EIGRP Theory and Commands Flashcards
What is EIGRP?
Enhanced Interior Gateway Routing Protocol - a Cisco proprietary routing protocol, known as a hybrid protocol because EIGRP’s routing metrics use attributes used by both distance vector and link state routing protocols.
What is the name of the algorithm used by EIGRP to calculate network paths?
DUAL - Diffusing Update Algorithm
What is the protocol number used by EIGRP?
Protocol 88
What is the multicast address used by EIGRP to communicate with its neighbors?
224.0.0.10
What is the command to enable EIGRP on a Cisco router?
R1(config)# router eigrp {AS-number}
Example: router eigrp 1
What is the command to advertise a network prefix into EIGRP?
R1(config-router)# network {prefix} {wildcard-mask}
Example: network 10.1.1.0 0.0.0.255
What is the Successor Route in EIGRP?
The route from EIGRP that was the best route and installed to the routing table (RIB)
What is the Successor in EIGRP?
The first next-hop router for a given successor route.
What is the Reported Distance in EIGRP?
The metric to reach a subnet as reported by a given upstream router.
NOTE: When looking at the EIGRP topology table, the reported distance is the second number in the parenthesis next to the reporting router.
What is the Feasible Distance in EIGRP?
The value of the metric of an EIGRP route in the routing table (the Successor)
What is a Feasibility Condition in EIGRP?
When a route has a feasible distance that is “next best” to the Successor Route and could be considered the backup route.
What is a Feasible Successor in EIGRP?
The backup route that meets the Feasibility condition.
What are two things that make EIGRP unique?
1.) Maintains a topology table of all routes within an AS
2.) Only has knowledge of routes within its own AS
What symbol in the routing table (RIB) denotes an EIGRP learned route?
The letter “D”
What is the Administrative Distance of EIGRP?
90
What are the five different packet types used by EIGRP?
1.) Hello
2.) Request
3.) Update
4.) Query
5.) Reply
What are the default hello and hold down timers on a standard Ethernet connection between two EIGRP routers?
Hello is 5 seconds, Hold-down is 15 seconds
What are the default hello and hold down timers on a slow connection (like a T1) between two EIGRP routers?
Hello is 60 seconds, Hold-down is 180 seconds
What are the two elements that influence the calculation of the EIGRP metric?
1.) Worst bandwidth through the path
2.) Sum of delays
What is the newer method for calculating EIGRP called and what makes it different than the Classic Metrics?
Wide Metrics - it addresses scalability issues that come with higher speed interfaces by adding an additional K-value to the calculation.
What is the command that will display the EIGRP database information on a Cisco router?
show ip eigrp topology
What is the Reported Distance in EIGRP?
The metric that was advertised from a neighbor regarding the cost of a specific route. In other words, the advertised metric by the perspective of the neighbor device.
What is a Feasible Successor?
If more than one route exists in the EIGRP topology database, the less desirable route could be installed to the routing table if the Successor Route were to go down.
What is the Feasibility Condition for a Feasible Successor to exist?
The reported distance for the Feasible Successor must be less than the Feasible Distance of the Successor Route.
NOTE: this is to prevent loops. Keep in mind the Feasible Distance will be the advertised distance plus link delay.
What is the command to enable unequal cost load balancing when a Feasible Successor exists?
R1(config-router)# variance {multiplier}
How is the Variance Multiplier calculated against a Feasible Successor?
If the Feasible Successor’s Feasible Distance is divided by the Successor Route’s Feasible Distance and it is less than or equal to the Variance Multiplier, then the Feasible Successor will be installed into the RIB as an unequal cost load balanced path.
Example where the FS metric is 5000, the Successor metric is 3000, and the multiplier is 2.
5000 / 3000 = 1.66; Less than the variable multiplier of 2 so it will be installed in the RIB.
What is the command to specify a passive interface in EIGRP?
R1(config-router)# passive-interface {interface-id}
What are the commands to create a summary route for EIGRP?
R1(config)# interface {int-id}
R1(config-if)# ip summary-address eigrp {AS-number} {prefix}/{bits}
Example:
R1(config)# int Fa1/1
R1(config-if)# ip summary-address eigrp 1 10.0.0.0/8
