Interpreting ping response? (the POD lives??)

Kevin D. Kinsey, DaleCo, S.P. kdk at
Sun Apr 18 15:10:29 PDT 2004

Stephen Fisher wrote:

>On Tue, Apr 13, 2004 at 09:46:21AM -0500, Kevin D. Kinsey, DaleCo, S.P. wrote:
>>Vr HL TOS  Len   ID Flg  off TTL Pro  cks      Src      Dst  
>>4  5  00 05dc 07bd   0 0000  3f  01 1677
>The device (router?) is sending a host unreachable message which can be 
>for a variety of reasons, the most common being that there is no route 
>available to the destination.  What address are you pinging from though?  
>You are trying to ping with a packet size of 2048 bytes (-s) but the MTU 
>of Ethernet is 1500 bytes.

First off, thank you *very much* for taking time to explain this.

A further question, if I may ... from a FBSD box at,
I can ping up to  { -s 65507 }.  Windows XP at *.*.*.10
responds as long as { -s < 25153 } ... if Ethernet Maximum is 1500,
and that's the reason for the error <?>  why doesn't FreeBSD, or
even Windows, elicit a similar response?  Nah, maybe that's a bad
question ... they aren't the same OS ... :-(

So, MTU is an OS feature/stat rather than general Ethernet?

>You don't need to understand the information below to troubleshoot this
>but here is an explanation anyway :)  It's just a dump of the IP packet 
>headers that came back in the destination host unreachable message:
>Vr 4	   IP version 4
>HL 5	   Packet header length
>TOS 0	   Type of Service: Routine traffic
>Len 05dc   Packet length in hex (1500 bytes)
>ID 07bd	   Identification - unique number to tell the ICMP packets apart
>Flg 0      Flags - 3 bits: 0 (reserved), 0 (fragment if necessary), 0 
>	   (last fragment)
>Off 0000   Fragment offset (not used since it is not a fragment)
>TTL 3f     Time to Live in hex (63 hops) - number of hops before packet 
>	   is discarded
>Pro 01	   IP protocol type (01 = ICMP, what ping uses)
>Cks 1677   Packet header checksum
>Src	   Source address that sent the "host unreachable" message
>Dst	   Recipient of the "host unreachable" message - your machine

Thank you.  This was what I was fishing for, an explanation,
for me to learn *something* from this experience, besides
the fact that this "other" OS seems to behave badly in the
presence of any kind of adverse networking conditions, including
big pings and any kind of real latency ...

We've just decided we're going to have to baby this one.  Wish
it was a *BSD instead; seems like nothing much bothers BSD  ;-)

Kevin Kinsey
DaleCo, S.P.

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