Chapter 4: Fundamental Eigrp Concepts

Front 1

EIGRP Configuration Overview

Back 1

1. Neighboring routers' router eigrp asn commands must be configured with the same ASN parameter to become neighbors.
2. Cisco IOS enables only EIGRP on interfaces matched by an EIGRP network command. When enabled the router will attempt to discover EIGRP neighbors on that interface by sending multicast EIGRP Hello messages and Advertise to other neighbors about the subnet connected to the interface.
3. If no wild card mask is configured on the EIGRP network command, the command's single parameter should be a classful network number.
   
4. If no wildcard mask is configured on the EIGRP network command, the command enables EIGRP on all of that router's interfaces directly connected to the configured network.
5. If the network command includes a wildcard mask, the router performs access control list logic when comparing the net-id configured in the network command with each interface's IP address, using the configured wildcard mask as an ACL wildcard mask.
   

Front 2

List the working interfaces on which EIGRP is enabled (based on the network commands); it omits passive interfaces.

Back 2

show ip eigrp interfaces

Front 3

Lists the contents of the network configuration commands for each routing process, and a list of neighbor IP addresses.

Back 3

show ip protocols

Front 4

Lists known neighbors; does not list neighbors for which some mismatched parameter is preventing a valid EIGRP neighbor relationship.

Back 4

show ip eigrp neighbors

Front 5

Lists all successor and feasible successor routes known to this router. It does not list all known topology details.

Back 5

show ip eigrp topology

Front 6

Lists the contents of the IP routing table, listing EIGRP-learned routes with a code of D on the left side of the output.

Back 6

show ip route

Front 7

EIGRP Neighbor Discovery

Back 7

EIGRP routers send Hello messages to discover potential neighboring EIGRP routers and perform basic parameter checks to determine which routers should become neighbors.

Front 8

EIGRP Topology Exchange

Back 8

Neighbors exchange full topology updates when the neighbor relationship comes up, and then only partial updates as needed based on changes to the network topology.

Front 9

EIGRP Choosing Routes

Back 9

Each router analyzes its respective EIGRP topology table, choosing the lowest-metric route to reach each subnet.

Front 10

EIGRP Multicast Address

Back 10

224.0.0.10

Front 11

EIGRP Metric Calculation (Default K-Values)

Back 11

Metric = ((10^7/least-bandwidth) + cumulative-delay)*256

Front 12

EIGRP Feature - Transport

Back 12

IP, protocol type 88 (does not use UDP or TCP).

Front 13

EIGRP Feature - Metric

Back 13

Based on constrained bandwidth and cumulative delay by default, and optionally load and reliability.

Front 14

EIGRP Feature - Hello Interval

Back 14

Interval at which a router sends EIGRP Hello messages on an interface.

Front 15

EIGRP Feature - Hold Timer

Back 15

Timer used to determine when a neighboring router has failed, based on a router not receiving any EIGRP messages, including Hellos, in this timer period.

Front 16

EIGRP Feature - Update Destination Address

Back 16

Normally sent to 224.0.0.10, with retransmissios being sent to each neighbor's unicast IP address. Can also be sent to the neighbor's unicast IP address.

Front 17

EIGRP Feature - Full or Partial Updates

Back 17

Full updates are used when new neighbors are discovered; otherwise, partial updates are used.

Front 18

EIGRP Feature - Authentication

Back 18

Supports MD5 authentication only.

Front 19

EIGRP Feature - VLSM/classless

Back 19

EIGRP includes the mask with each route, also allowing it to support discontiguous networks and VLSM.

Front 20

EIGRP Feature - Route Tags

Back 20

Allows EIGRP to tag routes as they are redistributed into EIGRP.

Front 21

EIGRP Feature - Next-hop field

Back 21

Supports the advertisement of routes with different next-hop router than the advertising router.

Front 22

EIGRP Feature - Manual Route Summarization

Back 22

Allows route summarization at any point in the EIGRP network.

Front 23

EIGRP Feature - Automatic Summarization

Back 23

EIGRP supports, and defaults to use, automatic route summarization at classful network boundaries.

Front 24

EIGRP Feature - Multiprotocol

Back 24

Supports the advertisement of IPX, AppleTalk, IPv4, and IPv6 routes.

Front 25

Configure EIGRP Hello and Hold Timers

Back 25

• To configure EIGRP Hello Timer use the interface command - ip hello-interval eigrp asn timer
• To configure EIGRP Hold Timer use the interface command - ip hold-interval eigrp asn timer
  

Front 26

Verify EIGRP Hello/Hold Timers

Back 26

• Verify using either the show running-config command or - show ip eigrp interfaces detail type number command
  

Front 27

How to advertise subnet while disallowing EIGRP neighborships on interface (2)

Back 27

• Enable EIGRP on the interface using the EIGRP network command, but tell the router to not send any EIGRP messages on the interface by making the interface passive using the passive-interface router command.
• Do not enable EIGRP on the interface, and advertise the connected route using route redistribution (and the redistribute connected configuration command). This can cause problems because it will advertise the route as an external EIGRP route.
  

Front 28

EIGRP - Verify Passive Interfaces

Back 28

show ip protocols

Front 29

Configure EIGRP Static Neighbors

Back 29

• Configure the static neighbor using the following router subcommand
  
• neighbor ip-address outgoing-interface
  
• This command will disable multicast packets from be processed on the configured outgoing interface.
  

Front 30

Verify EIGRP Static Neighbor

Back 30

• show ip eigrp neighbors will show the neighbor but not identify it as static.
• show ip eigrp neighbors detail will identify a neighbor as static
  

Front 31

Neighbor Requirements for EIGRP

Back 31

• Routers must be able to send/receive IP packets to one another
• Interfaces' primary IP addresses must be in the same subnet.
• Must not be passive on the connected interface.
• Must use the same ASN in the router configuration command
• Must pass neighbor authentication
• K-values must match
  

Front 32

Configure K-Values

Back 32

• Use the following router sub command to configure k-values
• metric weights tos(0) k1 k2 k3 k4 k5
  

Front 33

Verify K-Values

Back 33

show ip protocols

Front 34

EIGRP Router ID Determination Process

Back 34

1. Use the configured value (using the eigrp router-id a.b.c.d EIGRP subcommand).
2. Use the highest IPv4 address on an up/up loopback interface.
3. Use the highest IPv4 address on an up/up nonloopback interface.