,9 @@ ovn-nbctl --wait=sb set logical_router_port R1-PUB 
> options:redirect-type=bridged
>  ovn-sbctl dump-flows R1 > R1flows
>  AT_CAPTURE_FILE([R1flows])
>
> -AT_CHECK([grep "lr_in_arp_resolve" R1flows | grep priority=90 | sort], [0], 
> [dnl
> -  table=17(lr_in_arp_resolve  ), priority=90   , match=(outport == "R1-PUB" 
> && ip4.src == 10.0.0.3 && is_chassis_resident("S0-P0")), 
> action=(get_arp(outport, reg0); next;)
> -  table=17(lr_in_arp_resolve  ), priority=90   , match=(outport == "R1-PUB" 
> && ip6.src == 1000::3 && is_chassis_resident("S0-P0")), 
> action=(get_nd(outport, xxreg0); next;)
> +AT_CHECK([grep "lr_in_arp_resolve" R1flows | grep priority=90 | sed 
> 's/table=../table=??/' | sort], [0], [dnl
> +  table=??(lr_in_arp_resolve  ), priority=90   , match=(outport == "R1-PUB" 
> && ip4.src == 10.0.0.3 && is_chassis_resident("S0-P0")), 
> action=(get_arp(outport, reg0); next;)
> +  table=??(lr_in_arp_resolve  ), priority=90   , match=(outport == "R1-PUB" 
> && ip6.src == 1000::3 && is_chassis_resident("S0-P0")), 
> action=(get_nd(outport, xxreg0); next;)
>  ])
>
>  AT_CLEANUP
> @@ -10966,3 +10966,38 @@ Status: active
>
>  AT_CLEANUP
>  ])
> +
> +OVN_FOR_EACH_NORTHD_NO_HV([
> +AT_SETUP([check DHCP RELAY AGENT])
> +ovn_start NORTHD_TYPE
> +
> +check ovn-nbctl ls-add ls0
> +check ovn-nbctl lsp-add ls0 ls0-port1
> +check ovn-nbctl lsp-set-addresses ls0-port1 02:00:00:00:00:10
> +check ovn-nbctl lr-add lr0
> +check ovn-nbctl lrp-add lr0 lrp1 02:00:00:00:00:01 192.168.1.1/24
> +check ovn-nbctl lsp-add ls0 lrp1-attachment
> +check ovn-nbctl lsp-set-type lrp1-attachment router
> +check ovn-nbctl lsp-set-addresses lrp1-attachment 00:00:00:00:ff:02
> +check ovn-nbctl lsp-set-options lrp1-attachment router-port=lrp1
> +check ovn-nbctl lrp-add lr0 lrp-ext 02:00:00:00:00:02 192.168.2.1/24
> +
> +dhcp_relay=$(ovn-nbctl create DHCP_Relay servers=172.16.1.1)
> +check ovn-nbctl set Logical_Router_port lrp1 dhcp_relay=$dhcp_relay
> +rp_uuid=$(ovn-nbctl --bare --colum=_uuid list logical_router_port lrp1)
> +check ovn-nbctl set Logical_Switch ls0 dhcp_relay_port=$rp_uuid
> +
> +check ovn-nbctl --wait=sb sync
> +
> +ovn-sbctl lflow-list > lflows
> +AT_CAPTURE_FILE([lflows])
> +
> +AT_CHECK([grep -e "DHCP_RELAY_" lflows | sed 's/table=../table=??/'], [0], 
> [dnl
> +  table=??(lr_in_ip_input     ), priority=110  , match=(inport == "lrp1" && 
> ip4.src == 0.0.0.0 && ip4.dst == 255.255.255.255 && udp.src == 68 && udp.dst 
> == 67), 
> action=(dhcp_relay_req(192.168.1.1,172.16.1.1);ip4.src=192.168.1.1;ip4.dst=172.16.1.1;udp.src=67;next;
>  /* DHCP_RELAY_REQ */)
> +  table=??(lr_in_ip_input     ), priority=110  , match=(ip4.src == 
> 172.16.1.1 && ip4.dst == 192.168.1.1 && udp.src == 67 && udp.dst == 67), 
> action=(next;/* DHCP_RELAY_RESP */)
> +  table=??(lr_in_dhcp_relay_resp_fwd), priority=110  , match=(ip4.src == 
> 172.16.1.1 && ip4.dst == 192.168.1.1 && udp.src == 67 && udp.dst == 67), 
