RIP not doing "triggered update" following route deletion

[Tore Anderson]

I've noticed that BIRD doesn't withdraw (i.e., advertising them with
metric 16) RIP routes when they disappear from the routing table. This
means that the neighbour router ends up waiting for the route to time
out before ceasing to send traffic to the BIRD router, rather than doing
so immediately.

I'm running v1.4.0 with a bird.conf containing:

log syslog { info, remote, warning, error, auth, fatal };
router id 192.0.2.1;
protocol device {}
protocol direct {}
protocol rip {
interface "*" {
mode nolisten;
ttl security on;
};
import none;
export all;
}

To reproduce the issue, look at "tcpdump -v port 520" while doing:

1) ip address add 192.0.2.2/32 dev lo
-> a triggered update appears (advertising 192.0.2.2/32)
2) ip address delete 192.0.2.2/32 dev lo
-> a triggered update doesn't appear (it should have)

For what it's worth, step #2 does increase the RIP protocol's "Export
withdraws" counter. This issue also applies to RIPng/bird6.

AFAICT, not sending these triggered updates immediately is a standards
violation. Quoting RFC 1812 F.2: «A router MUST send a triggered update
when routes are deleted or their metrics are increased.» Also see RFC
2453 section 3.10.1.

Tore

[Ondrej Filip]

Post by Tore Anderson
I've noticed that BIRD doesn't withdraw (i.e., advertising them with
metric 16) RIP routes when they disappear from the routing table. This
means that the neighbour router ends up waiting for the route to time
out before ceasing to send traffic to the BIRD router, rather than doing
so immediately.

Hi Tore,
unfortunately, the current RIP code is broken. I tried to fix this in
git branch rip, but hasn't been merged into master yes. But if you
have some capacity to test this branch, it would be very helpful.

Ondrej

Post by Tore Anderson
log syslog { info, remote, warning, error, auth, fatal };
router id 192.0.2.1;
protocol device {}
protocol direct {}
protocol rip {
interface "*" {
mode nolisten;
ttl security on;
};
import none;
export all;
}
1) ip address add 192.0.2.2/32 dev lo
-> a triggered update appears (advertising 192.0.2.2/32)
2) ip address delete 192.0.2.2/32 dev lo
-> a triggered update doesn't appear (it should have)
For what it's worth, step #2 does increase the RIP protocol's "Export
withdraws" counter. This issue also applies to RIPng/bird6.
AFAICT, not sending these triggered updates immediately is a standards
violation. Quoting RFC 1812 F.2: «A router MUST send a triggered update
when routes are deleted or their metrics are increased.» Also see RFC
2453 section 3.10.1.
Tore

[Tore Anderson]

* Ondrej Filip

Post by Ondrej Filip
unfortunately, the current RIP code is broken. I tried to fix this in
git branch rip, but hasn't been merged into master yes. But if you
have some capacity to test this branch, it would be very helpful.

Hi Ondrej,

I'll be happy to help out testing this branch. Here's my initial
observations:

1) Routes that are removed from the routing table do get advertised with
metric infinity (16), and this update gets retransmitted five times. Great!

2) RIP seems to only be sending updates only at regular tick intervals
(every 30 seconds). This means that there is a delay after
adding/removing an address of up to 30 seconds before the neighbours get
informed of the change. BIRD 1.4.0 fares better (for additions).

FWIW, here are the timestaps of when I added/removed addresses and when
BIRD passed that information along. I confirmed that the
additions/removals showed up in "birdc[6] show route" pretty much
instantly, so it's the RIP protocol that's laggy:

09:45:11 - ip address add 192.0.2.1/32
09:45:22 (+11s) - RIP announcement going out

09:46:23 - ip address add 2001:db8::1/128
09:46:51 (+28s) - RIP announcement going out

09:47:45 - ip address del 192.0.2.1/32
09:47:53 (+8s) - RIP announcement going out

09:48:24 - ip address del 2001:db8::1/128
09:48:51 (+27s) - RIP announcement going out

3) RIPng appears to be advertising some bogus routes (but only when it's
also advertising a sane route), as seen here:

09:47:21.635383 IP6 fe80::225:b5ff:fe00:ce.ripng > ff02::9.ripng: ripng-resp 3: ffff:3:2c:114:9912:753::/0 2001:db8::1/128 (1) ffff:1:c917:28a0:b99c:3132:fd5d:283b/96 [48667] (166)
09:47:51.906476 IP6 fe80::225:b5ff:fe00:ce.ripng > ff02::9.ripng: ripng-resp 3: ffff:3:2c:114:b812:753::/0 2001:db8::1/128 (1) ffff:1:917e:57b1:6814:f716:c44b:a652/187 [57261] (210)

The PCAP and config files are attached.

Tore

[Tore Anderson]

Hello Ondrej,

I wonder if anything more happened with this problem? As far as I can
tell, the issue persist with BIRD 1.4.5, no triggered updates with
metric 16 is transmitted when a route is removed. Also, the "rip" branch
fails to compile for me now.

Tore

* Tore Anderson

Post by Tore Anderson
* Ondrej Filip

Post by Ondrej Filip
unfortunately, the current RIP code is broken. I tried to fix this in
git branch rip, but hasn't been merged into master yes. But if you
have some capacity to test this branch, it would be very helpful.

Hi Ondrej,
I'll be happy to help out testing this branch. Here's my initial
1) Routes that are removed from the routing table do get advertised with
metric infinity (16), and this update gets retransmitted five times. Great!
2) RIP seems to only be sending updates only at regular tick intervals
(every 30 seconds). This means that there is a delay after
adding/removing an address of up to 30 seconds before the neighbours get
informed of the change. BIRD 1.4.0 fares better (for additions).
FWIW, here are the timestaps of when I added/removed addresses and when
BIRD passed that information along. I confirmed that the
additions/removals showed up in "birdc[6] show route" pretty much
09:45:11 - ip address add 192.0.2.1/32
09:45:22 (+11s) - RIP announcement going out
09:46:23 - ip address add 2001:db8::1/128
09:46:51 (+28s) - RIP announcement going out
09:47:45 - ip address del 192.0.2.1/32
09:47:53 (+8s) - RIP announcement going out
09:48:24 - ip address del 2001:db8::1/128
09:48:51 (+27s) - RIP announcement going out
3) RIPng appears to be advertising some bogus routes (but only when it's
09:47:21.635383 IP6 fe80::225:b5ff:fe00:ce.ripng > ff02::9.ripng: ripng-resp 3: ffff:3:2c:114:9912:753::/0 2001:db8::1/128 (1) ffff:1:c917:28a0:b99c:3132:fd5d:283b/96 [48667] (166)
09:47:51.906476 IP6 fe80::225:b5ff:fe00:ce.ripng > ff02::9.ripng: ripng-resp 3: ffff:3:2c:114:b812:753::/0 2001:db8::1/128 (1) ffff:1:917e:57b1:6814:f716:c44b:a652/187 [57261] (210)
The PCAP and config files are attached.
Tore