[c-nsp] OSPF design

[Benjamin Lovell]

If you are doing MPLE TE then you really don't want more than one area as then you get into inter-area TE tunnels which makes TE optimal path selection harder(not possible in some cases). 

-Ben

On Oct 25, 2010, at 4:50 AM, Rin wrote:

> Dear all, 
> 
> Thank you for your replies. 
> 
> We use OSPF basically to advertise each router's loopback so that we can
> deploy L2 , L3 VPN between routers. There'll be no other external route
> advertised into OSPF. Thus, we will not configure summarization on any ABR
> router as well as stubby areas. 
> 
> I agree with Geoff's post that separating network into different OSPF areas
> cannot reduce LSDB size. If we separate into different areas, LSA1,2,3 are
> generated and all routers must trigger SPF for a topology change inside an
> area. If we do not separate into different areas, only LSA1,2 are generated
> and all routers must also trigger SPF for a topology change inside an area. 
> 
> According to below statement, iSPF helps each router to run SPF only on the
> changed portion of the topology. This means neither separating network into
> areas nor configuring inside an area will benefit from iSPF. Correct me if
> I'm wrong at this. 
> 
> "OSPF uses Dijkstra's SPF algorithm to compute the shortest path tree (SPT).
> During the computation of the SPT, the shortest path to each node is
> discovered. The topology tree is used to populate the routing table with
> routes to IP networks. When changes to a Type-1 or Type-2 link-state
> advertisement (LSA) occur in an area, the entire SPT is recomputed. In many
> cases, the entire SPT need not be recomputed because most of the tree
> remains unchanged. Incremental SPF allows the system to recompute only the
> affected part of the tree. Recomputing only a portion of the tree rather
> than the entire tree results in faster OSPF convergence and saves CPU
> resources. Note that if the change to a Type-1 or Type-2 LSA occurs in the
> calculating router itself, then the full SPT is performed"  (source:
> http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/ospfispf.html) 
> 
>> From your advice, I'm more likely to configure those 100 routers inside an
> OSPF area now.
> 
> The reason why we design OSPF up to UPE devices because we also have FTTH
> switches configure as Layer 2, also we can deploy different Layer 3
> redundancy techniques such Layer 3 loop prevention, MPLS TE..up to UPE
> layer.
> 
> Thanks,
> 
> Rin
> 
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Heath Jones
> Sent: Saturday, October 23, 2010 6:05 AM
> To: Robert Crowe (rocrowe)
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] OSPF design
> 
>> Just remember
>> that you cannot summarize (today) your main Loopback used for your
>> LDP/BGP ID as there needs to be a full LSP from ingress-to-egress PE
>> across areas, if you providing L2/L3VPN services.
> 
> Is this because the lsp is label in label (outer being pe, inner being
> customer route)?
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
> 
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/