Is-Is Pdus - HP FlexFabric 12900E Series Configuration Manual

As shown in
adjacency with each other.
Figure 38 DIS in the IS-IS broadcast network
L2 adjacencies
L1 adjacencies
The DIS creates and updates pseudonodes, and generates LSPs for the pseudonodes, to describe
all routers on the network.
A pseudonode represents a virtual node on the broadcast network. It is not a real router. In IS-IS, it is
identified by the system ID of the DIS and a 1-byte Circuit ID (a non-zero value).
Using pseudonodes simplifies network topology and can reduce the amount of resources consumed
by SPF.
NOTE:
On an IS-IS broadcast network, all routers establish adjacency relationships, but they synchronize
their LSDBs through the DIS.

IS-IS PDUs

PDU
IS-IS PDUs are encapsulated into link layer frames. An IS-IS PDU has two parts, the headers and
the variable length fields. The headers comprise the PDU common header and the PDU specific
header. All PDUs have the same PDU common header. The specific headers vary by PDU type.
Figure 39 PDU format
PDU common header
Table 11 PDU types
Type
15
16
17
18
20
24
25
Figure 38, the same level routers on a network, including non-DIS routers, establish
L1/L2
L1
DIS
PDU specific header
PDU Type
Level-1 LAN IS-IS hello PDU
Level-2 LAN IS-IS hello PDU
Point-to-Point IS-IS hello PDU
Level-1 Link State PDU
Level-2 Link State PDU
Level-1 Complete Sequence Numbers PDU
Level-2 Complete Sequence Numbers PDU
L1/L2
L2
DIS
Variable length fields (CLV)
137
Acronym
L1 LAN IIH
L2 LAN IIH
P2P IIH
L1 LSP
L2 LSP
L1 CSNP
L2 CSNP