On Tue, Apr 13, 2004 at 09:46:21AM -0500, Kevin D. Kinsey, DaleCo, S.P. wrote:

> Can anyone help me interpret the following output? I read the ping
> manpage, but came to the end before I learned much that helps me
> here....

> <[EMAIL PROTECTED]> [/home/kdk] [16:25]
> #sudo ping -s 2048 app
> PING app.southuni.com ( 2048 data bytes
> 36 bytes from app.southuni.com ( Destination Host Unreachable

> 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.

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

Stephen Fisher
San Jose, CA USA

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