Nondefault TPID

The Tag Protocol Identifier (TPID) is a 16-bit field that identifies the frame as an IEEE 802.1Q-tagged frame. The TPID is set to the default value of 0x8100, but the user can change this value.

The TPID field is located at the same position as the EtherType/length field in untagged frames, and is thus used to distinguish the frame from untagged frames. If you require support for dual tagging or provider backbone bridge (PBB), the outer TPID of the packet must be configured to a value different from the default.

The raw pass-through support for an untagged LIF requires you to configure the interface TPID to a value that allows it to treat all traffic received on that port as untagged. You can configure the TPID on port and LAG interfaces.

Important

When the tag type is changed on interface, the interface is brought down first, causing all learned MAC addresses to be flushed.

Hardware limitations of the SLX-9540/SLX-9640

The TPID feature has the following limitations:

Tagging: The TPID configuration is supported for an outer tag. If dual-tagging needs to be supported on the interface, the inner tag must be 0x8100.
TPID: Up to four TPIDS are supported system-wide. One is used by default (TPID = 0x8100) and cannot be changed.
LSP FRR: Hardware support for LSP FRR is available only for TPID 0x8100. If you require a label switched path with fast reroute (LSP FRR) configuration, note that none of the routable interfaces (whether a router port or a LIF of a VE) can have any nondefault TPID configuration, because FRR always assumes that the link layer has the default TPID of 0x8100.

Note

The LSP FRR limitation is for any tag-type configured in the device. You can configure either FRR or tag-type on any interface in the device, as in the following example.

device(config-router-mpls-lsp-to-avalanche-1)# frr
                        %Error: Not allowed, when a non-default TPID (tag-type) is configured on any port-channel or physical interfaces.
                        device(config-router-mpls-lsp-to-avalanche-1)#

Hardware Limitation of SLX 9740

The TPID feature has the following limitation:

TPID: Up to two TPIDS are supported system-wide. One is used by default (TPID = 0x8100) and cannot be changed. Therefore, only one addition TPID is available for user configuration. For dual tagged packets, the inner TPID must always be the default TPID (0x8100).