[j-nsp] (Again) Rewriting IP precedence

[Sorin CONSTANTINESCU]

On 1/10/06, Rafal Szarecki (WA/EPO) <rafal.szarecki at ericsson.com> wrote:
> Sorin,

Hi, Rafal.

>
> If your rewrite rule is is applied on R2 interfaces, then system works as designed.
>
> On Router 2, for traffic going to host_B, the lookup_key (notification cell) do not contain DS.-field/ToS. Also egress I/O manager is not able to rewrite filds in IP header. As you notice you can rewrite EXP. But then R4 has to do DS.-field/ToS rewrite, becouse only this router has access to IP header at egress B-chip. And note that default rewrite rule for IPv4 is " do nothing".
>
> The reason why traffic going to Host_C is fine, is obvoius if your networ is going to implement PHP/explicit null label (default) or if you know that implicit null label is stripped by ingess B-chip. (and create somthing like logical interface.) Thus, from IP II and egress B-chip point of view traffic to Host_C is regular IP traffic.
>

Thanks for the answer :)

> Rafał Szarecki JNCIE
>
> skype me <callto://Rafal_Szarecki/>
>
>
>
> > -----Original Message-----
> > From: juniper-nsp-bounces at puck.nether.net
> > [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of
> > Sorin CONSTANTINESCU
> > Sent: Tuesday, January 10, 2006 1:52 PM
> > To: juniper-nsp at puck.nether.net
> > Subject: [j-nsp] (Again) Rewriting IP precedence
> >
> > Hi,
> >
> > It's not the first time i run into this problem, but i hope
> > this time i'll be able to explain the problem better to you
> > and get some help :)
> >
> > - R1 -
> > Hardware: Juniper M5
> > Software:  7.3R1.6
> >
> > I have the following topology:
> >
> > _Host_A_ ---> R1 -> R2 -> R3 -> R4 ---> _Host_B_
> >                                 |
> >                           _Host_C_
> >
> > The network is configured to run MPLS.
> >
> > On the ingress interface (dot1q gigabit subinterface), i have
> > a firewall filter that changes the default forwarding-class
> > (best-effort) to assured-forwarding with plp low.
> >
> > Under [class-of-service], i've defined a rewrite rule for
> > inet-precedence:
> >
> > === cut here ===
> > rewrite-rules {
> >     inet-precedence clear-inet-precedence {
> >         forwarding-class assured-forwarding {
> >             loss-priority low code-point 000;
> >         }
> >     }
> > }
> > === and here ===
> >
> > If i ping Host C from Host A, the precedence is correctly
> > rewriten to 000. If i ping Host B from Host A, the precedence
> > is not cleared.
> >
> > The difference is that traffic from A to B is label-switched,
> > and from A to C is not.
> >
> > I've also configured a rewrite-rule to clear exp precedence ,
> > but the precedence of the IPV4 packet inside is not cleared to 0x00.
> >
> > Thanks,
> > --
> > Sorin CONSTANTINESCU
> > JNCIS-M, CCNP
> > consta at gmail.com
> >
> > _______________________________________________
> > juniper-nsp mailing list juniper-nsp at puck.nether.net
> > http://puck.nether.net/mailman/listinfo/juniper-nsp
> >
>


--
Sorin CONSTANTINESCU
JNCIS-M, CCNP
consta at gmail.com