3Com Switch 7700 Configuration Manual page 145

By default, the Hello failure interval is 30 seconds. If the level is not specified, it
defaults to setting the Hello packet failure interval Level-1.
Setting the Priority for DIS Election
In the broadcast network, the IS-IS needs to elect a DIS from all the routers.
In IS-IS, both a Level-1 and a Level-2 DIS are selected, based on priority. An
IS/router with a higher priority will be selected as DIS over a router with a lower
priority. If there are two or more routers with the highest priority in the broadcast
network, the one with the greatest MAC address will be selected. If all the
adjacent routers' priorities are 0, the one with the greatest MAC address will be
selected.
The DISs of Level-1 and Level-2 are elected separately. You can set different
priorities for DIS election at different levels.
Perform the following configuration in VLAN interface view..
Table 64 Setting Priority for DIS Election
Operation
Set the priorities for DIS election on the
interface
Restore the default priorities for DIS election
on the interface
By default, the interface priority is 64. If the level is not specified, it defaults to the
priority of Level-1.
Setting the Interface Circuit Level
Perform the following configuration in VLAN interface view..
Table 65 Setting the Interface Circuit Level
Operation
Set the interface circuit level
Restore the default interface circuit level
You can set the circuit level to limit what type of adjacency can be established for
the interface. For example, a Level-1 interface can only establish a Level-1
adjacency. A Level-2 interface can only establish a Level-2 adjacency. For the
Level-1-2 router, you can configure some interfaces as Level-2 to prevent
transmitting Level-1 Hello packets on the Level-2 backbone and conserve
bandwidth. However Level-1 and Level-2 use the same kind of Hello packet over
the p2p link, and therefore such a setting is unnecessary.
By default, the circuit-level on an interface is level-1-2.
Setting IS-IS Authentication
Setting IS-IS authentication involves tasks described in the following three
sections.
Command
isis dis-priority value [ level-1 | level-2 ]
undo isis dis-priority [ level-1 | level-2 ]
Command
isis circuit-level [ level-1 | level-1-2 | level-2
]
undo isis circuit-level
IS-IS 137