LSP size
Load isis.cfg
Enable wide metrics everywhere. Configure R1 and XR2 so that their LSP is fragmented once is it bigger than 128 bytes.
Answer
Explanation
By default, an LSP is fragmented at 1500 bytes. We can control this by setting the lsp-mtu. When the router’s own LSP becomes larger than the specified MTU size, it is split into multiple LSPs.
LSP IDs are in the format <Sys ID>.<Circuit ID>-<LSP fragment>. For example, LSP R6.02-00 is R6’s pseudonode LSP on the LAN segment with circuit ID 02. For p2p circuits, the circuit ID is always 00. If a router needs to fragment its LSP, it increments the last portion. For example, R1.00-00, R1.00-01, R1.00-02, etc.
In ISIS, each LSP fragment is treated as its own LSP. It is flooded, has a seq number, etc. A router “combines” all LSP fragments from a single router in order to build the ISIS topology graph.
In our network, we should see two routers that have LSP fragments, R1 and XR2:
The TLVs are simply distributed among the multiple LSP fragments in order to fit within the LSP-mtu size.
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