EIGRP Interview Questions & Answers

What is EIGRP?

EIGRP is a Routing Protocol used for IP Networks. It is classless, Distance Vector & Hybrid type of Routing protocol. It was released in 1993.

Is EIGRP a Cisco proprietary protocol or open source protocol?

EIGRP is partially open source routing protocol.

It was a Cisco proprietary protocol till 2013. Then Cisco submitted a portion of EIGRP to the IETF for consideration as a potential standard. The entire protocol has not yet been accepted as a standard and remains proprietary to Cisco.

Therefore, some portion of EIGRP is open standard & some portion of it is still Cisco proprietary.

Is EIGRP a Cisco proprietary protocol or open source protocol?

EIGRP is partially open source routing protocol.

What is EIGRP SIA (Stuck In Active) condition?

EIGRP Stuck in Active is the condition when a route becomes unreachable and not all queries for it are answered.

What is EIGRP FD (Feasible Distance)?

EIGRP Feasible Distance is the cost to the next hop as well as Administrative Distance.

What is EIGRP RD (Reported Distance)?

EIGRP Reported Distance is the distance (metric) towards a destination as advertised by an upstream neighbor.

What is EIGRP FS (Feasible Successor)?

EIGRP Feasible Successor is a backup route that can be used in the event of a topology change without having to recalculate routes” “A particular destination to a next hop router that is guaranteed not to be a part of a routing loop”

How does EIGRP Router ID is elected?

Cisco routers use the following order to select EIGRP router ID:

1. Router ID (manually configured)
2. Highest loopback interface, if router ID is not configured
3. Highest Physical interface in “up/up” state (if loopback interface is not configured)

What are EIGRP timer (EIGRP Intervals) values?

Below are EIGRP Timer values:

What is an EIGRP Stub Router?

A Router through which core transit traffic should not flow. It advertises only a subset of routes and is omitted from the route query process.

What is EIGRP Stub Routing?

Stub routing is an EIGRP feature which has been designed to conserve local router resources, such as memory and CPU, and improve network stability. The stub routing feature is most commonly used in hub-and-spoke networks.

How many types of EIGRP packet types do we have?

EIGRP has five types of Routers which are:

1. Hello
2. Update
3. Query
4. Reply
5. ACK

Does EIGRP has any loop prevention mechanisms?

Yes, EIGRP has two major loop prevention mechanisms:

1. Split horizon
2. DUAL (Diffusing Update Algorithm)

What are the differences between EIGRP Classic mode & EIGRP Named mode?

How many EIGRP (DUAL) status flags are there in EIGRP? What is the usage of each flag?

Below are EIGRP status flags:

P (Passive): Indicates an available and stable network which can be installed into the Routing Table

A (Active): Indicates an unavailable network which has outstanding queries and cannot be installed into the Routing Table

U (Update): Indicates that a network is being updated and the Router is waiting for an Ack for the update packet

Q (Query): Indicates that a network has an outstanding Query or the Router is waiting for an Ack for a Query Packet

R (Reply): Indicates that the Router is generating a reply for the network or is waiting for an Ack for the reply packet

r (Reply Status): Indicates that the Router is waiting for the Reply to a Query packet from a neighboring Router

How many EIGRP Tables are there in EIGRP?

There are three tables in EIGRP:

1. Neighbor Table: All Adjacent Routers List
2. Topology Table: LSA’s Table (complete info about the networks in same area)
3. Routing Table: Best Routes

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