Configuring Rewrite Rules
You define markers in the rewrite rules section of the CoS configuration hierarchy and reference them in the logical interface configuration. This model supports marking on the DSCP, DSCP IPv6, IP precedence, IPv6 precedence, IEEE 802.1, and MPLS EXP CoS values.
To configure a rewrite-rules mapping and associate it with the
appropriate forwarding class and code-point alias or bit set, include
the rewrite-rules statement at the [edit class-of-service] hierarchy level:
[edit class-of-service] rewrite-rules { (dscp | dscp-ipv6 | exp | ieee-802.1 |ieee-802.1ad | inet-precedence | inet6-precedence) rewrite-name { import (rewrite-name | default); forwarding-class class-name { loss-priority level code-point (alias | bits); } } }
The inet-precedence statement is supported
on PTX Series routers only when network services is set to enhanced-mode. For more information, see enhanced-mode.
The rewrite rule sets the code-point aliases and bit patterns for a specific forwarding class and packet loss priority (PLP). The inputs for the map are the forwarding class and the PLP. The output of the map is the code-point alias or bit pattern. For more information about how CoS maps work, see Mapping CoS Component Inputs to Outputs.
By default, IP precedence rewrite rules alter the first three
bits on the type-of-service (ToS) byte while leaving the last three
bits unchanged. This default behavior is not configurable. The default
behavior applies to rules you configure by including the inet-precedence statement at the [edit class-of-service rewrite-rules] hierarchy level. The default behavior also applies to rewrite rules
you configure for MPLS packets with IPv4 payloads. You configure these
types of rewrite rules by including the mpls-inet-both or mpls-inet-both-non-vpn option at the [edit class-of-service
interfaces interface-name unit logical-unit-number rewrite-rules exp rewrite-rule-name protocol] hierarchy level.
Starting with Junos OS
Release 18.1R1, MX Series routers with MPCs support rewrite rules
that rewrite the first three bits of the IPv6 DSCP value through the inet6-precedence statement at the [edit class-of-service
rewrite-rules] hierarchy level. This
allows you to set a 3-bit code point for a particular forwarding class
and loss priority for IPv6 traffic. This rewrite rule option can also
be applied to packets entering an MPLS LSP by including the protocol mpls statement when applying the rewrite rule to a logical
interface.
On the M320, T1600, and MX960 routers and EX Series switches,
if you configure vlan-vpls encapsulation and add an IEEE
802.1 header on a Gigabit Ethernet or 10 Gigabit Ethernet interface
to output traffic, but do not apply an IEEE 802.1 rewrite rule, then
the default IEEE 802.1 rewrite rule is ignored and the IEEE 802.1p
bits are set to match the forwarding class queue.
Integrated
Bridging and Routing (IRB) interfaces are used to tie together Layer
2 switched and Layer 3 routed domains on MX routers. MX routers support
classifiers and rewrite rules on the IRB interface at the [edit
class-of-service interfaces irb unit logical-unit-number] level
of the hierarchy. All types of classifiers and rewrite rules are allowed,
including IEEE 802.1p.
The IRB classifiers and rewrite rules are used only for routed packets; in other words, it is for traffic that originated in the Layer 2 domain and is then routed through IRB into the Layer 3 domain, or vice versa. Only IEEE classifiers and IEEE rewrite rules are allowed for pure Layer 2 interfaces within a bridge domain.
The forwarding class and loss priority are determined by ingress classification.
inet6-precedence statement at the [edit class-of-service
rewrite-rules] hierarchy level.