IPV6 very slow, not respecting MTU??


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Question IPV6 very slow, not respecting MTU??

Hi,

Curious problem with IPV6. Situation is wget request from squid proxy via intermediate router. With IPV4 (wget -4) speed is ~100MB/sec. With IPV6 (wget -6) it drops to 30KB/sec.

Examining the traffic with tcpdump shows that the squid box is regularly sending out over-sized packets (>MTU) and receiving "ICMP6 packet too big" responses from the router. It then behaves for a few packets before trying it on again. With IPV4 it never sends an oversize packet (same route over same interfaces).

Any suggestions where to poke appreciated!


Some configuration details:

Code:
# ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:0C:29:80:23:32  
          inet addr:192.168.1.228  Bcast:192.168.1.255  Mask:255.255.255.224
          inet6 addr: fd01:0:0:5::228/64 Scope:Global
          inet6 addr: fe80::20c:29ff:fe80:2332/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:35761 errors:0 dropped:0 overruns:0 frame:0
          TX packets:61105 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:6665731 (6.3 MiB)  TX bytes:79820556 (76.1 MiB)

All platforms are Centos 6.0 on VMware ESXi 4.1, using the vmxnet3 driver.

All offload is disabled (had issues with this on the vmxnet3 driver before) :

Code:
# /sbin/ethtool -k eth1
Offload parameters for eth1:
rx-checksumming: off
tx-checksumming: off
scatter-gather: off
tcp-segmentation-offload: off
udp-fragmentation-offload: off
generic-segmentation-offload: off
generic-receive-offload: off
large-receive-offload: off


tcpdump extract - IPv6:

Code:
19:20:46.404077 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [S], seq 2248635961, win 5760, options [mss 1440,sackOK,TS val 10748669 ecr 0,nop,wscale 6], length 0
19:20:46.404097 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [S.], seq 912987542, ack 2248635962, win 5712, options [mss 1440,sackOK,TS val 3826645070 ecr 10748669,nop,wscale 6], length 0
19:20:46.405102 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 1, win 90, options [nop,nop,TS val 10748671 ecr 3826645070], length 0
19:20:46.405168 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [P.], seq 1:246, ack 1, win 90, options [nop,nop,TS val 10748671 ecr 3826645070], length 245
19:20:46.405177 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], ack 246, win 106, options [nop,nop,TS val 3826645071 ecr 10748671], length 0
19:20:46.405568 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 1:2857, ack 246, win 106, options [nop,nop,TS val 3826645071 ecr 10748671], length 2856
19:20:46.409916 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [P.], seq 2857:3993, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748671], length 1136
19:20:46.409984 IP6 fd01:0:0:5::225 > fd01:0:0:5::228: ICMP6, packet too big, mtu 1500, length 1240
19:20:46.410069 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 1, win 90, options [nop,nop,TS val 10748676 ecr 3826645071,nop,nop,sack 1 {2857:3993}], length 0
19:20:46.410091 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 3993:5421, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 1428
19:20:46.410187 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 1, win 90, options [nop,nop,TS val 10748676 ecr 3826645071,nop,nop,sack 1 {2857:5421}], length 0
19:20:46.410199 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 1:1429, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 1428
19:20:46.410294 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 1429, win 135, options [nop,nop,TS val 10748676 ecr 3826645076,nop,nop,sack 1 {2857:5421}], length 0
19:20:46.410304 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 5421:6849, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 1428
19:20:46.410390 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 1429, win 135, options [nop,nop,TS val 10748676 ecr 3826645076,nop,nop,sack 1 {2857:6849}], length 0
19:20:46.410401 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 1429:2857, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 1428
19:20:46.410489 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 6849, win 180, options [nop,nop,TS val 10748676 ecr 3826645076], length 0
19:20:46.410500 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 6849:8277, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 1428
19:20:46.410586 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 8277, win 224, options [nop,nop,TS val 10748676 ecr 3826645076], length 0
19:20:46.410597 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 8277:9705, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 1428
19:20:46.410606 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 9705:11133, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 1428
19:20:46.410713 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 9705, win 269, options [nop,nop,TS val 10748676 ecr 3826645076], length 0
19:20:46.410725 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 11133:13989, ack 246, win 106, options [nop,nop,TS val 3826645076 ecr 10748676], length 2856
19:20:46.416490 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 11133, win 314, options [nop,nop,TS val 10748676 ecr 3826645076], length 0
19:20:46.416506 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 13989:15417, ack 246, win 106, options [nop,nop,TS val 3826645082 ecr 10748676], length 1428
19:20:46.416554 IP6 fd01:0:0:5::225 > fd01:0:0:5::228: ICMP6, packet too big, mtu 1500, length 1240
19:20:46.416629 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 11133, win 314, options [nop,nop,TS val 10748682 ecr 3826645076,nop,nop,sack 1 {13989:15417}], length 0
19:20:46.416637 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 15417:16845, ack 246, win 106, options [nop,nop,TS val 3826645082 ecr 10748682], length 1428
19:20:46.416729 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 11133, win 314, options [nop,nop,TS val 10748682 ecr 3826645076,nop,nop,sack 1 {13989:16845}], length 0
19:20:46.416741 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 16845:18273, ack 246, win 106, options [nop,nop,TS val 3826645082 ecr 10748682], length 1428
19:20:46.416817 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 11133, win 314, options [nop,nop,TS val 10748682 ecr 3826645076,nop,nop,sack 1 {13989:18273}], length 0
19:20:46.416830 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 11133:12561, ack 246, win 106, options [nop,nop,TS val 3826645083 ecr 10748682], length 1428
19:20:46.416907 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 12561, win 358, options [nop,nop,TS val 10748683 ecr 3826645083,nop,nop,sack 1 {13989:18273}], length 0
19:20:46.416917 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 12561:13989, ack 246, win 106, options [nop,nop,TS val 3826645083 ecr 10748683], length 1428
19:20:46.417059 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 18273, win 403, options [nop,nop,TS val 10748683 ecr 3826645083], length 0
19:20:46.417070 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 18273:19701, ack 246, win 106, options [nop,nop,TS val 3826645083 ecr 10748683], length 1428
19:20:46.417251 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 19701, win 447, options [nop,nop,TS val 10748683 ecr 3826645083], length 0
19:20:46.417261 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 19701:22557, ack 246, win 106, options [nop,nop,TS val 3826645083 ecr 10748683], length 2856
19:20:46.422347 IP6 fd01:0:0:5::225 > fd01:0:0:5::228: ICMP6, packet too big, mtu 1500, length 1240
19:20:46.623094 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 19701:21129, ack 246, win 106, options [nop,nop,TS val 3826645289 ecr 10748683], length 1428
19:20:46.623288 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 21129, win 492, options [nop,nop,TS val 10748889 ecr 3826645289], length 0
19:20:46.623309 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 22557:25413, ack 246, win 106, options [nop,nop,TS val 3826645289 ecr 10748889], length 2856
19:20:46.628608 IP6 fd01:0:0:5::225 > fd01:0:0:5::228: ICMP6, packet too big, mtu 1500, length 1240
19:20:46.823830 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 21129:22557, ack 246, win 106, options [nop,nop,TS val 3826645490 ecr 10748889], length 1428
19:20:46.824019 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 22557, win 537, options [nop,nop,TS val 10749089 ecr 3826645490], length 0
19:20:46.824037 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 22557:23985, ack 246, win 106, options [nop,nop,TS val 3826645490 ecr 10749089], length 1428
19:20:46.824057 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 23985:25413, ack 246, win 106, options [nop,nop,TS val 3826645490 ecr 10749089], length 1428
19:20:46.824141 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 23985, win 581, options [nop,nop,TS val 10749090 ecr 3826645490], length 0
19:20:46.824155 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 25413:28269, ack 246, win 106, options [nop,nop,TS val 3826645490 ecr 10749090], length 2856
19:20:46.830031 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 25413, win 626, options [nop,nop,TS val 10749090 ecr 3826645490], length 0
19:20:46.830042 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 28269:29697, ack 246, win 106, options [nop,nop,TS val 3826645490 ecr 10749090], length 1428
19:20:46.830080 IP6 fd01:0:0:5::225 > fd01:0:0:5::228: ICMP6, packet too big, mtu 1500, length 1240
19:20:46.830164 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 25413, win 626, options [nop,nop,TS val 10749096 ecr 3826645490,nop,nop,sack 1 {28269:29697}], length 0
19:20:46.830175 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 29697:31125, ack 246, win 106, options [nop,nop,TS val 3826645496 ecr 10749096], length 1428
19:20:46.830263 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 25413, win 626, options [nop,nop,TS val 10749096 ecr 3826645490,nop,nop,sack 1 {28269:31125}], length 0
19:20:46.830273 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 31125:32553, ack 246, win 106, options [nop,nop,TS val 3826645496 ecr 10749096], length 1428
19:20:46.830366 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 25413, win 626, options [nop,nop,TS val 10749096 ecr 3826645490,nop,nop,sack 1 {28269:32553}], length 0
19:20:46.830380 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 25413:26841, ack 246, win 106, options [nop,nop,TS val 3826645496 ecr 10749096], length 1428
19:20:46.830484 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 26841, win 671, options [nop,nop,TS val 10749096 ecr 3826645496,nop,nop,sack 1 {28269:32553}], length 0
19:20:46.830496 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 26841:28269, ack 246, win 106, options [nop,nop,TS val 3826645496 ecr 10749096], length 1428
19:20:46.830595 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 32553, win 715, options [nop,nop,TS val 10749096 ecr 3826645496], length 0
19:20:46.830607 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 32553:33981, ack 246, win 106, options [nop,nop,TS val 3826645496 ecr 10749096], length 1428
19:20:46.830703 IP6 fd01:0:0:6::195.44083 > fd01:0:0:5::228.squid: Flags [.], ack 33981, win 760, options [nop,nop,TS val 10749096 ecr 3826645496], length 0
19:20:46.830713 IP6 fd01:0:0:5::228.squid > fd01:0:0:6::195.44083: Flags [.], seq 33981:36837, ack 246, win 106, options [nop,nop,TS val 3826645496 ecr 10749096], length 2856
19:20:46.835516 IP6 fd01:0:0:5::225 > fd01:0:0:5::228: ICMP6, packet too big, mtu 1500, length 1240