> action=(dhcp_relay_resp_fwd(192.168.1.1,172.16.1.1);ip4.src=192.168.1.1;udp.dst=68;outport="lrp1";output;
>  /* DHCP_RELAY_RESP */)
> +  table=??(ls_in_l2_lkup      ), priority=100  , match=(inport == 
> "ls0-port1" && eth.src == 02:00:00:00:00:10 && ip4.src == 0.0.0.0 && ip4.dst 
> == 255.255.255.255 && udp.src == 68 && udp.dst == 67), 
> action=(eth.dst=02:00:00:00:00:01;outport="lrp1-attachment";next;/* 
> DHCP_RELAY_REQ */)
> +])
> +
> +AT_CLEANUP
> +])
> diff --git a/tests/ovn.at b/tests/ovn.at
> index e8c79512b..839c07ce2 100644
> --- a/tests/ovn.at
> +++ b/tests/ovn.at
> @@ -21905,7 +21905,7 @@ eth_dst=00000000ff01
>  ip_src=$(ip_to_hex 10 0 0 10)
>  ip_dst=$(ip_to_hex 172 168 0 101)
>  send_icmp_packet 1 1 $eth_src $eth_dst $ip_src $ip_dst c4c9 
> 0000000000000000000000
> -AT_CHECK_UNQUOTED([as hv1 ovs-ofctl dump-flows br-int metadata=0x$lr0_dp_key 
> | awk '/table=28, n_packets=1, n_bytes=45/{print $7" "$8}'],[0],[dnl
> +AT_CHECK_UNQUOTED([as hv1 ovs-ofctl dump-flows br-int metadata=0x$lr0_dp_key 
> | awk '/table=29, n_packets=1, n_bytes=45/{print $7" "$8}'],[0],[dnl
>  
> priority=80,ip,reg15=0x$lr0_public_dp_key,metadata=0x$lr0_dp_key,nw_src=10.0.0.10
>  actions=drop
>  ])
>
> @@ -28964,7 +28964,7 @@ AT_CHECK([
>          grep "priority=100" | \
>          grep -c 
> "ct(commit,zone=NXM_NX_REG11\\[[0..15\\]],.*exec(move:NXM_OF_ETH_SRC\\[[\\]]->NXM_NX_CT_LABEL\\[[32..79\\]],load:0x[[0-9]]->NXM_NX_CT_MARK\\[[16..31\\]]))"
>
> -        grep table=25 hv${hv}flows | \
> +        grep table=26 hv${hv}flows | \
>          grep "priority=200" | \
>          grep -c 
> "move:NXM_NX_CT_LABEL\\[[\\]]->NXM_NX_XXREG1\\[[\\]],move:NXM_NX_XXREG1\\[[32..79\\]]->NXM_OF_ETH_DST"
>      done; :], [0], [dnl
> @@ -29089,7 +29089,7 @@ AT_CHECK([
>          grep "priority=100" | \
>          grep -c 
> "ct(commit,zone=NXM_NX_REG11\\[[0..15\\]],.*exec(move:NXM_OF_ETH_SRC\\[[\\]]->NXM_NX_CT_LABEL\\[[32..79\\]],load:0x[[0-9]]->NXM_NX_CT_MARK\\[[16..31\\]]))"
>
> -        grep table=25 hv${hv}flows | \
> +        grep table=26 hv${hv}flows | \
>          grep "priority=200" | \
>          grep -c 
> "move:NXM_NX_CT_LABEL\\[[\\]]->NXM_NX_XXREG1\\[[\\]],move:NXM_NX_XXREG1\\[[32..79\\]]->NXM_OF_ETH_DST"
>      done; :], [0], [dnl
> @@ -29586,7 +29586,7 @@ if test X"$1" = X"DGP"; then
>  else
>      prio=2
>  fi
> -AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=25, 
> n_packets=1,.* 
> priority=$prio,ip,$inport.*$outport.*metadata=0x${sw_key},nw_dst=10.0.1.1 
> actions=drop" -c], [0], [dnl
> +AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=26, 
> n_packets=1,.* 
> priority=$prio,ip,$inport.*$outport.*metadata=0x${sw_key},nw_dst=10.0.1.1 
> actions=drop" -c], [0], [dnl
>  1
>  ])
>
> @@ -29605,13 +29605,13 @@ AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep 
> "actions=controller" | grep
>
>  if test X"$1" = X"DGP"; then
>      # The packet dst should be resolved once for E/W centralized NAT purpose.
