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L1_A IS in area 2 must have area 1’s address added to its configuration and the L1
IS in area 1 must have area 2’s address added to its configuration. For areas 3 and
4 to be synonymous, each area’s address must be added to the others L1 IS.
IS to IS Hello (IIH) Message
The IIH message enables an IS to determine the existence of other ISs and to
establish adjacencies. There are three types of IIH messages: L1, L2, and
point-to-point.
Each IS contains a local hello timer and holding timer. Each time the hello timer
expires, an IIH is multicast over the IS’s interface to any adjacent ISs. When the
hello message is received, the recipient establishes or updates (refreshes) the
adjacency information. This information remains current for amount of time
(seconds) specified by the holding timer. If the holding timer expires, the adjacency
is brought down.
L1 IIH Message
The L1 IIH message is multicast over the interface when its local hello timer
expires. The L1 IS places the following information in its IIH:
v Source ID
v Any manual area addresses that it services
N1
N1
N1
N1
N2
N2
N2
N2
N3
N3
N3
N3
Area 1
Area 3
Area 2
Area 4
L1
L1
L1_A
L1/L2
L1
L1
L1
L1
Synonymous
Area
Synonymous
Area
L2
L2
Figure 25. Synonymous Areas
Using OSI/DECnet V
292
MRS V3.2 Protocol Config Ref Vol 2