Re: [ovs-dev] [RFC ovn] northd: set max priority for automatic routes
Hi guys, On 2/18/21 12:16 AM, Han Zhou wrote: On Wed, Feb 17, 2021 at 2:36 PM Tim Rozet wrote: On Tue, Feb 16, 2021 at 4:21 AM Han Zhou wrote: On Wed, Feb 10, 2021 at 2:17 PM Lorenzo Bianconi < lorenzo.bianc...@redhat.com> wrote: Increase priority for automatic routes (routes created assigning IP addresses to OVN logical router interfaces) in order to always prefer them over static routes since the router has a direct link to the destination address (possible use-case can be found here [0]). [0] https://bugzilla.redhat.com/show_bug.cgi?id=1891516 Hi Lorenzo, Tim, While the patch may solve the problem in the bug report, I think there is something more fundamental to be discussed. The problem is caused by ovn-k8s's use of "src-ip" in static routes which overrides the direct-connected route. I think the implementation of "src-ip" support in the static route is somehow flawed. The priorities of the flows generated by static routes are calculated according to the prefix length, so that longest prefix routes are prioritised when there are multiple route matches, which is correct when comparing matches among "dst-ip" routes or among "src-ip" routes, but is not correct between "dst-ip" and "src-ip" routes. Comparison of prefix length between these two types of static routes doesn't make sense, because they match by different fields (src-ip v.s. dst-ip). For example, when there are static routes: 1. 192.168.0.0/24 via 100.64.0.1 src-ip 2. 10.0.0.0/20 via 100.64.0.2 dst-ip In this example, a packet from 192.168.0.1 to 10.0.0.1 matches both routes, but it is unreasonable to say it should follow the 1st route just because it has longer prefix length. Instead, we should prioritize one type over the other. It seems in physical router implementation policy based routing always has higher priority than destination routing, so we should probably enforce it in a similar way in OVN, i.e. set "src-ip" flows with higher priority than all the "dst-ip" flows. In fact, the policy routing table already supported this behavior because it is examined before the static route table. Since the "src-ip" feature in the static route table is flawed, and can be replaced by the policy routing table, I'd suggest to deprecate it. For I agree. correctness, users (like ovn-k8s) should use the policy routing table instead for the src-ip based routing rules. Users have full control of how they want the packets to be routed. For the use case mentioned in the bug report, it should have two rules in the policy routing table: 100 ip.dst == 100.64.0.0/16 accept # for directly connected destination, skip the src-ip rules 90 ip.src == 10.244.0.0/24 nexthop 100.64.0.1 # src-ip rules Would this better satisfy the need of ovn-k8s? I believe this is correct. src-ip matching should be done in the policy table so traditional dest based routing is handled in default routing table. Need to go double check though. One example, but should be the same for all "traditional" routers, "The Policy-Based Routing feature is a process whereby a device puts packets through a route map before routing the packets.": https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pi/configuration/15-mt/iri-15-mt-book/iri-pbr.html If the above is agreed, the priority change of directly connected routes from this patch is irrelevant to the problem reported in the bug, because policy routing rules are examined before the static routing table anyway, so no matter how high the route priority is, it wouldn't matter. In addition, it seems to me no real use cases would benefit from this change, but I could be wrong and please correct me if so. I disagree with this. Trying to override a directly connected route is fundamentally wrong, which is why real routers specifically stop a user from being able to do this. What if a user who had a router attached to 100.64.0.0/16, adds a /32 route for 100.64.0.1 via another interface/subnet? That would take precedence over the directly attached route in OVN iiuc and pretty much guarantee improper networking. Directly connected routes should always take precedence, and therefore the default route lflows that get installed should always have the highest possible priority. I think there's some confusion here. In "traditional" routers, longest prefix match has priority in the route selection process. If two routes (from different protocols, including "directly connected") are available for the *same* prefix *and* length then, and only then, the one with the lowest administrative distance is selected. Most of the times "directly connected" routes have a lower admin distance by default compared to static routes so they are preferred *if* such a selection has to happen. The admin distance is also usually configurable (although not usually recommended) and allows users to override the default preference of routes. Back to the example above, in a "traditional" router, when the t
Re: [ovs-dev] [RFC ovn] northd: set max priority for automatic routes
