RE: Ping TOS to test QOS...

As Jason mentioned, it can be done and is pretty useful for testing QOS.

The TOS byte value is required to be entered in hex (between 00 and FF).
Essentially, just set the value to the hexadecimal equivalent to the TOS
value that you want and you are set.

The annoying thing is that most of us think in terms of IP Precedence or
DSCP, so we need to enter those values into the appropriate bits (padding
the trailing bits with zeros unless you are using TCP ECN for some reason to
test) and then we can send our pings.

So for DSCP of EF which is 101110 in the top 6 bits, change it to 10111000
(adding the extra two trailing bits that TCP ECN could use) then convert the
full byte back to hex: B8 in this case.

Cheers,
 
Jared Scrivener CCIE3 #16983 (R&S, Security, SP), CISSP
Sr. Technical Instructor - IPexpert, Inc.
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
Mailto: jscrivener_at_ipexpert.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Jason Madsen
Sent: Wednesday, 22 April 2009 5:17 PM
To: Modular
Cc: Cisco certification
Subject: Re: Ping TOS to test QOS...

Yes, you can test using the TOS CLI extended ping setting. As for the
conversions, IPP to TOS = IPP value * 8 and DSCP to TOS = DSCP value * 4.
Don't forget that if you're going through a switch and QoS is enabled, all
interfaces are "not trusted" by default.

Note, that if you have a real lab and also want to test with a Windows PC,
there is a "-v" TOS option at the command line, but you will have to modify
your TCP/IP settings in your registry for it to actually work...at least in
some versions. The TOS feature in Cisco devices works fine out of the box
though.

Jason

On Wed, Apr 22, 2009 at 3:07 PM, Modular <modulartx_at_gmail.com> wrote:

> I had a thought, (don't laugh, it happens), is it possible to use the TOS
> setting
> in extended Ping to test QOS classification? I did a little research on
> conversion
> of TOS byte setting to IPP or DSCP and the best I could come up with is
> that
> a TOS of 1 or 8 would convert to IPP 1 or DSCP 8? I played around with it
> for awhile, setting up a policy-map to match DSCP 1, DSCP 8 and IPP 1
> and then set to TOS in the extended ping on a different router to 1 and
> none of the class maps in the policy map had packet counts greater than 0.
>
> Either I'm converting TOS to IPP/DSCP wrong or I'm completely off base
with
> this.?.?
>
>
> Bryan R.
>
>
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Received on Wed Apr 22 2009 - 17:27:11 ART