1. Chapter 9 EIGRP – Part 1 of 2 CIS 82 Routing Protocols and Concepts
Rick Graziani
Cabrillo College
Last Updated: 4/20/2009

2. Note My web site is www.cabrillo.edu/~rgraziani.
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3. For further information
This presentation is an overview of what is covered in the curriculum/book.
For further explanation and details, please read the chapter/curriculum.
Book:
Routing Protocols and Concepts
By Rick Graziani and Allan Johnson
ISBN:
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4. Topics Introduction to EIGRP
EIGRP: An Enhanced Distance Vector Routing Protocol
EIGRP Message Format
Protocol-Dependent Modules
RTP and EIGRP Packet Types
Hello Protocol
EIGRP Bounded Updates
DUAL: An Introduction
Administrative Distance
Authentication
Basic EIGRP Configuration
EIGRP Network Topology
Autonomous Systems and Process IDs
The router eigrp Command
The network Command
Verifying EIGRP
Examining the Routing Table
EIGRP Metric Calculation
EIGRP Composite Metric and the K Values
EIGRP Metrics
Using the bandwidth Command
Calculating the EIGRP Metric
DUAL
DUAL Concepts
Successor and Feasible Distance
Feasible Successors, Feasibility Condition, and Reported Distance
Topology Table: Successor and Feasible Successor
Topology Table: No Feasible Successor
Finite State Machine
More EIGRP Configurations
The Null0 Summary Route
Disabling Automatic Summarization
Manual Summarization
EIGRP Default Route
Fine-Tuning EIGRP

5. Introduction to EIGRP
EIGRP: An Enhanced Distance Vector Routing Protocol
EIGRP Message Format
Protocol-Dependent Modules
RTP and EIGRP Packet Types
Hello Protocol
EIGRP Bounded Updates
DUAL: An Introduction
Administrative Distance
Authentication

6. Introduction to EIGRP
Enhanced Interior Gateway Routing Protocol (EIGRP)
Distance vector
Classless routing protocol
Released in 1992 with Cisco IOS Software Release 9.21.
Enhancement of Cisco Interior Gateway Routing Protocol (IGRP).
Both are Cisco proprietary
Operate only on Cisco routers.
Enhanced Interior Gateway Routing Protocol (EIGRP)
Distance vector
Classless routing protocol
Released in 1992 with Cisco IOS Software Release 9.21.
Enhancement of Cisco Interior Gateway Routing Protocol (IGRP).
Both are Cisco proprietary
Operate only on Cisco routers.

7. Introduction to EIGRP
The term hybrid routing protocol is sometimes used to define EIGRP.
Misleading, not a hybrid between distance vector and link-state
Solely a distance vector routing protocol.
The term hybrid routing protocol is sometimes used to define EIGRP.
Misleading, not a hybrid between distance vector and link-state
Solely a distance vector routing protocol.

8. Introduction to EIGRP
Instead of hop count, both IGRP and EIGRP use metrics composed of bandwidth, delay, reliability, and load.
Only bandwidth and delay are used by default.

9. EIGRP Message Format EIGRP Header field
Data field = Type/Length/Value, or TLV.
Encapsulated in an IP packet.
Protocol field = 88 (EIGRP)
Destination IP address = multicast
If the EIGRP packet is encapsulated in an Ethernet frame:
Destination MAC, multicast address: E A

10. EIGRP Message Format
Opcode specifies the EIGRP packet type as one of the following:
Update
Query
Reply
Hello
Autonomous system number
Specifies the EIGRP routing process.
Unlike RIP, Cisco routers can run multiple instances of EIGRP. (more later)
EIGRP packet types are discussed later in this chapter.

11. EIGRP TLV Message Format
EIGRP uses weights for its composite metric.
Default, only bandwidth (K1) and delay (K3) are weighted (used)
Set to 1.
Other K values are set to 0 (affect load and reliability).
More later.
The hold time
Amount of time the EIGRP neighbor receiving this message should wait before considering the advertising router to be down.
More later

12. IP Internal Routes TLV MTU is not a metric used by EIGRP.
Metric fields:
Delay and Bandwidth
Reliability and Load
(more later)
Subnet mask field (Prefix Length):
Example, the prefix length for is 24 (/24)
Destination field:
The destination network.
Some EIGRP literature might incorrectly state that the maximum transmission unit (MTU) is one of the metrics used by EIGRP.
MTU is not a metric used by EIGRP.
The MTU is included in the routing updates, but it is not used to determine the routing metric.
MTU is not a metric used by EIGRP.
The MTU is included in the routing updates, but it is not used to determine the routing metric.

