Chris Davies on 18/10/10 13:15, wrote:
Adam Hardy <adam....@cyberspaceroad.com> wrote:
I tried lowering the MTU to 1400 but it made no difference.
So ping -s 1372 failed? I thought you said it worked up to -s 1472
(packets of 1500 bytes)?
When you drop your MTU to 1400, that means that your local data packets
are fragmented as necessary to stay within the maximum packet size. If
you generate data with a "do not fragment" ("DF") label attached to it,
you have to ensure that each packet is no larger than the available
size. (All fairly obvious so far, I trust.)
If something between you and the destination is eating the "Hey you're
MTU's too big for this link" messages then there's no way of handling
overly large packets - as far as the recipient is concerned they have
been discarded en route.
Remember that although your packets might be the right size, there is
(AFAICR) nothing there that limits the size of the packets being returned
to you. And if the "too big" ICMP messages relating to data from the
far end back to you are being discarded then the sender can't know it
needs to reduce the packet size in order to reach you.
So if there is a "black hole router" between me and the server I'm having
problems with, I still haven't identified it. When I said I reduced my MTU, that
was just on the one machine that runs the software that communicates so poorly
with the server at mktgw1.ibllc.com
I did detect a host at hop 5 on the traceroute to the server which was losing
packets according to my monitoring programs, but now the traceroute has changed
and that server's not on the route. Actually now I'm checking again, it is back.
British Telecom are playing around obviously.
I have a question about traceroute that might be relevant. I haven't figured out
the traceroute options because on lenny, my traceroute doesn't complete. The
last hop to mktgw1.ibllc.com doesn't show - it just counts stars up to 30. But
on windows it does complete at 23 - where mktgw1.ibllc.com is the last hop /
target. Does this betray anything?
lenny traceroute (from gateway 192.168.0.2)
1 192.168.1.1 (192.168.1.1) 0.577 ms 1.303 ms 1.282 ms
2 217.32.146.168 (217.32.146.168) 7.520 ms 7.742 ms 8.567 ms
3 217.32.146.222 (217.32.146.222) 10.190 ms 11.197 ms 11.333 ms
4 213.120.177.58 (213.120.177.58) 11.760 ms 12.444 ms 13.441 ms
5 213.120.176.62 (213.120.176.62) 14.376 ms 14.843 ms 15.810 ms
6 213.120.176.182 (213.120.176.182) 16.794 ms 6.072 ms 6.350 ms
7 acc2-10GigE-0-2-0-4.l-far.21cn-ipp.bt.net (109.159.249.225) 7.532 ms
acc2-10GigE-0-2-0-5.l-far.21cn-ipp.bt.net (109.159.249.227) 7.672 ms
acc2-10GigE-0-0-0-4.l-far.21cn-ipp.bt.net (109.159.249.194) 9.562 ms
8 core2-te0-14-4-0.ealing.ukcore.bt.net (109.159.249.157) 10.984 ms
core2-te0-11-5-0.ealing.ukcore.bt.net (109.159.249.141) 11.736 ms
core2-te0-14-4-0.ealing.ukcore.bt.net (109.159.249.157) 12.092 ms
9 transit2-xe0-1-0.ealing.ukcore.bt.net (194.72.17.82) 12.067 ms 13.004 ms
