BGP Load-Balanced with Two ISP

Answered Question
Jun 1st, 2007

hi all,

Was trying to test this concept described in http://www.ccnalab.net/load_sharing_bgp.php

but after prepending my own AS, BGP still select only one default-route, did i missed something ?

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ISP1:

router bgp 7374

no synchronization

bgp log-neighbor-changes

neighbor 120.1.1.1 remote-as 65001

neighbor 120.1.1.1 ebgp-multihop 2

neighbor 120.1.1.1 update-source Loopback0

neighbor 120.1.1.1 default-originate

neighbor 120.1.1.1 soft-reconfiguration inbound

neighbor 170.1.1.1 remote-as 4434

neighbor 170.1.1.1 ebgp-multihop 2

neighbor 170.1.1.1 update-source Loopback0

neighbor 170.1.1.1 soft-reconfiguration inbound

maximum-paths 2

no auto-summary

========================================

ISP2:

router bgp 1231

no synchronization

bgp log-neighbor-changes

neighbor 120.1.1.1 remote-as 65001

neighbor 120.1.1.1 ebgp-multihop 2

neighbor 120.1.1.1 update-source Loopback0

neighbor 120.1.1.1 default-originate

neighbor 120.1.1.1 soft-reconfiguration inbound

neighbor 170.1.1.1 remote-as 4434

neighbor 170.1.1.1 ebgp-multihop 2

neighbor 170.1.1.1 update-source Loopback0

neighbor 170.1.1.1 soft-reconfiguration inbound

no auto-summary

=========================================

CE1:

router bgp 65001

no synchronization

bgp log-neighbor-changes

network 202.1.1.0 mask 255.255.255.252

network 203.127.9.0

network 203.127.10.0

network 203.160.220.0 mask 255.255.255.252

network 203.160.220.4 mask 255.255.255.252

neighbor 100.1.1.1 remote-as 7374

neighbor 100.1.1.1 ebgp-multihop 2

neighbor 100.1.1.1 update-source Loopback0

neighbor 100.1.1.1 soft-reconfiguration inbound

neighbor 100.1.1.1 route-map prepend-AS-65001 in

neighbor 130.1.1.1 remote-as 1231

neighbor 130.1.1.1 ebgp-multihop 2

neighbor 130.1.1.1 update-source Loopback0

neighbor 130.1.1.1 soft-reconfiguration inbound

neighbor 130.1.1.1 route-map prepend-AS-65001 in

maximum-paths 4

no auto-summary

route-map prepend-AS-65001 permit 10

set as-path prepend 65001

=========================================

CE1#sh ip bgp

BGP table version is 7, local router ID is 203.127.10.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 0.0.0.0 130.1.1.1 0 65001 1231 i

*> 100.1.1.1 0 65001 7374 i

*> 202.1.1.0/30 0.0.0.0 0 32768 i

*> 203.127.9.0 0.0.0.0 0 32768 i

*> 203.127.10.0 0.0.0.0 0 32768 i

*> 203.160.220.0/30 0.0.0.0 0 32768 i

*> 203.160.220.4/30 0.0.0.0 0 32768 i

CE1#

CE1#

=========================================

CE1#sh ip bgp 0.0.0.0

BGP routing table entry for 0.0.0.0/0, version 2

Paths: (4 available, best #3, table Default-IP-Routing-Table)

Multipath: eBGP

Advertised to non peer-group peers:

130.1.1.1

65001 1231

130.1.1.1 from 130.1.1.1 (130.1.1.1)

Origin IGP, localpref 100, valid, external

1231, (received-only)

130.1.1.1 from 130.1.1.1 (130.1.1.1)

Origin IGP, localpref 100, valid, external

65001 7374

100.1.1.1 from 100.1.1.1 (100.1.1.1)

Origin IGP, localpref 100, valid, external, best

7374, (received-only)

100.1.1.1 from 100.1.1.1 (100.1.1.1)

Origin IGP, localpref 100, valid, external

CE1#

========================================

I have this problem too.
0 votes
Correct Answer by Harold Ritter about 9 years 6 months ago

Kian,

By default, BGP multipath will only work properly if both prefixes are received from the same AS. The trick of adding our AS doesn't work anymore as extra validations have been implemented to check that both aspaths are identical before using them both for BGP multipath.

This check can be relaxed via the following hidden command that was implemented in 12.3T.

router bgp

bgp bestpath as-path multipath-relax.

Note that it is ok to use this command for a stub site but it would certainly not be recommended for a transit network.

Hope this helps,

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Correct Answer
Harold Ritter Fri, 06/01/2007 - 09:03

Kian,

By default, BGP multipath will only work properly if both prefixes are received from the same AS. The trick of adding our AS doesn't work anymore as extra validations have been implemented to check that both aspaths are identical before using them both for BGP multipath.

This check can be relaxed via the following hidden command that was implemented in 12.3T.

router bgp

bgp bestpath as-path multipath-relax.

Note that it is ok to use this command for a stub site but it would certainly not be recommended for a transit network.

Hope this helps,

leungcm Sat, 06/02/2007 - 23:06

Hi,

Does it mean that the in/out traffic are 50%, 50% for both links within the same ISP (one ISP with two links)

if we have two different ISPs, any solution for load balancing (50%, 50% in/out traffic)?

Best regards

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