H3C S5800 Series Configuration Manual page 186

To do...
Configure a virtual system ID
After LSP fragment extension is enabled for an IS-IS process, the MTUs of all the interfaces
running the IS-IS process must not be less than 512; otherwise, LSP fragment extension will not
take effect.
At least one virtual system needs to be configured for the router to generate extended LSP
fragments. An IS-IS process allows 50 virtual systems at most.
Limiting LSP flooding
In well connected NBMA networks, many P2P links exist. The following figure shows a fully meshed
network, where Switchs A, B, C and D run IS-IS. When Switch A generates an LSP, it floods the LSP
out VLAN-interface 100, VLAN-interface 200 and VLAN-interface 300. After receiving the LSP from
VLAN-interface 100, Switch D floods it out VLAN-interface 200 and VLAN-interface 300 to Switch B
and Switch C, which however has received the LSP from Router A. In this case, LSP flooding
consumes extra bandwidth.
Figure 5-14 Network diagram of a fully meshed network
To avoid this, you can configure some interfaces as a mesh group or/and configure the blocked
interfaces.
After receiving an LSP, a member interface in a mesh group floods it out the interfaces that does
not belong to the mesh group.
If an interface is blocked, it does not send LSPs unless the neighbor sends LSP requests to it.
Use the command...
virtual-system virtual-system-id
5-31
Remarks
Required
Not configured by default