13.899 ms
10 t2c2-ge11-0-0.uk-eal.eu.bt.net (166.49.168.61) 14.442 ms 15.320 ms
16.005 ms
11 so-6-0-2.edge1.London2.Level3.net (212.113.11.253) 17.451 ms 17.698 ms
18.323 ms
12 ae-32-52.ebr2.London2.Level3.net (4.68.117.62) 27.142 ms 8.414 ms 19.868
ms
13 ae-3-3.ebr1.London1.Level3.net (4.69.141.189) 8.819 ms 9.165 ms 10.011 ms
14 ae-100-100.ebr2.London1.Level3.net (4.69.141.166) 10.478 ms 11.449 ms
12.280 ms
15 ae-41-41.ebr1.NewYork1.Level3.net (4.69.137.66) 81.797 ms 82.604 ms
ae-42-42.ebr1.NewYork1.Level3.net (4.69.137.70) 83.437 ms
16 ae-4-4.ebr1.NewYork2.Level3.net (4.69.141.18) 83.826 ms 84.588 ms 85.464
ms
17 ae-1-51.edge2.NewYork2.Level3.net (4.69.138.195) 86.162 ms 86.585 ms
87.297 ms
18 mci-level3-oc48-washington1.level3.net (4.68.127.22) 95.632 ms
mci-level3-xe.newyork2.Level3.net (4.68.110.106) 87.545 ms
0.ge-2-0-0.BR3.NYC4.ALTER.NET (204.255.173.53) 87.854 ms
19 0.ae3.XL4.NYC4.ALTER.NET (152.63.16.186) 88.335 ms 88.235 ms
0.ae2.XL4.NYC4.ALTER.NET (152.63.3.117) 88.418 ms
20 0.so-7-1-0.XL4.BOS4.ALTER.NET (152.63.0.221) 91.572 ms 92.351 ms
0.ge-7-0-0.XL3.BOS4.ALTER.NET (152.63.0.165) 92.589 ms
21 POS7-0-0.GW12.BOS4.ALTER.NET (152.63.22.181) 91.460 ms 91.469 ms
POS6-0-0.GW12.BOS4.ALTER.NET (152.63.22.177) 92.245 ms
22 interactivebrokers-gw.customer.alter.net (208.192.181.62) 100.881 ms
101.943 ms 102.812 ms
23 * * *
24 * * *
25 * * *
26 * * *
27 * * *
28 * * *
29 * * *
30 * * *
and the windows traceroute:
1 1 ms <1 ms <1 ms isengard.localdomain [192.168.0.2]
2 4 ms 1 ms 1 ms 192.168.1.1
3 7 ms 7 ms 6 ms 217.32.146.168
4 7 ms 7 ms 7 ms 217.32.146.222
5 9 ms 11 ms 9 ms 213.120.177.58
6 7 ms * 8 ms 213.120.176.54
7 8 ms 7 ms 8 ms 213.120.176.182
8 7 ms 7 ms 7 ms acc2-10GigE-0-1-0-4.l-far.21cn-ipp.bt.net
[109.159.249.198]
9 9 ms 8 ms 8 ms core2-te0-14-4-0.ealing.ukcore.bt.net
[109.159.249.157]
10 8 ms 8 ms 8 ms transit2-xe11-1-0.ealing.ukcore.bt.net
[194.72.17.194]
11 8 ms 8 ms 8 ms t2c2-ge13-0-0.uk-eal.eu.bt.net [166.49.168.53]
12 9 ms 9 ms 8 ms 195.50.91.169
13 9 ms 13 ms 18 ms ae-32-52.ebr2.London2.Level3.net [4.68.117.62]
14 9 ms 8 ms 9 ms ae-3-3.ebr1.London1.Level3.net [4.69.141.189]
15 9 ms 7 ms 9 ms ae-100-100.ebr2.London1.Level3.net
[4.69.141.166]
16 78 ms 78 ms 77 ms ae-41-41.ebr1.NewYork1.Level3.net [4.69.137.66]
17 77 ms 77 ms 77 ms ae-4-4.ebr1.NewYork2.Level3.net [4.69.141.18]
18 98 ms 78 ms 77 ms ae-1-51.edge2.NewYork2.Level3.net [4.69.138.195]
19 105 ms 80 ms 81 ms 4.68.111.138
20 80 ms 81 ms 81 ms 0.ae3.XL3.NYC4.ALTER.NET [152.63.16.182]
21 88 ms 87 ms 87 ms 0.so-7-1-0.XL3.BOS4.ALTER.NET [152.63.0.209]
22 88 ms 92 ms 87 ms POS6-0-0.GW12.BOS4.ALTER.NET [152.63.22.177]
23 96 ms 95 ms 95 ms interactivebrokers-gw.customer.alter.net
[208.192.181.62]
24 95 ms 96 ms 96 ms mktgw1.ibllc.com [208.245.107.9]
(The route is slightly different, I copied the traceroute from the windows
machine yesterday but took the lenny traceroute today)
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