Load Balancing

Unanswered Question
Jul 27th, 2009

We have two routers of Cisco 7206VXR series, with one DS3 link

terminating on each of these routers. These links are MPLS links

providing WAN connectivity to our office. We need to achieve

load-balancing on these links. How can I achieve this?

I have this problem too.
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Giuseppe Larosa Mon, 07/27/2009 - 23:34

Hello Deepa,

these are seen as equal cost paths by any routing protocol you can achieve load balancing using OSPF for example by redistruting with same metric type and seed metric in the OSPF domain at both C7206VXR.

So inner more internal L3 devices can route to both for destination subnets reachable via the two MPLS links.

Also EIGRP can be used for this.

What protocol do you use to talk with MPLS service provider?

Is it a L3 MPLS VPN service or a form of L2 VPN?

What IGP is in use in the main site?

Hope to help

Giuseppe

deepa.muralidharan Mon, 07/27/2009 - 23:37

Hello Giuseppe,

The router is running BGP as the External routing-protocol & EIGRP as the internal routing protocol at the LAN end. All the EIGRP routes are getting distributed into BGP & BGP routes into EIGRP.

How do I achieve Load balancing?

Also, since these are MPLS links, teh load balancing will be applicable to the outbound trafffic alone.

Giuseppe Larosa Mon, 07/27/2009 - 23:57

Hello Deepa,

also EIGRP allows for redistributionof BGP with same seed metric.

This would allow for outbound load balancing.

I would suggest you or to use network commands under EIGRP or to use route tags if you want to go on with mutual redistribution between EIGRP and BGP.

You should be able to implement outbound load balancing also on the other side:

if the remote site has only eBGP sessions with PE nodes you may use maximum-paths 2

if remote sites are not multihomed usage of both DS3 links can be achieved by MPLS service provider.

You may want to use the same MED on advertised central site prefixes on the two eBGP sessions.

The service provider should implement

maximum paths eibgp 2

on each remote PE in address family ipv4 vrf Your.VRF and should use a different route distinguisher on the two PE nodes where the two DS3 links.

Check with SP tech people what they are doing.

Hope to help

Giuseppe

deepa.muralidharan Tue, 07/28/2009 - 00:15

Giuseppe,

IP-CEF is enabled on our routers & bothe the links are equal cost. Doesn't this mean that for all outbound traffic from these two routers there should be 'per destination' based load-balancing done?

For the inbound traffic from MPLS, the Service-provider needs to look into this & work out on load-balancing at their end.

Is this correct?

Giuseppe Larosa Tue, 07/28/2009 - 00:22

Hello Deepa,

>> Is this correct?

yes you have per destination flow based load balancing in the outbound direction.

SP controls inbound direction

hope to help

Giuseppe

deepa.muralidharan Tue, 07/28/2009 - 00:23

Giuseppe,

I have spoken to the Service-provider & they need us to specify the how many max paths we require.

I am not clear on this.

Giuseppe Larosa Tue, 07/28/2009 - 00:57

Hello Deepa,

BGP defaults to maximum-paths 1 also on the SP side.

in your case the max paths has to be raised to 2.

This is the answer you should give them

Hope to help

Giuseppe

deepa.muralidharan Tue, 07/28/2009 - 01:19

Thanks Guiseppe.

Is the max path = 2 because the load balancing is done for 2 links? Also, AS configured for both the links are different. How will SP acheive this?

Can you please provide some links which can help me understand this concept better?

Giuseppe Larosa Tue, 07/28/2009 - 01:41

Hello Deepa,

look at the following the feature is named iBGP multipath for MPLS VPN

http://www.cisco.com/en/US/docs/ios/iproute/configuration/guide/irp_bgp_ebgp_ibgp_ps6441_TSD_Products_Configuration_Guide_Chapter.html

some additional hidden command may be needed to support eBGP multipath over different peer AS

bgp as relax multi-path

(not sure about the exact syntax but yes this is possible and it is on the SP side)

I find strange you are using two different AS numbers on your routers but this can be handled.

Hope to help

Giuseppe

deepa.muralidharan Tue, 07/28/2009 - 02:20

Thanks Giuseppe.

I am still unable to get the logic of having two differnt AS to the same location. What would happen if we configure the same AS for both the links?

Giuseppe Larosa Tue, 07/28/2009 - 03:54

Hello Deepa,

if you are using the same AS number on your routers this is fine.

I had misunderstood you ignore any comment about different AS numbers on your side.

Hope to help

Giuseppe

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