[c-nsp] OSPF on Ring Networks

[Mohammad Khalil]

actually the main ring consists of 11 routers , 2 Cisco 7606-S and 9 ME6524 Cisco switches
there are small sub-rings connected to the main ring
right now i dont have BGP running inside my network except for OSPF on area 0

> Date: Sat, 14 May 2011 17:50:39 +0100
> From: nick at foobar.org
> To: christian at errxtx.net
> CC: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] OSPF on Ring Networks
> 
> On 14/05/2011 16:05, Christian Meutes wrote:
> > Here it depends. If the next-hop changes OSPF will in most cases converge
> > faster than BGP. So if there aren't that many routes and you can live with
> > less policy possibilities I would prefer OSPF over BGP for carrying
> > non-infrastructure networks.
> 
> yes if the next-hop changes, but network topology change events will often 
> not cause a next-hop change, just a SFP recalculation - which means that if 
> your SFP domain is smaller, it will converge faster.  I.e. the router's FIB 
> may be updated, but ibgp will not be aware of the topology change.
> 
> The things that cause next-hop changes are customer edge flaps.
> 
> As regards carrying non-infrastructure prefixes in OSPF, it really depends 
> on how big your network is.  For small networks it doesn't matter very 
> much.  For large networks, there is no choice other than ibgp because 
> having a functional prefix management system is more important than shaving 
> a couple of seconds off a customer edge link-up event.  For networks in the 
> middle, they usually start out by putting non-infrastructural prefixes into 
> the IGP but change later on because it doesn't scale well and having a 
> flexible interior routing policy becomes more important than fast convergence.
> 
> > BFD, MPLS-FRR, SPF- and Flood-Tuning for even faster convergence.
> 
> ...and for even more CPU load.
> 
> Nick
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