If you really want to use MPLS applications extensively and have a plan in using IPv6 in future. Why don't you think about ISIS instead of talking about OSPF areas.
Just a suggestion, you better look into the comparison of ISIS and OSPF and all the implications. BR// Masood On 26-Oct-2010, at 12:49 PM, Rin wrote: Hi all, Thank you all for your replies. I summarize some discussion points for my case: + For 7600 routers, it is possible to design OSPF area 0 with 100 routers + If we do not configure summarization on ABR router, separating the network into different OSPF areas has no meaning in reducing LSDB size. + iSPF feature cannot preventing OSPF advertise topology changes to different OSPF areas. + Deploying inter-area TE tunnels makes TE optimal path selection harder >From these points, I am confident to configure all routers (~100) in OSPF area 0. However, our network might be expanded in the future and more routers will participate into OSPF. So if the recommendation of maximum 50 routers inside an OSPF area is no longer suitable for "strong" router (i.e 7600), which threshold (number of routers, number of routes, TCAM utilization...???) should we care when design OSPF areas in ISP network? Thanks, Rin -----Original Message----- From: Benjamin Lovell [mailto:[email protected]] Sent: Monday, October 25, 2010 9:22 PM To: Rin Cc: Heath Jones; Robert Crowe (rocrowe); cisco-nsp NSP Subject: Re: [c-nsp] OSPF design 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: [email protected] [mailto:[email protected]] On Behalf Of Heath Jones Sent: Saturday, October 23, 2010 6:05 AM To: Robert Crowe (rocrowe) Cc: [email protected] 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 [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
