EIGRP MD5 Authentication Configuration

EIGRP MD5 Authentication Configuration

This chapter is about EIGRP MD5 Authentication Configuration on Cisco Router. EIGRP supports authentication of routing protocols using MD5. For better understanding we will share MD5 Authentication examples and Cisco configuration commands for you.

ROUTING PROTOCOL AUTHENTICATION

Network administrators should keep in mind that routers are at the same risk of attacks as devices for end users. Anyone with a packet detector program, such as Wireshark , can read the information that is propagated between the routers. In general, routing systems can be attacked by interrupting peer devices or falsifying routing information.
Peer interruption is the less critical attack of the two, because the routing protocols repair themselves, which makes the interruption only last a little longer than the attack itself. Forgery of routing information is a more subtle attack class that aims at the information that is transported within the routing protocol. The consequences of falsifying routing information are the following:

• Traffic redirection to create routing loops
• Traffic redirection for control on an unsecured line
• Redirect traffic to discard it

One method to protect the routing information of the network is to authenticate the packets of the routing protocol using the message 5 (MD5) synthesis algorithm . MD5 allows routers to compare signatures that should be the same, in order to confirm that they come from a credible origin. The three components of this system are the following:

• Encryption algorithm, generally public knowledge
• Key used in the encryption algorithm, a secret shared by routers that authenticate packets
• Package content

Routing protocols such as RIPv2, EIGRP, OSPF, IS-IS and BGP support various forms of MD5 authentication.

EIGRP CONFIGURATION WITH MD5 AUTHENTICATION

EIGRP message authentication ensures that routers only accept routing messages from other routers that know the same previously shared key. Without configured authentication, if an unauthorized person enters another router with different or conflicting route information, it can damage the routing tables of legitimate routers, which may be accompanied by a DoS attack.
So, when authentication is added to the EIGRP messages that are sent between routers, it prevents someone from adding another router to the network - by the way or by accident - and causing a problem. EIGRP supports authentication of routing protocols using MD5. The configuration of the EIGRP message authentication consists of two steps: the creation of a keychain and a key, and the configuration of the EIGRP authentication to use the keychain and the key.

 STEP 1. CREATE A KEYCHAIN AND A KEY

To function, routing authentication requires a key in a keychain. In order for authentication to be enabled, create a keychain and at least one key.

• to. In global configuration mode, create the keychain. Although several keys can be configured, this section focuses on the use of a single key.

Router (config) # key chain  name-of-chain

• b. Specify the key ID. The key ID is the number used to identify an authentication key within a keychain. The key range is from 0 to 2 147 483 647. It is recommended that the key number be the same on all routers in the configuration.

Router (config-keychain) # key  key-id

• C. Specify the key chain for the key. The key chain is similar to a password. Routers that exchange authentication keys must be configured with the same key chain.

Router (config-keychain-key) # key-string  key-string-text

STEP 2. CONFIGURE EIGRP AUTHENTICATION WITH THE KEYCHAIN AND KEY

Configure EIGRP to perform message authentication with the key defined above. Complete this configuration on all interfaces enabled for EIGRP.

• to. In global configuration mode, specify the interface on which you will configure EIGRP message authentication.

Router (config) # interface  type number

• b. Enable EIGRP message authentication. The md5 keyword indicates that the MD5 hash will be used for authentication.

Router (config-if) # ip authentication mode eigrp  as-number md5

• C. Specify the keychain to be used for authentication. The name-of-chain argument specifies the keychain that was created in step 1.

Router (config-if) # ip authentication key-chain eigrp  as-number name-of-chain
Each key has its own key ID , which is stored locally. The combination of the key ID and the interface associated with the message uniquely identifies the authentication algorithm and the MD5 authentication key in use. The keychain and routing update are processed with the MD5 algorithm to produce a unique signature.

EIGRP AUTHENTICATION EXAMPLE

To authenticate routing updates, all interfaces with EIGRP enabled must be configured to support authentication. In Image, the IPv4 topology and interfaces that have authentication configured are shown.

In 2nd Image, the configuration for router R1 with the EIGRP_KEY keychain and the cisco123 key chain is shown .

Once R1 is configured, the other routers receive authenticated routing updates. Adjacencies are lost until routing protocol authentication is configured in neighbors.

