BGP Loadsharing not happening

[MachadoGB]

Hello

I have a design question about BGP.

I have two EBGP peers from backbone to one remote site with two routers, so each remote router is connected to one Backbone router via point-to-point link (all /30 ip networks). Between the two backbone routers I am running IBGP and between the two remote routers, for the internal connection, I am running EIGRP.

I am not getting a perfect load sharing between the two point-to-point links (with same physical speed). Majority of the traffic from the backbone to the remote routers are flowing via one link only.

Considering the Cisco model – “load sharing when dual homed” (link below) IBGP is necessary between the two remote routers. Is that really necessary? Can I get it using EIGRP between the two remote routers?

Please let me know. Thanks.

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

[Giuseppe Larosa · Accepted solution]

Hello MachadoGB,

>> I am not getting a perfect load sharing between the two point-to-point links (with same physical speed).

>>. Majority of the traffic from the backbone to the remote routers are flowing via one link only.

BGP router-ids count in choicing BGP best path amd BGP by default uses only one path the best one, you should see how the routes are seen on a device that is upstream the two core routers.

on remote-site client facing Vlans you could consider the use of GLBP instead of HSRP/VRRP and you may have internal routers in the remote site running EIGRP.

>> Can I get it using EIGRP between the two remote routers?

as far as I see you are already using EIGRP on the remote site, your question may be:

what if I use EIGRP instead of BGP?

the answer depends on how the remote site is connected to the central site:

a)

If you are using an MPLS L3 VPN service your routers are peering with SP devices not directly between them.

b)

if you use a L2 service or you have dedicated lines in between you could move to EIGRP on the links between core routers and remote site routers and you could get also a better load balancing as well

in case a) if you agreed on using BGP with provider PE nodes, the iBGP session is recommended

Hope to help

Giuseppe

[MachadoGB]

Thank you, Giuseppe.

Considering your observations:

1 – I will use iBGP between the two remote routers (internally) since it is an internal standard.

2 – The links from Core routers (POPs) to the remote routers are point-to-point links using layer 2 only. No MPLS-VPNs are used in this scenario.

3- Yes I am aware that we are not going to have a perfect load sharing scenario and BGP will pick the best path.

4 – I cannot use GLBP, do not have the hardware in place. And no HSRP is involved.

5 – I do have EIGRP between the remote routers today.

What about using “ebgp multihop”?  Can that be a value tool when you have 4 routers each two linked by a point to point circuit?

Please let me know, I will implement the iBGP scenario tomorrow and inform the results.

[Giuseppe Larosa · Accepted solution]

Hello MachadGB,

>> What about using “ebgp multihop”?  Can that be a value tool when you have 4 routers each two linked by a point to point circuit?

as the name says it applies only to eBGP sessions allowing to increase TTL of eBGP packets from default value of one

you have iBGP sessions instead

1 – I will use iBGP between the two remote routers (internally) since it is an internal standard.

you can setup four iBGP sessions and you can use

bgp maximum-paths ibgp

see

http://www.cisco.com/en/US/docs/ios/iproute_bgp/command/reference/irg_bgp3.html#wp1105004

but you should find a way to make appear same cost the BGP next-hops in IP routing table

(you can do it with static routes but they create other issues)

Hope to help

Giuseppe

[MachadoGB]

Hi Giuseppe

You are correct on itme 1. I have just applied the maximum-path for IBGP and it is working very well.

We did dtected that the way the topology is set one path will be preferred than the other considering the number of hops and the source and destination. But BGP is showing two routes for the destination.

We do not want to apply route-maps and give preferences for specific networks since we will have a lot to manage. IN order to achive an elegant design we do need to change our topology.

So I think you got this one.

Many Thanks for your help.

[MachadoGB]

Hi Giuseppe,

I did implement the iBGP between the routers the load sharing is better now, but I am facing redistribution problems with EIGRP.

But that is another subject.. I will opena new discussion.

You have pointed to the right direction.

Thanks.