All,
I was trying to bring up an AMPRNet IPIP tunnel in my lab network, but when
I did a packet capture on the WAN side of the gateway I am setting up, I
noticed that on average, about 80% of the IPIP packets I receive from the
UCSD gateway have their inner headers corrupted. As far as I can tell, the
first 4 bytes of the inner header are being overwritten with a garbage byte
sequence (hex 00-04-00-00). I have included a packet capture showing what's
going on. At packet 63, the RIP announcement starts, and continues through
packet 100, so there's some known-good traffic in there.
Has anyone seen anything like this before?
I have another AMPRNet IPIP tunnel set up on a datacenter server, and it
has no such problem, so this is an isolated issue (i.e., not an issue with
the UCSD gateway). The only other thing I could suspect is that the
ISP-issued modem/gateway combo unit. Of course, I have no visibility into
traffic upstream of this unit, so I don't have a way to know if it is
causing the corruption. Unfortunately, my ISP doesn't let me disable the
gateway function of the unit, so I have to suspect the firmware of this
device.
Any and all help is appreciated. I am going to call my ISP tomorrow and see
if they are aware of any issues with these modem/gateway units.
Thanks,
Eric Johnson - AE0JE
