On 2023-10-23 11:06 p.m., Heinrich Schuchardt wrote:
On 10/24/23 02:21, seanedm...@linux.microsoft.com wrote:
From: Sean Edmond <seanedm...@microsoft.com>
This patch introduces 3 improvements to align with RFC 951:
- retransmission backoff interval maximum is configurable
- initial retranmission backoff interval is configurable
- transaction ID is kept the same for each BOOTP/DHCPv4 request
In applications where thousands of nodes are serviced by a single DHCP
server, maximizing the retransmission backoff interval at 2 seconds (the
current u-boot default) exerts high pressure on the DHCP server and
network layer.
RFC 951 “7.2. Client Retransmission Strategy” states that the
retransmission backoff interval should maximize at 60 seconds. This
%s/maximize at/be limited to/
patch allows the interval to be configurable using the environment
variable "bootpretransmitperiodmax"
If there is an RFC defining the value, why do we need an environment
variable?
The intention with this patch is to provide the option to satisfy RFC,
while giving the option to preserve the existing behavior. The
retransmission timing parameters in u-boot have been the same for the
last ~10 years, so I'm guessing some have gotten used to this behavior
(even though it's not correct).
The initial retranmission backoff period defaults to 250ms, which is
also too small for these scenarios with many clients. This patch makes
the initial retransmission interval to be configurable using the
environment variable "bootpretransmitperiodinit".
Also, on a retransmission it is not expected for the transaction ID to
change (only the 'secs' field should be updated). Let's save the
transaction ID and use the same transaction ID for each BOOTP/DHCPv4
exchange.
Signed-off-by: Sean Edmond <seanedm...@microsoft.com>
---
net/bootp.c | 56 ++++++++++++++++++++++++++++++++++++++---------------
1 file changed, 40 insertions(+), 16 deletions(-)
diff --git a/net/bootp.c b/net/bootp.c
index 6800290963..bab17a9ceb 100644
--- a/net/bootp.c
+++ b/net/bootp.c
@@ -42,6 +42,17 @@
*/
#define TIMEOUT_MS ((3 + (CONFIG_NET_RETRY_COUNT * 5)) * 1000)
+/*
+ * According to rfc951 : 7.2. Client Retransmission Strategy
+ * "After the 'average' backoff reaches about 60 seconds, it should be
+ * increased no further, but still randomized."
+ *
+ * U-Boot has saturated this backoff at 2 seconds for a long time.
+ * To modify, set the environment variable "bootpretransmitperiodmax"
+ */
+#define RETRANSMIT_PERIOD_MAX_MS 2000
This does not match RFC 951. Please, why shouldn't we use the standard
value by default?
You're right, better to use the standard value by default.
+#define RETRANSMIT_PERIOD_INIT_MS 250
This constant should be described too.
Will add a description.
+
#ifndef CFG_DHCP_MIN_EXT_LEN /* minimal length of extension
list */
#define CFG_DHCP_MIN_EXT_LEN 64
#endif
@@ -53,6 +64,7 @@
u32 bootp_ids[CFG_BOOTP_ID_CACHE_SIZE];
unsigned int bootp_num_ids;
int bootp_try;
+u32 bootp_id;
ulong bootp_start;
ulong bootp_timeout;
char net_nis_domain[32] = {0,}; /* Our NIS domain */
@@ -60,6 +72,7 @@ char net_hostname[32] = {0,}; /* Our hostname */
char net_root_path[CONFIG_BOOTP_MAX_ROOT_PATH_LEN] = {0,}; /* Our
bootpath */
static ulong time_taken_max;
+static u32 retransmit_period_max_ms;
#if defined(CONFIG_CMD_DHCP)
static dhcp_state_t dhcp_state = INIT;
@@ -414,8 +427,8 @@ static void bootp_timeout_handler(void)
}
} else {
bootp_timeout *= 2;
- if (bootp_timeout > 2000)
- bootp_timeout = 2000;
+ if (bootp_timeout > retransmit_period_max_ms)
+ bootp_timeout = retransmit_period_max_ms;
RFC 951 requires that the backoff time is randomized.
I'll can look into adding randomization to this as well.
Best regards
Heinrich
net_set_timeout_handler(bootp_timeout, bootp_timeout_handler);
bootp_request();
}
@@ -711,10 +724,14 @@ static int bootp_extended(u8 *e)
void bootp_reset(void)
{
+ char *ep; /* Environment pointer */
+
bootp_num_ids = 0;
bootp_try = 0;
bootp_start = get_timer(0);
- bootp_timeout = 250;
+
+ bootp_timeout = env_get_ulong("bootpretransmitperiodinit", 10,
RETRANSMIT_PERIOD_INIT_MS);
+
}
void bootp_request(void)
@@ -726,7 +743,6 @@ void bootp_request(void)
#ifdef CONFIG_BOOTP_RANDOM_DELAY
ulong rand_ms;
#endif
- u32 bootp_id;
struct in_addr zero_ip;
struct in_addr bcast_ip;
char *ep; /* Environment pointer */
@@ -742,6 +758,9 @@ void bootp_request(void)
else
time_taken_max = TIMEOUT_MS;
+ retransmit_period_max_ms =
env_get_ulong("bootpretransmitperiodmax", 10,
+ RETRANSMIT_PERIOD_MAX_MS);
+
#ifdef CONFIG_BOOTP_RANDOM_DELAY /* Random BOOTP delay */
if (bootp_try == 0)
srand_mac();
@@ -801,18 +820,23 @@ void bootp_request(void)
extlen = bootp_extended((u8 *)bp->bp_vend);
#endif
- /*
- * Bootp ID is the lower 4 bytes of our ethernet address
- * plus the current time in ms.
- */
- bootp_id = ((u32)net_ethaddr[2] << 24)
- | ((u32)net_ethaddr[3] << 16)
- | ((u32)net_ethaddr[4] << 8)
- | (u32)net_ethaddr[5];
- bootp_id += get_timer(0);
- bootp_id = htonl(bootp_id);
- bootp_add_id(bootp_id);
- net_copy_u32(&bp->bp_id, &bootp_id);
+ /* Only generate a new transaction ID for each new BOOTP request */
+ if (bootp_try == 1) {
+ /*
+ * Bootp ID is the lower 4 bytes of our ethernet address
+ * plus the current time in ms.
+ */
+ bootp_id = ((u32)net_ethaddr[2] << 24)
+ | ((u32)net_ethaddr[3] << 16)
+ | ((u32)net_ethaddr[4] << 8)
+ | (u32)net_ethaddr[5];
+ bootp_id += get_timer(0);
+ bootp_id = htonl(bootp_id);
+ bootp_add_id(bootp_id);
+ net_copy_u32(&bp->bp_id, &bootp_id);
+ } else {
+ net_copy_u32(&bp->bp_id, &bootp_id);
+ }
/*
* Calculate proper packet lengths taking into account the
