[j-nsp] re-write rules - query

[Dmitry Perelman]

Shiva,

Can you provide the exact version of 8.4 that you're using? If your
configuration follows Masood's example you shouldn't have a problem, so that
error message leads me down the path of something specific to either 8.4 or
the J-series.



On Fri, Jul 31, 2009 at 9:28 AM, <masood at nexlinx.net.pk> wrote:

> Yes, you can re-write MPLS packets using rewrite and same goes for regular
> IP packets.
> Let me put this another way; rewrite rules can be configured that rewrite
> the DSCP, IP precedence, MPLS EXP, or IEEE 802.1p bits of a packet before it
> is transmitted.If no rewrite rules are configured, the outgoing packet is
> marked according to the forwarding class and PLP assigned by the classifier.
>
> As I am sitting right next to the router, here is a sample template...
>
>
> jahil at Voyager> show configuration class-of-service rewrite-rules
> dscp dscp-rewrite {
>     forwarding-class NC {
>         loss-priority high code-point 111000;
>         loss-priority low code-point 110000;
>     }
>     forwarding-class EF {
>         loss-priority low code-point 101110;
>     }
>     forwarding-class AF {
>         loss-priority high code-point 001100;
>         loss-priority low code-point 001010;
>     }
>     forwarding-class BE {
>         loss-priority high code-point dscp-BE;
>         loss-priority low code-point dscp-BE1;
>     }
> }
> exp exp-rewrite {
>     forwarding-class NC {
>         loss-priority high code-point 111;
>         loss-priority low code-point 110;
>     }
>     forwarding-class EF {
>         loss-priority low code-point 101;
>     }
>     forwarding-class AF {
>         loss-priority high code-point 011;
>         loss-priority low code-point 100;
>     }
>     forwarding-class BE {
>         loss-priority high code-point 001;
>         loss-priority low code-point 000;
>     }
> }
>
> {master}
> jahil at Voyager>
>
> jahil at Voyager> show configuration class-of-service interfaces
> ge-2/0/0 {
>      unit * {
>           rewrite-rules {
>             dscp dscp-rewrite;
>             exp exp-rewrite;
>         }
>     }
> }
>
> Regards,
> Masood
> Blog: http://weblogs.com.pk/jahil/
>
>
> > Dmitry, Thanks for the clarification. In a specific example, on an
> > interface
> > can I have both exp and dscp rewrite rules, so that
> >
> > (i) I can re-write MPLS packets using exp rewrite and
> > (ii) for ip packets (not using mpls) to re-write dscp using dscp re-write
>
> > rules.
> >
> > I have seen errors in log messages when I use dscp re-write rule in the
> > above scenario, saying 'invalid rewrite table type 1'. This was in J
> > series
> > using Junos 8.4.
> >
> > Cheers
> > Shiva
> > On Thu, Jul 30, 2009 at 6:25 PM, Dmitry Perelman
> > <dmitrynyc at gmail.com>wrote:
> >
> >> 1. You can rewrite DSCP (all 6 bits) for IPv4 packets only. The
> >> restriction
> >> that is referenced (3-bit TOS) in your example exists when the rewrite
> >> is
> >> done on the IPv4 payload ingress to an LSP.
> >>
> >> 2. The link below covers how to modify the EXP and TOS bits at LSP
> >> ingress.
> >> To sum it up: You are able to rewrite the EXP bits along with the TOS
> >> bits
> >> only at LSP ingress (via exp rewrite rule) which makes sense because of
> >> IPv4
> >> payload visibility. Since you have no visibility into the IPv4 payload
> >> on
> >> transit nodes you only have the option to rewrite the EXP bits. You do
> >> then
> >> have the ability to rewrite the full DSCP field on the egress PE
> >> interface.
> >>
> >>
> >>
> http://www.juniper.net/techpubs/en_US/junos9.5/information-products/topic-collections/config-guide-cos/cos-rewriting-mpls-and-ipv4-packet-headers.html#id-11667692
> >>
> >>
> >>
> >> On Thu, Jul 30, 2009 at 11:13 AM, Shiva Shankar
> >> <shankarks at gmail.com>wrote:
> >>
> >>> Gents, Try to understand in depth re-write rules in M/J series...From
> >>> JUNOS
> >>> 9.5 notes I found the following:
> >>>
> >>> *For every incoming packet, the ingress classifier decodes the ingress
> >>> CoS
> >>> bits into a forwarding class and packet loss priority (PLP)
> >>> combination.
> >>> The
> >>> egress CoS information depends on which type of rewrite marker is
> >>> active,
> >>> as
> >>> follows: *
> >>>
> >>> - *For Multiprotocol Label Switching (MPLS) EXP and IEEE 802.1
> >>> rewrite
> >>> markers, values are derived from the forwarding class and PLP values
> >>> in
> >>> rewrite rules. MPLS EXP and IEEE 802.1 markers are not preserved
> >>> because
> >>> they are part of the Layer 2 encapsulation. *
> >>> - *For IP precedence and DiffServ code point (DSCP) rewrite markers,
> >>> the
> >>> marker alters the first three bits on the type-of-service (ToS) byte
> >>> while
> >>> leaving the last three bits unchanged. *
> >>>
> >>> *Questions:
> >>> *
> >>> *1. Does it mean that on Juniper M series routers, I can never chnage
> >>> the
> >>> last 3 bits of the TOS byte...meaning never use the full potential of
> >>> the
> >>> DSCP (6 bits)?
> >>> *
> >>> *2. So, can't I use dscp and exp re-write rules for a MPLS packet
> >>> entering
> >>> a
> >>> LSP on a specific interface..? It means that again I can't use DSCP in
> >>> MPLS
> >>> evnvironment?
> >>>
> >>> *Cheers
> >>> _______________________________________________
> >>> juniper-nsp mailing list juniper-nsp at puck.nether.net
> >>> https://puck.nether.net/mailman/listinfo/juniper-nsp
> >>>
> >>
> >>
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