IPV6 EIGRP AUTHENTICATION CONFIGURATION 

The algorithms and the configuration to authenticate EIGRP messages for IPv6 are the same as those corresponding to EIGRP for IPv4. The only difference is that in the commands of the interface configuration mode, ipv6 is used instead of ip .
Router (config-if) # ipv6 authentication mode eigrp  as-number  md5
Router (config-if) # ipv6 authentication key-chain eigrp  as-number name-of-chain
In following Image, the commands for configuring EIGRP authentication for IPv6 on router R1 are shown using the EIGRP_IPV6_KEY keychain and the cisco123 key chain .

Similar configurations are introduced in R2 and R3.

VERIFICATION OF EIGRP AUTHENTICATION

Once EIGRP message authentication is configured on a router, any adjacent neighbor that has not been configured for authentication is no longer an EIGRP neighbor.
For example, when the Serial 0/0/0 interface of R1 was configured with MD5 authentication, but R2 was not yet configured, the following IOS message appeared on R1:
% DUAL-5-NBRCHANGE: EIGRP-IPv4 1: 
Neighbor 172.16.3.2 (Serial0 / 0/0) is 
down: authentication mode changed
When the adjacent Serial 0/0/0 interface is configured on R2, the adjacency is re-established and the following IOS message appears on R1.
% DUAL-5-NBRCHANGE: EIGRP-IPv4 1: 
Neighbor 172.16.3.2 (Serial0 / 0/0) is 
up: new adjacency
Similar messages also appear on R2.
Adjacencies are only formed when both connection devices have authentication configured, as shown in Image.

To verify that the correct EIGRP adjacencies have formed after configuring them for authentication, use the show ip eigrp neighbors command on each router.
In Image, it is shown that the three routers re-established neighbor adjacencies after EIGRP authentication was configured.

Finally, to verify the neighbors of EIGRP neighbors for IPv6, use the show ipv6 eigrp neighbors command .

EIGRP Equal Cost Load Balancing IPV4 IPV6

EIGRP Equal Cost Load Balancing

This article is on EIGRP interface bandwidth configuration and how to configure EIGRP Equal Cost Load Balancing. This article will also give to a short introduction of EIGRP hello and hold down timer.

EIGRP Bandwidth Configuration For IPv4

By default, EIGRP uses only up to 50% of the bandwidth of an interface for EIGRP information. This prevents the EIGRP process from overusing the links and not allowing enough bandwidth for normal traffic routing.
Use the ip bandwidth-percent eigrp command to configure the percentage of bandwidth that EIGRP can use in an interface.
Router (config-if) # ip bandwidth-percent eigrp  as-number 
In Image, R1 and R2 share a very slow 64 kb / s link.

The configuration to limit the bandwidth used by EIGRP is shown below.
R1 (config) # interface serial 0/0/0
R1 (config-if) # ip bandwidth-percent eigrp 1 40
R1 (config-if) #
R2 (config) # interface serial 0/0/0
R2 (config-if) # ip bandwidth-percent eigrp 1 40
R2 (config-if) # The ip bandwidth-percent eigrp command uses the configured bandwidth (or the default bandwidth) to calculate the percentage that EIGRP can use. In this example, EIGRP is limited to no more than 40% of the link bandwidth. Therefore, EIGRP never uses more than 32 kb / s of link bandwidth for EIGRP packet traffic. To restore the default value, use version no of this command.

IPv6 EIGRP Bandwidth Configuration

To configure the percentage of bandwidth that EIGRP can use for IPv6 on an interface, use the ipv6 bandwidth-percent eigrp command in interface configuration mode. To restore the default value, use version no of this command. The following shows the configuration of the interfaces between R1 and R2 to limit the bandwidth used by EIGRP for IPv6.

R1 (config) # interface serial 0/0/0
R1 (config-if) # ipv6 bandwidth-percent eigrp 2 40
R1 (config-if) #
R2 (config) # interface serial 0/0/0
R2 (config-if) # ipv6 bandwidth-percent eigrp 2 40
R2 (config-if) #

Hello Timer & holddown timer for EIGRP IPV4

EIGRP uses a lightweight greeting protocol to establish and control the connection status of neighbors. The timeout tells the router the maximum amount of time to wait to receive the next greeting, before declaring that the neighbor is unreachable. Hello Timer and timeouts can be configured per interface and do not have to match other EIGRP routers to establish or maintain adjacencies. The command to configure a different greeting interval is as follows:
Router (config-if) # ip hello-interval eigrp  as-number seconds
If you change the greeting interval, make sure that the timeout value is equal to or greater than the greeting interval. Otherwise, neighbor adjacency is deactivated after the timeout expires and before the next greeting interval. To set a different timeout, use the following command:
Router (config-if) # ip hold-time eigrp  as-number secondsThe value of seconds for the greeting and timeout intervals can be from 1 to 65,535. The R1 configuration is shown below to use a 50 second greeting interval and a 150 second timeout. You can use the form no of the two commands to restore the default values.
R1 (config) # interface s0 / 0/0
R1 (config-if) # ip hello-interval eigrp 1 50
R1 (config-if) # ip hold-time eigrp 1 150It is not necessary for the greeting interval time and the waiting time to match for two routers to form an EIGRP adjacency.