13. IP External Routes TLV
In this chapter, we import or redistribute a default static route into EIGRP.
Additional fields
All the fields used by the IP Internal TLV

14. Protocol-Dependent Modules
EIGRP uses protocol-dependent modules (PDM). to route different protocols, including:
IP, Internetwork Packet Exchange (IPX)
AppleTalk,
PDMs are responsible for the specific routing tasks for each network layer protocol.
Example The IP-EIGRP module is responsible for:
Sending and receiving EIGRP packets that are encapsulated in IP.
Using DUAL to build and maintain the IP routing table.
EIGRP uses protocol-dependent modules (PDM). to route different protocols, including: IP
Internetwork Packet Exchange (IPX)
AppleTalk,
PDMs are responsible for the specific routing tasks for each network layer protocol.

15. RTP and EIGRP Packet Types
Reliable Transport Protocol (RTP)
Delivery and reception of EIGRP packets.
Cannot use the services of UDP or TCP
RTP includes both reliable delivery and unreliable delivery of EIGRP packets:
Reliable RTP requires an acknowledgment (like TCP).
Unreliable RTP does not require an acknowledgment (like UDP).
Reliable Transport Protocol (RTP)
Delivery and reception of EIGRP packets.
Cannot use the services of UDP or TCP
IPX and AppleTalk do not use protocols from the TCP/IP protocol suite.
RTP includes both reliable delivery and unreliable delivery of EIGRP packets:
Reliable RTP requires an acknowledgment (like TCP).
Unreliable RTP does not require an acknowledgment (like UDP).
RTP can send packets either as a unicast or a multicast ( ).

16. EIGRP Packet Types – Hello Packet
Hello packets are used by EIGRP to:
Discover neighbors
Form adjacencies with those neighbors
EIGRP hello packets:
Multicasts
Unreliable delivery
Hello packets are used by EIGRP to:
Discover neighbors
Form adjacencies with those neighbors
EIGRP hello packets:
multicasts
unreliable delivery

17. EIGRP Packet Types – Update and Acknowledgement Packets
EIGRP uses triggered updates
Update Packets
Contains only the routing information needed (a change occurs)
Sent only to those routers that require it.
Uses reliable delivery.
Acknowledgment (ACK) Packets
Sent when reliable delivery is used (update, query, and reply packets).
Unreliable unicast.
Update Packets
Contains only the routing information needed (a change occurs)
Sent only to those routers that require it.
Uses reliable delivery.
Multicast when sent to multiple routers
Unicast when sent to a single router
Acknowledgment (ACK) Packets
Sent when reliable delivery is used (update, query, and reply packets).
Sent as an unreliable unicast.

18. EIGRP Packet Types – Query and Reply Packets
Why Query? Another router could be attached to the same LAN.
Used by DUAL when searching for networks and other tasks.
Queries and replies use reliable delivery.
DUAL is discussed in a later section.
Used by DUAL when searching for networks and other tasks.
Queries and replies use reliable delivery.
To keep this example simple, acknowledgments were omitted in the graphic.
All neighbors must send a reply regardless of whether they have a route to the downed network.
Queries can use multicast or unicast, whereas replies are always sent as unicast.
DUAL is discussed in a later section.
Queries and replies packets are discussed in more detail in CCNP.

19. Hello Protocol
Before any EIGRP packets can be exchanged between routers, EIGRP must first discover its neighbors.
EIGRP routers discover neighbors and establish adjacencies with neighbor routers using the hello packet.
Before any EIGRP packets can be exchanged between routers, EIGRP must first discover its neighbors.
EIGRP routers discover neighbors and establish adjacencies with neighbor routers using the hello packet.

20. Hello Protocol
An EIGRP router assumes that as long as it is receiving hello packets from a neighbor, the neighbor and its routes remain viable.
Most networks, EIGRP hello packets are sent every 5 seconds.
On multipoint nonbroadcast multiaccess (NBMA) networks such as X.25, Frame Relay, and ATM interfaces with access links of T1 (1.544 Mbps) or slower, hellos are unicast every 60 seconds.
An EIGRP router assumes that as long as it is receiving hello packets from a neighbor, the neighbor and its routes remain viable.

21. Hello Protocol
Hold time - maximum time the router should wait to receive the next hello before declaring that neighbor as unreachable.
Default hold time - 3 times the hello interval
If the hold time expires:
EIGRP declares the route as down
DUAL searches for a new path in the topology table or by sending out queries.
More later.
Hold time - maximum time the router should wait to receive the next hello before declaring that neighbor as unreachable.
Default hold time - 3 times the hello interval,
15 seconds on most networks
180 seconds on low-speed NBMA networks
If the hold time expires:
EIGRP declares the route as down
DUAL searches for a new path in the topology table or by sending out queries.
More later.

22. EIGRP Bounded Updates
EIGRP uses the terms partial and bounded when referring to its update packets.
EIGRP sends its updates only when the metric for a route changes.
Partial - update only includes information about the route changes.
Bounded - propagation of partial updates sent only to those routers that are affected by the change.
This minimizes the bandwidth required to send EIGRP packets.
EIGRP uses the terms partial and bounded when referring to its update packets.
EIGRP sends its updates only when the metric for a route changes.
The term partial means that the update only includes information about the route changes.
The term bounded refers to the propagation of partial updates sent only to those routers that are affected by the change.
This minimizes the bandwidth required to send EIGRP packets.

