MPLS - OSPF as IGP

[aretsu]

Hello,

Two MPLS/VPN questions:

1) If using OSPF as the IGP on a MPLS/VPN network, what is the recommendation, using single-area or can i use a multiple-area topology?

2) Are there any limitations about number of VRFs on a PE-router? or the routes on a particular VRF? or just memory issues?

Thanks!

[steven-dunn]

1 I would deploy multiple areas in your IGP so that it can scale and keep the memory consuption to a minimum. There are many cisco reccommendations regarding the maximum number of devices per area.

2 Each VR will put a memory and CPU overhead on your router. Eventually you will hit the limit. I'm not sure if there is a software limit or if you keep adding until the machine crashes. Setup a nms to monitor the CPU and memory so you can pro-actively manage any additions to the box. Keep in mind one VR may consume more resources than others.

[chen__nan]

1/ In my opinion, For MPLS/VPN application, there's no area limited for cisco routers, you can use single area or multiareas as your network demand. But if you also want to develope MPLS/TE in your network, you should consider your IOS software version, because older version dose not support TE in multiareas.

2/ The major limit about numbers of VRFs on a single PE are the memory and the CPU powerhouse, especially the memory. Here's some memory caculate rule:

Mp = (N*128) + (Np*60) + (P*60) + (Pa * 24) + (Ec * 24)

Mp = Total memory used for BGP table by PE in Bytes

N = Number of BGP network entries

Np = Number of BGP path entries

P = Number of path attribute entries

Pa = Number of AS_PATH entries

Ec = Number of Extended Community entries

Also, CEF(Fib) and RIB in VRF will consume memory, too.

Finally, if you use dynamic routing process between CE and PE, such as OSPF, you need more memory to serve them.