BGP (Border Gateway Protocol) is the routing protocol of the Internet, and due to the size of the global network, it is also the slowest.
It does not see each individual router on the Internet, but it knows how to reach autonomous systems, which are large network pools. Internet service providers are autonomous systems, and large companies like Microsoft and Google are as well.
This post is for reference only and assumes the ISP configuration below, which runs BGP and connects the edge router to this BGP network:
hostname ISP no ip domain-lookup interface L0 ip address 10.10.10.10 255.255.255.255 interface Serial0/0/1 ip address 200.200.200.1 255.255.255.252 no shut ip route 0.0.0.0 0.0.0.0 l0 router bgp 65001 bgp log-neighbor-changes network 0.0.0.0 neighbor 200.200.200.2 remote-as 65000 end
Note: 10.10.10.10 simulates the Internet on the ISP side, 200.200.200.1 is the ISP router’s address, and 200.200.200.2 is the address of your network connected to the ISP (meaning the ISP router must be configured to exchange routing information with your network).
Join your router to the ISP BGP network:
router bgp 65000 neighbor 200.200.200.1 remote-as 65001 network 200.100.100.0 mask 255.255.255.0
Note: 200.200.200.1 is the ISP address and 200.100.100.0 is the internal network you will advertise on the Internet through the ISP router.
Useful commands for troubleshooting:
show ip route show ip bgp show ip bgp summary
This post is a quick reference guide for commands, based on Cisco Lab 3.5.3.5. Consider looking up the source material for more detailed information.