Ryan J M
2009-Mar-31 11:00 UTC
[CentOS] CentOS5U2 waiting too long when ssh login to other linux servers
The waiting time is about 50s on my CentOS box now. "yum remove
openssh* "and "yum install openssh*" can't make it right.
"mv
~/.ssh{,.bak}" not works either.
Here comes my tcpdump log, I am not an expert on SSH, Can anyone here
get me out of this?
Thanks
Ryan
[root at centos5u2 ~]# tcpdump -s 1520 -nn port 22
tcpdump: WARNING: peth0: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on peth0, link-type EN10MB (Ethernet), capture size 1520 bytes
18:53:04.999533 IP 192.168.7.24.52315 > 192.168.7.252.22: S
1156562748:1156562748(0) win 5840 <mss 1460,sackOK,timestamp 5097684
0,nop,wscale 7>
18:53:04.999610 IP 192.168.7.252.22 > 192.168.7.24.52315: S
875773864:875773864(0) ack 1156562749 win 5792 <mss
1460,sackOK,timestamp 20270023 5097684,nop,wscale 7>
18:53:04.999654 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 1 win
46 <nop,nop,timestamp 5097684 20270023>
18:53:05.007974 IP 192.168.7.252.22 > 192.168.7.24.52315: P 1:21(20)
ack 1 win 46 <nop,nop,timestamp 20270032 5097684>
18:53:05.008090 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 21 win
46 <nop,nop,timestamp 5097687 20270032>
18:53:05.008344 IP 192.168.7.24.52315 > 192.168.7.252.22: P 1:21(20)
ack 21 win 46 <nop,nop,timestamp 5097688 20270032>
18:53:05.008471 IP 192.168.7.252.22 > 192.168.7.24.52315: . ack 21 win
46 <nop,nop,timestamp 20270032 5097688>
18:53:05.008715 IP 192.168.7.24.52315 > 192.168.7.252.22: P
21:733(712) ack 21 win 46 <nop,nop,timestamp 5097688 20270032>
18:53:05.009062 IP 192.168.7.252.22 > 192.168.7.24.52315: . ack 733
win 57 <nop,nop,timestamp 20270033 5097688>
18:53:05.009908 IP 192.168.7.252.22 > 192.168.7.24.52315: P
21:725(704) ack 733 win 57 <nop,nop,timestamp 20270033 5097688>
18:53:05.010074 IP 192.168.7.24.52315 > 192.168.7.252.22: P
733:757(24) ack 725 win 57 <nop,nop,timestamp 5097688 20270033>
18:53:05.012850 IP 192.168.7.252.22 > 192.168.7.24.52315: P
725:877(152) ack 757 win 57 <nop,nop,timestamp 20270036 5097688>
18:53:05.014563 IP 192.168.7.24.52315 > 192.168.7.252.22: P
757:901(144) ack 877 win 68 <nop,nop,timestamp 5097689 20270036>
18:53:05.037296 IP 192.168.7.252.22 > 192.168.7.24.52315: P
877:1597(720) ack 901 win 68 <nop,nop,timestamp 20270061 5097689>
18:53:05.039423 IP 192.168.7.24.52315 > 192.168.7.252.22: P
901:917(16) ack 1597 win 79 <nop,nop,timestamp 5097695 20270061>
18:53:05.079686 IP 192.168.7.252.22 > 192.168.7.24.52315: . ack 917
win 68 <nop,nop,timestamp 20270103 5097695>
18:53:05.079723 IP 192.168.7.24.52315 > 192.168.7.252.22: P
917:965(48) ack 1597 win 79 <nop,nop,timestamp 5097705 20270103>
18:53:05.079857 IP 192.168.7.252.22 > 192.168.7.24.52315: . ack 965
win 68 <nop,nop,timestamp 20270104 5097705>
18:53:05.079933 IP 192.168.7.252.22 > 192.168.7.24.52315: P
1597:1645(48) ack 965 win 68 <nop,nop,timestamp 20270104 5097705>
18:53:05.080312 IP 192.168.7.24.52315 > 192.168.7.252.22: P
965:1029(64) ack 1645 win 79 <nop,nop,timestamp 5097706 20270104>
18:53:05.082778 IP 192.168.7.252.22 > 192.168.7.24.52315: P
1645:1725(80) ack 1029 win 68 <nop,nop,timestamp 20270106 5097706>
18:53:05.120169 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 1725
win 79 <nop,nop,timestamp 5097716 20270106>
18:54:15.679137 IP 192.168.7.24.52315 > 192.168.7.252.22: P
1029:1173(144) ack 1725 win 79 <nop,nop,timestamp 5115354 20270106>
18:54:15.681497 IP 192.168.7.252.22 > 192.168.7.24.52315: P
1725:1757(32) ack 1173 win 79 <nop,nop,timestamp 20340699 5115354>
18:54:15.681533 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 1757
win 79 <nop,nop,timestamp 5115355 20340699>
18:54:15.681887 IP 192.168.7.24.52315 > 192.168.7.252.22: P
1173:1237(64) ack 1757 win 79 <nop,nop,timestamp 5115355 20340699>
18:54:15.685510 IP 192.168.7.252.22 > 192.168.7.24.52315: P
1757:1805(48) ack 1237 win 79 <nop,nop,timestamp 20340703 5115355>
18:54:15.685763 IP 192.168.7.24.52315 > 192.168.7.252.22: P
1237:1685(448) ack 1805 win 79 <nop,nop,timestamp 5115356 20340703>
18:54:15.701415 IP 192.168.7.252.22 > 192.168.7.24.52315: P
1805:1853(48) ack 1685 win 90 <nop,nop,timestamp 20340719 5115356>
18:54:15.701472 IP 192.168.7.252.22 > 192.168.7.24.52315: P
1853:1949(96) ack 1685 win 90 <nop,nop,timestamp 20340719 5115356>
18:54:15.701588 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 1949
