Why the route is invalid when published the route from direct connected EBGP nei

Latest reply: Feb 19, 2016 09:26:16 1338 1 0 0

Why the route is invalid when published the route from direct connected EBGP neighbor to IBGP neighbor?

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Created Feb 19, 2016 09:26:16 Helpful(0) Helpful(0)

The next hop processing is different in BGP when sending routing to IBGP and EBGP neighbors. When advertising a route to EBGP neighbors (spread between the ASs) ,The next-hop will be change to the export IP address.(When the hop address is subject to third-party next hop before and after the modification, it will not be modified); when advertising a route to IBGP neighbors (spread within the AS), the next-hop is the same.
Because the BGP did not modify the next hop address when forwarding to other IBGP neighbors from EBGP's routing.
So, if the IBGP neighbor's device does not have the route to the next hop address, it will cause the routing failure for the neighbor route from the IBGP neighbor routing is unreachable.
There are several solutions:
You can configure the next-hop-local, thus when received EBGP route which send to the IBGP neighbor will force to change the next hop for the address of their outgoing interface; Within Autonomy system all devices are configured IBGP neighbors and full links, learning the next hop by bgp, Then we can Ensure that all the device within the autonomous system can know all the interface address by BGP protocol.
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