Hello Timer  and holddown timer for EIGRP IPV6

EIGRP for IPv6 uses the same hello and wait interval times as EIGRP for IPv4. The interface configuration mode commands are similar to those used for IPv4:
Router (config-if) # ipv6 hello-interval eigrp  as-number seconds
Router (config-if) # ipv6 hold-time eigrp  as-number secondsNext, the configuration of the greeting and waiting interval times for R1 and R2 with EIGRP for IPv6 is shown.
R1 (config) # inter serial 0/0/0
R1 (config-if) # ipv6 hello-interval eigrp 2 50
R1 (config-if) # ipv6 hold-time eigrp 2 150
R2 (config) # inter serial 0/0/0
R2 (config-if) # ipv6 hello-interval eigrp 2 50
R2 (config-if) # ipv6 hold-time eigrp 2 150

IPV4 EIGRP Equal Cost Load Balancing 

Load balancing of equal cost is the ability of a router to distribute outbound traffic across all interfaces that have the same metric from the destination address. Load balancing uses network segments and bandwidth more efficiently. In the case of IP, Cisco IOS software applies load balancing by default with up to four routes of equal cost.
In Image shown below is a EIGRP network topology.

In this topology, R3 has two EIGRP routes of equal cost to the network between R1 and R2, 172.16.3.0/30. One route is through R1 at 192.168.10.4/30, and the other is through R2 at 192.168.10.8/30.

LOAD BALANCING EXAMPLE

The show ip protocols command can be used to verify the amount of routes of equal cost that are currently configured on the router. The result of Image 4 shows that R3 uses the default option of four routes of equal cost.

The routing table maintains both routes. In Image 5, it is shown that R3 has two EIGRP routes of equal cost for the 172.16.3.0/30 network. One route is through R1 in 192.168.10.5, and the other is through R2 in 192.168.10.9.

If the topology of Image 3 is observed, it may seem that the route through R1 is the best route, because there is a 1544 kb / s link between R3 and R1, while the link to R2 is only 1024 kb / s
However, EIGRP only uses the slowest bandwidth in the composite metric, which is the 64 kb / s link between R1 and R2. The two routes have the same 64 kb / s link as the slowest bandwidth, which results in both routes being equal. When process switching is applied to a package, load balancing of routes of equal cost is produced per package. When fast switching is applied to the packets, the load balancing of routes of equal cost is produced by destination. Cisco Express Forwarding (CEF) can perform load balancing by package and destination.

THE MAXIMUM-PATHS COMMAND

By default, the Cisco IOS allows load balancing to use up to four routes of equal cost. However, this can be modified. With the maximum-paths command of the router configuration mode, up to 32 routes of equal cost can be maintained in the routing table.
Router (config-router) # maximum-paths  value
The value argument refers to the number of routes that must be maintained for load balancing. If the value is set to 1 , load balancing is disabled.

IPV6 EIGRP Equal Cost Load Balancing 

In Image 6, the EIGRP network topology for IPv6 is shown. Serial links in the topology have the same bandwidth that is used in the EIGRP topology for IPv4.

Similar to the previous situation for IPv4, R3 has two EIGRP routes of equal cost for the network between R1 and R2, 2001: DB8: CAFE: A001 :: / 64. One route is through R1 on FE80 :: 1, and the other is through R2 on FE80 :: 2.
In following Figure, it is shown that the EIGRP metrics for the 2001: DB8: CAFE: A001 :: / 64 and 172.16.3.0/30 networks are the same in the IPv6 routing table and in the IPv4 routing table.

This is because the composite metric of EIGRP is the same in EIGRP for IPv6 and for IPv4.

LOAD BALANCING WITH DIFFERENT COST

EIGRP for IPv4 and for IPv6 can also balance traffic on several routes with different metrics. This type of balancing is called “ load balancing with different costs ”. Setting a value with the variance command in router configuration mode allows EIGRP to install multiple routes without loops and at a different cost in a local routing table.

