13 Jan
2025
13 Jan
'25
12:14 a.m.
Hi Eric.
A shame you're not able to directly connect to your ISP's incoming
interface, with their modem being a mysterious blackbox it's going to be
hard. Do you have any controls at all on the ISP modem, perhaps features
like its VPN passthrough is interfering?
I just did a packet capture for a while from my link, and I'm receiving
nothing but good traffic from the USCD gateway. (although in practice it
is incredibly slow here in Australia - less than 1Mbit/sec)
If you need a far-end node to set up some packet captures with or set up
an iperf node or the like, let me know.
73
Gavin
VK6HGR
On 13/01/2025 12:57 pm, Eric Johnson via 44net 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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