[j-nsp] CoS clarification on MPLS interface

[Nilesh Khambal]

If the traffic is identified as MPLS traffic at ingress i.e. It is a  
tagged packet at ingress, exp classification will be applied to it.  
Other non-tagged traffic will be classified according to the protocol  
and applied classifiers. If it is an IPv4 and you have DSCP classifier  
applied at ingress then that will be applied to the IPv4 packet  
without tag. You can have multiple classification types applied at an  
ingress interface. Search for "Applying a Classifier to a Logical  
Interface" link in JUNOS "Class of Service" documentation.

For rewrite rule, same logic applies to the most part. However, when  
traffic exits an MPLS interface at an ingress PE (and only at ingress)  
you can additionally copy the 3 exp bits from the exp rewrite rule at  
egress interface to the IP precedence bits in the IP header in the  
Payload. Look for the keywords "mpls-inet-both" and "mpls-inet-both- 
non-vpn" in the documentation. If you do not specifiy these keywords  
in the exp rewrite rule, IPv4 header is not touched at the ingress PE  
on its egress interface towards MPLS core. If you have a DSCP rewrite  
rule applied to an egress MPLS interface, it will alter the IPv4 DSCP  
value of the non-MPLS switched traffic only (at least from what I  
understand). Please correct me if you find any contradicting  
documented or tested behavior.

Thanks,
Nilesh


--------------------------------------------------
Sent from my mobile handheld device

On May 24, 2009, at 1:10 PM, "Andrew Jimmy" <good1 at live.com> wrote:

> The question is not what to use (I do know we use EXP because packet  
> is not
> being processed on IP layer). The question was, what if you have  
> configured
> both DSCP/EXP classifier and rewriting rules on an MPLS switching  
> interface
> for the MPLS switching traffic (not regular IP traffic), what  
> behavior would
> you expect  from a Juniper J-Series or M-Series router. Will it use  
> DSCP
> classification or not? Will it rewrite DSCP value or not?
>
> Regards,
> Andrew
>
> -----Original Message-----
> From: Fahad Ali Khan [mailto:fahadak at cyber.net.pk]
> Sent: Sunday, May 24, 2009 9:03 PM
> To: Andrew Jimmy
> Subject: Re: [j-nsp] CoS clarification on MPLS interface
>
> In my opinion n experience, on mpls core interface only EXP bits r  
> used 4
> classification n rewriting. DSCP based classification n rewriting b  
> used
> only when IP traffic (non switched) passed the interface.
>
> Now ur question may b that in what scenario mpls interface b used 4  
> both
> routing n mpls swutching. Consider if my policy is to carry only VPN  
> traffic
> over mpls lsp n won't used IGP forwarding to use LSP. In normal
> circumstances only Mpls vpn (whose next-hop) is available via BGP in  
> Inet3
> table will use lsp...all other will follow IGP forwarding rules.  
> Where this
> behaviour can b changed.
>
> Regards
>
> Fahad
> ------Original Message------
> From: Andrew Jimmy
> Sender: juniper-nsp-bounces at puck.nether.net
> To: juniper-nsp at puck.nether.net
> Subject: [j-nsp] CoS clarification on MPLS interface
> Sent: May 25, 2009 1:51 AM
>
> Which policy will took place, if you apply a CoS DSCP/EXP  
> classification and
> DSCP/EXP rewrite policy on an MPLS switching interface (keeping in  
> mind
> packet is being switched using MPLS shim header), I know MPLS EXP
> classification and rewriting will defiantly be used but what about  
> DSCP
> classification and rewriting. The confusing is packet is being  
> switched on
> MPLS header without touching regular IP header while DSCP value set  
> in IP
> header. I just wana know how Juniper router (J Series and M Series)  
> treats a
> packet in MPLS core facing interface while both DCSP/MPLS EXP  
> classifier and
> rewriting are configured.
>
>
>
> OR in simple words . Is it possible to use DSCP classification/ 
> rewriting on
> MPLS core interface (while packet is being switched using MPLS shim  
> header).
>
>
>
> Regards,
>
> Andrew
>
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