3Com S7906E Configuration Manual page 739

Configure a proper LSP retransmission interval to avoid unnecessary retransmissions.
Specifying LSP lengths
IS-IS messages cannot be fragmented at the IP layer because they are directly encapsulated in frames.
Therefore, IS-IS routers in an area need to send LSPs smaller than the smallest interface MTU in this
area.
If the IS-IS routers have different interface MTUs, it is recommended to configure the maximum size of
generated LSP packets to be smaller than the smallest interface MTU in this area. Otherwise, the
routers have to dynamically adjust the LSP packet size to fit the smallest interface MTU, which takes
time and affects other services.
Follow these steps to specify LSP lengths:
To do...
Enter system view
Enter IS-IS view
Specify the maximum length of
generated Level-1 LSPs or
Level-2 LSPs
Specify the maximum length of
received LSPs
Enabling LSP flash flooding
Since changed LSPs may trigger SPF recalculation, you can enable LSP flash flooding to advertise the
changed LSPs before the router recalculates routes. Doing so can speed up network convergence.
Follow these steps to enable LSP flash flooding:
To do...
Enter system view
Enter IS-IS view
Enable LSP flash
flooding
Enabling LSP fragment extension
Follow these steps to enable LSP fragment extension:
To do...
Enter system view
Use the command...
system-view
isis [ process-id ] [ vpn-instance
vpn-instance-name ]
lsp-length originate size [ level-1 |
level-2 ]
lsp-length receive size
Use the command...
system-view
isis [ process-id ] [ vpn-instance
vpn-instance-name ]
flash-flood [ flood-count flooding-count |
max-timer-interval flooding-interval | [ level-1 |
level-2 ] ] *
Use the command...
system-view
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1497 bytes by default
1497 bytes by default
Remarks
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Required
Not enabled by
default
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