mirage-www

[David Scott <scott.dj@xxxxxxxxx>]

Hi,

I've built mirage-www for xen and modified the static IP to fit my
environment. (I tried DHCP first but this didn't work -- if I get the
time I'll try to debug).

I can ping the server fine, and it's certainly receiving a lot of
traffic on my (probably fairly busy) local network. When I try to
fetch a URL the TCP connection hangs. On the console I get:

Dispatch: dynamic URL /
... irrelevant spam
TCP retransmission on timer seq = -889321980

I've attached a small tcpdump of the conversation. I started with ping
and then tried HTTP. According to tcpdump/wireshark it went like this:

$ tcpdump -r mirage.pcap -n
reading from file mirage.pcap, link-type EN10MB (Ethernet)
13:47:07.543119 IP 10.80.2.32 > 10.80.239.140: ICMP echo request, id
9300, seq 1, length 64
13:47:07.543756 IP 10.80.239.140 > 10.80.2.32: ICMP echo reply, id
9300, seq 1, length 64
13:47:08.542112 IP 10.80.2.32 > 10.80.239.140: ICMP echo request, id
9300, seq 2, length 64
13:47:08.542422 IP 10.80.239.140 > 10.80.2.32: ICMP echo reply, id
9300, seq 2, length 64
13:47:09.541288 IP 10.80.2.32 > 10.80.239.140: ICMP echo request, id
9300, seq 3, length 64
13:47:09.541609 IP 10.80.239.140 > 10.80.2.32: ICMP echo reply, id
9300, seq 3, length 64
13:47:10.541286 IP 10.80.2.32 > 10.80.239.140: ICMP echo request, id
9300, seq 4, length 64
13:47:10.541580 IP 10.80.239.140 > 10.80.2.32: ICMP echo reply, id
9300, seq 4, length 64
13:47:11.541286 IP 10.80.2.32 > 10.80.239.140: ICMP echo request, id
9300, seq 5, length 64
13:47:11.541932 IP 10.80.239.140 > 10.80.2.32: ICMP echo reply, id
9300, seq 5, length 64

-- so far so good, this is just my initial pings. Switching to 'wget
http://10.80.239.140/'

13:47:14.241216 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [S], seq
2284582709, win 5840, options [mss 1460,sackOK,TS val 909789846 ecr
0,nop,wscale 6], length 0
13:47:14.242365 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [S.],
seq 3536243828, ack 2284582710, win 65535, options [mss 1380,wscale
2,eol], length 0
13:47:14.242387 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [.], ack
1, win 92, length 0

-- TCP connection established

13:47:14.242417 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [P.],
seq 1:112, ack 1, win 92, length 111

-- HTTP GET / sent

13:47:14.242869 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 1:18, ack 112, win 65535, length 17

-- HTTP/1.1 200 OK replied

13:47:14.242880 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [.], ack
18, win 92, length 0
13:47:14.243369 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 18:68, ack 112, win 65535, length 50

-- "content-length..." replied

13:47:14.243556 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 68:1448, ack 112, win 65535, length 1380

... after this chunks of the blog post are transmitted

13:47:14.243562 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [.], ack
18, win 92, length 0
13:47:14.243566 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 1448:2828, ack 112, win 65535, length 1380
13:47:14.243571 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [.], ack
18, win 92, length 0
13:47:14.243575 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 2828:4164, ack 112, win 65535, length 1336
13:47:14.243579 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [.], ack
18, win 92, length 0
13:47:14.243602 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 4164:5544, ack 112, win 65535, length 1380
13:47:14.243608 IP 10.80.2.32.37158 > 10.80.239.140.80: Flags [.], ack
18, win 92, length 0
13:47:14.243776 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 18:68, ack 112, win 65535, length 50

-- fast retransmit of the "content-length" packet

13:47:18.242606 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 18:68, ack 112, win 65535, length 50

-- and again

13:47:20.242782 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 18:68, ack 112, win 65535, length 50

-- and again

13:47:24.242904 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 18:68, ack 112, win 65535, length 50

-- and again

13:47:32.243159 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 18:68, ack 112, win 65535, length 50

-- and again

13:47:48.243262 IP 10.80.239.140.80 > 10.80.2.32.37158: Flags [P.],
seq 18:68, ack 112, win 65535, length 50

I tried a ping flood, and all is ok at this level:

djs@ely:~$ sudo ping -f 10.80.239.140
PING 10.80.239.140 (10.80.239.140) 56(84) bytes of data.
.^C
--- 10.80.239.140 ping statistics ---
9930 packets transmitted, 9929 received, 0% packet loss, time 2556ms
rtt min/avg/max/mdev = 0.166/0.242/1.762/0.064 ms, ipg/ewma 0.257/0.252 ms


It looks like a problem in TCP. Anyone got any hints where to look?

Cheers,
-- 
Dave Scott

Attachment: mirage.pcap
Description: Binary data