• To be installed in the local routing table, a route that is discovered through EIGRP must meet two criteria:
• The route must not have loops and must be a feasible successor or have a reported distance less than the total distance.
• The route metric must be less than the best route metric (the successor) multiplied by the variation configured on the router.

For example, if the variation is 1, only routes with the same metric as the successor are installed in the local routing table. If the variation is 2, any route discovered by EIGRP with a metric less than double the successor's metric is installed in the local routing table.
To control how traffic is distributed between routes when there are several routes with different costs for the same destination network, use the traf fi c-share balanced command . Traffic is distributed proportionally according to the proportion of costs.

Configuration of Default Routes in EIGRP

Configuration of Default Routes in EIGRP

In this post you will find the method on how to Configuration of Default Routes in EIGRP. One method to configure a default route within the EIGRP routing domain is by using the redistribute static command . You will find EIGRP Verification commands to include this static route in EIGRP updates to other routers.

Configuration of Default Static Routes in EIGRP

The use of a static route at 0.0.0.0/0 as the default route does not constitute protocol dependent routing. The default static route " quad zero " can be used with any routing protocol currently supported. In general, the default static route is configured on the router that has a connection to a network outside the EIGRP routing domain; for example, to an ISP. In below image, R2 is the gateway router that connects the EIGRP routing domain to the Internet.

When the default static route is configured, it is necessary to propagate that route throughout the EIGRP domain, as shown in Image 2.

One method to propagate a default static route within the EIGRP routing domain is by using the redistribute static command . This command tells EIGRP to include static routes in its EIGRP updates to other routers.
The default static route configuration and the redistribute static command on router R2 are shown below.

R2 (config) # ip route 0.0.0.0 0.0.0.0 serial 0/1/0 
R2 (config) # router eigrp 1 
R2 (config-router) # redistribute static

Now, it is verified that router R2 received the default route and installed it in its IPv4 routing table.

R2 # show ip route | include 0.0.0.0
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
S * 0.0.0.0/0 is directly connected, Serial0 / 1/0 
R2 #

In image below, the show ip protocols command verifies that R2 redistributes static routes within the EIGRP routing domain.

Verification of Default Routes Configurations in EIGRP

In the illustration, a part of the IPv4 routing tables of R1 and R3 is shown.

In the routing tables of R1 and R3, observe the routing origin and administrative distance of the new default route that was discovered using EIGRP. The default route entry that was discovered by EIGRP is identified by the following:

• D : This route was discovered in an EIGRP routing update.
• * : The route is a candidate for a default route.
• EX : The route is an external EIGRP route, in this case, a static route outside the EIGRP routing domain.
• 170 : administrative distance of an external EIGRP route.

Note that R1 selects R3 as the successor to the default route, because it has a smaller feasible distance. Default routes provide a default route to exit the routing domain and, like summary routes, minimize the number of entries in the routing table.

EIGRP FOR IPV6: DEFAULT ROUTE

Remember that EIGRP maintains independent tables for IPv4 and IPv6, therefore, a default IPv6 route must be propagated separately, as shown in Image 5.

Similar to what happens in EIGRP for IPv4, a default static route is configured on the gateway router (R2), as shown in Figure:

R2 (config) # ipv6 route :: / 0 serial 0/1/0 
R2 (config) # ipv6 router eigrp 2 
R2 (config-rtr) # redistribute static

The prefix :: / 0 and the prefix length are equivalent to the address and subnet mask 0.0.0.0 0.0.0.0 used in IPv4. Both are addresses composed entirely of zeros and with a prefix length / 0. The default static IPv6 route is redistributed in the EIGRP domain for IPv6 using the same static redistribute command that was used in EIGRP for IPv4.
Note : Some Cisco IOS may require that the redistribute static command include the EIGRP metric parameters so that the static route can be redistributed.

Verification of IPv6 Default Routes in EIGRP

Finally, the propagation of the IPv6 default static route can be verified by reviewing the Rv IPv6 routing table with the show ipv6 route command , as shown in Image 6.

Note that the successor or address of the next hop is not R2, but R3. This is because R3 provides a better route to R2, with a lower metric cost than R1.

