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lixuewei / rt-n56u

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Bad UDP checksums on some traffic from router #1367

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
Using 085 firmware on an RT-N56U, I am seeing lots of traffic like this:

rt-n56u# tcpdump -vv -i br0 port 1900
tcpdump: listening on br0, link-type EN10MB (Ethernet), capture size 65535 bytes
10:40:01.735852 IP (tos 0x0, ttl 2, id 16776, offset 0, flags [DF], proto UDP 
(17), length 408)
    RT-N56U.11352 > 239.255.255.250.1900: [bad udp cksum 0xfc88 -> 0xa372!] UDP, length 380
10:40:01.736459 IP (tos 0x0, ttl 2, id 16777, offset 0, flags [DF], proto UDP 
(17), length 480)
    RT-N56U.11352 > 239.255.255.250.1900: [bad udp cksum 0xfcd0 -> 0x3474!] UDP, length 452
10:40:01.736994 IP (tos 0x0, ttl 2, id 16778, offset 0, flags [DF], proto UDP 
(17), length 417)
    RT-N56U.11352 > 239.255.255.250.1900: [bad udp cksum 0xfc91 -> 0xd72c!] UDP, length 389
10:40:01.737508 IP (tos 0x0, ttl 2, id 16779, offset 0, flags [DF], proto UDP 
(17), length 476)
    RT-N56U.11352 > 239.255.255.250.1900: [bad udp cksum 0xfccc -> 0x58a2!] UDP, length 448

These occur in burst of 20 or so frames, all with bad checksums, every minute 
or so.  The packet decode reveals that the frames contain SSDP NOTIFY messages.

a) Bad checksums aren't good!
b) It's not clear to me why the router is sending these SSDP NOTIFY messages.  
I am not running a UPNP server on the router.

Similar multicast traffic between other hosts, as seen on the router, does not 
have bad checksums:

10:35:04.342219 IP (tos 0x0, ttl 4, id 62733, offset 0, flags [DF], proto UDP 
(17), length 313)
    10.248.0.10.47626 > 239.255.255.250.1900: [udp sum ok] UDP, length 285

I at first suspected the hardware tcp/udp acceleration, but the issue is still 
there with hw accel turned off.

Any thoughts?

Original issue reported on code.google.com by rich...@richardreiner.com on 22 Nov 2014 at 3:55

GoogleCodeExporter commented 9 years ago 
Does the issue persist if you disable the ASUS Info Discovery Service?

Original comment by kitch2400 on 22 Nov 2014 at 8:57

GoogleCodeExporter commented 9 years ago 
It isn't enabled.

Original comment by rich...@richardreiner.com on 22 Nov 2014 at 8:59

GoogleCodeExporter commented 9 years ago 
This is not bug, raeth driver always perform HW TX checksumming 
PDMA -> [checksumming] -> GDMA ports

tcpdump is located before PDMA.

Original comment by andy.pad...@gmail.com on 12 Feb 2015 at 7:50