From: Church, Chuck (cchurch@wamnetgov.com)
Date: Mon Jun 28 2004 - 10:14:27 GMT-3
C:\Documents and Settings\cchurch>ping /?
Usage: ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS]
[-r count] [-s count] [[-j host-list] | [-k host-list]]
[-w timeout] destination-list
Options:
-t Ping the specified host until stopped.
To see statistics and continue - type Control-Break;
To stop - type Control-C.
-a Resolve addresses to hostnames.
-n count Number of echo requests to send.
-l size Send buffer size.
-f Set Don't Fragment flag in packet.
-i TTL Time To Live.
-v TOS Type Of Service.
-r count Record route for count hops.
-s count Timestamp for count hops.
-j host-list Loose source route along host-list.
-k host-list Strict source route along host-list.
-w timeout Timeout in milliseconds to wait for each reply.
So if you do a ping with a large size and set the 'Don't Fragment' flag, you can discover it. Example -
Ping -l 1476 -f will ping with 1476 bytes and set the don't fragment flag. If that 1476 is large than the MTU of a link it has to cross, that router should send you back an ICMP message. Keep increasing the ping size to narrow in on the MTU.
Chuck Church
Wam!Net Government Services - D&I Team
Lead Design Engineer
CCIE #8776, MCNE, MCSE
1210 N. Parker Rd.
Greenville, SC 29609
Office: 864-335-9473
Cell: 703-819-3495
cchurch@wamnetgov.com
PGP key: http://pgp.mit.edu:11371/pks/lookup?op=index&search=cchurch%40wamnetgov.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Tom Young
Sent: Monday, June 28, 2004 12:44 AM
To: Joe Chang
Cc: ccielab@groupstudy.com
Subject: Re: Cisco MTU calculation
If I use the ping command on the computer behind the router. May I find the useful MTU ?
thanks
--- Joe Chang <changjoe@earthlink.net> c c c.c!cc;c<c8
o<
> Isn't the lack of MTU discovery methods the reason why routing
> protocols like OSPF include MTU matching as part of their adjacency
> set-up?
>
>
>
> ----- Original Message -----
> From: "Tom Young" <gitsyoung@yahoo.co.jp>
> To: <ccielab@groupstudy.com>
> Sent: Sunday, June 27, 2004 10:17 PM
> Subject: Cisco MTU calculation
>
>
> > Hi , group
> >
> > A question about the calculation of MTU.
> > If a computer connection the cisco router and
> access a
> > site through some network such as internet vpn,
> firewall,
> > internet router with PPPoE. How can I know the max
> MTU for
> > the site accessible. May I use ping command to get
> it?
> >
> > Thanks alot
> >
> > __________________________________________________
> > Do You Yahoo!?
> > http://bb.yahoo.co.jp/
> >
> >
>
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