win 79 <nop,nop,timestamp 5115360 20340719>
18:54:15.840022 IP 192.168.7.252.22 > 192.168.7.24.52315: P
1949:2013(64) ack 1685 win 90 <nop,nop,timestamp 20340858 5115360>
18:54:15.840076 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2013:2061(48) ack 1685 win 90 <nop,nop,timestamp 20340858 5115360>
18:54:15.840188 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2061
win 79 <nop,nop,timestamp 5115394 20340858>
18:54:15.844887 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2061:2125(64) ack 1685 win 90 <nop,nop,timestamp 20340862 5115394>
18:54:15.884608 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2125
win 79 <nop,nop,timestamp 5115406 20340862>
18:55:15.170913 IP 192.168.7.24.52315 > 192.168.7.252.22: P
1685:1733(48) ack 2125 win 79 <nop,nop,timestamp 5130226 20340862>
18:55:15.171562 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2125:2173(48) ack 1733 win 90 <nop,nop,timestamp 20400184 5130226>
18:55:15.171574 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2173:2237(64) ack 1733 win 90 <nop,nop,timestamp 20400184 5130226>
18:55:15.171579 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2237:2301(64) ack 1733 win 90 <nop,nop,timestamp 20400184 5130226>
18:55:15.171633 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2173
win 79 <nop,nop,timestamp 5130226 20400184>
18:55:15.171639 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2237
win 79 <nop,nop,timestamp 5130226 20400184>
18:55:15.171644 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2301
win 79 <nop,nop,timestamp 5130226 20400184>
18:55:17.155112 IP 192.168.7.24.52315 > 192.168.7.252.22: P
1733:1781(48) ack 2301 win 79 <nop,nop,timestamp 5130722 20400184>
18:55:17.155432 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2301:2349(48) ack 1781 win 90 <nop,nop,timestamp 20402168 5130722>
18:55:17.155471 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2349
win 79 <nop,nop,timestamp 5130722 20402168>
18:55:17.155814 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2349:2413(64) ack 1781 win 90 <nop,nop,timestamp 20402168 5130722>
18:55:17.155851 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2413
win 79 <nop,nop,timestamp 5130722 20402168>
18:55:17.155860 IP 192.168.7.252.22 > 192.168.7.24.52315: P
2413:2477(64) ack 1781 win 90 <nop,nop,timestamp 20402168 5130722>
18:55:17.155891 IP 192.168.7.24.52315 > 192.168.7.252.22: . ack 2477
win 79 <nop,nop,timestamp 5130722 20402168>
50 packets captured
100 packets received by filter
0 packets dropped by kernel
[root at centos5u2 ~]#
[root at centos5u2 ~]#
--
FIXME if it is wrong.
Jim Perrin
2009-Mar-31 11:22 UTC
[CentOS] CentOS5U2 waiting too long when ssh login to other linux servers
On Tue, Mar 31, 2009 at 7:00 AM, Ryan J M <sync.jma at gmail.com> wrote:> The waiting time is about 50s on my CentOS box now. "yum remove > openssh* "and "yum ?install openssh*" can't make it right. "mv > ~/.ssh{,.bak}" not works either. > Here comes my tcpdump log, I am not an expert on SSH, Can anyone here > get me out of this?Usually ssh slowness is attributed to DNS problems with reverse lookups. You give ssh a host name to connect to, and it does a query to find the ip, then a reverse to make sure that the ip is who it claims to be. If there are no records, ssh will happily wait for the query to time out before proceeding. This is usually where people complain about slowness on home networks or in some hosted environments that aren't set up 100% correctly. The proper fix is to correct the DNS issue. Some folks simply hand jam an entry into /etc/hosts, or dive into the sshd_config and disable the check. How you resolve this is up to you. -- During times of universal deceit, telling the truth becomes a revolutionary act. George Orwell
Les Mikesell
2009-Mar-31 12:36 UTC
[CentOS] CentOS5U2 waiting too long when ssh login to other linux servers
Ryan J M wrote:> The waiting time is about 50s on my CentOS box now. "yum remove > openssh* "and "yum install openssh*" can't make it right. "mv > ~/.ssh{,.bak}" not works either. > Here comes my tcpdump log, I am not an expert on SSH, Can anyone here > get me out of this? >The answering sshd will do a reverse DNS lookup on the connecting IP address. That's about the right time to wait for timeouts from 2 DNS servers if they don't respond. -- Les Mikesell lesmikesell at gmail.com