thr3ads.net - openssh bugs - [Bug 1667] New: sshd slow connect with 'UseDNS yes' [Oct 2009]

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-26 23:30 UTC

[Bug 1667] New: sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

           Summary: sshd slow connect with 'UseDNS yes'
           Product: Portable OpenSSH
           Version: 5.2p1
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: major
          Priority: P2
         Component: sshd
        AssignedTo: unassigned-bugs at mindrot.org
        ReportedBy: brian.p.stamper at nasa.gov


ssh is slow to connect (25 seconds) when UseDNS is enabled, despite
quick name servers.  Disabling UseDNS is a poor workaround, especially
since I ask my users to anchor their ssh keys with "from=" lines in
their authorized_keys file.

If the client host is in /etc/hosts, the connection is immediate.  If
the client host is not in /etc/hosts, the connection takes 25 seconds. 
If I turn off UseDNS, the connection is once again instant.  My DNS
servers are near instant responses.

[root at server ~]# time nslookup <client ip>
Server:         x
Address:        x

<client ip>.in-addr.arpa    name = <client>

real    0m0.005s
user    0m0.000s
sys     0m0.004s
[root at server ~]# time nslookup <client>
Server:         x
Address:        x

Name:   <client>
Address: <client ip>

real    0m0.005s
user    0m0.001s
sys     0m0.003s
[root at server ~]#

I have confirmed that this seemingly affects all of my hosts running
Fedora 10 or later (openssh 5.2p1) but not my machines running Fedora 9
or earlier (openssh 5.1p1)

nsswitch.conf hosts is set to "files dns"

I've seen threads about this in the ubuntu and other forums, and
inevitably the answer is "Turn UseDNS to off"  That's not really a
great answer.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-27 00:02 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

Darren Tucker <dtucker at zip.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dtucker at zip.com.au

--- Comment #1 from Darren Tucker <dtucker at zip.com.au> 2009-10-27
11:02:24 EST ---
could you please run the server in debug mode (eg "/path/to/sshd -ddde
-p 2222" then point your client at port 2222) and add the output as an
attachment?  please indicate where in the output the delay(s) occur.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-27 16:12 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #2 from Brian <brian.p.stamper at nasa.gov> 2009-10-28
03:12:23 EST ---
Created an attachment (id=1711)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1711)
output of sshd -ddde

Attached as requested.  It's not one spot in the log where it pauses. 
I put numbers in roughly once a second at each step the debug output
hung.  So there are roughly 5 spots it hangs for 3-4 seconds.

It's probably also worth noting that there are delays cleaning up the
session on the server side too.  This is what happens when I
disconnect:

debug1: Received SIGCHLD.
debug1: session_by_pid: pid 16135
debug1: session_exit_message: session 0 channel 0 pid 16135
debug2: channel 0: request exit-status confirm 0
debug1: session_exit_message: release channel 0
debug2: channel 0: write failed
debug2: channel 0: close_write
debug2: channel 0: send eow
debug2: channel 0: output open -> closed
debug3: mm_request_send entering: type 28
debug3: monitor_read: checking request 28
debug3: mm_answer_pty_cleanup entering
debug1: session_by_tty: session 0 tty /dev/pts/2
debug3: mm_session_close: session 0 pid 16134
debug3: mm_session_close: tty /dev/pts/2 ptyfd 5
debug1: session_pty_cleanup: session 0 release /dev/pts/2
debug3: session_unused: session id 0 unused
debug3: mm_request_receive entering
debug2: channel 0: read<=0 rfd 10 len -1
debug2: channel 0: read failed
debug2: channel 0: close_read
debug2: channel 0: input open -> drain
debug2: channel 0: ibuf empty
debug2: channel 0: send eof
debug2: channel 0: input drain -> closed
debug2: channel 0: send close
debug2: notify_done: reading
debug3: channel 0: will not send data after close
debug2: channel 0: rcvd close
debug3: channel 0: will not send data after close
debug2: channel 0: is dead
debug2: channel 0: gc: notify user
debug1: session_by_channel: session 0 channel 0
debug1: session_close_by_channel: channel 0 child 0
debug1: session_close: session 0 pid 0
debug3: session_unused: session id 0 unused
debug2: channel 0: gc: user detached
debug2: channel 0: is dead
debug2: channel 0: garbage collecting
debug1: channel 0: free: server-session, nchannels 1
debug3: channel 0: status: The following connections are open:
  #0 server-session (t4 r0 i3/0 o3/0 fd -1/-1 cfd -1)