On Wed, Feb 17, 2021 at 2:36 PM Tim Rozet wrote: > > > > > On Tue, Feb 16, 2021 at 4:21 AM Han Zhou wrote: >> >> >> >> On Wed, Feb 10, 2021 at 2:17 PM Lorenzo Bianconi < lorenzo.bianc...@redhat.com> wrote: >> > >> > Increase priority for automatic routes (routes created assigning IP >> > addresses to OVN logical router interfaces) in order to always prefer them >> > over static routes since the router has a direct link to the destination >> > address (possible use-case can be found here [0]). >> > >> > [0] https://bugzilla.redhat.com/show_bug.cgi?id=1891516 >> > >> >> Hi Lorenzo, Tim, >> >> While the patch may solve the problem in the bug report, I think there is something more fundamental to be discussed. The problem is caused by ovn-k8s's use of "src-ip" in static routes which overrides the direct-connected route. I think the implementation of "src-ip" support in the static route is somehow flawed. The priorities of the flows generated by static routes are calculated according to the prefix length, so that longest prefix routes are prioritised when there are multiple route matches, which is correct when comparing matches among "dst-ip" routes or among "src-ip" routes, but is not correct between "dst-ip" and "src-ip" routes. Comparison of prefix length between these two types of static routes doesn't make sense, because they match by different fields (src-ip v.s. dst-ip). For example, when there are static routes: >> 1. 192.168.0.0/24 via 100.64.0.1 src-ip >> 2. 10.0.0.0/20 via 100.64.0.2 dst-ip >> >> In this example, a packet from 192.168.0.1 to 10.0.0.1 matches both routes, but it is unreasonable to say it should follow the 1st route just because it has longer prefix length. Instead, we should prioritize one type over the other. It seems in physical router implementation policy based routing always has higher priority than destination routing, so we should probably enforce it in a similar way in OVN, i.e. set "src-ip" flows with higher priority than all the "dst-ip" flows. In fact, the policy routing table already supported this behavior because it is examined before the static route table. >> >> Since the "src-ip" feature in the static route table is flawed, and can be replaced by the policy routing table, I'd suggest to deprecate it. For correctness, users (like ovn-k8s) should use the policy routing table instead for the src-ip based routing rules. Users have full control of how they want the packets to be routed. For the use case mentioned in the bug report, it should have two rules in the policy routing table: >> >> >> 100 ip.dst == 100.64.0.0/16 accept # for directly connected destination, skip the src-ip rules >> 90 ip.src == 10.244.0.0/24 nexthop 100.64.0.1 # src-ip rules >> >> Would this better satisfy the need of ovn-k8s? > > > I believe this is correct. src-ip matching should be done in the policy table so traditional dest based routing is handled in default routing table. Need to go double check though. > >> >> If the above is agreed, the priority change of directly connected routes from this patch is irrelevant to the problem reported in the bug, because policy routing rules are examined before the static routing table anyway, so no matter how high the route priority is, it wouldn't matter. In addition, it seems to me no real use cases would benefit from this change, but I could be wrong and please correct me if so. >> > I disagree with this. Trying to override a directly connected route is fundamentally wrong, which is why real routers specifically stop a user from being able to do this. What if a user who had a router attached to 100.64.0.0/16, adds a /32 route for 100.64.0.1 via another interface/subnet? That would take precedence over the directly attached route in OVN iiuc and pretty much guarantee improper networking. Directly connected routes should always take precedence, and therefore the default route lflows that get installed should always have the highest possible priority. > Hi Tim, Thanks for your inputs. Here are my thoughts: In the scenario we discussed, it is in fact the same output interfaces but just different nexthops in the 10.64.0.0/16 subnet. In this case, adding a more specific route with a specific nexthop on the directly connected subnet doesn't seem to be violating any routing principle, right? Use the topology in the bug report as an example ((In the diagram of the bug report I think there is a typo: 100.64.0.1 should be the DR's output port IP, and 100.64.0.2 & 100.64.0.3 belong to GR1 and GR2). 10.64.0.0/16 is directly connected, but the adjacent L2 network doesn't have to have all the /16 IPs directly connected. Some of the nodes can reside behind a L3 hop. For example, if we know that 10.64.1.0/24 is behind a router with IP 10.64.255.1, we can still add a route: 10.64.1.0/24 via 10.64.255.1, which should work with the current OVN implementation, while this patch would in fact break it. On the other hand, what I wanted to emphasize is not that we want
Re: [ovs-dev] [RFC ovn] northd: set max priority for automatic routes
