Re: dscp markings on icmp request

If no marking is involved in the network, sending a ping (request) with a
certain IP Precedence should come back (Reply) with this value intact (a
requirement for IPv4 routers: RFC1812)...... You mentioned from CE to CE, so
probably experimenting the (QoS) Pipe Mode.

Not sure what you mean by real life, but if you mean pinging sites on
Internet, it's very common that your Service Provider will re-write your IP
Precedence to 0 (Best Effort) on your Internet Access port.

Nicolas
http://ccie-en-espanol.blogspot.com/

On Sun, Jan 10, 2010 at 1:08 PM, Ovidiu Neghina <o.neghina_at_gmail.com> wrote:

> Hi,
> I have noticed doing some captures in my labs that when doing a ping
> from a cisco router to another the dscp markings of icmp reply are
> identical .For example if a ping from one CE to another CE with IPP=5
> the reply comes back with IPP5. This with no special configuration .
> I did test in real life pinging various sites from windows xp with
> ping -v 136 for example (136 is the value of the TOS byte =>AF41 in
> DSCP) . some sites reply with DSCP=0, others with same marking, others
> with different marking.
> Is any rule , rfc on icmp about his ? I did not find enaything pointing to
> this
>
> br,
> Ovidiu
>
>
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Received on Mon Jan 11 2010 - 10:50:45 ART