Understanding Fabricpath LID

[Eric Hansen]

I have a basic 77k 5k infrastructure.  Two 7706/F3lc on the top running layer 3 with Fabricpath connections going "south" crisscross to a pair of layer two 5k's on the bottom, and classical Ethernet VPC's out the bottom of the 5k's. Data is flowing, no major issues.  The two 77k's have a direct connection "east/west" that is Fabricpath enabled.

My 77k.A node is switch id 10, my 77k.B node is switch id 20.

When I type in "show mac address-table dynamic" I see some MAC addresses with the SWID.SSID.LID of 20.0.65535 on the 77k.A node.  Which clearly says that MAC lives on the 77k.B node.  But when you search for that MAC on the 77k.B node, it is not there.  Subsequently you see MAC entries with 10.0.65535 on the 77k.B node.

So I am curious about the Local ID on these MAC entries, there aren' many but they all have a LID of '65535'.  I don't have a lot of ports in my 77k's so it seems to me this is some sort of predefined Local ID.  What is it?  Or, is there a way to see which ports have been assigned what Local ID in Fabricpath?

much thanks

-e

[Amit Verma]

Hi Eric,

The port ID, also known as the Local Identifier (LID), can be used to identify the specific physical or logical interface on which the frame was sourced or is destined. When used, the value is locally significant to each switch. This field in the outer DA allows the egress FabricPath switch to forward the frame to the appropriate edge interface without requiring a MAC address table lookup. For frames sourced from or destined to a VPC+ port-channel, this field is set to a common value shared by both VPC+ peer switches, and the sSID is used by default to select the outgoing port instead.

As per my understanding LID is specific to the implementation:

• N7K the LID is generally the port index of the ingress interface.
• N5K/N6K LID most of the time will be 0.

[Eric Hansen]

Found out what it is, and I feel stupid for missing it but sometimes we want simple problems to be complex ones.  Its a broadcast.  65535 = 0xFFFF