Cisco CCNA Routing and Switching ICND2 200-101 Official Cert Guide

Verifying a GRE Tunnel

The ultimate test of the tunnel is whether it can pass end-user traffic. However, some other show commands from the router tell us a lot about the status before trying a ping or traceroute from the user’s device.

First, because the tunnel acts very much like a serial link, with interfaces on both routers, the usual commands that list interface status, IP addresses, and IP routes all show information about the GRE tunnel. For instance, Example 7-3 shows the familiar show ip interface brief command on R1, with R1’s tunnel0 interface highlighted.

Example 7-3 Displaying the Interface State and IP Addresses, Including the Tunnel Interface

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R1# show ip interface briefInterface                  IP-Address      OK? ...