23. DUAL: An Introduction
J. J. Garcia-Luna-Aceves
Diffusing Update Algorithm (DUAL) is the convergence algorithm used by EIGRP.
First proposed by E. W. Dijkstra and C. S. Scholten.
The most prominent work with DUAL has been done by J. J. Garcia-Luna-Aceves.
Distance vector routing protocols such as RIP prevent routing loops with hold-down timers and split horizon.
Although EIGRP uses both of these techniques, it uses them somewhat differently; the primary way that EIGRP prevents routing loops is with the DUAL algorithm.
Diffusing Update Algorithm (DUAL) is the convergence algorithm used by EIGRP.
First proposed by E. W. Dijkstra and C. S. Scholten.
The most prominent work with DUAL has been done by J. J. Garcia-Luna-Aceves.
Routing loops, even temporary ones, can be extremely detrimental to network performance.
Distance vector routing protocols such as RIP prevent routing loops with hold-down timers and split horizon.
Although EIGRP uses both of these techniques, it uses them somewhat differently; the primary way that EIGRP prevents routing loops is with the DUAL algorithm.

24. X DUAL: An Introduction .
1. A directly connected network on R2 goes down.
R2 sends an EIGRP update message to its neighbors indicating the network is down .
2. R1 and R3 return an EIGRP acknowledgment indicating that they have received the update from R2.
3. R2 does not have an EIGRP backup route known as a feasible successor. (more later.)
So, R2 sends an EIGRP query to its neighbors asking them whether they have a route to this downed network.
4. R1 and R3 return an EIGRP acknowledgment indicating that they have received the query from R2
5. R1 and R3 send an EIGRP reply message in response to the query sent by R2.
In this case, the reply would state that the router does not have a route to this network.
6. R2 returns an acknowledgment indicating that it received the reply.
Note: Much more later! .

25. Administrative Distance
When compared to other interior gateway protocols (IGP), EIGRP is the most preferred by the Cisco IOS software because it has the lowest AD.
Later in this chapter, you learn how to configure EIGRP summary routes.
When compared to other interior gateway protocols (IGP), EIGRP is the most preferred by the Cisco IOS software because it has the lowest AD.
Later in this chapter, you learn how to configure EIGRP summary routes.

26. Authentication
Like other routing protocols, EIGRP can be configured for authentication.
It is good practice to authenticate transmitted routing information.
This practice ensures that routers will accept routing information only from other routers that have been configured with the same password or authentication information.
When authentication is configured on a router, the router authenticates the source of each routing update packet that it receives.
However, authentication does not encrypt the router’s routing table.
Like other routing protocols, EIGRP can be configured for authentication.
It is good practice to authenticate transmitted routing information.
This practice ensures that routers will accept routing information only from other routers that have been configured with the same password or authentication information.
When authentication is configured on a router, the router authenticates the source of each routing update packet that it receives.
However, authentication does not encrypt the router’s routing table.

27. Basic EIGRP Configuration
EIGRP Network Topology
Autonomous Systems and Process IDs
The router eigrp Command
The network Command
Verifying EIGRP
Examining the Routing Table

28. Topology Download: cis82-EIGRP-A-student.pkt
may not
Includes the addition of the ISP router.
R1 and R2 routers have subnets that are part of the /16.
Download: cis82-EIGRP-A-student.pkt
Includes the addition of the ISP router.
R1 and R2 routers have subnets that are part of the /16.

29. R1’s running-config hostname R1 ! interface FastEthernet0/0
ip address
interface Serial0/0/0
ip address
clock rate 64000
interface Serial0/0/1
ip address

30. R2’s running-config
hostname R2 !
interface Loopback1
ip address
description Simulated ISP
interface FastEthernet0/0
ip address
interface Serial0/0/0
ip address
interface Serial0/0/1
ip address
clockrate 64000
ISP router does not physically exist in our configurations.
The connection between R2 and ISP is represented with a loopback interface on Router R2.
ISP router does not physically exist in our configurations.
The connection between R2 and ISP is represented with a loopback interface on Router R2.
This was done so that you only need 3 routers.

31. R3’s running-config hostname R3 ! interface FastEthernet0/0
ip address
interface Serial0/0/0
ip address
clockrate 64000
interface Serial0/0/1
ip address

32. Autonomous Systems and Process IDs
An autonomous system (AS) is a collection of networks under the administrative control of a single entity that presents a common routing policy to the Internet.
Described in RFC 1930.
AS numbers are assigned by IANA and its RIR.
Same authority that assigns IP address space.
An autonomous system (AS) is a collection of networks under the administrative control of a single entity that presents a common routing policy to the Internet.
Described in RFC 1930.
AS numbers are assigned by IANA and its RIR.