> -    AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=25, 
> n_packets=1,.* priority=100,reg0=0xa000101,reg15=.*metadata=0x${sw_key} 
> actions=mod_dl_dst:00:00:00:00:01:01,resubmit" -c], [0], [dnl
> +    AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=26, 
> n_packets=1,.* priority=100,reg0=0xa000101,reg15=.*metadata=0x${sw_key} 
> actions=mod_dl_dst:00:00:00:00:01:01,resubmit" -c], [0], [dnl
>  1
>  ])
>  fi
>
>  # The packet should've been finally dropped in the lr_in_arp_resolve stage.
> -AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=25, 
> n_packets=2,.* 
> priority=$prio,ip,$inport.*$outport.*metadata=0x${sw_key},nw_dst=10.0.1.1 
> actions=drop" -c], [0], [dnl
> +AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=26, 
> n_packets=2,.* 
> priority=$prio,ip,$inport.*$outport.*metadata=0x${sw_key},nw_dst=10.0.1.1 
> actions=drop" -c], [0], [dnl
>  1
>  ])
>  OVN_CLEANUP([hv1])
> diff --git a/tests/system-ovn.at b/tests/system-ovn.at
> index 7b9daba0d..591933a95 100644
> --- a/tests/system-ovn.at
> +++ b/tests/system-ovn.at
> @@ -12032,3 +12032,153 @@ as
>  OVS_TRAFFIC_VSWITCHD_STOP(["/failed to query port patch-.*/d
>  /connection dropped.*/d"])
>  AT_CLEANUP
> +
> +OVN_FOR_EACH_NORTHD([
> +AT_SETUP([DHCP RELAY AGENT])
> +AT_SKIP_IF([test $HAVE_DHCPD = no])
> +AT_SKIP_IF([test $HAVE_DHCLIENT = no])
> +AT_SKIP_IF([test $HAVE_TCPDUMP = no])
> +ovn_start
> +OVS_TRAFFIC_VSWITCHD_START()
> +
> +ADD_BR([br-int])
> +ADD_BR([br-ext])
> +
> +ovs-ofctl add-flow br-ext action=normal
> +# Set external-ids in br-int needed for ovn-controller
> +ovs-vsctl \
> +        -- set Open_vSwitch . external-ids:system-id=hv1 \
> +        -- set Open_vSwitch . 
> external-ids:ovn-remote=unix:$ovs_base/ovn-sb/ovn-sb.sock \
> +        -- set Open_vSwitch . external-ids:ovn-encap-type=geneve \
> +        -- set Open_vSwitch . external-ids:ovn-encap-ip=169.0.0.1 \
> +        -- set bridge br-int fail-mode=secure 
> other-config:disable-in-band=true
> +
> +# Start ovn-controller
> +start_daemon ovn-controller
> +
> +ADD_NAMESPACES(sw01)
> +ADD_VETH(sw01, sw01, br-int, "0", "f0:00:00:01:02:03")
> +ADD_NAMESPACES(sw11)
> +ADD_VETH(sw11, sw11, br-int, "0", "f0:00:00:02:02:03")
> +ADD_NAMESPACES(server)
> +ADD_VETH(s1, server, br-ext, "172.16.1.1/24", "f0:00:00:01:02:05", \
> +         "172.16.1.254")
> +
> +check ovn-nbctl lr-add R1
> +
> +check ovn-nbctl ls-add sw0
> +check ovn-nbctl ls-add sw1
> +check ovn-nbctl ls-add sw-ext
> +
> +check ovn-nbctl lrp-add R1 rp-sw0 00:00:01:01:02:03 192.168.1.1/24
> +check ovn-nbctl lrp-add R1 rp-sw1 00:00:03:01:02:03 192.168.2.1/24
> +check ovn-nbctl lrp-add R1 rp-ext 00:00:02:01:02:03 172.16.1.254/24
> +
> +dhcp_relay=$(ovn-nbctl create DHCP_Relay servers=172.16.1.1)
> +check ovn-nbctl set Logical_Router_port rp-sw0 dhcp_relay=$dhcp_relay
> +check ovn-nbctl set Logical_Router_port rp-sw1 dhcp_relay=$dhcp_relay
> +check ovn-nbctl lrp-set-gateway-chassis rp-ext hv1
