From the course: Cisco CCNP ENARSI v1.1 (300-410) Cert Prep: 2 VPN Technologies

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BGP multihop

BGP multihop

From the course: Cisco CCNP ENARSI v1.1 (300-410) Cert Prep: 2 VPN Technologies

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BGP multihop

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- [Narrator] By default, when we use EBGP, this requires two Cisco routers to be directly connected. If they're not directly connected, they'll fail to form a neighbor adjacency. And the reason is that EBGP, uses a TTL value, a time to live value, of one for BGP packets. Each time, a BGP packet traverses the device, and each time any packet traverses a device for that matter, we know that the TTL is decremented by one, and once that reaches zero, that packet is discarded. So, if we have a TTL value of one, and we have a topology like we see here, where the BGP routers are not directly connected, that packet will be discarded, and it will never reach the BGP peer. If you look at our topology, you can see we have three routers, we have R one, in autonomous system 65 100, we have R three, in AS 65 200, and in the middle, we have R two, which is a non BGP router. In a special case such as this, where two EBGP routers are not directly connected, we need to use BGP multihop. I'll also point…

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