33. Autonomous Systems and Process IDs
Who needs an autonomous system number?
ISPs
Internet backbone providers
Large institutions connecting to other entities that also have an autonomous system number.
What routing protocol is used between these providers?
Exterior gateway routing protocol BGP.
The vast majority of companies and institutions with IP networks do not need an autonomous system number because they come under the control of a larger entity such as an ISP.
Who needs an autonomous system number?
ISPs
Internet backbone providers
Large institutions connecting to other entities that also have an autonomous system number.
Uses exterior gateway routing protocol BGP.
The vast majority of companies and institutions with IP networks do not need an autonomous system number because they come under the control of a larger entity such as an ISP.

34. Process ID Must be same on all routers in EIGRP routing domain
Router(config)# router eigrp autonomous-system
Router(config)# router eigrp 1
Must be same on all routers in EIGRP routing domain
Both EIGRP and OSPF use a process ID to represent an instance of their respective routing protocol running on the router.
EIGRP refers to “autonomous-system” number
Actually functions as a process ID.
1 and 65,535
Both EIGRP and OSPF use a process ID to represent an instance of their respective routing protocol running on the router.
Although EIGRP refers to the parameter as an “autonomous-system” number, it actually functions as a process ID.
AS parameter is between 1 and 65,535.
All routers in this EIGRP routing domain must use the same process ID number (autonomous system number).

35. The router eigrp Command
Enable EIGRP with process ID of 1 on all three routers (R1, R2, R3).
R1(config)# router eigrp 1
R1(config-router)#
R2(config)# router eigrp 1
R2(config-router)#
R3(config)# router eigrp 1
R3(config-router)#
EIGRP is enabled on all three routers using the process ID of 1.
EIGRP is enabled on all three routers using the process ID of 1.

36. The network Command
Router(config-router)# network network-address
R2(config-router)# network
The network command in EIGRP has the same function as in other IGP routing protocols:
What does it do?
Any interface on this router that matches the network address in the network command will be enabled to send and receive EIGRP updates.
This network (or subnet) will be included in EIGRP routing updates.
The network command in EIGRP has the same function as in other IGP routing protocols:
Any interface on this router that matches the network address in the network command will be enabled to send and receive EIGRP updates.
This network (or subnet) will be included in EIGRP routing updates.

37. The network Command Adjacency
Configure the network command for on R1 and R2.
R1(config-router)# network
R2(config-router)# network
%DUAL-5-NBRCHANGE: IP-EIGRP 1: Neighbor (Serial0/0) is up: new adjacency
The network-address is the classful network address for this interface.
includes both /24 and /30 subnets.
When EIGRP is configured on R2, DUAL sends a notification message to the console stating that a neighbor relationship with another EIGRP router has been established.
This new adjacency happens automatically because both R1 and R2 are using the same EIGRP 1 routing process and both routers are now sending updates on the network.
The network-address is the classful network address for this interface.
R1: includes both /24 and /30 subnets.
R2: includes both /24 and /30 subnets.
A new adjacency happens automatically because both R1 and R2 are using the same EIGRP 1 routing process and both routers are now sending updates on the network.

38. The network Command with a Wildcard Mask
Router(config-router)# network network-address
Router(config-router)# network network-address [wildcard-mask]
Network command
Classful network address:
All interfaces on the router that belong to that classful network address will be enabled for EIGRP.
For specific interface(s), subnets,:
Use the wildcard-mask option.
Network command – When uses classful network address:
All interfaces on the router that belong to that classful network address will be enabled for EIGRP.
To include only specific interface(s), subnets, to be enabled for EIGRP:
Use the wildcard-mask option.

39. The network Command with a Wildcard Mask
Subtract the subnet mask
Wildcard mask
R2(config-router)# network Or
R2(config-router)# network
Think of a wildcard mask as the inverse of a subnet mask.
The inverse of subnet mask is
To calculate the inverse of the subnet mask, subtract the subnet mask from
Some Cisco IOS software versions also let you just enter the subnet mask.
However, Cisco IOS software then converts the command to the wildcard mask format, as can be verified with the show running-config
Think of a wildcard mask as the inverse of a subnet mask.
To calculate the inverse of the subnet mask, subtract the subnet mask from
Some Cisco IOS software versions also let you just enter the subnet mask.

40. The network Command with a Wildcard Mask
R2(config-router)# network Or
R2(config-router)# network
R2# show running-config
<some output omitted> !
router eigrp 1
network
network
auto-summary
Newer Cisco IOS automatically converts the command to the wildcard mask format, as can be verified with the show running-config

41. The network Command with a Wildcard Mask
R1(config)# router eigrp 1
R1(config-router)# passive-interface fa 0/0
R1(config-router)# network
<will need other network commands as well>
The passive-interface command should not be used with EIGRP.
When the passive-interface command is configured, EIGRP stops sending hello packets on that interface.
Will not form an adjacency
Unable to send or receive routing updates.
The passive-interface command should not be used with EIGRP if there is a router on the link you wish to form an adjacency with.
When the passive-interface command is configured, EIGRP stops sending hello packets on that interface.
Will not form an adjacency
Unable to send or receive routing updates.

