** Also affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Description changed:
etup: amd64, xen0 = ubuntu 7.10 ("gutsy"), xenU = ubuntu 7.10 ("gutsy"),
network config with xenU routing via xen0.
scp xenU:file . very slow, ~50KB/s
scp xen0:file . several MB/s
on xen0:
scp xenU:file . many MB/s
had a look at tcpdump, I see lines like this:
- 10:55:30.319389 IP (tos 0x8, ttl 64, id 59286, offset 0, flags [DF], proto
TCP
- (6), length 2948) xenU.22 > desktop: . 47785:50681(2896) ack 0 win 404
+ 10:55:30.319389 IP (tos 0x8, ttl 64, id 59286, offset 0, flags [DF], proto TCP
+ (6), length 2948) xenU.22 > desktop: . 47785:50681(2896) ack 0 win 404
<nop,nop,timestamp 20681576 687514747>
- 10:55:30.319399 IP (tos 0xc8, ttl 64, id 52994, offset 0, flags [none], proto
- ICMP (1), length 576) xen0 > xenU: ICMP desktop unreachable - need to frag
- (mtu 1500), length 556 IP (tos 0x8, ttl 64, id 59286, offset 0, flags [DF],
- proto TCP (6), length 2948) xenU.22 > desktop.41056: . 47785:50681(2896) ack
+ 10:55:30.319399 IP (tos 0xc8, ttl 64, id 52994, offset 0, flags [none], proto
+ ICMP (1), length 576) xen0 > xenU: ICMP desktop unreachable - need to frag
+ (mtu 1500), length 556 IP (tos 0x8, ttl 64, id 59286, offset 0, flags [DF],
+ proto TCP (6), length 2948) xenU.22 > desktop.41056: . 47785:50681(2896) ack
0 win 404 <nop,nop,timestamp 20681576 687514747>[|icmp]
so the xenU is sending packets with size 2948? why?
ifconfig on xenU:
- eth0 Link encap:Ethernet HWaddr 00:16:3E:6D:03:2D
- inet addr:xenU Bcast:... Mask:255.255.255.255
- inet6 addr: fe80::216:3eff:fe6d:32d/64 Scope:Link
- UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
- RX packets:34918213 errors:0 dropped:0 overruns:0 frame:0
- TX packets:34262839 errors:0 dropped:0 overruns:0 carrier:0
- collisions:0 txqueuelen:1000
- RX bytes:12337072144 (11.4 GB) TX bytes:48486812526 (45.1 GB)
+ eth0 Link encap:Ethernet HWaddr 00:16:3E:6D:03:2D
+ inet addr:xenU Bcast:... Mask:255.255.255.255
+ inet6 addr: fe80::216:3eff:fe6d:32d/64 Scope:Link
+ UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
+ RX packets:34918213 errors:0 dropped:0 overruns:0 frame:0
+ TX packets:34262839 errors:0 dropped:0 overruns:0 carrier:0
+ collisions:0 txqueuelen:1000
+ RX bytes:12337072144 (11.4 GB) TX bytes:48486812526 (45.1 GB)
so the MTU is 1500 which is fine. xenU sending too big packets.
+
+ == WORK AROUND ==
+
+ It seems that turning off TX checksum offloading within the domU
+ eliminates the issue:
+
+ ethtool -K ethN tx off
--
xenU sending too big packets
https://bugs.launchpad.net/bugs/154271
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