Understanding Using Cos With Mpls Networks On Ex Series Switches; Guidelines For Using Cos Classifiers On Cccs - Juniper JUNOS OS 10.3 - SOFTWARE Manual

Understanding Using CoS with MPLS Networks on EX Series Switches

Guidelines for Using CoS Classifiers on CCCs

Copyright © 2010, Juniper Networks, Inc.
You can use class of service (CoS) within MPLS networks to prioritize certain types of
traffic during periods of congestion.
Juniper Networks EX Series Ethernet Switches support Differentiated Service Code Point
(DSCP) or IP precedence and IEEE 802.1p CoS classifiers on the customer-edge interfaces
of the ingress provider edge (PE) switch. DSCP or IP precedence classifiers are used for
Layer 3 packets. IEEE 802.1p is used for Layer 2 packets.
When a packet enters a customer-edge interface of the ingress PE switch, the switch
associates the packet with a particular CoS servicing level prior to putting the packet
onto the label-switched path (LSP). The switches within the LSP utilize the CoS value
set at the ingress PE switch. The CoS value that was embedded in the DSCP, IP
precedence, or IEEE 802.1 p classifier is translated and encoded in the MPLS header by
means of the EXP or experimental bits.
EX Series switches enable a default EXP classifier and a default EXP rewrite rule. You
can configure a custom EXP classifier and a custom EXP rewrite rule if you prefer. However,
the switch supports only one type of EXP classifier (default or custom) and only one EXP
rewrite rule (default or custom).
You do not bind the EXP classifier or the EXP rewrite rule to individual interfaces. The
switch automatically and implicitly applies the default or the custom EXP classifier and
the default or the custom EXP rewrite rule to the appropriate MPLS-enabled interfaces.
Because rewrite rules affect only egress interfaces, the switch applies the EXP rewrite
rule only to those MPLS interfaces that are transmitting MPLS packets (not to the MPLS
interfaces that are receiving the packets).
This topic includes:
Guidelines for Using CoS Classifiers on CCCs on page 3167
Using CoS Classifiers with IP over MPLS on page 3168
Default Classifiers and Default Rewrite Rules on page 3168
EXP Rewrite Rules on page 3168
Policer on page 3169
Schedulers on page 3169
When you are configuring CoS for MPLS over circuit cross-connect (CCC), there are some
additional guidelines, as follows:
You must explicitly bind a CoS classifier to the CCC interface on the ingress PE switch.
You cannot use more than one type of DSCP/IP precedence and not more than one
type of IEEE 802.1p classifier on the CCC interfaces. Thus, if you configure one CCC
interface to use DSCP1, you cannot configure another CCC interface to use DSCP2.
Likewise, if you configure one CCC interface to use IEEE1, you cannot configure another
Chapter 107: Class of Service (CoS)—Overview
3167