42. Network configurations
Configure the rest of network commands for R1, R2 and R3. R1
R1(config)# router eigrp 1
R1(config-router)# network
R1(config-router)# network
R2(config)# router eigrp 1
R2(config-router)# network
R2(config-router)# network
R3(config)# router eigrp 1
R3(config-router)# network
R3(config-router)# network R2 R3

43. Verifying EIGRP
EIGRP routers must first establish adjacencies with their neighbors before any updates can be sent or received.
show ip eigrp neighbors - view the neighbor table and verify that adjacencies with its neighbors.
If a neighbor is not listed:
Check the local interfaces to make sure it is activated with the show ip interface brief command.
Try pinging the IP address of the neighbor.
EIGRP routers must first establish adjacencies with their neighbors before any updates can be sent or received.
What if a neighbor is not listed:
Check the local interfaces to make sure it is activated with the show ip interface brief command.
Try pinging the IP address of the neighbor.

44. Verifying EIGRP Verifying EIGRP
What if the ping is successful and EIGRP still does not see the router as a neighbor?
Are both routers configured with the same EIGRP process ID?
Is the directly connected network included in the EIGRP network statements?
Is the passive-interface command inappropriately configured, thus preventing EIGRP hello packets on the interface?
If the ping is successful and EIGRP still does not see the router as a neighbor, examine the following configurations:
Are both routers configured with the same EIGRP process ID?
Is the directly connected network included in the EIGRP network statements?
Is the passive-interface command inappropriately configured, thus preventing EIGRP hello packets on the interface?

45. Some items to make note of. These will be explained later.
R1# show ip protocols
Routing Protocol is “eigrp 1”
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 1
Automatic network summarization is in effect
Automatic address summarization:
/24 for FastEthernet0/0, Serial0/0/0
Summarizing with metric
/16 for Serial0/0/1
Summarizing with metric 28160
Maximum path: 4
Routing for Networks:
Routing Information Sources:
Gateway Distance Last Update
(this router) :03:29
:02:09
:02:12
Distance: internal 90 external 170
Some items to make note of. These will be explained later.

46. Examining the Routing Table: R1
R1# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,
D - EIGRP, EX - EIGRP external, O - OSPF,
<Output omitted>
/24 is variably subnetted, 3 subnets, 2 masks
D /24 is a summary, 00:03:50, Null0
C /30 is directly connected, Serial0/0/1
D /30 [90/ ] via ,00:02:43, S0/0/1
/16 is variably subnetted, 4 subnets, 3 masks
D /16 is a summary, 00:10:52, Null0
C /24 is directly connected, FastEthernet0/0
D /24 [90/ ] via , 00:10:47, S0/0/0
C /30 is directly connected, Serial0/0/0
D /24 [90/ ] via , 00:02:31, S0/0/1
Notice that EIGRP routes are denoted in the routing table with a D, which stands for DUAL.
What code is used to denote EIGRP?
EIGRP routes are denoted in the routing table with a D, which stands for DUAL.

47. Examining the Routing Table: R2
R2# show ip route
<Output omitted>
/24 is variably subnetted, 3 subnets, 2 masks
D /24 is a summary, 00:04:13, Null0
D /30 [90/ ] via ,00:03:05,S0/0/1
C /30 is directly connected, Serial0/0/1
/16 is variably subnetted, 4 subnets, 3 masks
D /16 is a summary, 00:04:07, Null0
D /24 [90/ ] via , 00:11:11, S0/0/0
C /24 is directly connected, FastEthernet0/0
C /30 is directly connected, Serial0/0/0
/30 is subnetted, 1 subnets
C is directly connected, Loopback1
D /24 [90/ ] via , 00:02:54, S0/0/1
EIGRP is a classless routing protocol (includes the subnet mask in the routing update), it supports variable-length subnet masks (VLSM) and classless interdomain routing (CIDR).
Is EIGRP a classless routing protocol?
EIGRP is a classless routing protocol (includes the subnet mask in the routing update), it supports variable-length subnet masks (VLSM) and classless interdomain routing (CIDR).

48. Examining the Routing Table: R3
/16
R3# show ip route
<Output omitted>
/24 is variably subnetted, 3 subnets, 2 masks
D /24 is a summary, 00:03:11, Null0
C /30 is directly connected, Serial0/0/0
C /30 is directly connected, Serial0/0/1
D /16 [90/ ] via , 00:03:23, S0/0/0
[90/ ] via , 00:03:23, S0/0/1
C /24 is directly connected, FastEthernet0/0
/16
By default, EIGRP automatically summarizes routes at the major network boundary.
You can disable the automatic summarization with the no auto-summary command, just as you can for RIPv2.
Null0 summary routes will be explained next.
Both R1 and R2 are automatically summarizing the /16 network and sending it as a single routing update.
R1 and R2 are not propagating the individual subnets because of automatic summarization.
We will turn off automatic summarization later.
What do you notice about EIGRP in respect to R3 receiving the /16 route?
By default, EIGRP automatically summarizes routes at the major network boundary.
Automatic summarization can be disabled with the no auto-summary command (like RIPv2) - later.

