Exam HPE6-A73 topic 1 question 26 discussion

Answer is A, question is asking about OSPF routing changes and not about the neighbour going down. BFD is useful only when neighbour goes down. If you aggregate routes then there will be less chance of the individual routing change impacting this router

On ACSP Learning book, chapitre 6 Advanced OSPF section "Need for Route and LSA Aggregation Between Areas" : Router do not require granular knowledge of other area : - Causes unnecessary disruptions when small changes occur - Clutter the LSDB and routing table Simply dividing an AS into multiple areas begins to decrease the size of OSPF router's LSDBs and to reduce the complexity of SPF calculations. However, to achieve the true benefits of multiple areas, you should further reduce the number of LSAs advertised between areas... You need to aggregate the Type 3 LSAs to hide the unnecessary information and to smooth over small changes, thereby gaining the true benefits of a multiple area OSPF configuration" & Question is talking about OSPF routing changes, BFD is used when neighbor is down.

Page 368 Study Guide

Should be B. Fast convergence, including features like BFD, VSX operations with OSPF and OSPF graceful restart

BFD " We can tune timers for fast convergence, for example OSPF can be configured to use a dead interval of only one second. The problem however is that all of these protocols were never really designed for sub-second failover. Hello packets and such are processed by the control plane so there is quite some overhead. BFD was designed to be fast, its packets can be processed by some interface modules or line cards so there isn’t much overhead. BFD runs independent from any other (routing) protocols. Once it’s up and running, you can configure protocols like OSPF, EIGRP, BGP, HSRP, MPLS LDP etc. to use BFD for link failure detection instead of their own mechanisms. When the link fails, BFD will inform the protocol. "

A: the question implies a routing update has occurred so route aggregation is the only suitable answer

i think B makes most sense in this scenario. It is one VSX is AGGREGATION layer, not Core Layer, and affect the service from Access layer. when i see the route aggregation in A, the first the that came to mind is ABR. BTW, in study guide, Aruba explained the BFD and how to use it direct after the chapter OSPF Failover and Convergence.

OSPF aggregation combines groups of routes with common addresses into a single routing table entry. However, The Bidirectional Forwarding Detection (BFD) protocol is a simple hello mechanism that detects failures in a network. The question says "network changes occur," which in case a link failure or link flap, where BFD fits well.

For me, A makes most sense. As these are aggregation switches, aggregating the routes makes sense. B (BFD) concerns with a peer being not reachable anymore, so it does not apply in this case. C won't help, as it concerns also the reachability of peers. I fail to see the benefit in respond time of D

While I can certainly see that B would be the the answer, as it provides faster detection when a neighbor fails, the question states that the Administrator is concerned about network changes, and that the Agg-pair will respond slowly. Wouldn't Graceful Restart be the best option here?

The question is about an aggregation switch and not about a core, therefore A makes the most sense... B,C and D would make sense if we were talking about the Core.

BFD - those echos will fail faster than the ospf hello/dead timers.

B will reduce neigbor failure detection, aggregating route will reduce the possibility of route calculation when topology change

B is correct (Book 437 & 438)

B is correct (Book 437 & 438)

The correct Answer is B

I think the answer is B "BFD tests the connectivity between two IP addresses in a BFD session. BFD reports when connectivity is lost. The router (or routing switch) can then use that information to take the appropriate actions, depending on the functions to which you have tied BFD"