Configuring Basic EIGRP For IPv6 Cisco

Configuring Basic EIGRP For IPv6 Cisco

This section explain how to Configuring Basic EIGRP For IPv6 and compares the characteristics and operation of EIGRP for IPv4. It is also presented as an example to configure EIGRP for IPv6 in a small routed network.
Similar to its counterpart for IPv4, EIGRP for IPv6 exchanges routing information to complete the IPv6 routing table with remote prefixes. EIGRP for IPv6 has the same functionality as EIGRP for IPv4, but uses IPv6 as the network layer protocol, communicates with peers EIGRP for IPv6 and announces IPv6 routes. EIGRP for IPv6 also uses DUAL as a computation engine to ensure main and backup routes without loops throughout the entire routing domain. As with all IPv6 routing protocols, EIGRP for IPv6 has separate processes from those of its counterpart for IPv4. The processes and operations are basically the same as in the IPv4 routing protocol; however, they run independently.
EIGRP for IPv4 and EIGRP for IPv6 have EIGRP neighbor tables, EIGRP topology tables and separate IP routing tables. EIGRP for IPv6 is a separate protocol dependent module (PDM). The EIGRP configuration and verification commands for IPv6 are very similar to commands used to configure EIGRP for IPv4. These commands are described later in this section.

Comparison Between EIGRO For IPv4 & IPv6

The following is a comparison of the main features of EIGRP for IPv4 and EIGRP for IPv6:

• Routes announced : EIGRP for IPv4 announces IPv4 networks, while EIGRP for IPv6 announces IPv6 prefixes.
• Distance vector : EIGRP for IPv4 and IPv6 are advanced distance vector routing protocols. Both protocols use the same administrative distances.
• Convergence technology : EIGRP for both IPv4 and IPv6 use the DUAL algorithm. Both protocols use the same DUAL techniques and processes, including successor, FS, FD and RD.
• Metric : EIGRP for both IPv4 and IPv6 use bandwidth, delay, reliability and load for its composite metric.
• Transport protocol: the reliable transport protocol (RTP) is responsible for the guaranteed delivery of EIGRP packets to all neighbors for both protocols, EIGRP for IPv4 and IPv6.
• Update messages : EIGRP for both IPv4 and IPv6 sends incremental updates when the status of a destination changes. The terms "partial" and "limited" are used to refer to the updates of both protocols.
• Neighbor discovery mechanism : EIGRP for IPv4 and EIGRP for IPv6 both use a simple hello mechanism to discover neighboring routers and form adjacencies.
• Source and destination addresses: EIGRP for IPv4 sends messages to the multicast address 224.0.0.10. EIGRP for IPv6 sends its messages to the multicast address FF02 :: A.
• Authentication : EIGRP for IPv4 can use unencrypted text authentication or message 5 (MD5) synthesis authentication. EIGRP for IPv6 uses MD5.
• Router ID : EIGRP for IPv4 and EIGRP for IPv6 use a 32-bit number for the EIGRP router ID.

IPV6 Link-Local Addresses

Routers that execute a dynamic routing protocol, such as EIGRP, exchange messages between neighbors on the same subnet or link.
Routers only need to send and receive routing protocol messages with their directly connected neighbors. These messages are always sent from the source IP address of the router that is forwarding.

IPv6 link-local addresses are ideal for this purpose. A link-local IPv6 address allows a device to communicate with other devices with IPv6 enabled on the same link and only on that link (subnet).
Packets with a link-local source or destination address cannot be routed beyond the link on which the packet originated.
EIGRP messages for IPv6 are sent by the following:

• Source IPv6 address : this is the link-local IPv6 address of the output interface.
• Destination IPv6 address : When a packet must be sent to a multicast address, it is sent to the IPv6 multicast address FF02 :: A, the scope of all EIGRP routers with link-local. If the packet can be sent as a unicast address, it is sent to the link-local address of the neighboring router.

Configuration Example of EIGRP for IPv6

In Image, the network topology that is used to configure EIGRP for IPv6 is shown. If dual-stack is running on the network and IPv4 and IPv6 are used on all devices, EIGRP can be configured for both IPv4 and IPv6 on all routers. However, this section focuses only on EIGRP for IPv6 .

Only global unicast IPv6 addresses were configured on each router.
The interface startup configuration on each router is shown below.