debug3: channel 0: close_fds r -1 w -1 e -1 c -1
Connection closed by 143.232.109.139
debug1: do_cleanup
debug3: PAM: sshpam_thread_cleanup entering
Transferred: sent 3320, received 1728 bytes
Closing connection to 143.232.109.139 port 45031
debug3: mm_request_send entering: type 59
debug3: monitor_read: checking request 59
debug3: mm_answer_term: tearing down sessions
debug1: PAM: cleanup
debug1: PAM: deleting credentials
1
2
3
4
debug1: PAM: closing session
1
2
3
4


A tcpdump shows that every delay in the login and disconnect process
seems to correspond to a request to my DNS server.  I'm unsure why sshd
would need to do a lookup 8 distinct times per connection and 2 more on
disconnect.

Here is the response time from my dns server forward and reverse, so
it's not just DNS performance or latency:

[root at corvus ~]# time nslookup flux.arc.nasa.gov
Server:         128.102.0.34
Address:        128.102.0.34#53

Name:   flux.arc.nasa.gov
Address: 143.232.109.139


real    0m0.006s
user    0m0.001s
sys     0m0.003s
[root at corvus ~]# time nslookup 143.232.109.139
Server:         128.102.0.34
Address:        128.102.0.34#53

139.109.232.143.in-addr.arpa    name = flux.arc.nasa.gov.


real    0m0.006s
user    0m0.001s
sys     0m0.004s
[root at corvus ~]#

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-27 21:32 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #3 from Darren Tucker <dtucker at zip.com.au> 2009-10-28
08:32:54 EST ---
(From update of attachment 1711)>debug1: do_pam_account: called
>1 2 3 4
>debug3: PAM: do_pam_account pam_acct_mgmt = 0 (Success)
OK, we'll use this example since it's probably the simplest.  The code
that does this is in auth-pam.c:do_pam_account():

        debug("%s: called", __func__);
        if (sshpam_account_status != -1)
                return (sshpam_account_status);

        sshpam_err = pam_acct_mgmt(sshpam_handle, 0);
        debug3("PAM: %s pam_acct_mgmt = %d (%s)", __func__,
sshpam_err,
            pam_strerror(sshpam_handle, sshpam_err));

where previously the hostname was set via PAM_RHOST:

        sshpam_err = pam_set_item(sshpam_handle, PAM_RHOST, pam_rhost);

So in this case the blocking is happening inside either the PAM library
or a PAM module.  You can confirm this by repeating the same test but
UsePam=no.  There is one other delay marked in the output where the pty
is allocated.  I suspect you will still see the delay at the pty
allocation but overall it will be much faster (because sshd caches the
result of the name lookup).

I don't know why the lookups inside PAM take so long though.  Can you
capture the name lookups?  either strace/truss "/path/to/sshd -D" and
pick the requests out of the output or run "tcpdump -s 1500 port 53"
while connecting.  I suspect you'll find that it's either IPv6 AAAA
lookups or their inverse.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-27 21:44 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #4 from Brian <brian.p.stamper at nasa.gov> 2009-10-28
08:44:07 EST ---
Thanks for the response.  I probably can't work this today.  I'll get
you the output tomorrow.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-30 16:39 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #5 from Brian <brian.p.stamper at nasa.gov> 2009-10-31
03:39:29 EST ---
Created an attachment (id=1716)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1716)
pcap of one connection

pcap of one connection.  did not include disconnect.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-30 16:50 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #6 from Brian <brian.p.stamper at nasa.gov> 2009-10-31
03:50:45 EST ---
Created an attachment (id=1717)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1717)
strace /usr/sbin/sshd -D

