Comparison between LSP fragment extension mode-1 and mode-2
Mode-1
· Some routers on the network do not support LSP fragment extension.
Mode-2
· All routers on the network support the LSP fragment extension feature.
Mode-1
· The virtual system participates in SPF calculation. The LSP advertised by the system carries information about links to each virtual system. Similarly, the LSP advertised by the virtual system also includes link information of the initial system. In this way, the virtual system in the network looks the same as the real router connected to the initial system.
· The LSP of the virtual system contains the same area address and overload bit as the original LSP. The TLVs of other features must be the same.
· The neighbor information carried by the virtual system points to the initial system. The metric is the maximum value (the maximum value is 64 in narrow measurement) minus 1. The neighbor information carried in the initial system points to the virtual system, and the metric must be 0. In this way, when other routers calculate routes, the virtual system will become the downstream node of the initial system.
· The LSP generated by the virtual system contains only the initial system (the neighbor type is point-to-point), and the virtual system is considered as a leaf.
Mode-2
The virtual system does not participate in the SPF calculation. All routers on the network know that the LSP generated by the virtual system actually belongs to the initial system.
