EIGRP Interview Questions
What is EIGRP?
EIGRP stands for Enhance interior Gateway routing protocol and it is enhanced distance vector and open standard routing protocol which Uses DUAL Algorithm to calculate the best path. EIGRP supports classless routing and Variable-Length Subnet Masking, route summarization, load balancing and other features.
For EIGRP neighbor-ship, what are requirements?
The following fields in a hello packet must match for routers to become neighbors
- AS number (Autonomous-System)
- Same Authentication
- Primary address should be used
What is the administrative distance of EIGRP?
EIGRP have the administrative distance of 90 for internal-routes and 170 for external-routes.
What is Active-State & Passive State in EIGRP?
A active route in EIGRP is a route which is actively trying to up, yes.. :-).. Router for which the successor-route fails and no feasible-successor route exist moves to an active state and compelling the EIGRP process to send out query-packets and for reconverge.
A passive state in EIGRP is a route which is oky and have not issue, a route for have there is an active successor route. In a stable network there will be all routes in Passive state.
Which commands are used for implementing EIGRP on Cisco Router?
Router EIGRP <AS>
What are the EIGRP Tables?
Following are the EIGRP Tables:
What is EIGRP summary route and EIGRP external route?
When we advertise the multiples routes by summarizing multiple networks/subnets such route is called a summary route. In EIGRP External routes are the routes which are redistributed in EIGRP like route of other routing-protocol or static redistributed in EIGRP.
How to turn on classless routing in EIGRP?
You can use the no auto summary command, see other cisco commands here.
What is the maximum Hop-count for EIGRP?
Maximum Hop-count for EIGRP is 255 and 100 is the default.
Is it is necessary to have the same AS on routers participating in EIGRP?
Yes, it must be same on participating neighbors. AS number means a group of EIGRP routers working on a single protocol which also defines EIGRP Limits.
What are the different types of EIGRP Packets?
There are five different types of EIGRP packet:
- Hello packets: EIGRP uses hello-packets for finding neighbors. hellos are multicast to 184.108.40.206. By default, EIGRP sends hello on every after five seconds and 60s on WAN links with 1544 Mbps speeds or less
- Acknowledgment packets: An acknowledgment packet acknowledges the reception of an update packet. It is a hello packet with no data.
- Update Packets: Update-packets contain routing information for EIGRP’s destinations. EIGRP unicasts update packets to newly found neighbors, else it multicasts update-packets to a address 220.127.116.11 when a link or metric changes. Update-packets are acknowledged to ensure reliable transmission.
- Query Packets: EIGRP sends query packets to find feasible successors path to a destination. These packets are always multicast.
- Reply Packets: EIGRP sends reply to answer to query packets. Reply-packets deliver a feasible successor path to the sender of the query packet.
How two EIGRP router become neighbors with each other?
The neighbor process among two EIGRP router is as following:
Router-A will send out a hello message to router-B
Router-B sends back a hello-msg and an update. The update have routing info about new network
Router-A acknowledges the update
Router-A sends its updates
Router-B acknowledges back
A neighbor will be remove from routing table if no hello-msg is relieved during three hello messages.
What is Advertisement-Distance, Feasible-Distance, Successor route, Feasible Successor route in EIGRP?
Advertisement Distance is the cost as reported by an EIGRP neighbor, from neighbor to its interface.
Feasible Distance is the minimum of the best cost or metric.
-Successor = It is the best route in the routing table and router used this router for going to its destination.
– Feasible Successor = A backup route that can immediately be used if the primary path for routing in case of successor route fails
Which algorithm EIGRP use for finding best path?
It uses DUAL Diffusing-update algo for finding and calculating the best path for EIGRP routes.
What are the Hello, Hold timers in EIGRP for Normal and WAN Routes?
For normal EIGRP network EIGRO send hello the every after 5sec and Hold time is 15Sec when there is fast Link having Bandwidth >1.544 Mbps . On slow links < 1.544 Mbps it will have Hello as 60 seconds and Hold timer as 180 seconds just to reduce the traffic.
Why variance command is used in EIGRP?
For unequal-cost path load-balancing, we need to define the boundary of routes that will fall in unequal path load balancing which will happen by using variance command. Variance will have multiplier “x”. If Feasible distance is 20 and variance multiplier is 3. So all route with cost or metric till 20*3= 60 will come.
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