[isp-bgp] Re: Routing Information

[Pete Templin <petelists@...>]

James wrote:
> > When using IBGP internally is it typical to use internal AS#'s for the
> > internal routers/switches or do you use them all with your AS# and the
> > next-hop parameter?
>
> 	when using IBGP:
> 	 *) all routers in IBGP chain must speak using same ASN
> 	 *) all routers in IBGP must be peered in full mesh[1]
> 	[1]: exception of rr's
Or use confederations...

> > I'm thinking that it may be wise for me to have my Layer3 Switch advertise
> > my address blocks to my routers.  That way the routers will advertise to
> > each other also.
> 	my line of thinking is this. if you have both routers right now as
> 	you currently have, joined in IBGP peering, each announcing a /24..
> 	it doesn't seem to make a lot of difference to me than your current
> 	setup. what happens if one of the router's Ethernet to switch goes
> 	down? yes, it will realize its gone, so it will withdraw the announcement
> 	which will then still propagate to your upstream and cause a flap anyway.
> 	if you use floating static route to null on each router, even if the ethernet
> 	goes down, it will continue advertising the prefix as its manually announced
> 	using network a.b.c.d command.
Two routers peered by IBGP will SHARE their internal routes.  If ONE 
router loses connectivity to the switch, the other router will continue 
to announce the route to all IBGP routers, which will propagate the 
route to appropriate EBGP peers based on the local policy.  The route 
will not flap (assuming all parameters stay the same) to the outside world.







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