> On Tue, Feb 16, 2021 at 4:21 AM Han Zhou wrote: >> >> >> >> On Wed, Feb 10, 2021 at 2:17 PM Lorenzo Bianconi >> wrote: >> > >> > Increase priority for automatic routes (routes created assigning IP >> > addresses to OVN logical router interfaces) in order to always prefer them >> > over static routes since the router has a direct link to the destination >> > address (possible use-case can be found here [0]). >> > >> > [0] https://bugzilla.redhat.com/show_bug.cgi?id=1891516 >> > >> >> Hi Lorenzo, Tim, Hi Han, thx for the detailed reply :) >> >> While the patch may solve the problem in the bug report, I think there is >> something more fundamental to be discussed. The problem is caused by >> ovn-k8s's use of "src-ip" in static routes which overrides the >> direct-connected route. I think the implementation of "src-ip" support in >> the static route is somehow flawed. The priorities of the flows generated by >> static routes are calculated according to the prefix length, so that longest >> prefix routes are prioritised when there are multiple route matches, which >> is correct when comparing matches among "dst-ip" routes or among "src-ip" >> routes, but is not correct between "dst-ip" and "src-ip" routes. Comparison >> of prefix length between these two types of static routes doesn't make >> sense, because they match by different fields (src-ip v.s. dst-ip). For >> example, when there are static routes: >> 1. 192.168.0.0/24 via 100.64.0.1 src-ip >> 2. 10.0.0.0/20 via 100.64.0.2 dst-ip >> >> In this example, a packet from 192.168.0.1 to 10.0.0.1 matches both routes, >> but it is unreasonable to say it should follow the 1st route just because it >> has longer prefix length. Instead, we should prioritize one type over the >> other. It seems in physical router implementation policy based routing >> always has higher priority than destination routing, so we should probably >> enforce it in a similar way in OVN, i.e. set "src-ip" flows with higher >> priority than all the "dst-ip" flows. In fact, the policy routing table >> already supported this behavior because it is examined before the static >> route table. >> >> Since the "src-ip" feature in the static route table is flawed, and can be >> replaced by the policy routing table, I'd suggest to deprecate it. For >> correctness, users (like ovn-k8s) should use the policy routing table >> instead for the src-ip based routing rules. Users have full control of how >> they want the packets to be routed. For the use case mentioned in the bug >> report, it should have two rules in the policy routing table: >> >> >> 100 ip.dst == 100.64.0.0/16 accept # for directly connected destination, >> skip the src-ip rules >> 90 ip.src == 10.244.0.0/24 nexthop 100.64.0.1 # src-ip rules >> >> Would this better satisfy the need of ovn-k8s? > > > I believe this is correct. src-ip matching should be done in the policy table > so traditional dest based routing is handled in default routing table. Need > to go double check though. I agree on this point. > >> >> If the above is agreed, the priority change of directly connected routes >> from this patch is irrelevant to the problem reported in the bug, because >> policy routing rules are examined before the static routing table anyway, so >> no matter how high the route priority is, it wouldn't matter. In addition, >> it seems to me no real use cases would benefit from this change, but I could >> be wrong and please correct me if so. >> > I disagree with this. Trying to override a directly connected route is > fundamentally wrong, which is why real routers specifically stop a user from > being able to do this. What if a user who had a router attached to > 100.64.0.0/16, adds a /32 route for 100.64.0.1 via another interface/subnet? > That would take precedence over the directly attached route in OVN iiuc and > pretty much guarantee improper networking. Directly connected routes should > always take precedence, and therefore the default route lflows that get > installed should always have the highest possible priority. I do not have a strong opinion on it since I do not have any use cases for overwriting an automatic route with a static one. @Dumitru Ceara IIRC you mentioned a use case for it, right? Regards, Lorenzo > >> >> Thanks, >> Han >> >> > Signed-off-by: Lorenzo Bianconi >> > --- >> > northd/ovn-northd.c | 27 --- >> > 1 file changed, 16 insertions(+), 11 deletions(-) >> > >> > diff --git a/northd/ovn-northd.c b/northd/ovn-northd.c >> > index b2b5f6a1b..dc8706f2f 100644 >> > --- a/northd/ovn-northd.c >> > +++ b/northd/ovn-northd.c >> > @@ -7994,18 +7994,23 @@ build_route_prefix_s(const struct in6_addr >> > *prefix, unsigned int plen) >> > >> > static void >> > build_route_match(const struct ovn_port *op_inport, const char *network_s, >> > - int plen, bool is_src_route, bool is_ipv4, struct ds >> > *match, >> > - uint16_
Re: [ovs-dev] [RFC ovn] northd: set max priority for automatic routes
On Tue, Feb 16, 2021 at 4:21 AM Han Zhou wrote:
>
>
> On Wed, Feb 10, 2021 at 2:17 PM Lorenzo Bianconi <
> lorenzo.bianc...@redhat.com> wrote:
> >
> > Increase priority for automatic routes (routes created assigning IP
> > addresses to OVN logical router interfaces) in order to always prefer
> them
> > over static routes since the router has a direct link to the destination
> > address (possible use-case can be found here [0]).
