HP VPN Firewall Appliances Appendix Protocol Reference

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Figure 19 LSDB overload
SNP
A sequence number PDU (SNP) describes the complete or partial LSPs for LSDB synchronization.
SNPs include 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.
A CSNP describes the summary of all LSPs for LSDB synchronization between neighboring routers. On
broadcast networks, CSNPs are sent by the DIS periodically (10 seconds by default). On point-to-point
networks, CSNPs are only sent during the adjacency establishment.
The CSNP packet format is shown in Figure 20.
Figure 20 L1/L
2 CSNP format
A 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 missing LSPs from
a neighbor.