[Cerowrt-devel] TFO crashes cerowrt 3.7.1-1

Fri Jan 4 16:11:12 EST 2013

Hmm. I would lean towards there being an issue with the new (freshly
ported forward to 3.7.1) unaligned checksum code for mips based on
what you say here. Or an offload...

As for the 239.x multicast issue, hmm... separate issue entirely. Probably...

And then there's TFO. I note that in order to use it properly you need
to turn it on in proc. Last I remember that was

echo 3 > /proc/sys/net/ipv4/tcp_fastopen

However that's an old memory and there is this tcp_fastopen_key file I
don't know anything about yet (this is such bleeding edge stuff!)

... and with tcp_fastopen disabled things should still work right...
so I'm thinking something else is busted in the stack.

I've also observed a dns slowdown in what I've been testing but hadn't
dug into packet dumps. (and was assuming, until now, it was due to me
fiddling with ULAs inside the network) Thanks for digging this deep!

I never said this first attempt at 3.7 for cero was going to be
perfect, but we've entered a new age of subtle problems here.

I strongly suggest nobody else try this dev build as a default gw, and
that the TFO folk ignore the noise for now.

I just got a 3.7.1 box built on x86_64 so as to a/b some captures.
Regrettably I'm short on time through the weekend...

On Fri, Jan 4, 2013 at 12:42 PM, Maciej Soltysiak <maciej at soltysiak.com> wrote:
> I am seeing something strange here, with polipo related to TFO but also DNS.
> When I just took 3.7.1-1 and set my windows 7 laptop to use gw.home.lan:8123
> as http proxy it didn't work. What I observed was:
> A) after quite a while polipo's response to browser was 504 Host
> www.osnews.com lookup failed: Timeout
> b) this error in ssh console: Host osnews.com lookup failed: Timeout
> (131072)
> c) Disabling TFO by adding option useTCPFastOpen 'false' to config 'polipo'
> 'general' works around the problem
> d) Alternatively, you can keep TFO enabled in polipo but change option
> 'dnsUseGethostbyname' from 'reluctantly' to 'true' (!)
> This is very weird, because TFO is TCP and the DNS queries fired off by
> polipo are UDP:
> root at OpenWrt:/tmp/log# tcpdump -n -v -vv -vvv -x -X -s 1500 -i lo
> 20:21:56.160245 IP (tos 0x0, ttl 64, id 50129, offset 0, flags [DF], proto
> UDP (17), length 60)
> 127.0.0.1.47304 > 127.0.0.1.53: [bad udp cksum 0xfe3b -> 0xd17f!] 55396+ A?
> www.osnews.com. (32)
> 0x0000: 4500 003c c3d1 4000 4011 78dd 7f00 0001 E..<.. at .@.x.....
> 0x0010: 7f00 0001 b8c8 0035 0028 fe3b d864 0100 .......5.(.;.d..
> 0x0020: 0001 0000 0000 0000 0377 7777 066f 736e .........www.osn
> 0x0030: 6577 7303 636f 6d00 0001 0001 ews.com.....
> 20:21:56.160319 IP (tos 0x0, ttl 64, id 50130, offset 0, flags [DF], proto
> UDP (17), length 60)
> 127.0.0.1.47304 > 127.0.0.1.53: [bad udp cksum 0xfe3b -> 0xd164!] 55396+
> AAAA? www.osnews.com. (32)
> 0x0000: 4500 003c c3d2 4000 4011 78dc 7f00 0001 E..<.. at .@.x.....
> 0x0010: 7f00 0001 b8c8 0035 0028 fe3b d864 0100 .......5.(.;.d..
> 0x0020: 0001 0000 0000 0000 0377 7777 066f 736e .........www.osn
> 0x0030: 6577 7303 636f 6d00 001c 0001 ews.com.....
