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Groups > comp.os.linux.networking > #1767

Re: 192.168

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On 2012-10-20, Jorgen Grahn <grahn+nntp@snipabacken.se> wrote:
> On Sat, 2012-10-20, orcus@pwr.wroc.pl wrote:
>> Which fragment fragment of RFC they violate? They use private addresses 
>> inside their network and filter out routing information about this
>> subnets. I see no violation.
>
> You say you can see e.g. 192.168.1.2 in traceroute output.  That means
> you have actually received an ICMP time exceeded (or whatever it's
> called) message from that host.  Surely then it's not just "inside their
> network"?

In RFC traffic blocking is only recommendation. ISPs are blocking almost
all traffic with private sources or destinations, but:

http://www.rfc-editor.org/rfc/rfc1812.txt:
If the TTL is reduced to zero (or less), the packet MUST be
discarded, and if the destination is not a multicast address the
router MUST send an ICMP Time Exceeded message, Code 0 (TTL Exceeded
in Transit) message to the source.  

MUST in RFC is not a recommendation like SHOULD(I think there is RFC
about this words meaning).

> I may have a host 192.168.1.2 in my local network already. I cannot
> think right now of any bad effects of getting ICMP from a doppelganger
> (except for confusion in the logs) but I'd prefer for it never to
> happen!

That ICMP packet will contain IP header and some part of payload of
discarded packet. Any software that is logging network flows should 
be able to match it with correct stream. If you use "flat" network
packets logging(one packet - one entry) you should see which packet
was discarded. For example: linux iptables LOG target dumps discarded
IP header in square brackets.

-- 
Best Regards
orcus

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192.168 bob@coolfone.comze.com - 2012-10-17 08:37 -0700
  Re: 192.168 Richard Kettlewell <rjk@greenend.org.uk> - 2012-10-17 16:40 +0100
    Re: 192.168 ein <ein@no.spam> - 2012-10-17 20:04 +0200
      Re: 192.168 Marc Haber <mh+usenetspam1118@zugschl.us> - 2012-10-17 21:23 +0200
        Re: 192.168 ein <ein@no.spam> - 2012-10-17 22:37 +0200
          Re: 192.168 Marc Haber <mh+usenetspam1118@zugschl.us> - 2012-10-18 18:29 +0200
            Re: 192.168 ein <ein@no.spam> - 2012-10-19 07:54 +0200
  Re: 192.168 Maurizio Loreti <mlo@foobar.it> - 2012-10-17 20:37 +0200
  Re: 192.168 unruh <unruh@invalid.ca> - 2012-10-18 01:43 +0000
    Re: 192.168 Richard Kettlewell <rjk@greenend.org.uk> - 2012-10-18 09:22 +0100
      Re: 192.168 ein <ein@no.spam> - 2012-10-19 07:51 +0200
        Re: 192.168 Noob <root@127.0.0.1> - 2012-10-19 12:16 +0200
          Re: 192.168 orcus@pwr.wroc.pl - 2012-10-19 18:54 +0000
            Re: 192.168 Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-10-20 06:51 +0000
              Re: 192.168 orcus@pwr.wroc.pl - 2012-10-20 07:46 +0000
                Re: 192.168 Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-10-20 08:00 +0000
                Re: 192.168 orcus@pwr.wroc.pl - 2012-10-20 13:43 +0000
                Re: 192.168 Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-10-20 14:15 +0000
                Re: 192.168 orcus@pwr.wroc.pl - 2012-10-20 14:54 +0000
                Re: 192.168 Moe Trin <ibuprofin@painkiller.example.tld.invalid> - 2012-10-20 15:21 -0500
                Re: 192.168 Moe Trin <ibuprofin@painkiller.example.tld.invalid> - 2012-10-20 15:20 -0500
          Re: 192.168 Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2012-10-20 13:55 +0200
        Re: 192.168 unruh <unruh@invalid.ca> - 2012-10-21 00:33 +0000
          Re: 192.168 orcus@pwr.wroc.pl - 2012-10-21 10:22 +0000
            Re: 192.168 Markus Koßmann <mkossmann_n1@gmx.de> - 2012-10-21 15:53 +0200
          Re: 192.168 GangGreene <GangGreene@example.com> - 2012-10-21 07:06 -0400
  Re: 192.168 Vanni <Vanniz@nospam.thanks> - 2012-10-18 07:56 +0200
    Re: 192.168 Johann Klammer <klammerj@NOSPAM.a1.net> - 2012-10-18 06:40 +0200

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