This didn't seem to show a lot, though you may be better able to use
the info than I.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-30 16:51 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #7 from Brian <brian.p.stamper at nasa.gov> 2009-10-31
03:51:11 EST ---
Created an attachment (id=1718)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1718)
strace /usr/sbin/sshd -ddde

This seemed to have more info.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Oct-30 22:50 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #8 from Darren Tucker <dtucker at zip.com.au> 2009-10-31
09:50:55 EST ---
(In reply to comment #5)> Created an attachment (id=1716) --> (https://bugzilla.mindrot.org/attachment.cgi?id=1716)
[details]> pcap of one connection
> 
> pcap of one connection.  did not include disconnect.
I haven't gone through the other output yet but this seems suspicious. 
Go from the start:

03:37:12.425222 corvus.arc.nasa.gov.45215 > ns2.arc.nasa.gov.domain:
20988+ PTR? 139.109.232.143.in-addr.arpa. (46) (DF)
03:37:12.428942 ns2.arc.nasa.gov.domain > corvus.arc.nasa.gov.45215:
20988* 1/3/3 PTR flux.arc.nasa.gov. (179)

a reverse lookup of 143.232.109.139 (ipv4) and immediate response from
ns2.  Note the transaction ID "20988".

03:37:12.429217 corvus.arc.nasa.gov.44863 > ns2.arc.nasa.gov.domain:
55778+ A? flux.arc.nasa.gov. (35) (DF)
03:37:12.433199 ns2.arc.nasa.gov.domain > corvus.arc.nasa.gov.44863:
55778* 1/3/3 A flux.arc.nasa.gov (153)

A forward lookup of flux.arc.nasa.gov (ipv4).  Also answered
immediately by ns2.

03:37:15.155167 corvus.arc.nasa.gov.58329 > ns2.arc.nasa.gov.domain:
26977+ A? flux.arc.nasa.gov. (35) (DF)
03:37:15.155180 corvus.arc.nasa.gov.58329 > ns2.arc.nasa.gov.domain:
24837+ AAAA? flux.arc.nasa.gov. (35) (DF)

lookups of corvus.arc.nasa.gov for ipv4 (A) and ipv6 (AAAA) in
parallel.  no response, times out at 5sec.

03:37:20.154422 corvus.arc.nasa.gov.57585 > ns1.arc.nasa.gov.domain:
26977+ A? flux.arc.nasa.gov. (35) (DF)
03:37:20.154444 corvus.arc.nasa.gov.57585 > ns1.arc.nasa.gov.domain:
24837+ AAAA? flux.arc.nasa.gov. (35) (DF)
03:37:20.156796 ns1.arc.nasa.gov.domain > corvus.arc.nasa.gov.57585:
26977* 1/3/3 A flux.arc.nasa.gov (153)

retries the request on ns1, which responds only to the A (ipv4)
request.  this pattern is repeated later on ns2:

03:37:30.167249 corvus.arc.nasa.gov.57935 > ns2.arc.nasa.gov.domain:
39226+ A? flux.arc.nasa.gov. (35) (DF)
03:37:30.167283 corvus.arc.nasa.gov.57935 > ns2.arc.nasa.gov.domain:
59667+ AAAA? flux.arc.nasa.gov. (35) (DF)
03:37:30.170583 ns2.arc.nasa.gov.domain > corvus.arc.nasa.gov.57935:
39226* 1/3/3 A flux.arc.nasa.gov (153)
03:37:35.167403 corvus.arc.nasa.gov.57935 > ns2.arc.nasa.gov.domain:
39226+ A? flux.arc.nasa.gov. (35) (DF)

