From: Alexander Arsenyev (GU/ETL) (alexander.arsenyev@ericsson.com)
Date: Mon Feb 14 2005 - 11:05:51 GMT-3
Could be NAT or traceroute goes along MPLS LSP. They both are known to produce this effect.
Cheers
Aelxander
-----Original Message-----
From: Shahid Shafi [mailto:sshafi@gmail.com]
Sent: 13 February 2005 21:49
To: Alexander Arsenyev (GU/ETL)
Cc: ccielab@groupstudy.com
Subject: Re: Traceroute checksum errors
Thanks Alex,
What about same ip in multiple hops 10.222.148.8? This means atleast
three probe packets hit the same interface. What does that indicate?
On Sun, 13 Feb 2005 14:10:25 +0100, Alexander Arsenyev (GU/ETL)
<alexander.arsenyev@ericsson.com> wrote:
> Let me guess :-)
> The errors are on return path (ICMP TTL Exceeded has wrong ICMP checksum)
> and appear only after 6th hop (on 7th and 8th hops). Are you able to capture
> ICMP TTL exceeded packets and verify that ICMP checksum is definitely wrong?
> Or could it be just 0x0000 which is technically wrong but for a different reason
> (botched IP stack implementation)?
> Another guess is that you may have incorrectly working NAT after 6th hop which changes
> IP addresses embedded into ICMP message but forgets to update ICMP checksum.
> HTH,
> Cheers
> Alex
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]
> Sent: 13 February 2005 12:08
> To: ccielab@groupstudy.com
> Subject: Traceroute checksum errors
>
> Hi Gurus,
>
> traceroute to (10.222.148.8), 30 hops max, 38 byte packets
> 1 x.x.x.x 0.229 ms 0.203 ms 0.192 ms
> 2 y.y.y.y 0.223 ms 0.214 ms 0.207 ms
> 3 10.0.1.10 0.263 ms 0.251 ms 0.244 ms
> 4 10.0.4.97 0.505 ms 0.467 ms 0.861 ms
> 5 192.168.52.250 39.225 ms 39.079 ms 38.858 ms
> 6 10.222.148.8 40.300 ms 40.550 ms 40.570 ms
> 7 10.222.148.8 39.821 ms 40.539 ms 42.491 ms
> Icmp checksum is wrong
> 8 10.222.148.8 40.068 msIcmp checksum is wrong
> 40.314 msIcmp checksum is wrong
> 40.588 ms
>
> What can you say about this output? Checksum errors?
>
> Thx
>
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