[c-nsp] Monitoring ethernet circuits with GRE

[William]

Hi list,

With the increasing amount of Ethernet circuits being used within our
business I'm looking for a simple way to monitor the links. As we all
know, most of the time the WAN interface will be up/up even if there
is a problem in the 'cloud' it uses to get to the other end point.

I've been looking into using a simple GRE tunnel from one end to the
other, if there is a serious amount of packet loss on the link and the
tunnel goes up/down I can use one of our systems to alert us.

Config goes like this:

interface Tunnel1
 no ip address
 tunnel source 1.1.1.1
 tunnel destination 1.1.1.2


With the last two lines reversed for the other side, everything should
come up and just *work*

I'm currently testing this with a 2600 and 3550, the port on the 3550
is routed and has an ip address applied to it.

My problem consists of the tunnel being up/up, and sometimes just
being down. Having to issue a shut+no shut on either interface to
bring the tunnel back up. Sometimes the 3550 is reporting the tunnel
is up when the 2600 isn't contactable over IP!! (having shut down the
interface on the 2600)

Am I running into silly issues because the 3550 isn't capable of GRE?
Most of the networks I'm currently looking after consist of L3 3750's
with routed ports to connect to WANs. Just need some guidance if I'm
doing something wrong or if the hardware I'm dealing with just cant do
it!

Thank you for your time.

William