I susupect your nameservers are silently dropping AAAA lookups (this is
common enough that there's an RFC about it, RFC4074).  Try these:

host -t A flux.arc.nasa.gov. ns1.arc.nasa.gov.
host -t AAAA flux.arc.nasa.gov. ns1.arc.nasa.gov.
host -t A flux.arc.nasa.gov. ns2.arc.nasa.gov.
host -t AAAA flux.arc.nasa.gov. ns2.arc.nasa.gov.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Nov-03 14:40 UTC

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[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #9 from Brian <brian.p.stamper at nasa.gov> 2009-11-04
01:40:20 EST ---> Try these:
> 
> host -t A flux.arc.nasa.gov. ns1.arc.nasa.gov.
> host -t AAAA flux.arc.nasa.gov. ns1.arc.nasa.gov.
> host -t A flux.arc.nasa.gov. ns2.arc.nasa.gov.
> host -t AAAA flux.arc.nasa.gov. ns2.arc.nasa.gov.
[root at corvus ~]# time host -t A flux.arc.nasa.gov. ns1.arc.nasa.gov.
Using domain server:
Name: ns1.arc.nasa.gov.
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has address 143.232.109.139

real    0m5.026s
user    0m0.002s
sys     0m0.003s
[root at corvus ~]# time host -t AAAA flux.arc.nasa.gov. ns1.arc.nasa.gov.
Using domain server:
Name: ns1.arc.nasa.gov.
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has no AAAA record

real    0m5.009s
user    0m0.001s
sys     0m0.005s
[root at corvus ~]# time host -t A flux.arc.nasa.gov. ns2.arc.nasa.gov.
Using domain server:
Name: ns2.arc.nasa.gov.
Address: 128.102.0.34#53
Aliases: 

flux.arc.nasa.gov has address 143.232.109.139

real    0m5.008s
user    0m0.002s
sys     0m0.003s
[root at corvus ~]# time host -t AAAA flux.arc.nasa.gov. ns2.arc.nasa.gov.
Using domain server:
Name: ns2.arc.nasa.gov.
Address: 128.102.0.34#53
Aliases: 

flux.arc.nasa.gov has no AAAA record

real    0m5.007s
user    0m0.003s
sys     0m0.001s

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bugzilla-daemon at bugzilla.mindrot.org

2009-Nov-03 22:04 UTC

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[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #10 from Darren Tucker <dtucker at zip.com.au> 2009-11-04
09:04:32 EST ---
(In reply to comment #9)> [root at corvus ~]# time host -t A flux.arc.nasa.gov. ns1.arc.nasa.gov.
[...]> flux.arc.nasa.gov has address 143.232.109.139
> 
> real    0m5.026s
There's your problem: your DNS is taking 5s to respond.  I'm surprised
that it's happening for A records too given what I saw in the packet
trace, but I expected to see this for AAAA.

So your DNS (or resolver) is slow, and that's compounded by something
in PAM making multiple trips to the well.

The options I can think of are:
 * fix your DNS or resolver
 * make your resolver send only IPv4 requests
 * live with UseDNS=no
 * disable PAM.

You also could try building OpenSSH with "configure
--with-cflags=-DBROKEN_GETADDRINFO".  This will force the use of the
built-in getaddrinfo replacement that happens to speak only IPv4, but
it probably won't help the PAM bits.  I suspect this will make minimal
difference though.

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2009-Nov-05 17:52 UTC

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[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #11 from Brian <brian.p.stamper at nasa.gov> 2009-11-06
04:52:03 EST ---> There's your problem: your DNS is taking 5s to respond.
Well, something odd is going on.  I'm not convinced it's as simple as
DNS is taking 5 seconds to respond, though I may be willing to concede
the issue is not with openssh.  See the following:

[root at corvus ~]# time nslookup ns1.arc.nasa.gov 143.232.252.34
Server:         143.232.252.34
Address:        143.232.252.34#53

Name:   ns1.arc.nasa.gov
Address: 143.232.252.34


real    0m0.005s
user    0m0.001s
sys     0m0.002s
[root at corvus ~]# time nslookup ns1.arc.nasa.gov ns1.arc.nasa.gov
Server:         ns1.arc.nasa.gov
Address:        143.232.252.34#53