> >
> > [0] https://bugzilla.redhat.com/show_bug.cgi?id=1891516
> >
>
> Hi Lorenzo, Tim,
>
> While the patch may solve the problem in the bug report, I think there is
> something more fundamental to be discussed. The problem is caused by
> ovn-k8s's use of "src-ip" in static routes which overrides the
> direct-connected route. I think the implementation of "src-ip" support in
> the static route is somehow flawed. The priorities of the flows generated
> by static routes are calculated according to the prefix length, so that
> longest prefix routes are prioritised when there are multiple route
> matches, which is correct when comparing matches among "dst-ip" routes or
> among "src-ip" routes, but is not correct between "dst-ip" and "src-ip"
> routes. Comparison of prefix length between these two types of static
> routes doesn't make sense, because they match by different fields (src-ip
> v.s. dst-ip). For example, when there are static routes:
> 1. 192.168.0.0/24 via 100.64.0.1 src-ip
> 2. 10.0.0.0/20 via 100.64.0.2 dst-ip
>
> In this example, a packet from 192.168.0.1 to 10.0.0.1 matches both
> routes, but it is unreasonable to say it should follow the 1st route just
> because it has longer prefix length. Instead, we should prioritize one type
> over the other. It seems in physical router implementation policy based
> routing always has higher priority than destination routing, so we should
> probably enforce it in a similar way in OVN, i.e. set "src-ip" flows with
> higher priority than all the "dst-ip" flows. In fact, the policy routing
> table already supported this behavior because it is examined before the
> static route table.
>
> Since the "src-ip" feature in the static route table is flawed, and can be
> replaced by the policy routing table, I'd suggest to deprecate it. For
> correctness, users (like ovn-k8s) should use the policy routing table
> instead for the src-ip based routing rules. Users have full control of how
> they want the packets to be routed. For the use case mentioned in the bug
> report, it should have two rules in the policy routing table:
>
> 100 ip.dst == 100.64.0.0/16 accept # for directly connected destination,
> skip the src-ip rules
> 90 ip.src == 10.244.0.0/24 nexthop 100.64.0.1 # src-ip rules
>
> Would this better satisfy the need of ovn-k8s?
>
I believe this is correct. src-ip matching should be done in the policy
table so traditional dest based routing is handled in default routing
table. Need to go double check though.
> If the above is agreed, the priority change of directly connected routes
> from this patch is irrelevant to the problem reported in the bug, because
> policy routing rules are examined before the static routing table anyway,
> so no matter how high the route priority is, it wouldn't matter. In
> addition, it seems to me no real use cases would benefit from this change,
> but I could be wrong and please correct me if so.
>
> I disagree with this. Trying to override a directly connected route is
fundamentally wrong, which is why real routers specifically stop a user
from being able to do this. What if a user who had a router attached to
100.64.0.0/16, adds a /32 route for 100.64.0.1 via another
interface/subnet? That would take precedence over the directly attached
route in OVN iiuc and pretty much guarantee improper networking. Directly
connected routes should always take precedence, and therefore the default
route lflows that get installed should always have the highest possible
priority.
> Thanks,
> Han
>
> > Signed-off-by: Lorenzo Bianconi
> > ---
> > northd/ovn-northd.c | 27 ---
> > 1 file changed, 16 insertions(+), 11 deletions(-)
> >
> > diff --git a/northd/ovn-northd.c b/northd/ovn-northd.c
> > index b2b5f6a1b..dc8706f2f 100644
> > --- a/northd/ovn-northd.c
> > +++ b/northd/ovn-northd.c
> > @@ -7994,18 +7994,23 @@ build_route_prefix_s(const struct in6_addr
> *prefix, unsigned int plen)
> >
> > static void
> > build_route_match(const struct ovn_port *op_inport, const char
> *network_s,
> > - int plen, bool is_src_route, bool is_ipv4, struct ds
> *match,
> > - uint16_t *priority)
> > + int plen, bool is_src_route, bool is_ipv4, bool
> automatic,
> > + struct ds *match, uint16_t *priority)
> > {
> > +int prefix_len = plen;
> > const char *dir;
> > /* The priority here is calculated to implement longest-prefix-match
> > - * routing. */
> > + * routing. Automatic routes have max priority */
> > +if
Re: [ovs-dev] [RFC ovn] northd: set max priority for automatic routes
On Wed, Feb 10, 2021 at 2:17 PM Lorenzo Bianconi <
lorenzo.bianc...@redhat.com> wrote:
>
> Increase priority for automatic routes (routes created assigning IP
> addresses to OVN logical router interfaces) in order to always prefer them
> over static routes since the router has a direct link to the destination
> address (possible use-case can be found here [0]).
