On 11 Sep 2012, at 07:52, David Scott wrote: Heh, no problem. While I was debugging this I did a bit of "yak shaving" and now have a nice bit of code which can capture packets to a block device-- this may be useful in future.
oh- nice. can you point me to it please? (I can sense some student project proposals coming on :)
On Tuesday, September 11, 2012, Anil Madhavapeddy wrote:
That was my fault, sorry! This sort of thing should be fixed soon when
we can share C bindings more easily among the cross-compilation targets.
-anil
On 10 Sep 2012, at 22:31, David Scott <scott.dj@xxxxxxxxx> wrote:
> Right, problem solved: TCP checksum on xen was slightly broken. There
> was a fix made to Unix to cope with odd-length packets, this needed to
> be applied to xen as well. Many of the packets had valid checksums,
> and linux would ACK up to the sequence number in the last one of
> those.
>
> Now that the TCP bug is squashed, I can get back to writing my blog
> post -- all just a day in the life of a mirage hacker :-)
>
> On Sat, Sep 8, 2012 at 9:06 AM, Dave Scott <Dave.Scott@xxxxxxxxxxxxx> wrote:
>>
>>
>> On Sep 7, 2012, at 5:59 PM, "Anil Madhavapeddy" <anil@xxxxxxxxxx> wrote:
>>
>>> On Fri, Sep 07, 2012 at 02:02:45PM +0100, David Scott wrote:
>>>> 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:
--
Dave Scott
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