Name:   ns1.arc.nasa.gov
Address: 143.232.252.34


real    0m5.008s
user    0m0.001s
sys     0m0.003s

[root at corvus ~]# time host -t A flux.arc.nasa.gov ns1.arc.nasa.gov
Using domain server:
Name: ns1.arc.nasa.gov
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has address 143.232.109.139

real    0m5.008s
user    0m0.001s
sys     0m0.003s
[root at corvus ~]# time host -t A flux.arc.nasa.gov 143.232.252.34
Using domain server:
Name: 143.232.252.34
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has address 143.232.109.139

real    0m0.005s
user    0m0.000s
sys     0m0.004s
[root at corvus ~]# time host -t AAAA flux.arc.nasa.gov ns1.arc.nasa.gov
Using domain server:
Name: ns1.arc.nasa.gov
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has no AAAA record

real    0m5.008s
user    0m0.001s
sys     0m0.004s
[root at corvus ~]# time host -t AAAA flux.arc.nasa.gov 143.232.252.34
Using domain server:
Name: 143.232.252.34
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has no AAAA record

real    0m0.005s
user    0m0.002s
sys     0m0.003s
[root at corvus ~]# 

[root at corvus ~]# grep hosts /etc/nsswitch.conf
#hosts:     db files nisplus nis dns
hosts:      files dns
[root at corvus ~]# cat /etc/resolv.conf 
search arc.nasa.gov
nameserver 128.102.0.34
nameserver 143.232.252.34
[root at corvus ~]# 

Something with the resolver maybe?  Clearly basic name resolution of
the nameserver is plenty fast.  But when giving the hostname of the dns
server as an argument, it takes 5 seconds to respond.

[root at corvus ~]# time nslookup ns1.arc.nasa.gov
Server:         128.102.0.34
Address:        128.102.0.34#53

Name:   ns1.arc.nasa.gov
Address: 143.232.252.34


real    0m0.006s
user    0m0.001s
sys     0m0.003s
[root at corvus ~]# time nslookup ns2.arc.nasa.gov
Server:         128.102.0.34
Address:        128.102.0.34#53

Name:   ns2.arc.nasa.gov
Address: 128.102.0.34


real    0m0.006s
user    0m0.001s
sys     0m0.003s
[root at corvus ~]# time host -t AAAA flux.arc.nasa.gov
flux.arc.nasa.gov has no AAAA record

real    0m0.006s
user    0m0.000s
sys     0m0.003s
[root at corvus ~]# 

I'm not sure what changes when giving the hostname as an argument as
oppose to no argument or the ip.

"nslookup ns1.arc.nasa.gov"

listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
09:48:23.191397 IP corvus.arc.nasa.gov.50677 > ns1.arc.nasa.gov.domain:
62346+ A? ns1.arc.nasa.gov. (34)
09:48:23.191831 IP ns1.arc.nasa.gov.domain > corvus.arc.nasa.gov.50677:
62346* 1/3/2 A ns1.arc.nasa.gov (132)
09:48:23.191921 IP corvus.arc.nasa.gov.40824 > ns1.arc.nasa.gov.domain:
61200+ PTR? 34.252.232.143.in-addr.arpa. (45)
09:48:23.192382 IP ns1.arc.nasa.gov.domain > corvus.arc.nasa.gov.40824:
61200* 1/3/3 (173)

"nslookup ns1.arc.nasa.gov ns1.arc.nasa.gov"

