Huawei H12-821_V1.0 Based on Real Exam Environment

 IS-IS Overview: Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol. Routers exchangeLink State Packets (LSPs)to maintain a synchronized link-state database. These LSPs are categorized intoLevel-1 LSPs(intra-area routing) andLevel-2 LSPs(inter-area routing). Both types share the same packet format.

HCIP-Datacom-Core Technology Training Material (IS-IS LSPs and Packet Structure)​​.

 LSP ID Format: The LSP ID uniquely identifies each LSP and ensures accurate routing information. It comprises the following components:

System ID (C): A 6-byte identifier assigned to each router, derived from the router's NET (Network Entity Title). This identifier ensures unique identification of routers within the IS-IS domain.

Pseudonode ID (B): Assigned when a router acts as a Designated Intermediate System (DIS) on a broadcast network. It differentiates LSPs generated by the DIS from other routers.

LSP Number (A): A 1-byte field indicating the sequence number of the LSP. It helps distinguish multiple LSPs generated by the same router for the same level.

The operator betweenif-matchclauses under a node is AND, meaning all conditions must be satisfied. However, the operator between nodes is OR, meaning a route matching any node will pass the route-policy ​.

In BGP and other TCP-based protocols like OSPF and IS-IS, when devices havedifferent Hold Times, thesmaller value is chosenafter negotiation. This ensuresfaster detectionof communication loss.

The Keepalive and Hold Timers are negotiated during the establishment of a BGP session.

The smaller Hold Timeis used to maintain symmetry and prevent timeouts.

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

“When negotiating Hold Time, both ends agree to use the smaller of the two values. This value is used to detect failures faster.”

(Chapter: BGP Fundamentals – Section: BGP Session Establishment)

Inasynchronousmode, the local device sends BFD control packets at predefined intervals, and the remote device monitors the receipt of these packets to detect connectivity issues. This is one of the two operating modes in BFD, the other beingdemandmode ​.