49. Introducing the Null0 Summary Route
R2# show ip route
<Output omitted>
/24 is variably subnetted, 3 subnets, 2 masks
D /24 is a summary, 00:04:13, Null0
D /30 [90/ ] via ,00:03:05,S0/0/1
C /30 is directly connected, Serial0/0/1
/16 is variably subnetted, 4 subnets, 3 masks
D /16 is a summary, 00:04:07, Null0
D /24 [90/ ] via , 00:11:11, S0/0/0
C /24 is directly connected, FastEthernet0/0
C /30 is directly connected, Serial0/0/0
/30 is subnetted, 1 subnets
C is directly connected, Loopback1
D /24 [90/ ] via , 00:02:54, S0/0/1
The /24 and /16 routes do not actually represent a path to reach the parent networks.
If a packet does not match one of the level 2 child routes, it is sent to the Null0 interface.
In other words, if the packet matches the level 1 parent, but none of the subnets, the packet is discarded.
The /24 and /16 routes do not actually represent a path to reach the parent networks.
What would happen if a packet matches the parent route but does not match one of the level 2 child routes?
It is sent to the Null0 interface - dropped

50. Introducing the Null0 Summary Route
R2# show ip route
<Output omitted>
/24 is variably subnetted, 3 subnets, 2 masks
D /24 is a summary, 00:04:13, Null0
D /30 [90/ ] via ,00:03:05,S0/0/1
C /30 is directly connected, Serial0/0/1
/16 is variably subnetted, 4 subnets, 3 masks
D /16 is a summary, 00:04:07, Null0
D /24 [90/ ] via , 00:11:11, S0/0/0
C /24 is directly connected, FastEthernet0/0
C /30 is directly connected, Serial0/0/0
/30 is subnetted, 1 subnets
C is directly connected, Loopback1
D /24 [90/ ] via , 00:02:54, S0/0/1
EIGRP automatically includes a Null0 summary route as a child route whenever both of the following conditions exist:
There is at least one subnet that was learned via EIGRP.
Automatic summarization is enabled.
The Null0 summary route is removed when automatic summary is disabled (later).
EIGRP automatically includes a Null0 summary route as a child route whenever both of the following conditions exist:
There is at least one subnet that was learned via EIGRP.
Automatic summarization is enabled.
The Null0 summary route is removed when automatic summary is disabled.

51. EIGRP Metric Calculation
EIGRP Composite Metric and the K Values
EIGRP Metrics
Using the bandwidth Command
Calculating the EIGRP Metric

52. EIGRP Composite Metric and the K Values
EIGRP uses the following values in its composite metric to calculate the preferred path to a network:
Bandwidth
Delay
Reliability
Load
Note: Although MTU is included in the routing table updates, it is not a routing metric used by EIGRP or IGRP.
EIGRP uses the following values in its composite metric to calculate the preferred path to a network:
Bandwidth
Delay
Reliability
Load
Note: Although MTU is included in the routing table updates, it is not a routing metric used by EIGRP or IGRP.

53. The Composite Metric By default: K1 and K3 are set to 1,
K2, K4, and K5 are set to 0.
The result is that only the bandwidth and delay values are used in the computation of the default composite metric.
By default, K1 and K3 are set to 1, and K2, K4, and K5 are set to 0.
The result is that only the bandwidth and delay values are used in the computation of the default composite metric.
Note:
Modifying the metric weights is beyond the scope of this course, but their relevance is important in establishing neighbors and is discussed in a later section.
The tos (type of service) value is left over from IGRP and was never implemented. (The tos value is always set to 0.)

54. Verifying the K Values The K values on R1 are set to the default.
R1# show ip protocols
Routing Protocol is “eigrp 1”
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
<output omitted>
The K values on R1 are set to the default.
Changing these values to other than the default is not recommended unless the network administrator has a very good reason to do so.
Cisco recommends that these values are not modified. K1 K2 K3 K4 K5
The K values on R1 are set to the default.
Changing these values to other than the default is not recommended unless the network administrator has a very good reason to do so

55. Examining the Metric Values
R1# show interface serial 0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is GT96K Serial
Description: Link to R2
Internet address is /30
MTU 1500 bytes, BW 1544 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
<output omitted>
show interface command, lets you can examine the actual values used for bandwidth, delay, reliability, and load in the computation of the routing metric.
Default values:
bandwidth
delay
show interface command, lets you can examine the actual values used for bandwidth, delay, reliability, and load in the computation of the routing metric.
Default values:
bandwidth
delay

