An administrator has an aggregation layer of 8325CX switches configured as a VSX pair. The administrator is concerned that when OSPF network changes occur, the aggregation switches will respond to the changes slowly, and this will affect network connectivity, especially VoIP calls, in the connected access layer switches.
What should the administrator do on the aggregation layer switches to alleviate this issue?
In situations where network responsiveness is critical, especially with services like VoIP that can suffer from disruptions, implementing Bidirectional Forwarding Detection (BFD) is highly beneficial. BFD provides rapid detection of faults in the forwarding path between two routers, usually in milliseconds, which allows for faster failover and reduces the impact on network connectivity. This mechanism functions independently of any particular routing protocol, ensuring that any failures are swiftly reported, and corrective actions can be taken immediately, thereby alleviating concerns about the slow response to OSPF network changes.
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
100% Agree. Answer is A. "Network Changes" mean route table updates not neighbors going down which would be the only reason B would make sense.
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.
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"
It states " BFD reports when connectivity is lost." So this is about a peer failure, not a routing change. That's why I think A is correct
Page 368 Study Guide
The correct Answer is B
B will reduce neigbor failure detection, aggregating route will reduce the possibility of route calculation when topology change
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 " 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. "
B is correct (Book 437 & 438)
B is correct (Book 437 & 438)
BFD - those echos will fail faster than the ospf hello/dead timers.
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?
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
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.
A: the question implies a routing update has occurred so route aggregation is the only suitable answer
Should be B. Fast convergence, including features like BFD, VSX operations with OSPF and OSPF graceful restart
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.