7.6 EIGRP for IPv4 routing Flashcards
Describe (EIGRP) Enhanced Interior Gateway Protocol
a Cisco-proprietary, balanced-hybrid routing protocol that combines the best features of distance vector and link state routing.
Describe Convergence
The process of selecting an alternate route
Describe Advertised distance (AD)
Cost to the destination network as reported by the neighbor router. Also called the reported distance (RD).
Describe Feasible distance
Lowest total cost to a destination network. Identified for each destination network and is determined as follows:
For each neighbor, the total cost to the network through the neighbor is calculated by adding the AD to the cost required to reach the neighbor router.
The router compares the total cost of all routes. The lowest total cost to the destination network is the feasible distance to the network.
Although the total cost for each neighbor route is referred to as a feasible distance, the term more correctly identifies the lowest known cost to the network, not the total cost for each reported (possible) route.
Describe Successor
Route to a destination network with the lowest total cost:
When a new route is first learned, the total cost to the successor route is used as the feasible distance to that network.
The successor is copied from the topology table into the routing table.
There can be multiple successor routes if multiple routes to the same network exist with the same lowest metric.
Describe Feasible Successor
An alternate route to a destination network. The total cost to the route through the feasible successor is higher than the total cost of successor routes. To qualify as a feasible successor route, the advertised distance of the route through that neighbor must be less than the feasible distance used for that network (AD < FD).
Be aware of the following regarding feasible successors:
Describe Diffusing Update Algorithm (DUAL)
When a route fails and the route doesn’t have a feasible successor, EIGRP uses DUAL, to choose an alternate route. DUAL sends queries to the subnet in question. When a new route is found, DUAL adds it to the routing table. Convergence can take slightly longer using DUAL.
Describe a Contiguous network
A classful network in which packets sent between subnets pass only through subnets of that same classful network without having to pass through subnets of any other classful network. In other words, the networks are side by side.
Describe a Discontiguous network
A discontiguous network is a classful network in which packets sent between subnets must pass through one or more subnets of a different classful network. The address space for the subnet sending the packets and the subnet(s) the packets pass through are different.
Router#show ip route
Displays EIGRP learned routes.
Router#show ip eigrp neighbors
Displays neighboring routers from which EIGRP routes can be learned. Lists the IP address of the connected router.
Router#show ip eigrp interfaces
Displays the interfaces that are running EIGRP and the number of connected routers.
Router(config)#router eigrp [number]
Defines an EIGRP process. The number must match between routers for information to be shared.
Router(config‑router)#network [n.n.n.n]
Router(config‑router)#network [n.n.n.n] [w.w.w.w]
Identifies a network that participates in the routing process. Networks can be specified with or without the wildcard mask. If you do not use a wildcard mask, the network address you add is automatically truncated based on classful network boundaries. You must use a wildcard mask to identify VLSM subnets.
Router(config‑router)#no auto-summary
Turns off automatic route summarization. With automatic route summarization, subnets are summarized based on classful boundaries when advertising routes on networks with a different class boundary. You must disable automatic summarization if you have a network address (such as 10.0.0.0) subnetted into smaller subnets and separated by a network with a different classful network address (such as 12.0.0.0).
