Weight/AS_PATH_PREPENDS - W/O Inet BGP Table

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Jul 15th, 2008
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We have a customer that for all intents and purposes have 2 100Mbps Internet connections. They serve several customers with their own networks. My plan was to manipulate which links this traffic uses via Weight and AS Path Prepends with route maps and ACLs.

Note both ISPs are connected to the same 7600.

However, I just noticed that the carrier does not appear to be providing the usual Internet routing tables.

My question is will the AS Path Prepends propogate throughout the Internet? There IS a BGP neighbor that is up and active for each ISP, but not the full routing table like I've seen before.

Any help on this matter will be appreciated.

Take care

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Giuseppe Larosa Tue, 07/15/2008 - 13:09
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Hello Chris,

As path prepending will propagate all over the internet.

The only possible exception is your IP prefix will be part on an aggregate created somewhere and with specific options.

It is used to influence the return path with good results

The two ISPs are sending only default routes and may be some selected routes.

However, even if you are receiving only default routes you can use the neighbor weight command in order to have a preferred outgoing path.

Or in combination with maximum-paths 2 you could be able to install both default routes in your C7600 routing table

Hope to help


milan.kulik Wed, 07/16/2008 - 00:03
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it would be also good to check with your ISP if he permits your AS# prepending.

Some ISPs only expect the customer AS# appearing once in the AS-PATH incoming.

Using weight to influence your routing is OK if your 7600 is the only router running BGP within your AS. Otherwise, local preference would be more powerful.




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