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Re: Common operational misconceptions
From: Phil Regnauld <regnauld () nsrc org>
Date: Thu, 16 Feb 2012 17:53:08 +0100

        Borderline dns-ops, sorry folks! - but this is interesting
        as we've been talking about ipv6 being operational, and this
        is part of it...

Mark Andrews (marka) writes:

If you are seeing TC between the resolver and the server and the TCP query is being answers then
something in the path is intercepting the DNS queries.

        TC is on the answer from the remote server to my resolver, so yeah, seems
        like something is messing with the packets.

    Don't see any v6 fragments (that'd be a problem since PF doesn't handle
    them on this host).

You should see something like this on the wire.  The second query is to answer
dig's query over TCP.

        I'm not seeing fragments as you are.

        Here's what I see:

14:40:20.955876 IP6 2001:2000:1080:d::2.64561 > 2001:4f8:0:2::8.53: 52841 TXT? edns-v6-ok.isc.org. (36)
14:40:21.141948 IP6 2001:4f8:0:2::8.53 > 2001:2000:1080:d::2.64561: 52841*-| 0/0/0 (36)
14:40:21.142259 IP6 2001:2000:1080:d::2.53262 > 2001:4f8:0:2::8.53: Flags [S], seq 1112939462, win 65535, options [mss 
1440,nop,wscale 6,sackOK,TS val 2571957531 ecr 0], length 0
14:40:21.327895 IP6 2001:4f8:0:2::8.53 > 2001:2000:1080:d::2.53262: Flags [R.], seq 0, ack 1112939463, win 0, length 0


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