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Rising star
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This is the Q&A from "Technical Virtual bootcamp Session 10 -Configure and Troubleshoot IP Routing - EIGRP & OSPF"


Q:Suppose we have multiple routers in EIGRP on same link, will hello packet send to all the routers or only for directly connected routers?
A:In EIGRP Hello is sent as a multicast on broadcast links.


Q: What does stuck in active mean in EIGRP ?
A: When EIGRP returns a stuck in active (SIA) message, it means that it has not received a reply to a query. EIGRP sends a query when a route is lost and another feasible route does not exist in the topology table. The SIA is caused by two sequential events:

The route reported by the SIA has gone away.

An EIGRP neighbor (or neighbors) have not replied to the query for that route.

When the SIA occurs, the router clears the neighbor that did not reply to the query. When this happens, determine which neighbor has been cleared. Keep in mind that this router can be many hops away.


Q:How much time router will be stuck in active?
A:old code takes 3 min, new code up to 6 min.


Q:What is EIGRP summary route?
A:when you use the command 'ip summary-address x.x.x.x mask' it summarizes all the networks under that summary over that link before advertising. 


Q:What command or indication will show the best route in topology in eigrp?
A:show ip eigrp topology x.x.x.x/yy shows the topology. The best path shows on top. 


Q:Why do we need backbone area in OSPF?
A:The backbone area is created to create a hierarchical design in OSPF. Basically, we want all routes in OSPF to flow through area 0 or the backbone. It helps us keep track of all the networks and hence have a complete view of the topology.


Q:If BFD is configured in OSPF, and neighbourship down intermittently then what could be causes of this?
A:BFD or Bidirectional Forwarding detection is something that is used to detect link failures or intermittent link issues. It’s important to remember that BFD does not have anything to do with OSPF.It runs independent of OSPF. And if the link flaps BFD flaps and BFD tells OSPF to take itself down.Basically it’s not an OSPF feature but a feature on the router to speed up convergence.


Q:Is MTU also affected neighbor relationship?
A: yes in OSPF the IP MTU need to be the same between both neighbors.


Q:As OSPF uses LSA to exchange the network, how do we filter specific subnets to filter and come into the area?
A: Remember in OSPF you can only filter on two types of routers either ABR or ASBR So on ABR you can area X filter-list  in/out command to filter type3-LSA coming in or out between areas.


Q:What is DR other?
A:A router other than a DR on a broadcast segment from the perspective of the DR and BDR,  So basically it’s not DR or BDR but it is something 'other' than DR hence DR Other.


Q:In a one OSPF area how much router can be configure?
A:It is recommended to have at max 50 router per OSPF area.


Q:More than one OSPF process can be configured on one particular router, where do we need to configure that when it is required to run more than one process?
A:When you configure more than one OSPF process they create two different OSPF databases and run as two different processes. So basically it keeps the two separate in terms the effect of changes. You basically need to redistribute between the two processes in OSPF for the routes from one process to go to the other one.

Q:How to check advertised routes from an interface of an EIGRP router?
A:You don't have a command to check the routes being advertised from a particular interface, like bgp has 'show ip bgp neighor x.x.x.x advertised-routes’ is this what you meant?,you can check sh ip route and include the interface to see the routes learnt over that but that’s about it. 


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