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ICND2 – EIGRP Questions 3

October 12th, 2017 in ICND2 200-105 Go to comments

Question 1

Explanation

The “show ipv6 eigrp neighbors” command displays the neighbors discovered by the EIGRPv6. Notice that the neighbors are displayed by their link-local addresses.

show_ipv6_eigrp_neighbors.jpg

Question 2

Explanation

From the routing table we learn that network 192.168.10.0/30 is learned via 2 equal-cost paths (192.168.10.9 &192.168.10.5) -> traffic to this network will be load-balancing.

Question 3

Explanation

To configure EIGRP for IPv6 we must explicitly specify a router ID before it can start running. For example:

ipv6 router eigrp 1
eigrp router-id 2.2.2.2
no shutdown

Notice that EIGRP for IPv6 router-id must be an IPv4 address. EIGRP for IPv4 can automatically pick-up an IPv4 to use as its EIGRP router-id with this rule:
+ The highest IP address assigned to a loopback interface is selected as the router ID.
+ If there are not any loopback addresses configured, the highest IP address assigned to any other active interface is chosen as the router ID

EIGRPv3 also uses the AS number (for example: ipv6 eigrp 1 under interface mode).

Question 4

Explanation

When a packet with destination IP address of 10.1.1.4 arrives at HokesB, it will look up in the routing table to find the most specific path. In this case no path is found so HokesB must inform to the source host that the destination is unreachable on the interface it has received this packet (it is Fa0/0 because the network 192.168.2.0/28 is learned from this interface). So the best answer here should be C – send an ICMP message out of Fa0/0.

Question 5

Explanation

First we must notice that all the 4 answers are parts of the “show ip eigrp topology” output. As you can see, there are 2 parameters in the form of [FD/AD] in each answer. For example answer C has [46152000/41640000], it means that the FD of that route is 46152000 while the AD is 41640000.

To become a feasible successor, a router must meet the feasibility condition:

To qualify as a feasible successor, a router must have an AD less than the FD of the current successor route

In four answer above, only answer B has an AD of 128256 and it is smaller than the FD of the current successor route (41152000) so it is the feasible successor -> B is correct.

Question 6

Explanation

Feasible successor is a route whose Advertised Distance is less than the Feasible Distance of the current best path. A feasible successor is a backup route, which is not stored in the routing table but stored in the topology table.

Question 7

Explanation

The formula to caculate EIGRP metric is:

metric = [K1 * bandwidth + (K2 * bandwidth)/(256 – load) + K3 * delay] * [K5/(reliability + K4)]

By default, K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0 which means that the default values use only bandwidth & delay parameters while others are ignored. The metric formula is now reduced to:

metric = bandwidth + delay

Note: But remember the bandwidth here is defined as the slowest bandwidth in the route to the destination & delay is the sum of the delays of each link.

Question 8

Question 9

Explanation

When a router has no EIGRP feasible successor and the successor route to that destination network is in active status (the successor route is down, for example) a route recomputation occurs. A route recomputation commences with a router sending a query packet to all neighbors. Neighboring routers can either reply if they have feasible successors for the destination or optionally return a query indicating that they are performing a route recomputation. While in Active state, a router cannot change the next-hop neighbor it is using to forward packets. Once all replies are received for a given query, the destination can transition to Passive state and a new successor can be selected.

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f07.shtml#rout_states)

Comments (1) Comments
  1. Yoyo
    November 11th, 2017

    Explanation for 8; It is based on classfull routing

    10.0.0.0 /8 -> Class A, so it’s subnet mask is 255.0.0.0 or /8
    172.16.0.0/16 -> Class B, with a subnet mask is 255.255.0.0 or /16
    192.168.1.0/24 -> Class C, with a subnet mask is 255.255.255.0 or /24