Pass the Huawei HCIP-Datacom H12-821_V1.0 Questions and answers with CertsForce

Comprehensive and Detailed Step-by-Step Explanation:

BGP ConnectRetry Timer:

The ConnectRetry timer is used when establishing a TCP connection between BGP peers.

If the connection is successful, the timer is disabled.

If the connection fails, the timer restarts, and the router attempts to reconnect after the timer expires.

Behavior:

This timer prevents excessive connection attempts and ensures efficient resource utilization.

 BGP Next_Hop Attribute

Unlike IGP, the Next_Hop attribute in BGP does not necessarily have to be the IP address of a peer interface. For example, in multi-hop BGP configurations, the Next_Hop can point to a different router or interface within the network.

 HCIP-Datacom-Core Reference

Details of the Next_Hop attribute and its behavior are outlined in BGP path selection principles​​.

VRRP defines the following states:Initialize– The router is starting up or has not joined a VRRP group.Backup– The router is in standby and monitors the Master.Master– Theonly statewhere the deviceforwards trafficfor thevirtual IP address.Only the router in theMasterstate owns the virtual MAC and responds to ARP for the virtual IP.Reference from Huawei HCIP-Datacom-Core Technology Study Guide:“In VRRP, only the Master forwards packets destined for the virtual IP address. Backup routers take over only if the Master fails.”(Chapter: VRRP Concepts – Section: State Roles and Transitions)

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)

 Transitive vs. Non-Transitive Attributes

The Community attribute is atransitive optional attribute, meaning that if a router receives a route with this attribute and does not understand its purpose, the router retains and propagates it to other peers.

Other options, such as AS_Path and MED, are well-defined mandatory or optional attributes with specific purposes.

 HCIP-Datacom-Core Reference

The behavior of optional transitive attributes is detailed in the BGP protocol and attribute chapters​​.

BGP routes have a variety ofpath attributesthat describe their characteristics and influence route selection. These attributes include well-known mandatory attributes like AS-PATH and NEXT-HOP, as well as optional attributes like MED and LOCAL_PREF.

In Huawei devices, there is aHuawei-specific attributecalled"preference", which is a local parameter used to influence BGP route selection on the device.

Key Characteristics of "preference":

It is valid only locally on the router.

It is not shared with BGP peers.

It helps the router determine the best route when multiple routes exist for the same prefix.

It appears in the BGP routing table output in lowercase aspreference.

Thus, the correct answer ispreference(entered in lowercase as required).

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

R1imports thedirect route 10.1.1.0/24intoOSPF.

This route is advertised byR1 to R2 and R3viaOSPF.

BothR2 and R3are runningIS-IS, andbidirectional route redistributionis configured between OSPF and IS-IS.

R2 and R3 bothre-advertisethe OSPF-learned route into IS-IS and then potentiallyre-learnit back from the IS-IS domain, causingredistribution loopsunless properly controlled.

Now, the question focuses onR3’s routing table:

R3 already learns the routedirectly via OSPFfrom R1.

It also learns the same route again viaIS-ISfrom 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)

Comprehensive and Detailed Step-by-Step Explanation:

Interface ID in IPv6:

Theinterface IDis the last 64 bits of an IPv6 address, and it uniquely identifies an interface within a subnet.

It can be generated in three ways:

Manually Configured:Explicitly assigned by an administrator.

System-Generated:The operating system assigns a random or pseudo-random value.

EUI-64 Standard:Generated based on the MAC address of the interface.

Correct Statement:

IPv6 supports all three methods for generating interface IDs.

In BGP, theAS-Pathattribute is mandatory and must be included in allUPDATEmessages. It records the autonomous systems a route has traversed. Attributes likeLocal-Preference,MED, andPrefvalare optional and may not always be included. TheAS-Pathis crucial for loop prevention and route selection ​.

Hello packets are the most basic and essential type of OSPF packets used for the following purposes:

Neighbor discovery– Routers use Hello packets to discover other OSPF routers on the same link.

Neighbor relationship establishment– When two routers exchange matching Hello packets, they move from the "Init" state to "2-Way" and further into adjacency states.

Neighbor relationship maintenance– Hello packets are sent periodically to ensure that neighbors are still reachable. If Hello packets are missed within the dead interval, the neighbor is considered down.

Neighbor deletionis not a direct function of Hello packets. Neighbor deletion results indirectly from missed Hello packets.