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
Forgot the attachment.
On Sun, Jan 12, 2025 at 10:57 PM Eric Johnson via groups.io <micromashor=
gmail.com(a)groups.io> wrote:
> 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
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