[isp-bgp] Re: Routing Information

[James <haesu@...>]

> 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

> 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.

	that is probably the easiest idea.

	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.

	you can either run an igp, or redistribute static routes (eeeek.., which
	doesnt really solve the flap issues either) , etc

	or, just turn your layer3 switch to advertise the blocks upstream to both
	of your routers. put all 3 equipments in an igp, such as ospf, and PEER ibgp
	on *loopback* addresses, distributed by ospf. peering to loopbacks will ensure
	smooth non-flapping bgp sessions most of the time, as igp knows routes
	of loopbacks and physical interface states.

-J



-- 
James Jun                                            TowardEX Technologies, Inc.
Technical Lead                        Network Design, Consulting, IT Outsourcing
james@...                  Boston-based Colocation & Bandwidth Services
cell: 1(978)-394-2867           web: http://www.towardex.com , noc: www.twdx.net






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