[j-nsp] Junos ospf question

[Per Westerlund]

First let me see if I understand you correctly by rephrasing.

- Three sites A, B och C all connected with direct links
- Link A-B has high capacity
- Links A-C and B-C has lower capacity
- High volume storage traffic traverses link A-B and must not use links A-C or B-C, even if link A-B goes down
- There is also other low-volume traffic between all sites that should be routed around possible broken links.

Why not first try to solve it the easy way instead of using routing magic?

- If the high-volume storage traffic has static addressing that is unique, you can use static routes that are NOT exported into OSPF.

If the easy way does not apply, there is a slightly more complex way to do it:

- If you can classify storage traffic statically with a filter, use FBF to direct that traffic to a static default route in another routing instance.

I don't really recommend it, but there are high-tech alternatives that do about the same as FBF in this case, but in a more "interesting" way. Usually you should always think KISS in production, but I must mention it: Multitopology routing.

With MT routing one OSPF instance can have more than one topology active, in this case one with only A and B present, and another where all of A, B and C are present. You then classify the ingress traffic and assign it to one of the topologies (by using their specific routing/forwarding table).

Here is a link to where you can get started: http://www.juniper.net/techpubs/en_US/junos12.1/topics/usage-guidelines/routing-configuring-multitopology-routing-in-ospf.html .

Remember: I don't recommend it!

/Per

25 sep 2013 kl. 10:39 skrev R S <dim0sal at hotmail.com>:

> basically I've a triangulation A - B - C - A
> 
> single area 0
> 
> A-B link is 10Gbs
> A-C and B-C is 1 Gbs
> 
> since in A-B run a very high volume of traffic (storage), I do not want if A-B fails this traffic goes through C
> 
> C redistribute as well statics into OSPF
> 
> Hope it clear now