And with IPV4:

Code:
19:20:04.859626 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [S], seq 1535516733, win 5840, options [mss 1460,sackOK,TS val 10707125 ecr 0,nop,wscale 6], length 0
19:20:04.859651 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [S.], seq 193718998, ack 1535516734, win 5792, options [mss 1460,sackOK,TS val 3826603525 ecr 10707125,nop,wscale 6], length 0
19:20:04.859740 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 1, win 92, options [nop,nop,TS val 10707125 ecr 3826603525], length 0
19:20:04.859796 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [P.], seq 1:246, ack 1, win 92, options [nop,nop,TS val 10707125 ecr 3826603525], length 245
19:20:04.859803 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], ack 246, win 108, options [nop,nop,TS val 3826603525 ecr 10707125], length 0
19:20:04.860226 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 1:1449, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707125], length 1448
19:20:04.860237 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 1449:2897, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707125], length 1448
19:20:04.860239 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 2897:3993, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707125], length 1096
19:20:04.860328 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 1449, win 137, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860337 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 3993:5441, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860343 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 5441:6889, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860347 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 2897, win 182, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860350 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 6889:8089, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1200
19:20:04.860354 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 3993, win 227, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860372 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 8089:9537, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860377 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 9537:10985, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860379 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 10985:12185, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1200
19:20:04.860441 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 5441, win 273, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860461 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 6889, win 318, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860463 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 8089, win 363, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860464 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 9537, win 408, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860475 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 10985, win 454, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860484 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 12185:13633, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860491 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 13633:15081, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860493 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 15081:16281, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1200
19:20:04.860506 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 12185, win 499, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860528 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 16281:17729, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860534 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 17729:19177, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860536 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 19177:20377, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1200
19:20:04.860548 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 13633, win 544, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860569 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 20377:21825, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860575 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 21825:23273, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860583 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 15081, win 589, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860592 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 16281, win 635, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860597 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 23273:24473, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1200
19:20:04.860621 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 24473:25921, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860627 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 25921:27369, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860629 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 27369:28569, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1200
19:20:04.860640 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 17729, win 680, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860660 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 28569:30017, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860669 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 19177, win 725, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860677 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 30017:31465, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.860681 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 31465:32665, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1200
19:20:04.860728 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 20377, win 717, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860735 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 21825, win 696, options [nop,nop,TS val 10707126 ecr 3826603526], length 0
19:20:04.860748 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 32665:34113, ack 246, win 108, options [nop,nop,TS val 3826603526 ecr 10707126], length 1448
19:20:04.861122 IP 192.168.0.195.57674 > 192.168.1.228.squid: Flags [.], ack 40857, win 655, options [nop,nop,TS val 10707127 ecr 3826603526], length 0
19:20:04.861135 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 40857:42305, ack 246, win 108, options [nop,nop,TS val 3826603527 ecr 10707127], length 1448
19:20:04.861141 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 42305:43753, ack 246, win 108, options [nop,nop,TS val 3826603527 ecr 10707127], length 1448
19:20:04.861143 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 43753:45201, ack 246, win 108, options [nop,nop,TS val 3826603527 ecr 10707127], length 1448
19:20:04.861145 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 45201:46649, ack 246, win 108, options [nop,nop,TS val 3826603527 ecr 10707127], length 1448
19:20:04.861146 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [.], seq 46649:48097, ack 246, win 108, options [nop,nop,TS val 3826603527 ecr 10707127], length 1448
19:20:04.861148 IP 192.168.1.228.squid > 192.168.0.195.57674: Flags [P.], seq 48097:49049, ack 246, win 108, options [nop,nop,TS val 3826603527 ecr 10707127], length 952


TIA,
Ian.

Last edited by pludi; 10-14-2011 at 07:08 PM..
# 2  
This bug happened in kernels from 2008 or so. IPv6 transmissions would get their MTU from the wrong interface, I think the loopback.
# 3  
Quote:
Originally Posted by Corona688
This bug happened in kernels from 2008 or so. IPv6 transmissions would get their MTU from the wrong interface, I think the loopback.
This one?

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/254622

I'm using the latest Centos Kernel (2.6.32-71.29.1.el6.i686), I'd hope a fix from 2008 would be included in that...

Tried reducing the MTU for lo but made no difference.
# 4  
I'm two revisions newer with a kernel I compiled over a year ago... Doesn't sound that new.
# 5  
TCP also has MSS, which looks correct, so that has to be your ethernet driver...
# 6  
Solved...

Thanks for the suggestions.

Replaced the vNIC with an E1000 (instead of vmxnet3) and the problem disappears, so yes, it's the driver (or the underlying VMware implementation) that's at fault, not the TCP/IP stack.
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