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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.

Note

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.