Which statement is true about IS-IS hello (IIH) PDUs?

A.
The same IIH PDU is used for both point-to-point and broadcast networks.

B.
IIH PDUs maintain the link-state database synchronization.

C.
IIH PDUs provide the priority value used in DIS election.

D.
IIH PDUs are transmitted only at the beginning of adjacency establishment.

Explanation:
By default, IS-IS advertises a maximum of three areas in the IS-IS hello (IIH) PDUs and link-state PDUs. To advertise more than three ISO network addresses for a router, include the max-areas statement:
max-areas number; The range that you can configure is from 3 through 36, and the default is 3. This value is included in the Maximum Address Area field of the IS-IS common PDU header included in all outgoing PDUs.
NOTE: The maximum number of areas you can advertise is restricted to 36 to ensure that the IIH PDUs have enough space to include other type, length, and value (TLV) fields, such as the Authentication and IPv4 and IPv6 Interface Address TLVs.

By default, the routing device sends one link-state PDU packet out an interface every 100 milliseconds. To modify this interval, include the lsp-interval statement:
lsp-interval milliseconds;
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
To disable the transmission of all link-state PDU packets, set the interval to 0