Load Sharing Using BGP

[Dipesh Patel]

Dear Experts,

We have topology as shown in the diagram running with dual MPLS links from two different Service Providers.

Topology :

The sample configuration for the BGP at HQ1 is as shown :

BGP Configuration on TATA CE Router :

router bgp 65510

no synchronization

bgp log-neighbor-changes

network 10.3.1.0 mask 255.255.255.0

network 10.3.2.0 mask 255.255.255.0

network 10.3.3.0 mask 255.255.255.0

network 10.3.4.0 mask 255.255.255.0

network 10.3.5.0 mask 255.255.255.0

neighbor 172.1.30.169 remote-as 2511

no auto-summary

BGP Configuration on Airtel CE Router :

router bgp 65500

no synchronization

bgp log-neighbor-changes

network 10.3.1.0 mask 255.255.255.0

network 10.3.2.0 mask 255.255.255.0

network 10.3.3.0 mask 255.255.255.0

network 10.3.4.0 mask 255.255.255.0

network 10.3.5.0 mask 255.255.255.0

neighbor 172.200.10.33 remote-as 2577

neighbor 172.200.10.33 allowas-in 6

no auto-summary

Can you suggest how Can I configure theese two routers for Load Sharing using BGP?

Can you give the sample configuration for the same according to given one?

Regards,

[Edison Ortiz]

There are plenty of examples in the web with BGP load sharing. In short, you need to add the command maximum-paths on the routers receiving these prefixes so both can be installed.

You need to also keep in mind, to configure BGP equal-cost multipath load sharing, all path attributes  must be the same.

The path attributes include weight, local preference,  autonomous system path (entire attribute and not just the length), origin code, Multi Exit Discriminator (MED), and Interior Gateway Protocol (IGP) distance.

Here is one example of such configuration:

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

[Christopher Mark Mendoza]

I think you can only use this command when a single router is connected to two different ISP but on this case there are two routers with each of them connected to their respective ISPs. So, to achieve load balancing, a L3 Core switch will need to be put in place between the two routers and the rest of the network with the core switch acting as the default-gateway for all the end-users devices, which is now the case in this network.

Or...

Just use one router to connect to two different ISP and use the two BGP commands below:

maximum-paths

bgp bestpath as-path multipath-relax

[Marwan ALshawi]

hi there

in order to get you BGP to load share over multiple paths you will need to have the BGP attributes same over both paths as sated above by Edison

also using the above command will work if you peering with one BGP AS in your case you are peering with two differnt BGP AS numbers and you need to add the bellow hidden command to get your BGP load sharing working assuming all the above have met:

bgp bestpath as-path multipath-relax

HTH

if helpful Rate

[Dipesh Patel]

Dear Edition / Marwanshawi,

Yes, I understand to do loadsharing using BGP. But that is the case when I can do IBGP between my two CE routers as shown in Topplogy. Both are running different AS no's.

How Can I run iBGP betwen CE Routers with two different AS no's?

Can you give sample config according to the configuration I have shown?

It will be helpful to understand.

Regards,

[Marwan ALshawi]

from your topology you have two edge routers in each site with L3 core switches

the load sharing decision has to be made by the core switches not the edge routers

what you can do is run IGP between the Core switches and the edge routers using equal cost multipathing ECMP

and this way the core swithc will load cshare the traffic for remote prefixes on both edge routers per flow

and each edge router learns the relevant prefixes of remote site through directly connected eBGP peer

HTH

[Dipesh Patel]

Dear Marwanshawi,

Thanks,

Yes Thr Load balacning decesion will be taken care by CORE switch. We can run IGP - OSPF using ECMP and load balance but the problem is the BW of both the links are differen - unequall hence need to go with EIGRP but CORE switch switches are Nortel, Cisco and Juniper platforms.So eigrp will not work. hence searching the solution using BGP.

Is it posible using BGP in my case?

Regards,

[Marwan ALshawi]

With ospf you can assign the cost manually to make it equal cost

But keep In mind this design might lead to asymmetrical routing

HTH

Sent from Cisco Technical Support iPhone App

[shehinpm1]

Hi dipesh,

Can you post the BGP routing table out put,right now which path is using bgp to reach the destination.

pls check which attribute is used to select that link as best path

Message was edited by: SHEHIN PM

[Marwan ALshawi]

Shehin

We discussing here how to approach the solution using either bgp/igp not a bgp config issue

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