Route not advertised due to EIGRP zero successor

This article’s topic really fits in this blog’s genre. It focuses on a case of classic routing protocol behaviour inspection.

I was looking at the subnets in the routing tables when I noticed that a network I picked up was absent in one of the devices. It is a VLAN routed on a pair of core switches (SW1,SW2). The switches advertise the VLANs by EIGRP and all other routers learn it as external EIGRP routes (due to redistribute connected). However, there’s a router R2 connected to SW2 by a L3 link that doesn’t have the network in the routing table.

Let’s see R2’s EIGRP config :