If I build openssh from source and try it, the ToS bit is set
appropriately:
2012-10-16 17:32:16.173736 IP (tos 0x10, ttl 64, id 38386, offset 0, flags
[DF], proto TCP (6), length 52)
1.1.1.1.36327 2.2.2.2.22: Flags [.], cksum 0x2dcd (incorrect -
0x8a18), seq 3101, ack 3736, win 183, options [nop,nop,TS val 1670729064 ecr
2311548502], length 0
Furthermore, the manpage included with Ubuntu for ssh states:
The default is “lowdelay” for interactive sessions and “throughput” for
non-interactive sessions.
** Description changed:
- The openssh-client bundled with Ubuntu 12.04 fails to set the IP Type of
Service field to minimize delay (0x04) for interactive SSH sessions. Just
about any other flavor of Linux/UNIX does this without any trouble. Even if I
attempt to force the setting in /etc/ssh/sshd_config:
- IPQoS lowdelay
+ The openssh-client bundled with Ubuntu 12.04 fails to set the IP Type of
Service field to minimize delay (0x10) for interactive SSH sessions. Just
about any other flavor of Linux/UNIX does this without any trouble. Even if I
attempt to force the setting in /etc/ssh/sshd_config:
+ IPQoS lowdelay
The outgoing SSH packets do not have the bit set.
See this example with tcpdump output:
[steve.polyack@galvatron ~]$ sudo tcpdump -i eth0 -vvv - -n 'host 2.2.2.2
dst port 22'
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535
bytes
^Z
[1]+ Stopped sudo tcpdump -i eth0 -vvv - -n 'host
2.2.2.2 dst port 22'
[steve.polyack@galvatron ~]$ bg
[1]+ sudo tcpdump -i eth0 -vvv - -n 'host 2.2.2.2 dst port 22'
[steve.polyack@galvatron ~]$ ssh 2.2.2.2
2012-10-16 17:20:39.113321 IP (tos 0x0, ttl 64, id 58664, offset 0, flags
[DF], proto TCP (6), length 60)
- 1.1.1.1.36127 2.2.2.2.22: Flags [S], cksum 0x2dd5 (incorrect -
0x200d), seq 3930407303, win 14600, options [mss 1460,sackOK,TS val 1670554799
ecr 0,nop,wscale 7], length 0
+ 1.1.1.1.36127 2.2.2.2.22: Flags [S], cksum 0x2dd5 (incorrect -
0x200d), seq 3930407303, win 14600, options [mss 1460,sackOK,TS val 1670554799
ecr 0,nop,wscale 7], length 0
2012-10-16 17:20:39.298676 IP (tos 0x0, ttl 64, id 58665, offset 0, flags
[DF], proto TCP (6), length 52)
- 1.1.1.1.36127 2.2.2.2.22: Flags [.], cksum 0x2dcd (incorrect -
0x5cd6), seq 3930407304, ack 1359170341, win 115, options [nop,nop,TS val
1670554846 ecr 2310866035], length 0
+ 1.1.1.1.36127 2.2.2.2.22: Flags [.], cksum 0x2dcd (incorrect -
0x5cd6), seq 3930407304, ack 1359170341, win 115, options [nop,nop,TS val
1670554846 ecr 2310866035], length 0
2012-10-16 17:20:39.329979 IP (tos 0x0, ttl 64, id 58666, offset 0, flags
[DF], proto TCP (6), length 52)
- 1.1.1.1.36127 2.2.2.2.22: Flags [.], cksum 0x2dcd (incorrect -
0x5c8c), seq 0, ack 40, win 115, options [nop,nop,TS val 1670554853 ecr
2310866063], length 0
+ 1.1.1.1.36127 2.2.2.2.22: Flags [.], cksum 0x2dcd (incorrect -
0x5c8c), seq 0, ack 40, win 115, options [nop,nop,TS val 1670554853 ecr
2310866063], length 0
2012-10-16 17:20:39.330082 IP (tos 0x0, ttl 64, id 58667, offset 0, flags
[DF], proto TCP (6), length 91)
- 1.1.1.1.36127 2.2.2.2.22: Flags [P.], cksum 0x2df4 (incorrect -
0x9e6b), seq 0:39, ack 40, win 115, options [nop,nop,TS val 1670554853 ecr
2310866063], length 39
+ 1.1.1.1.36127 2.2.2.2.22: Flags [P.], cksum 0x2df4 (incorrect -
0x9e6b), seq 0:39, ack 40, win 115, options [nop,nop,TS val 1670554853 ecr
2310866063], length 39
2012-10-16 17:20:39.759001 IP (tos 0x0, ttl 64, id 58668, offset 0, flags
[DF], proto TCP (6), length 1324)
- 1.1.1.1.36127 2.2.2.2.22: Flags [P.], cksum 0x32c5 (incorrect -
0x916a), seq 39:1311, ack 776, win 126, options [nop,nop,TS val 1670554961 ecr
2310866492], length 1272
+ 1.1.1.1.36127 2.2.2.2.22: Flags [P.], cksum 0x32c5 (incorrect -
0x916a), seq 39:1311, ack 776, win 126, options [nop,nop,TS val 1670554961 ecr
2310866492], length 1272
-
- The problem persists even after login, once the SSH session is fully
interactive:
+ The problem persists even after login, once the SSH session is fully
+ interactive:
2012-10-16 17:20:49.626239 IP (tos 0x0, ttl 64, id 58694, offset 0, flags
[DF], proto TCP (6), length 116)
- 1.1.1.1.36127 2.2.2.2.22: Flags [P.], cksum 0x2e0d (incorrect -
0xb06e), seq 3479:3543, ack 5344, win 226, options [nop,nop,TS val 1670557427
ecr 2310876270], length 64
+ 1.1.1.1.36127 2.2.2.2.22: Flags [P.], cksum 0x2e0d (incorrect -
0xb06e), seq 3479:3543, ack 5344, win 226, options [nop,nop,TS val 1670557427
ecr 2310876270], length 64
-
- This causes problems in environements where QoS is used and IP ToS is obeyed.
+ This causes problems in environements where QoS is used and IP ToS is
+ obeyed.
ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: openssh-client 1:5.9p1-5ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-27.43-generic 3.2.21
Uname: Linux
