IS-IS Hello/Hold Timers

Default Hello timer is 10 seconds, and the default hello multiplier is 3, so Hold time is 30 seconds.
On broadcast links the DIS will be 3 times faster meaning a Hello Timer of 3.3 seconds.

In broadcast links, Hellos are sent with a multicast MAC address;
an IIH packet is sent for each Level the router belongs to.

In point-to-point links a single IIH packet is used which has a flag denoting if it's Level-1,2 or both.
Hello packets are sent to the unicast addresses.