CCNP Routing and Switching ROUTE 300-101 Official Cert Guide

Understanding Next-Hop Reachability Issues with iBGP

With IGPs, the IP routes added to the IP routing table list a next-hop IP address. With few exceptions, the next-hop IP address exists in a connected subnet. For example, the E1-E2 iBGP connection uses loopback interfaces 10.100.1.1 (E1) and 10.100.1.2 (E2). E1’s OSPF-learned route to reach 10.100.1.2 lists outgoing interface Fa0/1, next-hop 10.1.1.10—an address in the LAN subnet that connects E1 and E2. (See Figure 14-3 a few pages back for reference.)

Examples 14-4 and 14-6 also happened to show two examples of iBGP-learned routes and their next-hop addresses. The next-hop addresses were not in connected subnets; the next-hop addresses were not even IP addresses on a neighboring router. The ...