Re: [q] curious packets

In article <c6kfmd$1o55$1@sf1.isc.org>,
Hyo-Jeong Shin <shinhj@hana.ne.kr> wrote:

> Hello all,
> I captured some curious packets from our DNS servers with bind 8.2.7 on
> linux.
> Anybody knows why these packets are generated?
>
> [1] repeated ServFail =================================

The ServFail is because neither of the authoritative servers for
yourbusiness.com are responding. The repetition is because the client
isn't acknowledging the packet (we can't tell why that is). I'm not
sure why it went on for over 20 minutes, though; I'd expect the
retransmission limit to be much shorter than that.

> 16:02:57.053606 client.43312 > server.53: S 1054099647:1054099647(0) win
> 16384 <mss 1460,nop,nop,sackOK> (DF)
> 16:02:57.053639 server.53 > client.43312: S 2979146159:2979146159(0) ack
> 1054099648 win 5840 <mss 1460,nop,nop,sackOK> (DF)
> 16:02:57.086975 client.43312 > server.53: . ack 1 win 17520 (DF)
> 16:02:57.088947 client.43312 > server.53: P 1:37(36) ack 1 win 17520
> 7261+ MX? yourbusiness.com. (34) (DF)
> 16:02:57.088961 server.53 > client.43312: . ack 37 win 5840 (DF)
> 16:03:53.003632 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:03:56.002763 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:04:02.002729 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:04:14.002728 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:04:38.002728 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:05:26.002825 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:07:02.002781 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:09:02.002768 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:11:02.002764 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:13:02.002756 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:15:02.002740 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:17:02.002774 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:19:02.002742 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:21:02.002782 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:23:02.002750 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
> 16:25:02.002754 server.53 > client.43312: P 1:37(36) ack 37 win 5840
> 7261 ServFail 0/0/0 (34) (DF)
>
> [2] repeated SYN ================================================== =======

Not repeated SYN, repeated SYN-ACK. Apparently the server didn't see
the RST. I'm not sure why the client sent the RST in the first place,
since the SYN-ACK looks reasonable.

> 12:58:44.276476 client.59163 > server.53: S 3109183:3109183(0) win 8192
> <mss 1452,nop,nop,sackO
> K> (DF)
> 12:58:44.276510 server.53 > client.59163: S 3599383948:3599383948(0) ack
> 3109184 win 5840 <mss 1460,nop,nop,sackOK> (DF)
> 12:58:44.302861 client.59163 > server.53: R 3109184:3109184(0) win 0
> 12:58:48.407735 server.53 > client.59163: S 3599383948:3599383948(0) ack
> 3109184 win 5840 <mss 1460,nop,nop,sackOK> (DF)
> 12:58:55.778830 server.53 > client.59163: S 3599383948:3599383948(0) ack
> 3109184 win 5840 <mss 1460,nop,nop,sackOK> (DF)
> 12:59:07.931183 server.53 > client.59163: S 3599383948:3599383948(0) ack
> 3109184 win 5840 <mss 1460,nop,nop,sackOK> (DF)
> 12:59:33.431181 server.53 > client.59163: S 3599383948:3599383948(0) ack
> 3109184 win 5840 <mss 1460,nop,nop,sackOK> (DF)
> 13:00:21.442892 server.53 > client.59163: S 3599383948:3599383948(0) ack
> 3109184 win 5840 <mss 1460,nop,nop,sackOK> (DF)

I suspect some kind of communication problem between the client and
server, that's sensitive to particular packet contents.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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