EIGRP used DUAL for metric calculation, which permits rapid convergence. This algorithm allows for the following:
-Backup route determination if one is available
-support of vlsm
-dynamic route discoveries
-Querying neighbors for unknown alternate routes
-Sending out queries for an alternate route if no route can be found
One of the best features is that the routing protocol supports all of the major L3 routed protocols using protocol-dependent modules(PDMs), those being IP,
IPX, and Apple Talk.
Route tagging is used to distinguish routes learned by different EIGRP sessions. By defining a different AS number, EGRP can run multiple sessions on a single
router.Routers using the same ASN speak to each other and share routing information, which includes the routes learned and the advertisement of topology
using hello messages, EIGRP sessions establish and maintian neighbor relationships with neighboring routers.
Once the relationship is establish, the routers then exchange route information.
The only time EIGRP advertises its entire routing table is when two neighbors initiate communication.
Uses multicast instead of broadcast. EIGRP is called a advanced distance-vector protocol although it contains properties of tboh distance-vector and link
state routing protocols.
redundant Link calculation
The topology table can store up to six routes to a destination network, meaning that EIGRP can claculate the best path for upto six redundant paths.Using the
known metrics to the destination, the router must make a decision as to which path to make its primary and which to standby, then the primary route will be added
to the routing table as active or successor and standby will be listed as passive route or the feasible successor.
The path-cost calculation decisions are made based on BW and Delay.The route with the best metric contains the lowest metric value and is chosen as a
Update and Changes :
Two final steps:
1. If route information is eventually found, the route is added to the routing table, and an update is send
2. If the response from the adjacent routers does not contain any route information, the route is removed from the topology and routing tables.
After the routing table has been updated, the new information is sent to all adjacent routers via a multicast.
Bandwidth and delay have a range of values from 0 to 4,294,967,295 in kbps
Reliability ranges from 0 to 255 , with 255 as most reliable
Load ranges from 0 to 255 , 255 means link is completely loaded.
MTU has the same range as BW
When a router has more than one routed protocol configured , each EIGRP session is defined by a autonomous system no used when enabling EIGRP.Route
redistribution is a feature that allows for the exchange of route information among multiple protocols and multiple sessions.
the external routes are flagged with EX, while the internal routes have no flag. The D stands for an EIGRP learned route.
show ip route eigrp == Shows EIGRP entries in the routing table.
show ip eigrp neighbors == Shows all EIGRP neighbors.
show ip eigrp topology == Shows entries in the EIGRP topology table.
show ip eigrp traffic ==Shows the packet count for EIGRP packets sent and received.
show ip protocols == Shows information about the active protocol sessions.
show ip eigrp events == Shows a log of EIGRP events. These are routes being added or removed from the routing table.
metric = [K1 × Bw + (K2 × Bw) / (256 – Load) + K3 × Delay] × [K5 /
(Rel + K4)]
By default: K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0.
Delay is the sum of all the delays of the links along the paths.
Delay = [Delay in 10s of microseconds] × 256.
BW is the lowest bandwidth of the links along the paths.
BW = [10000000 / (bandwidth in Kbps)] × 256.
By default, metric = bandwidth + delay.
1. When does EIGRP recalculate its topology table?
A. On a synchronized schedule
B. When an administrator uses the redirect command
C. Automatically every 120 seconds
D. Only when there is a change in the network topology
Ans : D
2. The neighbor table uses which of the following timers? (Choose all
C. Hold timer
D. FwdDelay timer
E. MaxAge timer
Ans: A B C
3. When there are no feasible successors and only one link to a destination
network, even if the link cost is set to 100,000, the link will
always be in which of the following modes?
4. Which of the following are not routed protocols supported by EIGRP?
5. What are benefits of using a link-state routing protocol? (Choose all
A. It uses the Hello protocol to establish adjacencies.
B. It uses several components to calculate the metric of a route.
C. Updates are sent only when changes occur in the network.
D. It is a better protocol than distance-vector is.
Ans: A C
6. Which route type must be redistributed by a routing protocol if other
routers are to learn about it?
B. Default routes
C. Connected routes
D. Static routes
7. Why are passive interfaces used on interfaces where the router participates
in EIGRP Global mode processes?
A. To stop unwanted route information from entering the specified
B. To allow route information to be filtered by an access list
C. To allow routes to be sent out the specified interface, but deny
route information to enter the interface
D. To allow routes to enter the interface, but deny any route information
to exit the specified interface
8. How is a feasible successor chosen when the successor fails (assuming
that a redundant route exists)? (Choose all that apply.)
A. The route with the next-lowest metric is chosen.
B. If a router doesn’t have a feasible successor, queries are multicast
to neighboring routers in search of a feasible successor.
C. The route is removed from the routing table.
D. The route is flagged as an active state.
Ans: A B
9. Which command should be used to ensure proper metric conversion
when redistributing routes from different protocols?
A. distance distance-value
10. How is EIGRP implemented on a router?
A. ip router eigrp autonomous-system-number
B. router ip eigrp autonomous-system-number
C. router eigrp process-id
D. router eigrp autonomous-system-number
11. Which of the following are not features of EIGRP? (Choose all that
A. Incremental updates
B. Only one route per destination
C. Support for IP, IPX, and AT
D. Hybrid distance-vector and link-state routing protocol
E. Not a scalable protocol
F. Hello protocol used to establish adjacencies
Ans: B E
12. Which of the following problems may occur if route redistribution
A. Non-optimal route choices
B. Slow convergence
C. Routing loops
D. All of the above
13. When using the show ip route command, which of the following codes
indicate an EIGRP learned route?
14. When using EIGRP, the process number indicates which of the
A. Link-state value
B. Autonomous system number
C. Path cost
D. Number of ACKs
15. Which of the following commands can be used to learn the number of
EIGRP packets sent and received?
A. show ip eigrp mail
B. show ip eigrp sent
C. show ip eigrp traffic
D. show ip eigrp data
E. show ip eigrp counters
19. What is the maximum number of feasible successors that EIGRP can
place in its routing table?
20. Which of the following algorithms is used by EIGRP to determine the
A. Open Shortest Path First
D. Link-state routing
E. Advanced Distance Vector