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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Community NO-EXPORT
Hi Haas, Danny's reply is clear and right! I just want a little supplement. While full mesh IBGP in the transit backbone eliminate the need for synchronization, we usually flood all the IBGP/EBGP routers their next-hop via IGP. So you needn't worry about synchronization of the next-hops, but their reachibility. regards, ------------------------------------------------------ (Mr.) Yu(2) Ning(2) Int'l/Domestic Routing/Resource Man. ChinaNET(AS4134) Backbone Operation Center Networking Dep.,Datacom Bureau, China Telecom. ------------------------------------------------------ ----- Original Message ----- From: "Danny McPherson" <[email protected]> To: <[email protected]> Sent: Friday, August 25, 2000 5:55 AM Subject: Re: Community NO-EXPORT > > > No, BGP synchronization does indeed refer to the > requirement that the destination network be available > via the IGP. > > If it were just the BGP NEXT_HOP value it wouldn't be > of much use, as intermediate nodes perform forwarding > based on the DA in the packet and [if not synchronized] > won't find a match. As a result, the packet will be > discarded. > > Of course, most folks simply have full mesh IBGP > (perhaps via RR or confeds) and so there's no reason > too enable [or not disable] BGP synchronization. > > -danny > > > Color me confused, but isn't the synchronization waiting on the > > NEXT_HOPs showing up in your IGP, not the actual BGP route? > > > > After all, the issue is this: > > > > BR-A - (your internal network) - BR-B > > > > A route shows up at BR-A with a nexthop of some interface on BR-A > > (or the loopback interface of BR-A). It is then propogated via > > iBGP to BR-B. > > > > It is only unsafe to install said route and propogate it BR-B's peers > > if the route's nexthop is not reachable by BR-B. > > > > This is a far cry from having to inject your BGP into your IGP. > > > > I will note that this isn't how Cisco has it documented, and I don't know > > how they actually treat the sync issue. The documentation actually > > says it does wait for the route to show up in the IGP. > >
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