Troubleshooting Gre Configuration; The Tunnel Goes Down - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

N o t e

Troubleshooting GRE Configuration

You can use the show interfaces command to view:
the status of the tunnel (up or down)
the tunnel's IP address
packets transmitted and received over the tunnel
To track packets as the tunnel encapsulates and sends or receives and decap-
sulates them, use this enable mode command:
Syntax: debug interface tunnel
The show and debug commands are available from enable mode; however,
you can also enter them from configuration mode contexts by adding the do
option.

The Tunnel Goes Down

If you have configured a router interface as the tunnel source, verify that this
interface is up. The source interface must be up in order for the tunnel
interface to be up. (Loopback interfaces are always up.) See the Basic Man-
agement and Configuration Guide, Chapter 3: Configuring Ethernet Inter-
faces or Chapter 6: Configuring the Data Link Layer Protocol for E1, T1,
and Serial Interfaces for tips on troubleshooting logical interfaces.
One of the most common causes for a tunnel going down is recursive routing.
When a packet arrives on the tunnel interface, the router encapsulates it and
forwards it toward the tunnel destination. If the route table specifies that the
tunnel interface is the next hop on the way to this destination, then the router
will send the packet back through the tunnel. The packet will again be
encapsulated, forwarded toward the destination, sent back to the tunnel
interface, and so forth.
The ProCurve Secure Router will automatically shut down a tunnel that starts
a recursive loop.
You can fix recursive routing by making sure that the forwarding interface for
the tunnel destination is never a tunnel interface, but a logical interface, such
as PPP 1.
Configuring a Tunnel with Generic Routing Encapsulation
Troubleshooting GRE Configuration
9-13