From: sekchye goh (sekchye@gmail.com)
Date: Thu Jan 06 2005 - 22:06:42 GMT-3
Hi Sheahan,
When you ping a device, the device will respond with ICMP echo reply message.
The device that is responding to your ping with the echo reply is free
to set the packet to any TTL. For Cisco router, it will be 255, for
Catalyst, it will be 64, for Windows, TTL = 128, for Linux, TTL=255
If you ping a Cisco router, TTL for the ICMP echo reply generated by
the router will be set to 255. By the time the ICMP echo reply
reaches your PC, it will have traversed a few routers. As the icmp
echo reply message passed through each router, TTL will be decremented
by 1. Hence, you will see the TTL of the ICMP echo reply message as (
255 - # of hop the ICMP echo reply packet traversed from the device
back to you ).
Similary, if you ping a Cisco Catalyst 6500 switch, the TTL of the
echo reply generated by the switch generate is 64. Therefore, if the
returning path from the switch to your machine is 9 hops away, you
will see the TTL as 64 -9 = 55.
HTH
On Thu, 6 Jan 2005 17:57:28 -0500, Sheahan, John
<John.Sheahan@priceline.com> wrote:
> Why is it that when I PING certain network devices like routers, in my
> reply..I get TTL=251
>
> But when I PING a switch, my reply says TTL=55?
>
> Why are the numbers so different?
>
> Thanks
>
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