> +
> +check ovn-nbctl lsp-add sw0 sw0-rp -- set Logical_Switch_Port sw0-rp \
> +    type=router options:router-port=rp-sw0 \
> +    -- lsp-set-addresses sw0-rp router
> +check ovn-nbctl lsp-add sw1 sw1-rp -- set Logical_Switch_Port sw1-rp \
> +    type=router options:router-port=rp-sw1 \
> +    -- lsp-set-addresses sw1-rp router
> +
> +rp_uuid=$(ovn-nbctl --bare --colum=_uuid list logical_router_port rp-sw0)
> +check ovn-nbctl set Logical_Switch sw0 dhcp_relay_port=$rp_uuid
> +rp_uuid=$(ovn-nbctl --bare --colum=_uuid list logical_router_port rp-sw1)
> +check ovn-nbctl set Logical_Switch sw1 dhcp_relay_port=$rp_uuid
> +
> +check ovn-nbctl lsp-add sw-ext ext-rp -- set Logical_Switch_Port ext-rp \
> +    type=router options:router-port=rp-ext \
> +    -- lsp-set-addresses ext-rp router
> +check ovn-nbctl lsp-add sw-ext lnet \
> +        -- lsp-set-addresses lnet unknown \
> +        -- lsp-set-type lnet localnet \
> +        -- lsp-set-options lnet network_name=phynet
> +
> +check ovn-nbctl lsp-add sw0 sw01 \
> +    -- lsp-set-addresses sw01 "f0:00:00:01:02:03"
> +
> +check ovn-nbctl lsp-add sw1 sw11 \
> +    -- lsp-set-addresses sw11 "f0:00:00:02:02:03"
> +
> +AT_CHECK([ovs-vsctl set Open_vSwitch . 
> external-ids:ovn-bridge-mappings=phynet:br-ext])
> +
> +OVN_POPULATE_ARP
> +
> +check ovn-nbctl --wait=hv sync
> +
> +DHCP_TEST_DIR="/tmp/dhcp-test"
> +rm -rf $DHCP_TEST_DIR
> +mkdir $DHCP_TEST_DIR
> +cat > $DHCP_TEST_DIR/dhcpd.conf <<EOF
> +subnet 172.16.1.0 netmask 255.255.255.0 {
> +}
> +subnet 192.168.1.0 netmask 255.255.255.0 {
> +  range 192.168.1.10 192.168.1.10;
> +  option routers 192.168.1.1;
> +  option broadcast-address 192.168.1.255;
> +  default-lease-time 60;
> +  max-lease-time 120;
> +}
> +subnet 192.168.2.0 netmask 255.255.255.0 {
> +  range 192.168.2.10 192.168.2.10;
> +  option routers 192.168.2.1;
> +  option broadcast-address 192.168.2.255;
> +  default-lease-time 60;
> +  max-lease-time 120;
> +}
> +EOF
> +cat > $DHCP_TEST_DIR/dhclien.conf <<EOF
> +timeout 2
> +EOF
> +
> +touch $DHCP_TEST_DIR/dhcpd.leases
> +chown root:dhcpd $DHCP_TEST_DIR $DHCP_TEST_DIR/dhcpd.leases
> +chmod 775 $DHCP_TEST_DIR
> +chmod 664 $DHCP_TEST_DIR/dhcpd.leases
> +
> +
> +NETNS_DAEMONIZE([server], [dhcpd -4 -f -cf $DHCP_TEST_DIR/dhcpd.conf s1 > 
> dhcpd.log 2>&1], [dhcpd.pid])
> +
> +NS_CHECK_EXEC([server], [tcpdump -l -nvv -i s1  udp > pkt.pcap 2>tcpdump_err 
> &])
> +OVS_WAIT_UNTIL([grep "listening" tcpdump_err])
> +on_exit 'kill $(pidof tcpdump)'
> +
> +NS_CHECK_EXEC([sw01], [dhclient -1 -q -lf $DHCP_TEST_DIR/dhclient-sw01.lease 
> -pf $DHCP_TEST_DIR/dhclient-sw01.pid -cf $DHCP_TEST_DIR/dhclien.conf sw01])
> +NS_CHECK_EXEC([sw11], [dhclient -1 -q -lf $DHCP_TEST_DIR/dhclient-sw11.lease 
> -pf $DHCP_TEST_DIR/dhclient-sw11.pid -cf $DHCP_TEST_DIR/dhclien.conf sw11])
> +
> +OVS_WAIT_UNTIL([
> +    total_pkts=$(cat pkt.pcap | wc -l)
> +    test ${total_pkts} -ge 8
> +])
> +
