BGP can run load balance?

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Jul 21st, 2008
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Hi all,


Can BGP run load balance? As I know,

BGP will choose the BEST route and installed in the routing table. I just think only Load sharing can be done rather than load balance. Am I right ?

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guruprasadr Mon, 07/21/2008 - 20:13
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Hi, [Pls RATE if HELPS]


If the router receives and installs multiple paths with the same administrative distance and cost to a destination, load-balancing can occur. The number of paths used is limited by the number of entries the routing protocol puts in the routing table. Four entries is the default in IOS for most IP routing protocols with the exception of Border Gateway Protocol (BGP), where one entry is the default. Six different paths configured is the maximum number.


Per-destination or per-packet load-balancing depends on the type of switching scheme used for IP packets. By default, on most Cisco routers, fast switching is enabled under interfaces. This is a demand caching scheme that does per-destination load-balancing. To set per-packet load-balancing, enable process switching (or disable fast switching), use these commands:


Router# config t

Router(config)# interface Ethernet 0

Router(config-if)# no ip route-cache

Router(config-if)# ^Z


Now the router CPU looks at every single packet and load balances on the number of routes in the routing table for the destination. This can crash a low-end router because the CPU must do all the processing. To re-enable fast switching, use these commands:


Router# config t

Router(config)# interface Ethernet 0

Router(config-if)# ip route-cache

Router(config-if)# ^Z


Hope I am Informative.


Pls RATE if HELPS


Best Regards,


Guru Prasad R

acbenny Mon, 07/21/2008 - 21:30
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That means BGP can only perform load sharing , not load balancing .Right?

acbenny Tue, 07/22/2008 - 00:09
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Just like router A connect with Router B with 2 x serial link. Even though AD and metric is equal [20/0]. Only one route will be installed in routing table. Am I right?

michaelchoo Tue, 07/22/2008 - 00:29
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Simplest answer is: by default, BGP is configured only to choose a single BEST path.


You can configure "maximum-paths " in BGP routing process, where is the number of multiple equal cost paths that you want BGP to install to the routing table. Here's a URL about BGP decision process, including some blurbs about multiple paths: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml


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