VPP/Per-feature Notes

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This page contains a collection of Notes loosely organized by VPP feature.

VLAN

VLAN And Tags

If the interface is in L3 routing mode, packets with VLAN tags, either one or two, will need to match a sub-interface or will be dropped. It is not just QinQ packets that are dropped.

Once the packet is received, however, the VLAN tags are not removed in the L3 input processing path. So it is possible to perform classification on the VLAN tags to check cos fields, etc. When the packet is routed out an output interface, however, the L2 header will be replaced with whatever is the correct header according to the adjacency info of the output interface. I am not sure why you claim VLAN tag is removed unless you are on the output path when L2 header rewrite happens.

If an interface is put into an L2 mode and associated with a bridge domain, however, exact VLAN match will not be necessary. Sub-interface can still be setup and ethernet-input node will perform best-match sub-interface lookup. For example, if you have a sub-interface with VLAN 10 and another sub-interface with QinQ of outer VLAN 10 and inner VLAN 20 on this interface, then:

  • Any packet with QinQ matching 10/20 will be matched to that QinQ sub-interface.
  • Any packet with outer VLAN 10, with or without inner VLAN tags will be matched to the VLAN 10 sub-interface.
  • Any packet with no VLAN tag or outer VLAN tag other than 10 will be matched to the main interface.

When a (sub-)interface is in L2 mode, you can also add a tag-rewrite operation to push/pop/replace VLAN tags as needed to make packet forwarding in the bridge domain (BD) work properly when the BD have (sub-)interfaces that receive packets with different VLAN tags.