From experience I found that you need to keep all the timers in sync with all your peers. Something like this for every peer in your bgp config.
neighbor xxx.xx.xx.x timers 30 60 Make sure that this is communicated to your peer as well so that their timer setting are reflected the same. Zaid ----- Original Message ----- From: "Steve Bertrand" <steve@ibctech.ca> To: "nanog list" <nanog@nanog.org> Sent: Friday, May 22, 2009 3:45:20 PM GMT -08:00 US/Canada Pacific Subject: Multi-homed clients and BGP timers Hi all, I've got numerous single-site 100Mb fibre clients who have backup SDSL links to my PoP. The two services terminate on separate distribution/access routers. The CPE that peers to my fibre router sets a community, and my end sets the pref to 150 based on it. The CPE also sets a higher pref for prefixes from the fibre router. The SDSL router to CPE leaves the default preference in place. Both of my PE gear sends default-originate to the CPE. There is (generally) no traffic that should ever be on the SDSL link while the fibre is up. Both of the PE routers then advertise the learnt client route up into the core: *>i208.70.107.128/28 172.16.104.22 0 150 0 64762 i * i 172.16.104.23 0 100 0 64762 i My problem is the noticeable delay for switchover when the fibre happens to go down (God forbid). I would like to know if BGP timer adjustment is the way to adjust this, or if there is a better/different way. It's fair to say that the fibre doesn't 'flap'. Based on operational experience, if there is a problem with the fibre network, it's down for the count. While I'm at it, I've got another couple of questions: - whatever technique you might recommend to reduce the convergence throughout the network, can the same principles be applied to iBGP as well? - if I need to down core2, what is the quickest and easiest way to ensure that all gear connected to the cores will *quickly* switch to preferring core1? Steve