56. Bandwidth
R1# show interface serial 0/0/0
<output omitted>
MTU 1500 bytes, BW 1544 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
The bandwidth metric (1544 Kbps) is a static value used by some routing protocols such as EIGRP and OSPF to calculate their routing metric.
Kilobits per second (Kbps).
Most serial interfaces use the default bandwidth value of 1544 Kbps or 1,544,000 bps (1.544 Mbps).
The value of the bandwidth might or might not reflect the actual physical bandwidth of the interface.
Modifying the bandwidth value does not change the actual bandwidth of the link.
Should reflect actual bandwidth of the link. (coming).
The bandwidth metric (1544 Kbps) is a static value used by some routing protocols such as EIGRP and OSPF to calculate their routing metric.
kilobits per second (Kbps).
Most serial interfaces use the default bandwidth value of 1544 Kbps or 1,544,000 bps (1.544 Mbps).
The value of the bandwidth might or might not reflect the actual physical bandwidth of the interface.
Modifying the bandwidth value does not change the actual bandwidth of the link.
Should reflect actual bandwidth of the link. (next).

57. Delay
R1# show interface serial 0/0/0
<output omitted>
MTU 1500 bytes, BW 1544 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
Delay is a measure of the time it takes for a packet to traverse a route.
Based on the type of link, or interface
Expressed in microseconds (millionths of a second).
The router does not actually track how long packets are taking to reach the destination.
Like the bandwidth value, delay is a default value that can be changed by the network administrator.
Delay is a measure of the time it takes for a packet to traverse a route.
Based on the type of link, he interface
Expressed in microseconds (millionths of a second).
The router does not actually track how long packets are taking to reach the destination.
Like the bandwidth value, delay is a default value that can be changed by the network administrator.

58. Delay 100 microseconds for Fast Ethernet interfaces.
R1# show interface serial 0/0/0
<output omitted>
MTU 1500 bytes, BW 1544 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
100 microseconds for Fast Ethernet interfaces.
Default value is 20,000 microseconds for serial interfaces
100 microseconds for Fast Ethernet interfaces.
Default value is 20,000 microseconds for serial interfaces

59. Reliability – Optional Metric
R1# show interface serial 0/0/0
<output omitted>
MTU 1500 bytes, BW 1544 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
Reliability is a measure of the probability that the link will fail or how often the link has experienced errors.
Value between 0 and 255,
1 = a minimally reliable link
255 = 100 percent reliable.
By default EIGRP does not use reliability in its metric calculation.
Reliability is a measure of the probability that the link will fail or how often the link has experienced errors.
Measured dynamically with a value between 0 and 255, with 1 being a minimally reliable link and 255 being 100 percent reliable.
Reliability is calculated on a 5-minute weighted average to avoid the sudden impact of high (or low) error rates.
Reliability is expressed as a fraction of 255; the higher the value, the more reliable the link.
So, 255/255 would be 100 percent reliable, whereas a link of 234/255 would be 91.8 percent reliable.
Remember that by default EIGRP does not use reliability in its metric calculation.

60. Load – Optional Metric
R1# show interface serial 0/0/0
<output omitted>
MTU 1500 bytes, BW 1544 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
Load reflects the amount of traffic using the link.
Value between 0 and 255.
A lower load value is more desirable because it indicates less load on the link.
1/255 would be a minimally loaded link.
40/255 is a link at 16 percent capacity
255/255 is a link that is 100 percent saturated
By default EIGRP does not use load in its metric calculation.
Load reflects the amount of traffic using the link.
Value between 0 and 255.
Similar to reliability, load is expressed as a fraction of 255.
However, in this case, a lower load value is more desirable because it indicates less load on the link.
So, 1/255 would be a minimally loaded link. 40/255 is a link at 16 percent capacity, and 255/255 is a link that is 100 percent saturated.
Load is displayed as both an outbound, or transmit, load value (txload) and an inbound, or receive, load value (rxload).
This value is calculated on a 5-minute weighted average to avoid the sudden impact of high (or low) channel usage.
Remember that by default EIGRP does not use load in its metric calculation.

61. Using the bandwidth Command
Router(config-if)# bandwidth kilobits
Most serial links, the bandwidth metric defaults to 1544 Kbps.
Correct value for bandwidth is very important to the accuracy of routing information
bandwidth command - modifies the bandwidth metric.
no bandwidth - restores the default value.
Most serial links, the bandwidth metric defaults to 1544 Kbps.
Correct value for bandwidth is very important to the accuracy of routing information
Use the interface command bandwidth to modify the bandwidth metric.
Use the interface command no bandwidth to restore the default value.

