Border Gateway Protocol (BGP)
Inter-domain routing protocol.
Allow subnet to “advertise” its existence, and the destinations it can reach to the rest of Internet.
BGP provides each AS a mean to:
- eBGP
- iBGP
- we choose path based on policy
In the forwarding table:
- iBGP decides 1c
- OSPF decides 1 (in interface of the 1c dest)
Policy:
- inter-AS: admin wants to control over how its traffic routed, who routes through its network
- intra-AS: single admin, so policy less of an issue scale:
- hierarchical routing saves table size, reduced update traffic performance:
- intra-AS: can focus on performance
Hot potato: choose local gateway that has least intra-domain cost: don’t worry about inter-domain cost.
OSPF doesnt do load balancing → scared of cycles?