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Loadsharing for dual ISP

vicky.dhas
Level 1
Level 1

Friends,

I have taken MPLS from 2 ISPs and they are configured in active-back up using HSRP in LAN.Now i want to loadshare traffic between both ISPs to optimize my avaialbe resource.can you suggest best method to achieve that for forward and reverse traffic.

regards

Vicky

8 Replies 8

rsimoni
Cisco Employee
Cisco Employee

Hi Vicky,

with dual-home ISP's there is no way to achieve load balancing as BGP selects only the single best path to a destination among the BGP paths that are learned from different AS's.

What you can achieve is some degree of load sharing (which is not load balancing though) from your L3 switch perspective (which is the only router in your topology which has multiple paths towards the same destination). Provided that all your hosts in both sites use the local L3 switch as default gateway you might redistribute the routes coming from the 2 ISPs into OSPF (as external routes) making sure that the cost to reach TATA and Airtel CEs is equal (from L3 switch perspective). This way you will have equal cost sharing for the same remote prefixes on the L3 Switch.

However this way is not determistic and potentially risky as you might have asymetrical routing (i.e. host in Bangalore uses TATA to reach Plants host but replies travel through Airtel). Some applications might have issues with that and FWs could drops those flows.

Read this article which throws some ideas on how to achieve similar results:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

regards,

Riccardo