# SR LAN Adjacency SID (Walkthrough)

## ISIS

A LAN segment has been setup between R1, R2, and R3. R3 has been elected DIS.

Each router on the LAN advertises a **LAN-ADJ-SID**, one per node on the LAN. Each LAN-ADJ-SID sub TLV is attached to the Extended IS Reachability TLV which identifies the adjacency with the pseudonode.

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We can also see this using the same **show adjacency** command. As usual, both a FRR and non-FRR Adj-SID are allocated:

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This allows SR to operate on a LAN somewhat as if the LAN was a collection of p2p links. This is because, on a LAN, the router only advertises an adjacency with the pseudonode. However, with SR, we have a LAN-ADJ-SID per node on the LAN.

The DIS does not advertise any SR information:

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Note that while a FRR-eligible Adj-SID is allocated, these are not TI-LFA protected.

## OSPF <a href="#id-2559adb8-7a23-41a3-aaaa-1bca12db8e0e" id="id-2559adb8-7a23-41a3-aaaa-1bca12db8e0e"></a>

The OSPF LAN-Adj-SID works slightly differently. Each node advertises a normal Adj-SID with the DR, but a LAN-Adj-SID with each BDR/DROTHER.

For example, R3 is the DR. R1 advertises a LAN Adj-SID for R2, and a regular Adj SID for R1:

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The DR will have a LAN-Adj-SID with all nodes on the LAN:

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