What three major tasks are performed by a Designated Intermediate System in an ISIS
pseudonode environment? (Choose three.)
A.
updating the pseudonode LSP
B.
maintaining pseudonode link-state information
C.
creating the pseudonode LSP
D.
flooding LSPs over the LAN
E.
election of the pseudonode
Explanation:
Two major tasks are performed by the DIS:
· Creating and updating pseudonode LSP for reporting links to all systems on the broadcast
subnetwork. See the Pseudenode LSP section for more information.
· Flooding LSPs over the LAN.
Flooding over the LAN means that the DIS sends periodic complete sequence number protocol
data units (CSNPs) (default setting of 10 seconds) summarizing the following information:
LSP ID
Sequence Number
Checksum
Remaining Lifetime
The DIS is responsible for flooding. It creates and floods a new pseudonode LSP for each routing
level in which it is participating (Level 1 or Level 2) and for each LAN to which it is connected. A
router can be the DIS for all connected LANs or a subset of connected LANs, depending on the
IS-IS priority or the Layer 2 address.
The DIS will also create and flood a new pseudonode LSP when a neighbor adjacency is
established, torn down, or the refresh interval timer expires. The DIS mechanism reduces the
amount of flooding on LANs.