09:48:31.335862 IP corvus.arc.nasa.gov.53838 > ns1.arc.nasa.gov.domain:
16500+ A? ns1.arc.nasa.gov. (34)
09:48:31.335933 IP corvus.arc.nasa.gov.53838 > ns1.arc.nasa.gov.domain:
59525+ AAAA? ns1.arc.nasa.gov. (34)
09:48:31.336346 IP ns1.arc.nasa.gov.domain > corvus.arc.nasa.gov.53838:
16500* 1/3/2 A ns1.arc.nasa.gov (132)
09:48:36.336413 IP corvus.arc.nasa.gov.53838 > ns1.arc.nasa.gov.domain:
16500+ A? ns1.arc.nasa.gov. (34)
09:48:36.336812 IP ns1.arc.nasa.gov.domain > corvus.arc.nasa.gov.53838:
16500* 1/3/2 A ns1.arc.nasa.gov (132)
09:48:36.336920 IP corvus.arc.nasa.gov.53838 > ns1.arc.nasa.gov.domain:
59525+ AAAA? ns1.arc.nasa.gov. (34)
09:48:36.337318 IP ns1.arc.nasa.gov.domain > corvus.arc.nasa.gov.53838:
59525* 0/1/0 (81)
09:48:36.338002 IP corvus.arc.nasa.gov.43373 > ns1.arc.nasa.gov.domain:
56964+ A? ns1.arc.nasa.gov. (34)
09:48:36.338456 IP ns1.arc.nasa.gov.domain > corvus.arc.nasa.gov.43373:
56964* 1/3/2 A ns1.arc.nasa.gov (132)

Unfortunately another group here is responsible for the DNS servers, I
will engage them as well and see if they know what's causing the
behavior.  It looks as though something changed in the fedora resolver
though.  I don't get this behavior on fedora 6 and 7 boxes using the
same server from the same subnet.

[root at old-flux ~]# uname -r
2.6.22.1-32.fc6
[root at old-flux ~]# time nslookup ns1.arc.nasa.gov
Server:         128.102.0.34
Address:        128.102.0.34#53

Name:   ns1.arc.nasa.gov
Address: 143.232.252.34


real    0m0.456s
user    0m0.004s
sys     0m0.002s
[root at old-flux ~]# time nslookup ns1.arc.nasa.gov ns1.arc.nasa.gov
Server:         ns1.arc.nasa.gov
Address:        143.232.252.34#53

Name:   ns1.arc.nasa.gov
Address: 143.232.252.34


real    0m0.009s
user    0m0.004s
sys     0m0.003s
[root at old-flux ~]#

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bugzilla-daemon at bugzilla.mindrot.org

2009-Nov-05 17:54 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #12 from Brian <brian.p.stamper at nasa.gov> 2009-11-06
04:54:12 EST ---
[root at old-flux ~]# host -t A flux.arc.nasa.gov. ns1.arc.nasa.gov.
Using domain server:
Name: ns1.arc.nasa.gov.
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has address 143.232.109.139
[root at old-flux ~]# host -t AAAA flux.arc.nasa.gov. ns1.arc.nasa.gov.
Using domain server:
Name: ns1.arc.nasa.gov.
Address: 143.232.252.34#53
Aliases: 

flux.arc.nasa.gov has no AAAA record
[root at old-flux ~]# 

[root at old-flux ~]# cat /etc/resolv.conf
search arc.nasa.gov
nameserver 128.102.0.34
nameserver 143.232.252.34
[root at old-flux ~]# grep hosts /etc/nsswitch.conf
#hosts:     db files nisplus nis dns
hosts:      files dns
[root at old-flux ~]# 


More to suggest this is a change in the resolver on Fedora.

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bugzilla-daemon at bugzilla.mindrot.org

2009-Nov-05 18:15 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #13 from Brian <brian.p.stamper at nasa.gov> 2009-11-06
05:15:08 EST ---
Using the name servers from the fine folks at google and redhat, I seem
to see the same behavior.  So I'm not sure where I should be looking at
this point.  Do you know of a public DNS server that is definitely
configured properly for ipv6?  Since I don't see this behavior from
hosts that are not fedora 11 on the same subnets, I don't believe it's
a router or DNS server issue.  If you concur, I'll move this issue to
the fedora issues list.

