BGP Multihoming==Traffic load balancing

Unanswered Question
Sep 8th, 2009

Hi

I have 2 internet links from 2 diffrent service providers and terminating on 2 diffrent internet routers.both internet routers are connected to L3 switch on lan side.Both service provider give default route in BGP.presently the setup running with active -standby with default route from 2nd servcie provider redistributed in ospf in lan with higher metric.

now i want to do active-active setup.for inbound i will announce diffrent subnets with diffrent prererence.( e.g. 192.168.0.0/23 to servie provider 1 and 192.168.0.0/24 & 192.168.1.0/24 to service provider 2 so subnet 192.168.0.0/23will be preferred over service provider 2.similary will announce 192.168.2.0/23 to service provider2 and 192.168.2.0/24 and 192.168.3.0/24 to service provider1 so subnet 192.168.2.0/24 preferred on service provider1.

for outbound i will change the metric of default route announed to lan switch with same value so that Lan switch will have 2 diffrent route with equal cost and traffic will be load balanced.can i route specific subnet out on specific default route wih kind of route-map (Say 192.168.2.0/23 will prefer service provider 1 for outbound and 192.168.0.0/23 will prefer service provider2 for outbound traffic.

if any working scenario please share.

I have this problem too.
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Edison Ortiz Tue, 09/08/2009 - 08:46

Source based routing requires PBR.

You can configure a PBR on the switch with object tracking.

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Edison.

sameermunj Tue, 09/08/2009 - 09:16

Hi

Can i have sample config of this particular scenario to understand it better.

sameermunj Tue, 09/08/2009 - 21:23

Hi

So the port of L3 switch where the lan traffic for internet is hitting will have route map with ip matched with access list.so traffic which we want to out with SP1 will have next hop set as L3 switch interface pointing towards Internet router on which SP1 link terminated and traffic which we want to out with SP2 will have next hop set as L3 switch interface pointing towards Internet router on which SP2 link terminated.

apart from these 2 entries, anything else to be mentioned in the route map to ensure whenever any of the service provider link is donw (default route not availabe) all traffic will use available link.please clarify

Edison Ortiz Wed, 09/09/2009 - 05:07

apart from these 2 entries, anything else to be mentioned in the route map to ensure whenever any of the service provider link is donw (default route not availabe) all traffic will use available link.please clarify

PBR won't take care of that. Its job is to send the packet to the next hop. You could influence PBR with tracking but as I said, it depends on the IOS version you are running. A cleaner design would be running iBGP between the 2 WAN routers.

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Edison.

sameermunj Wed, 09/09/2009 - 20:45

Hi

I am running advance security software (c3845-advsecurityk9-mz.124-22.T1.bin).Attched is the setup.u want me ro run IBGP bewtween 2 routers using the loopbck ip's??

sameermunj Thu, 09/10/2009 - 05:13

Hi

i am ok for the inbound traffic.with most specific/less specific announcements i can manage same

for outbound raffic i have doubt here.if i run ibgp how i will ensure the outbound traffic for particular subnet via particular isp and in caseof failure of 1 isp all traffic via isp which is up.

which network i will announce in my IBGP session.

Edison Ortiz Thu, 09/10/2009 - 05:25

BGP Best Path Selection Algorithm - Step 1.

Highest Weight wins..

On your eBGP peer, apply a high weight on both routers.

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