62. Using the bandwidth Command
Configure the bandwidth commands for R1, R2 and R3.
R1(config)# inter s 0/0/0
R1(config-if)# bandwidth 64
R2(config)# inter s 0/0/0
R2(config-if)# bandwidth 64
R2(config)# inter s 0/0/1
R2(config-if)# bandwidth 1024
R3(config)# inter s 0/0/1
R3(config-if)# bandwidth 1024
Modify the bandwidth on the appropriate serial interfaces.
Be sure to modify both ends of the link.
Modify the bandwidth on the appropriate serial interfaces.
Be sure to modify both ends of the link.

63. Verify changes Verify the change using the show interface command.
R2# show interface serial 0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is PowerQUICC Serial
Internet address is /30
MTU 1500 bytes, BW 64 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
<some output omitted>
R2# show interface serial 0/0/1
Serial0/0/1 is up, line protocol is up
Internet address is /30
MTU 1500 bytes, BW 1024 Kbit, DLY usec,
Verify the change using the show interface command.
Verify the change using the show interface command.

64. Calculating the EIGRP Metric
Using the default values for K1 and K3, you can simplify this calculation to:
slowest bandwidth (or minimum bandwidth)
plus cumulative sum of all the delays
EIGRP route metric
Using the default values for K1 and K3, you can simplify this calculation to:
slowest bandwidth (or minimum bandwidth)
plus cumulative sum of all the delays
EIGRP route metric

65. Calculating the EIGRP Metric
Step 1. Determine the link with the slowest bandwidth.
That bandwidth is used for the (10,000,000/bandwidth) * 256 portion of the formula.
Step 2. Determine the delay value for each outgoing interface on the way to the destination.
Step 3. Sum the delay values and divide by 10 (sum of delay/10), and then multiply by 256 (* 256).
Step 4. Add the bandwidth and sum of delay values to obtain the EIGRP metric.
Step 1. Determine the link with the slowest bandwidth.
That bandwidth is used for the (10,000,000/bandwidth) * 256 portion of the formula.
Step 2. Determine the delay value for each outgoing interface on the way to the destination.
Step 3. Sum the delay values and divide by 10 (sum of delay/10), and then multiply by 256 (* 256).
Step 4. Add the bandwidth and sum of delay values to obtain the EIGRP metric.

66. Step 1. Determine the link with the slowest bandwidth.
(10,000,000/bandwidth kbps) * 256 = 2,499,840
Slowest bandwidth
Step 1. Determine the link with the slowest bandwidth.
The serial 0/0/1 interface on R2 has a bandwidth of 1024 Kbps, or 1,024,000 bps. (Slowest)
The Fast Ethernet 0/0 interface on R3 has a bandwidth of 100,000 Kbps, or 100 Mbps.
(10,000,000/bandwidth) * 256 = 2,499,840
Step 1. Determine the link with the slowest bandwidth.
The Fast Ethernet 0/0 interface on R3 has a bandwidth of 100,000 Kbps, or 100 Mbps.
The serial 0/0/1 interface on R2 has a bandwidth of 1024 Kbps, or 1,024,000 bps. (Slowest)
(10,000,000/1024) * 256 = 2,499,840

67. The serial 0/0/1 interface on R2 has a delay of 20,000 microseconds.
Step 2. Determine the delay value for each outgoing interface on the way to the destination.
The serial 0/0/1 interface on R2 has a delay of 20,000 microseconds.
The Fast Ethernet 0/0 interface on R3 has a delay of 100 microseconds.
Step 2. Determine the delay value for each outgoing interface on the way to the destination.
The serial 0/0/1 interface on R2 has a delay of 20,000 microseconds.
The Fast Ethernet 0/0 interface on R3 has a delay of 100 microseconds.

68. The delay portion of the composite metric is 514,560.
(20,000/ /10)256 = 514,560
Step 3. Sum the delay values and divide by 10 (sum of delay/10), and then multiply by 256 (* 256).
20,000/ /10 = 2,010
Then multiplied by 256, 2,010 * 256 = 514,560
The delay portion of the composite metric is 514,560.
Step 3. Sum the delay values and divide by 10 (sum of delay/10), and then multiply by 256 (* 256).
20,000/ /10 = 2,010
Multiply by 256: 2,010 * 256 = 514,560
The delay portion of the composite metric is 514,560.

69. Route Metric 2,499,840 + 514,560 = 3,014,400 Slowest bandwidth
Step 4. Add the bandwidth and sum of delay values to obtain the EIGRP metric.
Simply add the two values together, 2,499, ,560, to obtain the EIGRP metric of 3,014,400.
Step 4. Add the bandwidth and sum of delay values to obtain the EIGRP metric.
Bandwidth 2,499,840
+ Delay 514,560
= EIGRP metric of 3,014,400

70. Calculating the EIGRP Metric
R2# show ip route
<code output omitted>
D /24 [90/ ] via , 00:00:15, S0/0/1

71. End of Part 1

72. Chapter 9 EIGRP – Part 1 of 2 CIS 82 Routing Protocols and Concepts
Rick Graziani
Cabrillo College