H3C Technologies H3C S10500 Series Switches - Manual (Page 158)

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Figure 59 LSDB overload
• IS type: Type of the router generating the LSP.
SNP format
A sequence number PDU (SNP) acknowledges the latest received LSPs. It is similar to an Acknowledge
packet, but more efficient.
SNP involves Complete SNP (CSNP) and Partial SNP (PSNP), which are further divided into Level-1 CSNP,
Level-2 CSNP, Level-1 PSNP and Level-2 PSNP.
CSNP covers the summary of all LSPs in the LSDB to synchronize the LSDB between neighboring routers.
On broadcast networks, CSNP is sent by the DIS periodically (10s by default). On point-to-point networks,
CSNP is only sent during the adjacency establishment.
The CSNP packet format is shown in
Figure 60 .
Figure 60 L1/L2 CSNP format
PSNP only contains the sequence numbers of one or multiple latest received LSPs. It can acknowledge
multiple LSPs at one time. When LSDBs are not synchronized, a PSNP is used to request new LSPs from
neighbors.