Optimal -Suboptimal

[ranjeet_badhe]

Can any one explain me what do you mean by Optimal and Sub-optimal routing?I would appreciate if the examples are also given especially in the context of MPLS.

Warm Regards

Ranjeet

[Harold Ritter]

In an MPLS TE context, you use the term "optimal routing" to designate the path that would have been chosen by the IGP as opposed to "sub-optimal routing", which is the path selected by the Constraint SPF algorithm (CSPF) given a certain restriction (mainly bandwidth).

Let me know if that answers your question,

[ranjeet_badhe]

Dear Harold

Yes ,I got it now in the context of MPLS but in case of Peer-to-peer we say that routing is optimal what does this mean in general?I am not getting when do we use the term that routing is optimal or sub-optimal?

[Harold Ritter]

Generally, "Obtimal routing" is if you follow the shortest path to destination where as "sub-optimal routing" is if you follow a longer path for some reason. One example of sub-optimal routing in a non-mpls TE environment is for instance when you have two ABRs for a given area advertising a summary address into the non-backbone area. It is quite possible that one of the two ABRs is closer to a given subnet part of the summary address range but since the two ABRs advertise the same range traffic to that subnet from the non-backbone area might traverse the ABR that is farther from the destination subnet. In this case you could use the term "sub-optimal routing" to describe this behavior. If you didn't summarize at the ABRs, you would get optimal routing.

Hope this explanation helps,