Early IOSs had a problem with HSRP when ICMP redirects were enabled on the
same interface. If your IOS is not new, try disabling ICMP redirect
This manifested itself as a loss of connectivity.
interface a b/c
no ip redirects
standby priority ...
standby ip ...
From: Nathan Ward [mailto:firstname.lastname@example.org]
Sent: 2 November 2003 1:36 a.m.
Subject: [nznog] Strange BGP 'problem'
At the risk of posting something on topic..
I have 2 routers (lets call them A and B), talking to different upstream
providers, advertising 188.8.131.52/24 via BGP.
184.108.40.206/24 is subnetted, each subnet is on a different VLAN.
These routers talk to each other with iBGP, giving each other everything
(including 220.127.116.11/24 le 32).
I run HSRP between the 2 routers.
Router B prepends my ASN several times before advertising 18.104.22.168.
Relevant stuff (on both boxes):
router bgp 23729
ip route 22.214.171.124 255.255.255.0 Null0
With this config, reachability for 126.96.36.199/24 hosts alternates on and off
roughly every minute. 47% total loss over 10 minutes (ie 5 'bursts' of
These packets are all hitting my AS at router A.
I've turned HSRP off and on again to see if that was causing problems (it
Several solutions I've found:
- Turning the iBGP session to router B off. (uhh..)
- Turning syncronization on.
My understanding of BGP synchronization, is that BGP will only re-advertise
with eBGP prefixes learned via iBGP after learning them via another IGP if
one is running.
ec-br-1(config-router)#do sh run | inc router
router bgp 23729
bgp router-id 188.8.131.52
I'm not running any IGPs, so synchronization shouldn't be part of the
equation. In any case, I'm not a transit provider.
And, there seems to be no relation to readvertising routes here, the packets
AFAICT are getting to router A and being dropped.
I've got no problem running running with synchronization on at the moment,
but thats not the point. :-)
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