-Brian


[root at centroid ~]# time nslookup ns2.google.com 216.239.34.10
Server:         216.239.34.10
Address:        216.239.34.10#53

Name:   ns2.google.com
Address: 216.239.34.10


real    0m0.094s
user    0m0.001s
sys     0m0.003s
[root at centroid ~]# time nslookup ns2.google.com ns2.google.com
Server:         ns2.google.com
Address:        216.239.34.10#53

Name:   ns2.google.com
Address: 216.239.34.10


real    0m5.280s
user    0m0.002s
sys     0m0.002s
[root at centroid ~]# grep name /etc/resolv.conf 
#nameserver 128.102.0.34
#nameserver 143.232.252.34
nameserver 216.239.34.10


=======================================================
[root at centroid ~]# time nslookup ns1.redhat.com
Server:         66.187.233.210
Address:        66.187.233.210#53

Name:   ns1.redhat.com
Address: 66.187.233.210


real    0m0.091s
user    0m0.002s
sys     0m0.002s
[root at centroid ~]# time nslookup ns1.redhat.com ns1.redhat.com
Server:         ns1.redhat.com
Address:        66.187.233.210#53

Name:   ns1.redhat.com
Address: 66.187.233.210


real    0m5.267s
user    0m0.001s
sys     0m0.004s
[root at centroid ~]# time nslookup ns1.redhat.com 66.187.233.210
Server:         66.187.233.210
Address:        66.187.233.210#53

Name:   ns1.redhat.com
Address: 66.187.233.210


real    0m0.090s
user    0m0.001s
sys     0m0.002s
[root at centroid ~]# cat /etc/resolv.conf 
search arc.nasa.gov
#nameserver 128.102.0.34
#nameserver 143.232.252.34
nameserver 66.187.233.210

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bugzilla-daemon at bugzilla.mindrot.org

2009-Nov-05 18:41 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

Brian <brian.p.stamper at nasa.gov> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |brian.p.stamper at nasa.gov

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bugzilla-daemon at bugzilla.mindrot.org

2009-Nov-06 00:47 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

--- Comment #14 from Brian <brian.p.stamper at nasa.gov> 2009-11-06
11:47:35 EST ---
Well, I've identified a workaround, not really a fix.  And it's really
just disabling ipv6.  I'm not convinced my nameservers are the problem,
rather I think there's something broken with Fedora 11's use of ipv6,
or possibly the linux kernel post 2.6.27.

Added to /etc/modprobe.d/aliases.conf: (new file I created)
install net-pf-10 /bin/true
install ipv6 /bin/true

Added to /etc/modprobe.d/blacklist.conf:
# ipv6 die die die
blacklist ipv6

symptoms have completely cleared up, and I don't use ipv6, so I'm
happy.

Thank you for your assistance and patience in troubleshooting what
turned out to be not your problem.

-Brian

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bugzilla-daemon at bugzilla.mindrot.org

2009-Nov-06 02:07 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

Darren Tucker <dtucker at zip.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WORKSFORME

--- Comment #15 from Darren Tucker <dtucker at zip.com.au> 2009-11-06
13:07:06 EST ---
(In reply to comment #14)> Well, I've identified a workaround, not really a fix.  And it's
really
> just disabling ipv6.  I'm not convinced my nameservers are the problem,
> rather I think there's something broken with Fedora 11's use of
ipv6,
> or possibly the linux kernel post 2.6.27.
I mentioned earlier that it might be in the resolver, and based on your
results from disabling ipv6, I suspect that it's the resolver that it's
got some odd interaction with that.
> Thank you for your assistance and patience in troubleshooting what
> turned out to be not your problem.
You're welcome.

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bugzilla-daemon at bugzilla.mindrot.org

2010-Apr-16 05:50 UTC

head link

[Bug 1667] sshd slow connect with 'UseDNS yes'

https://bugzilla.mindrot.org/show_bug.cgi?id=1667

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #16 from Damien Miller <djm at mindrot.org> 2010-04-16
15:50:34 EST ---
Mass move of bugs RESOLVED->CLOSED following the release of
openssh-5.5p1

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