EIGRP - cbtv3 VID 38 ​- Feasible distance

Question 1

What are some of the benefits of Eigrp

Answer 1

backup routes (not topology of the whole network) fast convergence using dual algorithm
Metric ‘dual’ diffused update algorithm. This disced which route from topology table goes into routing table very fast.
Summaries anywhere
Unequal cost load balancing
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Question 2

on key advantage of Eigrp over OSPF

Answer 2

Super super fast convergence into feasible successor if successor fails.
in ospf it has to go back into topology database and recalculate new route.
EIGRP has already added feasible route and there could be many. It can super fast converge
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Question 3

What routes go into the routing table ?

Answer 3

Routing table - only the best routes go into the routing table.
But it can add more if unequal cost load balance is enabled
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Question 4

Whats is the best routes called ?

Answer 4

successor

Question 5

Whats is the 2nd best routes Called ?

Answer 5

feasible successor

Question 6

what is the primary and secondary route called ?

Answer 6

Successor - primary route
Feasible successor - 2nd route
both in Topology table

Question 7

What is an active and passive ?

Answer 7

Active route - broken & actively looking for routes
Passive - it’s passively working.
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Is it looking for new route ?
Active = Yes
Passive = No

Question 8

What is Feasible distance ?

Answer 8

how much the total cost is from me to a particular destination.

Question 9

what is Advertised distance ?

Answer 9

how far(cost) it is from the router that is telling you about the destination.

-It does not calculate cost to get to neighbour only the neighbours cost to get to destination.

(This makes sense because EIGRP is routing by rumour)
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Question 10

What is “ The Rule “

Answer 10

• To become feasible successor (backup route)
• My neighbor total cost to a destination has to be less than my total cost to the same destination.
• Advertised distance has to be has to be less then feasible distance
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  Official Rule below
  “ To be considered the feasible successor, the advertised distance must be less than the feasible distance of the successor. “
  (Not equal to but less)

Question 11

Why is the Rule a loop prevention ?

Answer 11

If advertised distance is more then
Feasible distance then there is a chance it learnt the route from me.
If it did learn it’s route from me then I’ll end up in a loop by trying to get to destination ‘A’ by using this neighbor but it will end up going through me to get to ‘A’ but my link is down hence creating a routing loop.

Question 12

What is the Fail over process

Answer 12

1 - If a link fails it first check its routing table/topology table.
To be considered the feasible successor, the advertised distance must be less than the feasible distance of the successor. (Not equal to but less)

2 - If there is no other route, it will send a query message to the neighbor even if it breaks the rule, asking does it have a route to this destination.

3 - If the reply is yes it can confirm (after testing) it definitely has a route to that destination than …

4 - It will break the rule and use this as the new successor route
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