> +on_exit 'kill `cat $DHCP_TEST_DIR/dhclient-sw01.pid` &&
> +kill `cat $DHCP_TEST_DIR/dhclient-sw11.pid` && rm -rf $DHCP_TEST_DIR'
> +
> +NS_CHECK_EXEC([sw01], [ip addr show sw01 | grep -oP 
> '(?<=inet\s)\d+(\.\d+){3}'], [0], [dnl
> +192.168.1.10
> +])
> +NS_CHECK_EXEC([sw11], [ip addr show sw11 | grep -oP 
> '(?<=inet\s)\d+(\.\d+){3}'], [0], [dnl
> +192.168.2.10
> +])
> +OVS_APP_EXIT_AND_WAIT([ovn-controller])
> +
> +as ovn-sb
> +OVS_APP_EXIT_AND_WAIT([ovsdb-server])
> +
> +as ovn-nb
> +OVS_APP_EXIT_AND_WAIT([ovsdb-server])
> +
> +as northd
> +OVS_APP_EXIT_AND_WAIT([NORTHD_TYPE])
> +
> +as
> +OVS_TRAFFIC_VSWITCHD_STOP(["/.*error receiving.*/d
> +/failed to query port patch-.*/d
> +/.*terminating with signal 15.*/d"])
> +AT_CLEANUP
> +])
> diff --git a/utilities/ovn-trace.c b/utilities/ovn-trace.c
> index 0b86eae7b..ae9dd77de 100644
> --- a/utilities/ovn-trace.c
> +++ b/utilities/ovn-trace.c
> @@ -2328,6 +2328,25 @@ execute_put_dhcp_opts(const struct ovnact_put_opts 
> *pdo,
>      execute_put_opts(pdo, name, uflow, super);
>  }
>
> +static void
> +execute_dhcpv4_relay_resp_fwd(const struct ovnact_dhcp_relay *dr,
> +                                const char *name, struct flow *uflow,
> +                                struct ovs_list *super)
> +{
> +    ovntrace_node_append(
> +        super, OVNTRACE_NODE_ERROR,
> +        "/* We assume that this packet is DHCPOFFER or DHCPACK and "
> +            "DHCP broadcast flag is set. Dest IP is set to broadcast. "
> +            "Dest MAC is set to broadcast but in real network this is 
> unicast "
> +            "which is extracted from DHCP header. */");
> +
> +    /* Assume DHCP broadcast flag is set */
> +    uflow->nw_dst = 0xFFFFFFFF;
> +    /* Dest MAC is set to broadcast but in real network this is unicast */
> +    struct eth_addr bcast_mac = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
> +    uflow->dl_dst = bcast_mac;
> +}
> +
>  static void
>  execute_put_nd_ra_opts(const struct ovnact_put_opts *pdo,
>                         const char *name, struct flow *uflow,
> @@ -3215,6 +3234,15 @@ trace_actions(const struct ovnact *ovnacts, size_t 
> ovnacts_len,
>                                    "put_dhcpv6_opts", uflow, super);
>              break;
>
> +        case OVNACT_DHCPV4_RELAY_REQ:
> +            /* Nothing to do for tracing. */
> +            break;
> +
> +        case OVNACT_DHCPV4_RELAY_RESP_FWD:
> +            
> execute_dhcpv4_relay_resp_fwd(ovnact_get_DHCPV4_RELAY_RESP_FWD(a),
> +                                    "dhcp_relay_resp_fwd", uflow, super);
> +            break;
> +
>          case OVNACT_PUT_ND_RA_OPTS:
>              execute_put_nd_ra_opts(ovnact_get_PUT_DHCPV6_OPTS(a),
>                                     "put_nd_ra_opts", uflow, super);
> --
> 2.36.6
>
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> https://mail.openvswitch.org/mailman/listinfo/ovs-dev
>
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