>
> [0] https://bugzilla.redhat.com/show_bug.cgi?id=1891516
>
Hi Lorenzo, Tim,
While the patch may solve the problem in the bug report, I think there is
something more fundamental to be discussed. The problem is caused by
ovn-k8s's use of "src-ip" in static routes which overrides the
direct-connected route. I think the implementation of "src-ip" support in
the static route is somehow flawed. The priorities of the flows generated
by static routes are calculated according to the prefix length, so that
longest prefix routes are prioritised when there are multiple route
matches, which is correct when comparing matches among "dst-ip" routes or
among "src-ip" routes, but is not correct between "dst-ip" and "src-ip"
routes. Comparison of prefix length between these two types of static
routes doesn't make sense, because they match by different fields (src-ip
v.s. dst-ip). For example, when there are static routes:
1. 192.168.0.0/24 via 100.64.0.1 src-ip
2. 10.0.0.0/20 via 100.64.0.2 dst-ip
In this example, a packet from 192.168.0.1 to 10.0.0.1 matches both routes,
but it is unreasonable to say it should follow the 1st route just because
it has longer prefix length. Instead, we should prioritize one type over
the other. It seems in physical router implementation policy based routing
always has higher priority than destination routing, so we should probably
enforce it in a similar way in OVN, i.e. set "src-ip" flows with higher
priority than all the "dst-ip" flows. In fact, the policy routing table
already supported this behavior because it is examined before the static
route table.
Since the "src-ip" feature in the static route table is flawed, and can be
replaced by the policy routing table, I'd suggest to deprecate it. For
correctness, users (like ovn-k8s) should use the policy routing table
instead for the src-ip based routing rules. Users have full control of how
they want the packets to be routed. For the use case mentioned in the bug
report, it should have two rules in the policy routing table:
100 ip.dst == 100.64.0.0/16 accept # for directly connected destination,
skip the src-ip rules
90 ip.src == 10.244.0.0/24 nexthop 100.64.0.1 # src-ip rules
Would this better satisfy the need of ovn-k8s?
If the above is agreed, the priority change of directly connected routes
from this patch is irrelevant to the problem reported in the bug, because
policy routing rules are examined before the static routing table anyway,
so no matter how high the route priority is, it wouldn't matter. In
addition, it seems to me no real use cases would benefit from this change,
but I could be wrong and please correct me if so.
Thanks,
Han
> Signed-off-by: Lorenzo Bianconi
> ---
> northd/ovn-northd.c | 27 ---
> 1 file changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/northd/ovn-northd.c b/northd/ovn-northd.c
> index b2b5f6a1b..dc8706f2f 100644
> --- a/northd/ovn-northd.c
> +++ b/northd/ovn-northd.c
> @@ -7994,18 +7994,23 @@ build_route_prefix_s(const struct in6_addr
*prefix, unsigned int plen)
>
> static void
> build_route_match(const struct ovn_port *op_inport, const char
*network_s,
> - int plen, bool is_src_route, bool is_ipv4, struct ds
*match,
> - uint16_t *priority)
> + int plen, bool is_src_route, bool is_ipv4, bool
automatic,
> + struct ds *match, uint16_t *priority)
> {
> +int prefix_len = plen;
> const char *dir;
> /* The priority here is calculated to implement longest-prefix-match
> - * routing. */
> + * routing. Automatic routes have max priority */
> +if (automatic) {
> +prefix_len = is_ipv4 ? 32 : 128;
> +prefix_len++;
> +}
> if (is_src_route) {
> dir = "src";
> -*priority = plen * 2;
> +*priority = prefix_len * 2;
> } else {
> dir = "dst";
> -*priority = (plen * 2) + 1;
> +*priority = (prefix_len * 2) + 1;
> }
>
> if (op_inport) {
> @@ -8172,7 +8177,7 @@ build_ecmp_route_flow(struct hmap *lflows, struct
ovn_datapath *od,
>
> char *prefix_s = build_route_prefix_s(&eg->prefix, eg->plen);
> build_route_match(NULL, prefix_s, eg->plen, eg->is_src_route,
is_ipv4,
> - &route_match, &priority);
> + false, &route_match, &priority);
> free(prefix_s);
>
> struct ds actions = DS_EMPTY_INITIALIZER;
> @@ -8246,7 +8251,7 @@ build_ecmp_route_flow(struct hmap *lflows, struct
ovn_datapath *od,
> static void
> add_route(struct hmap *lflows, const struct ovn_port *op,
>const char
