Good Afternoon
All,
I am currently
trying to resolve an issue where we are having trouble sending data across a
tunnel running GRE encryption. With this encryption employed the MTU size
allowed is decreased to 1476. When we attempt to send traffic (email, ftp,
etc...) through the tunnel, we are finding that it does not
work.
My sniffer trace is
showing that the frames being sent are setting the DF bit, which I would
expect. I would then expect that if the router is unable to send the
packet, it would drop it and return an ICMP message back to the source
telling it to decrease the packet size and try it again. I am not seeing
any of these messages.
We are running HSRP
on the ethernet interfaces that connect to my LAN. I believe we are
running a 12.0 IOS release, although I am not sure of the actual
version.
Does anyone have any
ideas why this might be happening? I am trying to resolve this issue while
having no CLI access to the routers. I have been informed by the
controlling body that there are no access lists prohibiting ICMP messages from
being sent, and there are no firewall rules in place that would be dropping the
ICMP messages.
Any and all
explanations of possible causes/resolutions would be
appreciated.
Steve D.
