BGP neighbor next-hop-self

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Nov 1st, 2008
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hi,

Suppose B and C are IBGP routers. On B we set the BGP neighbor next-hop-self.

The only advatage I see of this command is to avoid having a static route, on C, to the exterior EBGP link.

Are there any other benefits?

Correct Answer by Giuseppe Larosa about 8 years 6 months ago

Hello Wassim,

in a IP only network the only advantage can be that of being able to satisfy the BGP next hop reachability check (first check in the hierarchy of criteria used to choice the BGP best path)without adding a route as explained by Jon and Amit.


In a MPLS network there are some scenarios were implementing inter-AS MPLS VPN where the next-hop-self is required to be able to forward MPLS VPN packets at the AS boundary routers. In practice the BGP next-hop-self in that cases allow to "join" two MPLS label paths at the boundary.



Hope to help

Giuseppe


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Jon Marshall Sat, 11/01/2008 - 06:09
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Wassim


This is the main reason to use the next-hop-self. Because if B is peering via EBGP with another router then unless you use the next-hop-self B will advertise the route to C with the next hop of the external BGP router. C probably won't know how to get there unless as you say you add it as a route to C.


Jon

Amit Singh Sat, 11/01/2008 - 06:18
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Jon,


Sorry, I think I didnt see you post before replying. Its just a wrong timing.


-amit singh

Jon Marshall Sat, 11/01/2008 - 06:19
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Amit


No need to apologize, always good to have your input.


Jon

Amit Singh Sat, 11/01/2008 - 06:16
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Yes its kindaa true. Any EBGP route learned inside the BGP AS, carries the EBGP neigbor ID as the next hop. Your all the router in the BGP AS has to have a route to reach that next-hop IP otherwise the routes learned wont show up in BGP table. You can have the reachability to that neigbor either via static route or using some routing protocol. BGP " next-hop-self " command advertises your router ID which is peering with the EBGP router as the next-hop for all the external AS routes learned and will be the easiest way to exit out from the AS as all the IBGP routers will have peering to your EBGP router.


-amit singh

Correct Answer
Giuseppe Larosa Sat, 11/01/2008 - 08:24
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Hello Wassim,

in a IP only network the only advantage can be that of being able to satisfy the BGP next hop reachability check (first check in the hierarchy of criteria used to choice the BGP best path)without adding a route as explained by Jon and Amit.


In a MPLS network there are some scenarios were implementing inter-AS MPLS VPN where the next-hop-self is required to be able to forward MPLS VPN packets at the AS boundary routers. In practice the BGP next-hop-self in that cases allow to "join" two MPLS label paths at the boundary.



Hope to help

Giuseppe


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