Hi,
Imagine if you will a head office and a remote office. Each site uses the OSPF routing protocol.
Two ISP network's interconnect the two sites using BGP on each provider network. At each site the ISP has provided 2
Customer Edge Routers that redistribute OSPF to BGP and via versa at the remote office, e.g :
Head office Head Office CE Router Remote Office CE Router Remote Office
----------- ---------------------- ----------------------- -------------
OSPF Routing -> Redistribute OSPF to BGP -> Redistribute BGP to OSPF -> OSPF Routing
Routes from the office are advertised down to the remote office over both ISP networks. Routes from the remote office
are advertised up to the head office over both ISP networks.
OSPF timers between our companies routers that connect to the service provider CE routers have been reduced so that if one
of the provider networks fails, OSPF will quickly flush out routes learnt from the failed network and force all traffic
to pass over the working provider "cloud".
The problem is this :
OSPF is flushing out the entries in about 3-4 seconds, but it is taking the failed provider network about 30 seconds to
flush out the routes being advertised back up to head office.
Is there any way in which a triggered update can be configured, or the timers at each ISP CE be modified so that the routes
learnt over the failed network are flushed out of the routing tables quicker ?
The ISP cannot modify the backbone BGP timers on the PE routers as this could potentially affect the whole design / convergence
of the total backbone, on which many customers operate.
I am sure that there is something we can do on the CE routers at each site where re-distribution takes place to
perhaps trigger a flush of the lost routes, or to speed up the aging out of the lost routes but am unsure
exactly what :)
Thanks in advance
