Equal path costs

Answered Question
Oct 6th, 2008
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Dear All,


If we have 2 or paths for the same destination and these 2 paths have equal cost, equal administrative distance........etc.

(the only difference between them is the next hop IP address)


which one will be added to the routing table?

Correct Answer by arianto.wibowo about 8 years 7 months ago

hi,


both paths will be appear in routing table except if you use BGP.


cheers.

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Giuseppe Larosa Mon, 10/06/2008 - 05:16
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Hello Nour,

with the exception of BGP all other routing protocols and static routes allow to install up to 4 parallel paths (with same AD and metric) to a destination prefix without any explicit configuration.


With BGP an explicit configuration is needed under router bgp if both paths are eBGP.

If BGP paths are iBGP the capability to support both paths is release dependent and if supported require an explicit command under router bgp (the feature is called iBGP multipath).

Maximum number of parallel paths was once 6 paths now should be 8 paths in most IOS releases


Hope to help

Giuseppe


nourelrayes Wed, 10/08/2008 - 16:08
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Hi quislar,


What if only one path is allowed to be added to the routing table.

Some refrences states that both routes will be added is this correct.

Giuseppe Larosa Thu, 10/09/2008 - 22:55
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Hello Nour,

if you do or see the following


router ospf 10

maximum-paths 1


only one path will be installed but this is not default configuration that is maximum-paths 4


BGP is the exception because it defaults to:


router bgp 50

maximum-paths 1


Hope to help

Giuseppe


Correct Answer
arianto.wibowo Thu, 10/09/2008 - 20:04
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hi,


both paths will be appear in routing table except if you use BGP.


cheers.

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