3Com MSR 50 Series Configuration Manual page 886

886 C 57: IS-IS C
HAPTER ONFIGURATION
Figure 261 L1/L2 LSP format
Intradomain routing protocol discriminator
Length indicator
Version/Protocol ID extension
ID length
R R R
Version
Reserved
Maximum area address
PDU length
Remaining lifetime
LSP ID
Sequence number
Checksum
P ATT
Variable length fields
PDU Length: Total length of the PDU in bytes.
■
Remaining Lifetime: LSP remaining lifetime in seconds.
■
LSP ID: Consists of the system ID, the pseudonode ID (one byte) and the LSP
■
fragment number (one byte).
Sequence Number: LSP sequence number.
■
Checksum: LSP checksum.
■
P (Partition Repair): Only related with L2 LSP, indicates whether the router
■
supports partition repair.
ATT (Attachment): Generated by the L1/L1 router, only related with L1 LSP,
■
indicates that the router generating the LSP is connected with multiple areas.
OL (LSDB Overload): Indicates that the LSDB is not complete because the router
■
is running out of system resources. In this condition, other routers will not send
packets to the overloaded router, except packets destined to the networks
directly connected to the router. For example, in
Router B to forward its packets to Router C in normal condition. Once other
routers know the OL field on Router B is set to 1, Router A will send packets to
Router C via Router D and Router E, but still send to Router B packets destined
to the network directly connected to Router B.
No. of Octets
1
1
1
1
PDU type 1
1
1
1
2
2
ID length+2
4
2
1
OL IS type
Figure 262, Router A uses