An EBGP Multihop configuration is a topology where external BGP neighbors are not connected to the same subnet. Such neighbors are logically, but not physically connected. For example, BGP can be run between external neighbors across non-BGP routers.
Be aware that no IP traffic can pass to advertised BGP routes until an IGP protocol or static route is configured for those prefixes on the middle router.
See EBGP Multihop Peering Topology for a presentation of the multihop EBGP basic peering configuration example topology.
Router 1
Router 1(rw)->configure Router 1(rw-config)->interface vlan 12 Router 1(rw-config-intf-vlan.0.12)->ip address 192.168.12.111 255.255.255.0 Router 1(rw-config-intf-vlan.0.12)->no shutdown Router 1(rw-config-intf-vlan.0.12)->exit Router 1(rw)->configure Router 1(rw-config)->router bgp 1 Router 1(su-config-bgp)->bgp router-id 1.1.1.1 Router 1(su-config-bgp)->neighbor 192.168.13.111 remote-as 2 Router 1(su-config-bgp)->redistribute static Router 1(su-config-bgp)->
Router 2
Router 2(rw)->configure Router 2(rw-config)->interface vlan 12 Router 2(rw-config-intf-vlan.0.12)->ip address 192.168.12.112 255.255.255.0 Router 2(rw-config-intf-vlan.0.12)->no shutdown Router 2(rw-config-intf-vlan.0.12)->exit Router 2(rw-config)->interface vlan 13 Router 2(rw-config-intf-vlan.0.13)->ip address 192.168.13.111 255.255.255.0 Router 2(rw-config-intf-vlan.0.13)->no shutdown Router 2(rw-config-intf-vlan.0.13)->exit
Router 3
Router 3(rw)->configure Router 1(rw-config)->interface vlan 13 Router 1(rw-config-intf-vlan.0.13)->ip address 192.168.13.112 255.255.255.0 Router 1(rw-config-intf-vlan.0.13)->no shutdown Router 1(rw-config-intf-vlan.0.13)->exit Router 1(rw)->configure Router 1(rw-config)->ip route 192.168.12.0/24 192.168.12.111 interface vlan 13 Router 1(rw-config)->router bgp 2 Router 1(su-config-bgp)->bgp router-id 2.2.2.2 Router 1(su-config-bgp)->neighbor 192.168.12.111 remote-as 1 Router 1(su-config-bgp)->redistribute static Router 1(su-config-bgp)->
Multihop BGP Basic Peering Configuration is a simple configuration intended for multihop BGP propagation.
Multihop BGP Basic Peering Configuration
| Step | Task | Command |
|---|---|---|
| 1 | In configuration mode, configure static routes between BGP routers to allow IP traffic transmission between remote routers. | ip route {prefix mask | prefix/prefix-length} {ip-address [recursive | interface interface-name] | interface interface-name | vlan vlan-id | vrf egress-vrf | blackhole | reject} [distance] [tag tag-id] |
| 2 | In configuration mode, configure loopback and physical addresses and acquire interface configuration mode. | interface {vlan vlan-id | loopback loopback-id | interface-name} |
| 3 | In interface configuration mode, configure the IP address for the interface that serves as the BGP speaker. | ip address {ip-address ip-mask | ip-address/prefixLength} [primary | secondary] |
| 4 | In configuration mode, specify an AS number for the router and enter BGP Configuration mode. | router bgp as-number |
| 5 | In BGP configuration mode, configure a BGP-specific router ID to override the global router ID. | bgp router-id router-id |
| 6 | In BGP configuration mode, specify the network you want routes imported from and advertised to. | network prefix/length [route-map name][aspath-limit limit] [origin code] [med value] [local-pref value] |
| 7 | In BGP configuration mode, configure the peer by identifying its IP address and AS. | neighbor ip-address remote-as as-num |
| 8 | In BGP configuration mode, redistribute routes into BGP, optionally specifying a route-map. Supported route-types are connected, static, OSPF, and RIP. | redistribute route-type [aspath-limit limit] [origin code] [med value] [local-pref value] [route-map name] |
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