Maximum ip routes that can be handled by isis and ospf

Question

Hello All,
Is there any limitation on the number of ip routes that isis can handle? I was going through one of the documentations which mentioned that the limit is 30K routes. This is due to the max number of fragments ( 256 ) with each containing not more than 121 routes.?
Do the following commands  help to change this number?
lsp-mtu
and clns-mtu
Has anyone seen any such limitation for OSPF ?
Regards,
Shreeram

Answer 1

Hello Shreeram,
Hmm Qestion is quit logical, But what can I say is, believe me OSPF can handle lot of routes. It completly depends upon your Routers Processor and Memory.
In no I can say more than 6000 routes (reference https://supportforums.cisco.com/thread/10496)
For OSPF not to suffer, we must follow some rules when we make areas, it is because it is a linkstate algorithm, below are the same
for more information you can browse here
http://www.ciscopress.com/articles/article.asp?p=1763921&seqNum=6
Factors Influencing OSPF Scalability
Scaling is determined by the utilization of three router resources: memory, CPU, and interface bandwidth. The workload that OSPF imposes on a router depends on these factors:
Number of adjacent neighbors for any one router: OSPF floods all link-state changes to all routers in an area. Routers with many neighbors have the most work to do when link-state changes occur. In general, any one router should have no more than 60 neighbors.
Number of adjacent routers in an area: OSPF uses a CPU-intensive algorithm. The number of calculations that must be performed given n link-state packets is proportional to n log n. As a result, the larger and more unstable the area, the greater the likelihood for performance problems associated with routing protocol recalculation. Generally, an area should have no more than 50 routers. Areas that suffer with unstable links should be smaller.
Number of areas supported by any one router: A router must run the link-state algorithm for each link-state change that occurs for every area in which the router resides. Every ABR is in at least two areas (the backbone and one adjacent area). In general, to maximize stability, one router should not be in more than three areas.
Designated router (DR) selection: In general, the DR and backup designated router (BDR) on a multiaccess link (for example, Ethernet) have the most OSPF work to do. It is a good idea to select routers that are not already heavily loaded with CPU-intensive activities to be the DR and BDR. In addition, it is generally not a good idea to select the same router to be the DR on many multiaccess links simultaneously.
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Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."