Configure basic BGP on Cisco router

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Configure basic BGP on Cisco router

As such BGP is quite vast and complex topic. However, we can get simple BGP configuration done on a Cisco router such as Cisco CSR V1000 virtual router for sending and receiving routes via BGP. To do that use following steps:

1. Login into router via console / ssh. Go to enable mode and enter enable password ('enable'), if required. Go to configure terminal

   config t

2. Decide AS number to be used for BGP. We can use AS in range 64512 to 65534 for private purposes. Hence we can start from 65000 and use a few AS numbers as per requirement.
3. Configure BGP with chosen AS number:

   router bgp 65000

   where 65000 is the AS number to be used in current BGP configuration

4. Give a router-ID (We can use unique largest IPv4 interface IP of router to avoid conflicts with other routers)

   bgp router-id 10.1.6.1

   where 10.1.6.1 is unique router-id for this router

5. Configure address family with route-redistribution and networks

   address-family ipv4 unicast
   network 0.0.0.0 mask 0.0.0.0
   redistribute static
   redistribute connected
   exit

   Here we are configuring ipv4 unicast based BGP router. This router will advertize default-route 0.0.0.0/0 to its peer because of 'network 0.0.0.0' line. This router will also advertize all static and connected routes to its neighbors

6. Define neighbor routers along with their AS numbers for BGP communication

   neighbor 10.1.5.2 remote-as 65000
   neighbor 10.1.5.3 remote-as 65000
   neighbor 10.1.6.2 remote-as 65000
   neighbor 10.1.6.3 remote-as 65000

   where 10.1.5.2, 10.1.5.3, etc. are BGP routers in same AS 65000 where we want BGP connection to be established for routing table exchange.

7. We can check status of BGP via various show commands:

   show bgp all
   show bgp ipv4 unicast summary
   show bgp ipv4 unicast neighbors
   show bgp ipv4 unicast nexthops
   show bgp ipv4 received-paths

Refer:

• https://networklessons.com/bgp/bgp-private-and-public-as-range
• https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus6000/sw/unicast/6_x/cisco_n6k_layer3_ucast_cfg_rel_602_N2_1/l3_bgp.html
• https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-16/irg-xe-16-book/bgp-multi-paths-redistribute.html
• https://community.cisco.com/t5/networking-documents/how-to-configure-bgp-to-send-the-default-route-to-a-neighbor/ta-p/3131059

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