H12-821_V1.0 Leak Questions

Let ' s break it down step by step based on Huawei ' s routing protocol behavior:

R1 imports the direct route 10.1.1.0/24 into OSPF .

This route is advertised by R1 to R2 and R3 via OSPF .

Both R2 and R3 are running IS-IS , and bidirectional route redistribution is configured between OSPF and IS-IS.

R2 and R3 both re-advertise the OSPF-learned route into IS-IS and then potentially re-learn it back from the IS-IS domain, causing redistribution loops unless properly controlled.

Now, the question focuses on R3’s routing table :

R3 already learns the route directly via OSPF from R1.

It also learns the same route again via IS-IS from R2 (looped back due to bidirectional redistribution).

Reference from Huawei HCIP-Datacom-Core Technology Study Guide:

“OSPF ASE routes are assigned a default preference of 150. If a route is redistributed from another protocol (like IS-IS) into OSPF, and then re-learned, it is considered an ASE route.” (Chapter: OSPF Advanced Features – Section: Route Redistribution Behavior)

The Forwarding Information Base (FIB) is derived from the router ' s routing table and contains the exact forwarding entries used to route packets. It directly guides packet forwarding decisions by matching incoming packets with the correct output interface or next-hop address ​.

Comprehensive and Detailed Step-by-Step Explanation:

IS-IS Area Division:

IS-IS divides areas by routers , not by links. A router is assigned to a specific IS-IS area, but it can belong to multiple levels:

Level 1: Maintains the LSDB (Link State Database) for the local area only.

Level 2: Maintains the LSDB for the backbone area and exchanges routes between areas.

Behavior of a Level 1-2 Router:

A router configured as Level 1-2 must maintain two separate LSDBs:

One for intra-area routes (Level 1).

One for inter-area routes (Level 2).

Incorrect Statement:

The statement that an IS-IS router only needs to maintain the LSDB of its area is incorrect because Level 1-2 routers maintain LSDBs for both levels.

To compress the IPv6 address 2001:0DB8:0000:C030:0000:0000:09A0, the following rules are applied:

Remove leading zeros in each hextet (e.g., 0DB8 becomes DB8).

Replace contiguous blocks of zeros with :: (only once in the address). Thus, the compressed form is 2001:DB8:0:C030::9A0 ​.