Understanding IEEE 802.1p Inheritance push and swap from a Transparent Tag
M320 router interfaces and MX Series router interfaces on Modular Interface Cards (MIC) or Modular Port Concentrators (MPCs) support configurable IEEE 802.1p inheritance of push and swap bits from the transparent tag of each incoming packet which allows you to classify incoming packets based on the IEEE 802.1p bits from the transparent tag.
During a tagging operation, Junos OS by default inherits the IEEE 802.1p bits from incoming tags in swap and push operations from the known tags configured on the interface.
It can be useful to override the default behavior by configuring
Junos OS to inherit the IEEE 802.1p bits from a transparent tag, and
to classify incoming packets based on the IEEE 802.1p bits of the
incoming transparent tag. The configuration statements swap-by-poppush
and transparent
enable Junos OS to do this.
By default, during a swap operation, the IEEE 802.1p bits of
the VLAN tag remain unchanged. When the swap-by-poppush
operation is enabled on a logical interface, the swap operation is treated as a pop
operation followed
by push
operation. The pop
operation removes
the existing tag and the associated IEEE 802.1p bits and the push
operation copies the inner VLAN IEEE 802.1p bits to the IEEE bits
of the VLAN or VLANs being pushed. As a result, the IEEE 802.1p bits
are inherited from the incoming transparent tag.
To classify incoming packets based on the IEEE 802.1p bits from
the transparent tag, include the transparent
statement
at the [edit class-of-service interfaces
interface-name unit
logical-unit-number classifiers
ieee-802.1 vlan-tag]
hierarchy level.
To configure Junos OS to inherit the IEEE 802.1p bits from the
transparent tag, include the swap-by-poppush
statement
at the [edit interfaces interface-name unit logical-unit-number]
hierarchy
level.
IEEE 802.1p Inheritance push and swap is only supported on untagged and single-tagged logical interfaces, and is not supported on dual-tagged logical interfaces.