Question 1 –Tell us something about EIGRP?
- Its an Enhancement of IGRP.
- IGP and Hybrid Routing Protocol.
- Was an Cisco Proprietary routing protocol till 2013. Now open standard.
- Its metric is an composite metric in which by default bandwidth & delay are considered.
- Uses DUAL (Diffusing Update Algorithm) to find best route from source to destination.
- Don’t use TCP or UDP. Works on top of IP using Protocol number 88.
Question 2 –What is the metric in EIGRP?
- Composite Metric.
- It don’t consider single criteria to calculate the metric but uses number of criteria which includes Bandwidth , Load , Delay ,Reliability and MTU.
- The weightage of these criteria's is defined by something know as K values i.e. Metric Weight.
- By default K values for Bandwidth and Delay are 1 . Hence while calculating the metric only Bandwidth and Delay are considered.
Question 3 –What is criteria for EIGRP Neighborship?
- Must be directly connected.
- Must belong to same AS.
- K values must match.
- Interfaces primary IP address must be in the same subnet.
- Must not be passive on the connected interface.
- Must pass neighbor authentication (incase it is configured).
Note :- Passive interface – Don’t send or receive update on that interface.
EIGRP supports MD5
Question 4 –Tell us about control packets in EIGRP?
“H Q U R A”
- Hello – Establish neighbor relationship. – UDP , Mulitcast
- Query – Ask neighbor about routing information.-TCP , Unicast / Multicast
- Update – Send routing update.-TCP , Unicast / Mulicast
- Reply – Respond to the Query packet –TCP , Unicast
- Acknowledgement – Acknowledgement of an reliable packet – UDP / Unicast
Note: EIGRP use Multicast Address -220.127.116.11
Question 5 –What are the AD values in EIGRP?
- Internal EIGRP – 90
- External EIGRP – 170
- Summary EIGRP - 5
Question 6 –What are the External routes in EIGRP?
- The routes learned from Different AS (in EIGRP) or Different Routing Protocols (like OSPF , RIP etc.) are known as External Routes.
- These routes are less trusted and hence have AD value -170.
- In routing table Internal Routes appears as “ D “ whereas External Routers appears as “D EX”.
Question 7 –What is Feasibility condition in EIGRP?
- When EIGRP calculates the best route (Successor –Routing, Topology table) it will also calculate next best route (Feasible Successor –Topology table).
- But EIGRP to calculate the Feasible Successor need to meet the rule of DUAL which is know an Feasibility condition in EIGRP.
- It says that “ a route to become Feasible Successor its Advertised Distance (AD) value should be less than the Current Successor’s Feasible Distance (FD) value.
Note :- Advertised Distance (AD) value - Cost between Next-Hop and Destination.
Feasible Distance (FD) value – Cost between local router and Destination.
Question 8 –Timers in EIGRP?
- On higher bandwidth links (equal to greater than T1 – 1.54 Mbps) the hellos are sent every 5 secs. whereas for lower bandwidth links (less than T1) the hellos are sent every 60 secs.
- Hold down timers are 3 times the Hello timers.
Question 9 –What is SIA in EIGRP?
- When an EIGRP routers loses a route to a destination and don't have any Feasible successor for the destination network .then the EIGRP will mark the route as Active and send EIGRP Query messages to its neighbors .These Query message contains the query regarding the route to reach destination.
- Until the router receives reply for all the sent queries no successor is selected.
- The EIGRP router will wait for 3 minutes for the reply of the Queries sent by it and if it don’t receive an reply the router becomes in Stuck in Active and reset the neighbor relationship with the neighbor that didn’t not reply.
Question 10 –How EIGRP achieve Load balancing over unequal metric paths?
- By default EIGRP can perform load balancing on 4 equal metric paths.
- By using Max –paths commands load balancing can be achieved on 16 equal metric path.
- EIGRP can achieve Load balancing over unequal metric paths using “Variance “command.
- Variance is a multiplier (1-128).
- Traffic will be load balanced on the links that has metric less than the best multiplied by the Variance.