Load Balancing in Router

[manikandanbabu]

Hi Team,

Please find the below observations. Kindly help me to find a solution for the load balancing issue that we are facing in Cisco 7600 Series Router. 

1. In MPLS Router, there are 5 STM-6 media and normally the traffic is sharing by all media.
2. In case of any one media goes down; the particular traffic is not sharing by remaining all media, instead only ISP-3 media utilization becomes high that time.
3. Our End using SUP32 (not supporting hierarchal service policies) card, But other End using ES20 card.
4. Both side interfaces are configured with OSPF cost value 2 for all media. OSPF configuration is Point to Point.
5. Pinging Destination IP with source IP and Packet Size 1600, we are getting following latency in all media.

ISP-1          4/5/60 ms
ISP-2          4/5/60 ms
ISP-3          4/7/24 ms
ISP-4          4/4/44 ms
ISP-5          4/4/28 ms

Kindly help.

Thanks,

Manikandan

[Mark Malone]

Hi

have you got CEF enabled, specifically on each interface I would try set ip load-sharing per-packet this should allow for each link to be used once the costs/metrics are the same for each link .

[manikandanbabu]

Hi Sir,

 CEF is not enabled. Load-balancing working properly when all Media are up. Issue we are facing only when one Media goes down.

Total 5 LL(Lease Line) Media configured in Our End Router to Remote Office Router. Network type is OSPF Point to Point. OSPF cost value is same for all interfaces at both end. Outbound traffic from Our End is shown as properly balanced. Issue facing only for the inbound traffic to Our End. All Media are 900 Mbps. When one Media goes down, Inbound traffic in ISP-3 Media utilization becomes high, but not sharing the traffic to remaining 3 Media.

Kindly give advise to troubleshoot this issue. 

Thanks,

Manikandan

[Richard Burts]

Manikandan

You have provided helpful information when  you tell us that the issue is for incoming traffic but not for outgoing traffic. This means that your router is load sharing as it should and that the issue is how load sharing is configured and is working at the remote end.

HTH

Rick

[manikandanbabu]

Hi Team,

      Please note that the inbound traffic load balancing also working properly when all the 5 Media are up. The issue happening to inbound traffic load balancing only when any Media goes down. That is the most confusing fact.

Kindly advise me to do the troubleshooting step we can do on remote end.

[Richard Burts]

Manikandan

For troubleshooting this issue I would start with a review of the configuration of the other side. How is routing and load sharing configured on that side? Perhaps there is some configuration issue that can be identified. As a next step I would have a look at the routing and load sharing during normal operation so that you have a base line to compare to. Then when one media is down I would look at routing and load sharing (show ip route and show interface) and try to identify why the load is not shared as expected.

HTH

Rick

[Mark Malone]

If its point-point on far end how are they load balancing from there side, if your side is working on LB then you need to get onto there routers and see what exactly way they are setup and why traffic is returning only on 1 link, are there metrics equal on there end as its there return traffic that's coming back wrong

[paul driver]

Hello

I would say with per-packet load sharing, although its an option and possibly applicable it can produce unwarranted results to traffic patterns. -here

With per packet LB scr/dest traffic would no doubt take different paths  thus possibly introducing reordering of these packets, resulting in them being out of sequence , which I guess wouldn’t be good to certain applications

Can you post your configuration please.

res

Paul