[j-nsp] re-write rules - query
Shiva Shankar
shankarks at gmail.com
Fri Jul 31 09:54:04 EDT 2009
Dmitry, Based on mytesting in the lab, waht I found that on J series, you
can configure dscp-based rewrite-rules along with exp rewrite-rules for MPLS
packet with ipv4 payload....This seems to be cosmetic issue...The actual
JUNOS I use is 8.4R2.3....On testing with JUNOS 8.5, i didn't see this
issue....
Cheers
On Fri, Jul 31, 2009 at 2:30 PM, Dmitry Perelman <dmitrynyc at gmail.com>wrote:
> 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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>>
>
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