Top EIGRP Interview Questions (2024)
What is EIGRP?
What are the advantages of EIGRP over other routing protocols?
How does EIGRP work?
How do you enable EIGRP on a Cisco router?
How does EIGRP calculate the metric for route selection?
How do you configure load balancing in EIGRP?
What is the administrative distance in EIGRP?
What is the difference between EIGRP classic and EIGRPv6?
How does EIGRP achieve fast convergence?
How does EIGRP handle route summarization?
What is the meaning of the EIGRP stuck in active (SIA) state?
How can you troubleshoot EIGRP neighbor adjacency issues?
How do you verify EIGRP neighbor adjacencies?
What is the default administrative distance for external EIGRP routes?
How do you configure EIGRP authentication?
Q: What is EIGRP?
Ans:
Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-proprietary advanced distance-vector routing protocol used for complex IP routing within a network. It functions at the network layer and includes features of both distance-vector and link-state routing protocols.
Q: What are the advantages of EIGRP over other routing protocols?
Ans:
EIGRP has several advantages, including:
- Low bandwidth consumption: EIGRP only transmits updates when there is a change and uses incremental updates, which lowers bandwidth usage.
- Equal-cost load balancing across several paths is supported by EIGRP for load balancing.
- Rapid convergence: In the event that the network topology changes, EIGRP uses the Diffusing Update Algorithm (DUAL) to provide rapid convergence.
- EIGRP includes advanced functionality such as route summarization, route filtering, and authentication.
Q: How does EIGRP work?
Ans:
The Diffusing Update Algorithm (DUAL) is used by EIGRP to determine the optimum route to a target network. It keeps track of a topology table and a routing table, sharing routing data via hello packets and updates with nearby routers. EIGRP groups routers based on the principle of autonomous systems (AS).
Q: How do you enable EIGRP on a Cisco router?
Ans:
Users must perform the following actions in order to enable EIGRP on a Cisco router:
- Specify global configuration mode: configure terminal
- Enable EIGRP:
router eigrp [AS number] - Configure EIGRP networks:
network [network_address] - User can also specify additional options, such as timers and authentication.
- Exit configuration mode:
exit - Save the configuration:
copy running-config startup-config
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Q: How does EIGRP calculate the metric for route selection?
Ans:
EIGRP determines the metric depending on the path's MTU (Maximum Transmission Unit), bandwidth,
delay, reliability, load, and other factors. By default, the metric calculation just considers
bandwidth and delay.
Formula for calculating the EIGRP metric:
metric = (K1 * bandwidth) + (K2 * bandwidth) / (256 - load)
+ (K3 * delay) + (K5 * sum of reliability)/(K4 + reliability) * 256
Q: How do you configure load balancing in EIGRP?
Ans:
Load balancing is supported by EIGRP by default. It is necessary to make sure that all of the paths have equal metrics before configuring load balancing. This can be done by configuring each parallel link's bandwidth and delay to be the same or by adjusting the metric weights using the metric weights command.
Q: What is the administrative distance in EIGRP?
Ans:
Routers utilize the metric of administrative distance to assess the reliability of a routing system. EIGRP routes are given preference over those from other routing protocols whose administrative distances are higher since EIGRP's administrative distance is 90 by default.
Q: What is the difference between EIGRP classic and EIGRPv6?
Ans:
For IPv4 networks, EIGRP classic is utilized, while for IPv6 networks, EIGRPv6 is used. IPv6 addressing is used by EIGRPv6, which is an extension of EIGRP. In contrast to EIGRPv6, EIGRPv4 has different packet formats, message types, and configuration commands.
Q: How does EIGRP achieve fast convergence?
Ans:
DUAL (Diffusing Update Algorithm) is used by EIGRP to achieve fast convergence. In the event of a topology change, DUAL enables routers to immediately identify loop-free paths and converge on a new best path. When a network change happens, routers communicate about it and use DUAL to determine the new routes.
Q: How does EIGRP handle route summarization?
Ans:
Route summarization is supported by EIGRP, which helps in minimizing the size of the routing
table. When more than one subnet can be represented by a single summary route, summarization is
completed. Under the EIGRP configuration, this can be configured using the
summary-address command.
Q: What is the meaning of the EIGRP stuck in active (SIA) state?
Ans:
When a router is unable to identify an appropriate successor for a route, it enters the SIA (Stuck in Active) state in EIGRP. To locate a different route, it queries its neighbors. A router enters the SIA state if no response is received after a predetermined amount of time. This may result in unstable routing and longer convergence times.
Q: How can you troubleshoot EIGRP neighbor adjacency issues?
Ans:
Follow these steps to troubleshoot EIGRP neighbor adjacency problems:
- Examine both routers EIGRP configurations for issues.
- A firewall rule or access-list that is preventing EIGRP packets should be checked.
- Check that the routers authentication settings and EIGRP AS numbers are same.
- Check to see if the routers connected interfaces are active and functioning.
- Make sure both interfaces IP addresses and subnet masks are set up properly.
- To find out more, use debugging commands like
debug eigrp packetsordebug eigrp neighbors.
Q: How do you verify EIGRP neighbor adjacencies?
Ans:
The following commands can be used to confirm EIGRP neighbor adjacencies:
show ip eigrp neighbors: Shows a list of EIGRP neighbor along with information about each of them.show ip eigrp topology: Shows the routes discovered across neighboring networks in the EIGRP topology table.show ip route eigrp: Shows the routes chosen for forwarding in the EIGRP routing table.
Q: What is the default administrative distance for external EIGRP routes?
Ans:
By default, external EIGRP routes have a 170 administrative distance. In other words, internal EIGRP routes are given priority over external ones.
Q: How do you configure EIGRP authentication?
Ans:
The security provided by EIGRP authentication is achieved by having a password while creating neighbor adjacencies. Users can use these steps to configure EIGRP authentication:
- EIGRP configuration mode :
router eigrp [AS number] - Activate authentication using
authentication mode [md5 | text] - The authentication key should be set as follows:
authentication key-chain [key_chain_name] - Create the key chain with password by following configurations:
key chain [key_chain_name], followed by key [key_id] and key-string [password] - Save the configuration and exit the EIGRP configuration mode.