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When the prefix is first injected into BGP, the next hop is set by the BGP speaker that injects the prefix. The next hop’s value depends on how the prefix is injected. If the prefix is injected by the aggregate-address command, the prefix’s BGP next hop is the BGP speaker doing the aggregation. If the prefix is injected by the network command or redistribution, the IGP next hop before the injection becomes the BGP next hop. For example, if an OSPF prefix is redistributed into BGP, the BGP next hop is not necessarily the BGP speaker doing the redistribution, but rather is the original next hop of the OSPF prefix. Thus, in this case, it is advisable to reset the next hop at the redistributio...


Cover of BGP Design and Implementation


Note that iBGP does not change the next hop value when the routes are sent from one iBGP peer to another iBGP peer - the reason being that it considers all the routers to be fully meshed.