tcpdump on RT-AC66U causes reboot

[highwire]

This post is kind of hail-Mary. When I had Merlin's 374.43 firmware on a RT-AC66U, I could ssh to the router and run tcpdump (I installed it via entware), and it would run flawlessly. I could even send the info via wireless to my MacBook Pro running WireShark like this:

ssh name@router tcpdump -U -s0 -w - | /Applications/Wireshark.app/Contents/Resources/bin/wireshark -k -i -

and it would run pretty much forever.

I installed 376.44, cleared NVRAM and did my standard setup. The jffs and /opt/var partitions survived, as did my startup scripts.

Anyhow, now when I run tcpdump, such as:

tcpdump -ieth0 -U -s0 net 10.0.1.x, it will run for about a minute or two and then the router reboots. The system logs -> general logs don't shed any light as to why this is happening.

Any advice on how I can debug this? Thanks.

 

[Fighter]

I have to admit I have exactly the same issue, but I have N66U router.
And for me it was similar history - on the earlier versions it was working fine and after upgrade it does not.

Does anyone have any clue how to fix the problem?
For me it becomes really critical since I cannot log http traffic anymore.

 

[Grump]

You could try installing strace and seeing which call causes the reboot. I suspect it's a kernel bug. Might help to compare to the old firmware too.

 

[highwire]

Here's the tail of the strace output of 'strace -oblah.txt tcpdump -ieth0 -U -s0 net 10.0.1.29'. I have no idea what this means, but the router rebooted as usual...

write(2, " (", 2) = 2
write(2, "Ethernet", 8) = 8
write(2, "), capture size ", 16) = 16
write(2, "65535", 5) = 5
write(2, " bytes\n", 7) = 7
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3, 0x7ff12a3c, MSG_TRUNC) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL, si_value={int=1, ptr=0x1}} ---
recvmsg(3,

~

 

[Fighter]

Guys, after some experiments I found out that disabling NAT acceleration under LAN -> Switch Control helps in my case. No reboots with tcpdump (and tcpflow and tshark as well for which actually i found issue first) observed after disabling this option.

 

[highwire]

Guys, after some experiments I found out that disabling NAT acceleration under LAN -> Switch Control helps in my case. No reboots with tcpdump (and tcpflow and tshark as well for which actually i found issue first) observed after disabling this option.

Good catch. I enabled per-IP stats which disables HW acceleration and no more crashes while running tcpdump. Thanks.

 

[stonith]

Thanks for this, been running into this as well.