> 20:21:56.169942 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP
> (17), length 123)
> 127.0.0.1.53 > 127.0.0.1.47304: [bad udp cksum 0xfe7a -> 0x5f73!] 55396 q:
> A? www.osnews.com. 1/2/0 www.osnews.com. [29m3s] A 74.86.31.159 ns:
> osnews.com. [29m3s] NS ns2.swelter.net., osnews.com. [29m3s] NS
> ns1.swelter.net. (95)
> 0x0000: 4500 007b 0000 4000 4011 3c70 7f00 0001 E..{.. at .@.<p....
> 0x0010: 7f00 0001 0035 b8c8 0067 fe7a d864 8180 .....5...g.z.d..
> 0x0020: 0001 0001 0002 0000 0377 7777 066f 736e .........www.osn
> 0x0030: 6577 7303 636f 6d00 0001 0001 c00c 0001 ews.com.........
> 0x0040: 0001 0000 06cf 0004 4a56 1f9f c010 0002 ........JV......
> 0x0050: 0001 0000 06cf 0011 036e 7332 0773 7765 .........ns2.swe
> 0x0060: 6c74 6572 036e 6574 00c0 1000 0200 0100 lter.net........
> 0x0070: 0006 cf00 0603 6e73 31c0 40 ......ns1.@
> 20:21:56.173901 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP
> (17), length 135)
> 127.0.0.1.53 > 127.0.0.1.47304: [bad udp cksum 0xfe86 -> 0x8ecb!] 55396 q:
> AAAA? www.osnews.com. 1/2/0 www.osnews.com. [54m44s] AAAA
> 2607:f0d0:1002:62::3 ns: osnews.com. [29m3s] NS ns1.swelter.net.,
> osnews.com. [29m3s] NS ns2.swelter.net. (107)
> 0x0000: 4500 0087 0000 4000 4011 3c64 7f00 0001 E..... at .@.<d....
> 0x0010: 7f00 0001 0035 b8c8 0073 fe86 d864 8180 .....5...s...d..
> 0x0020: 0001 0001 0002 0000 0377 7777 066f 736e .........www.osn
> 0x0030: 6577 7303 636f 6d00 001c 0001 c00c 001c ews.com.........
> 0x0040: 0001 0000 0cd4 0010 2607 f0d0 1002 0062 ........&......b
> 0x0050: 0000 0000 0000 0003 c010 0002 0001 0000 ................
> 0x0060: 06cf 0011 036e 7331 0773 7765 6c74 6572 .....ns1.swelter
> 0x0070: 036e 6574 00c0 1000 0200 0100 0006 cf00 .net............
> 0x0080: 0603 6e73 32c0 4c ..ns2.L
> This is the only DNS traffic I saw during the attempts. The tcpdumps have
> udp bad checksum but when I disabled TFO in polipo, the UDP where still bad
> checksum but they worked.
> Really weird.
> p.s. UPNP still works for port forwarding negotiation as it did in 3.6.11-4
> I still couldn't get the UPNP/SSDP broadcasts (udp to 239.255.255.250) to
> being forwarded between se00 and sw00/sw10. Last time it worked was ~3.3.8.
> I'm starting not to question why it doesn't work, I'm starting to wonder why
> it did work then ;-)
> Regards,
> Maciej
> On Fri, Jan 4, 2013 at 6:33 PM, Dave Taht <dave.taht at gmail.com> wrote:
>>
>> On Fri, Jan 4, 2013 at 9:27 AM, Eric Dumazet <edumazet at google.com> wrote:
>> > Sorry, could you give us a copy of the panic stack trace ?
>>
>> I will get a serial console up on a wndr3800 by sunday. (sorry, just
>> landed in california, am in disarray)
>>
>> The latest dev build of cero for the wndr3800 and wndr3700v2 is at:
>>
>> http://snapon.lab.bufferbloat.net/~cero2/cerowrt/wndr/3.7.1-1/
>>
>> --
>> Dave Täht
>>
>> Fixing bufferbloat with cerowrt:
>> http://www.teklibre.com/cerowrt/subscribe.html
>> _______________________________________________
>> Cerowrt-devel mailing list
>> Cerowrt-devel at lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>
>

-- 
Dave Täht

Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html