Are you preparing for the role of a Network Engineer? If yes, then it is a must to have in-depth knowledge about routing protocols. One of the in-demand routing protocols is the Enhanced Interior Gateway Routing Protocol (EIGRP).
We will cover the most frequently asked EIGRP interview questions and their answers. These questions and answers would help you to crack interviews for the network engineer and network administrator roles. EIGRP is an important concept to learn during the Cisco Certified Network Professional (CCNP) course.
Let us now begin with the list of EIGRP interview questions and answers!
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1. What do you understand by EIGRP?
EIGRP is one of the most popular routing protocols and is partially an open-source protocol made by Cisco, which stands for Enhanced Interior Gateway Routing Protocol (EIGRP), released in 1993. After 2013, it was made open for public use.
EIGRP is used for Internet Protocol (IP) networks and is a classless and advanced distance vector routing protocol used in a computer network for automating routing decisions and configurations. It is also mentioned as a hybrid routing protocol since it uses information from link-state routing protocols and distance vector routing protocols.
The primary function of EIGRP is to share routes with other routers present in an autonomous system (AS). Therefore, this routing protocol gets used in a router and is distinct from other routing protocols like RIP since it does not send updates in one go, which reduces the workload on a router where data can get transferred easily in smaller packets.
EIGRP is an advanced version of Interior Gateway Routing Protocol (IGRP). Since the networks shifted to using classless IPv4 addresses in the Internet Protocol that IGRP could not support, EIGRP got invented.
2. Mention and explain various tables used in EIGRP.
There are three types of EIGRP tables, namely-
- Neighbour table
- Topology table
- IP routing table
The explanations of these EIGRP tables are as follows-
- This table performs the task of tracking neighbour relationships.
- These help EIGRP in routing and converging.
- Whenever a new neighbour gets discovered, an entry with the address and interface of the neighbour gets made in the table.
- The command to display this table is – show IP EIGRP neighbours.
- The benefit of this table is that it allows the delivery of data packets in a sequence.
- The topology table directs a router in choosing the best route.
- This table comprises the possible and available paths in an autonomous system.
- This table includes EIGRP updated messages.
- The chosen ways get added to the respective IP routing table.
- The routes to a particular destination get saved in the IP routing table.
- It also contains details of the next hop, network ID, and cost of packet path.
3. What are the conditions for two EIGRP routers to be neighbors?
EIGRP neighbours must satisfy the following conditions-
- Both routers must be present in the same primary subnet.
- The k-values with variables such as bandwidth, load, delay, reliability, and MTU of the configured routers must be the same. The k-values represent the complete EIGRP composite cost metric. The value could lie anywhere between 0 to 128.
- The configured routers must be present in the Autonomous System (AS).
- The interfaces of the configured routers must be active. If the interfaces of the neighbouring routers are passive, they cannot send out or process “hello” messages which prevent EIGRP from forming neighbours.
The authentication and configuration of both routers must be the same.
4. Does EIGRP need an IP default-network command to propagate a default route?
Even though EIGRP can propagate a default route with the default network method, it is not required for EIGRP to use an IP default-network command. All the default routes are redistributed directly by EIGRP.
5. How many kinds of EIGRP packets are there?
There are five kinds of EIGRP packets to enable communication between two neighbouring routers, namely-
- The hello packets are the EIGRP packets sent to discover the neighbouring routers.
- If a router does not receive a hello packet within the hold time of 15 seconds, that particular router is considered ‘dead’.
- Timing allotted – 5 seconds.
- The hello packets are multicast to 220.127.116.11.
- All the routing information about destinations gets saved in these packets.
- Update packets get sent at the time of discovering new neighbours.
- Update Packets allow the formation of the topology table by the neighbour router.
- These packets can be unicast or multicast.
- These packets perform the function of sending an ‘acknowledgement’ message when an update message is received.
- You can consider it as a ‘hello’ packet without any data.
- Acknowledgement packets are always unicast.
- These are commonly known as ack packets.
- The query packets get sent when the destination enters the active state.
- These packets can be unicast or multicast.
- The query packets get used to extract specific information from a neighbour router.
- These packets get sent as a reply to the query packets by EIGRP in a router.
- These packets always get unicasted.
- They use RTP.
6. Why is EIGRP a preferred routing protocol over others like RIP?
The advantages of using the EIGRP routing protocol are as follows-
- The convergence rate of the EIGRP routing protocol is faster than other routing protocols.
- It can support both IPv4 and IPv6 networks.
- It is a hybrid routing protocol that can automate routing decisions.
- It can work efficiently in unequal cost load sharing and through Equal-Cost Multi-Path (ECMP).
- It has the least hello timer – 1 second.
- It uses the k-values concepts that measure delay, bandwidth, reliability, hop count and MTU, which causes the protocol to work more efficiently.
- It gets used for WAN routing since it provides encryption.
7. How do routers select an EIGRP routing ID?
The routers select EIGRP routing ID as follows-
- Router IDs are usually manually configured.
- If not manually configured, routers look for the highest loopback interface.
- If the loopback interface does not configure, the router looks for the highest physical interface in the ‘up/up’ state.
8. Does EIGRP support secondary addresses?
Since all the data packets get sourced from the primary addresses by EIGRP, it prioritizes finding neighbouring routers with primary addresses. It is hard to make it work with routers of primary addresses if it chooses a secondary address.
Still, EIGRP supports secondary addresses.
9. Mention all the EIGRP timer values.
EIGRP link type
Hold Dow interval
High speed link (broadcast/LAN)
Low speed links (NBMA/WAN)
10. What is the use of no-auto summary command?
The subnet mask is not visible with the routing information in EIGR by default. This command unmasks the subnet mask information and the routing information.
11. What is the feasible distance?
The feasible distance is the distance between the source and the destination network. It is the most efficient distance travelled to transfer information.
12. What is meant by ‘stuck inactive’?
The stuck inactive message is sent by a router when it does not receive a reply to its query. If the path mentioned gets erased, the “stuck inactive” message pops up.
That is all for the top most-asked EIGRP interview questions and answers. It is mandatory to first enroll in a CCNP course to learn in-depth about these routing protocols.