Saturday, October 3, 2009

Choking Bandwidth Wan HSRP

In previous post of HSRP, a problem has highlighted of reverse and forwarding traffic when customer use the HSRP in LAN. This post is highlighting the problems when HSRP runs in PE-CE wan. Below is the diagram shown for reference purpose.

Customer R6 is connected with two PE routers for high availability. R3 is the active router with priority 255 and R2 is the standby router with priority 200. R1 ie receiving the lan routes from R2 as well as from R3 but selecting R2 as the best path because of smallest router-id assuming the cost of the both links in cloud is same. So the forwarding from R6 is happening via R3 router and reverse traffic is coming via R2.
Which Problems Could Come
1.The different reverse and forwarding could cause problems ofin customers applications if applications are jitter or latency senstive.
2. If the primary and backup path has different bandwidth allocation, In that case backup could be obstructed at anytime.

How to overcome the problem
1.Change the IGP path cost which may bring other difficulties.
2.Change the router id.

Apart from these remedies I am seeking another solution which could solve the current problem. If anyone is having anyidea , please share.

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Roggy said...

Have you tried explict path definition with a backup path with a traffic engineered link?

shivlu jain said...

That option is there but if you are having huge number of customers what will be done in that case and TE will consume lot of processes.
Thanks for the suggestion.

Akinsola Oyelakin said...

I think i have a way to make this happen. Most people may not like this though.
you can use NAT (either a different NAT pool per CE or NAT overload on each CE) this will force the PE to send traffic back to that same CE. so if HSRP fails to the standby, the NEW NAT address will be used and the PE will equally send traffic back to the right CE over the right link. making the routing to be symetrical. My 5 cents

shivlu jain said...

good option :)

CGV said...

Mhhh..The NAT will be placed on the CE or on the 2 PE configured with HSRP?