use the same commands we used on Router A, but reverse the source and destination: Router-D(config)#int tu 0 23:45:13: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnelo, changed state to Router-D(config-if)# ip address 172.16.0.2 255.255.255.0 Router-D(config-if)# tunnel source lo 0 Router-D(config-if)# tunnel destination 10.100.100.100 Router-D(config-if)# 23:47:06: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnelo, changed state to up Now we have a live link between these routers, which appear to be directly connected. However, the Ethernet network on Router D, which was known through the serial link, is still known through the serial link, and not the tunnel. If the tunnel is theoretically directly connected to both routers, why isn't the tunnel the preferred path? GRE Tunnels Digging into our EIGRP expertise, we can use the show ip eigrp topology command to see what EIGRP knows about the paths: Router-A#sho ip eigrp top 5d18h: %SYS-5-CONFIG I: Configured from console by console IP-EIGRP Topology Table for AS(100)/ID(192.168.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, S - sia Status P 10.20.20.0/24, 1 successors, FD is 3196416 via 192.168.1.2 (3196416/2684416), Serial0/1 via 172.16.0.2 (297246976/28160), Tunnelo P 10.10.10.0/24, 1 successors, FD is 281600 via Connected, Etherneto/1 P 192.168.1.0/24, 1 successors, FD is 2169856 via Connected, Serial0/1 Both paths appear in the table, but the distance on the tunnel path is huge compared with that of the serial interface. To find out why, let's take a look at the virtual tunnel interface: Router-A#sho int tu 0 Tunnelo is up, line protocol is up Hardware is Tunnel Internet address is 172.16.0.1/24 MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation TUNNEL, loopback not set Keepalive not set Tunnel source 10.100.100.100 (Loopback0), destination 10.200.200.200 Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled Checksumming of packets disabl