[nsp] Load Balancing with BGP over unequal-cost circuits

Wed, 2 Oct 2002 14:53:21 +1000

Cheeyong,

There's a doc on CCO that explains this but I can't seem to find it. :-(
Basically, here, BGP isn't load sharing but the router is load sharing
to the BGP next hop. All routes that your customer receives have a next
hop of 192.168.255.202 and there are two static routes to this address
using the two serials. Presumably this next hop is the loopback of the
router at the other end and this configuration is duplicated on the
other side. This is why you need the "ebgp-multihop" statement. Needless
to say, this is imperfect load sharing as depending on the route-caching
configuration, you will only load share sessions.
Hope this helps.
Marcus.

-----Original Message-----
From: Tay Chee Yong [mailto:tcy@pacific.net.sg]=20
Sent: 02 October 2002 14:00
To: cisco-nsp@puck.nether.net
Subject: [nsp] Load Balancing with BGP over unequal-cost circuits

Hi all,

My understanding is that BGP doesn't do load balancing because of its
nature of selection of best path, however load sharing can be achieved.

I have a customer who is doing load balancing over an E1 (2Mbps) and a
1Mbps circuit (unequal bandwidth) using BGP, and it seems to work.

Could someone advise how was the load-balancing achieved?

Following is the config :

* Note : Both circuits are terminated to the same router on both ends. *

interface Loopback0
 ip address 172.16.255.10 255.255.255.255
!

interface Serial0/1
 description =3D=3D> Link 1Mbps
 bandwidth 1024
 ip address 192.168.252.206 255.255.255.252
 no ip redirects
 no ip proxy-arp
 ip load-sharing per-packet
 no fair-queue
 hold-queue 4096 out
!
interface Serial0/2
 description =3D=3D> Link 2Mbps
 bandwidth 2048
 ip address 192.168.252.202 255.255.255.252
 no ip redirects
 no ip proxy-arp
 ip load-sharing per-packet
 no fair-queue
 hold-queue 1024 out
!

 network 172.16.0.0 mask 255.255.192.0
 network 172.16.64.0 mask 255.255.192.0
 network 172.16.128.0 mask 255.255.192.0
 network 172.16.192.0 mask 255.255.192.0
 neighbor 192.168.255.202 remote-as 65500
 neighbor 192.168.255.202 ebgp-multihop 3
 neighbor 192.168.255.202 update-source Loopback0
 neighbor 192.168.255.202 version 4
 neighbor 192.168.255.202 soft-reconfiguration inbound
 neighbor 192.168.255.202 route-map ksc-in in
 neighbor 192.168.255.202 route-map ksc-out out

ip route 172.16.0.0 255.255.192.0 Null0
ip route 172.16.64.0 255.255.192.0 Null0
ip route 172.16.128.0 255.255.192.0 Null0
ip route 172.16.192.0 255.255.192.0 Null0
ip route 192.168.255.202 255.255.255.255 Serial0/1
ip route 192.168.255.202 255.255.255.255 Serial0/2

access-list 21 permit any
access-list 22 permit 172.16.0.0 0.0.255.255

route-map ksc-out permit 10
 match ip address 22
!

route-map ksc-in permit 10
 match ip address 21
 set local-preference 500
!

Serial0/1 is up, line protocol is up
  Hardware is DSCC4 Serial
  Description: =3D=3D> Link 1Mbps
  Internet address is 192.168.252.206/30
  MTU 1500 bytes, BW 1024 Kbit, DLY 20000 usec,
     reliability 255/255, txload 242/255, rxload 211/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:05, output hang never
  Last clearing of "show interface" counters 18:14:54
  Queueing strategy: fifo
  Output queue 971/4096, 138782 drops; input queue 0/75, 54 drops
  5 minute input rate 848000 bits/sec, 213 packets/sec
  5 minute output rate 973000 bits/sec, 345 packets/sec

Serial0/2 is up, line protocol is up
  Hardware is DSCC4 Serial
  Description: =3D=3D> Link 2Mbps
  Internet address is 192.168.252.202/30
  MTU 1500 bytes, BW 2048 Kbit, DLY 20000 usec,
     reliability 255/255, txload 211/255, rxload 209/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:08, output 00:00:09, output hang never
  Last clearing of "show interface" counters 18:17:34
  Queueing strategy: fifo
  Output queue 1023/1024, 3212912 drops; input queue 0/75, 60 drops
  5 minute input rate 1686000 bits/sec, 425 packets/sec
  5 minute output rate 1702000 bits/sec, 517 packets/sec

Thanks.

Regards,
Cheeyong

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