R1 # show running-config
interface GigabitEthernet0 / 0
 ipv6 address 2001: DB8: CAFE: 1 :: 1/64
!
Serial interface0 / 0/0
 ipv6 address 2001: DB8: CAFE: A001 :: 1/64
 clock rate 64000
!
Serial interface0 / 0/1
 ipv6 address 2001: DB8: CAFE: A003 :: 1/64

R2 # show running-config
!
interface GigabitEthernet0 / 0
 ipv6 address 2001: DB8: CAFE: 2 :: 1/64
!
Serial interface0 / 0/0
 ipv6 address 2001: DB8: CAFE: A001 :: 2/64
!
Serial interface0 / 0/1
 ipv6 address 2001: DB8: CAFE: A002 :: 1/64
 clock rate 64000
!
Serial interface
 ipv6 address 2001: DB8: FEED: 1 :: 1/64

R3 # show running-config
!
interface GigabitEthernet0 / 0
 ipv6 address 2001: DB8: CAFE: 3 :: 1/64
!
Serial interface0 / 0/0
 ipv6 address 2001: DB8: CAFE: A003 :: 2/64
 clock rate 64000
! 
Serial interface0 / 0/1
 ipv6 address 2001: DB8: CAFE: A002 :: 2/64

Observe the interface bandwidth values ​​of the EIGRP configuration for previous IPv4 . Because EIGRP uses the same metrics for IPv4 and IPv6, modifying the bandwidth parameters influences both routing protocols.

EIGRP IPV6 LINK-LOCAL ADDRESS CONFIGURATION

Link-local addresses are created automatically when a global unicast IPv6 address is assigned to the interface. Global unicast addresses are not required on an interface, but link-local IPv6 addresses are required.
Unless configured manually, Cisco routers create the link-local address using the FE80 :: / 10 prefix and the EUI-64 process.
EUI-64 involves using the 48-bit Ethernet MAC address, inserting FFFE in the middle and inverting the seventh bit. For serial interfaces, Cisco uses the MAC address of an Ethernet interface. A router with several serial interfaces can assign the same link-local address to each IPv6 interface, because link-local addresses only need to be local on the link.
Link-local addresses created with the EUI-64 format or, in some cases, with random interface IDs, make it difficult to recognize and remember those addresses. Because IPv6 routing protocols use link-local IPv6 addresses for unicast addressing and next hop address information in the routing table, it is usually sought to be an easy address to recognize. Configuring the link-local address manually allows you to create a recognizable address and easier to remember.
Link-local addresses can be configured manually using the same interface configuration mode command that is used to create global unicast IPv6 addresses, but with different parameters:
Router (config-if) # ipv6 address link-local-address link-local
A link-local address has a prefix within the range FE80 to FEBF. When an address begins with this hextet (16-bit segment), the link-local keyword must be written after the address.

EIGRP CONFIGURATION EXAMPLE

The following shows the configuration of a link-local address using the ipv6 address command of the interface configuration mode.
R1 (config) # interface s 0/0/0 
R1 (config-if) # ipv6 address fe80 :: 1?
 link-local Use link-local address

R1 (config-if) # ipv6 address fe80 :: 1 link-local 
R1 (config-if) # exit 
R1 (config) # interface s 0/0/1 
R1 (config-if) # ipv6 address fe80 :: 1 link -local 
R1 (config-if) # exit 
R1 (config) # interface g 0/0 
R1 (config-if) # ipv6 address fe80 :: 1 link-local 
R1 (config-if) #
The FE80 :: 1 link-local address is used so that it is easily recognized that it belongs to router R1. The same link-local IPv6 address is configured on all R1 interfaces. You can configure FE80 :: 1 on each link, because it only has to be unique on that link.
Similar to R1, router R2 is configured with FE80 :: 2 as the link-local IPv6 address on all its interfaces.
R2 (config) # interface s 0/0/0
R2 (config-if) # ipv6 address fe80 :: 2 link-local
R2 (config-if) # exit
R2 (config) # interface s 0/0/1
R2 (config-if) # ipv6 address fe80 :: 2 link-local
R2 (config-if) # exit
R2 (config) # interface s 0/1/0
R2 (config-if) # ipv6 address fe80 :: 2 link-local
R2 (config-if) # exit
R2 (config) # interface g 0/0
R2 (config-if) # ipv6 address fe80 :: 2 link-local
R2 (config-if) #
As shown in Image, the show ipv6 interface brief command is used to verify IPv6 link-local and global unicast addresses on all interfaces.

 CONFIGURATION OF THE EIGRP ROUTING PROCESS FOR IPV6

The ipv6 unicast-routin g command of the global configuration mode enables IPv6 routing on the router. This command is necessary before you can configure any IPv6 routing protocol. It is not required to configure IPv6 addresses on the interfaces, but it is necessary to enable the router as an IPv6 router.

EIGRP FOR IPV6

The following global configuration mode command is used to enter router configuration mode for EIGRP for IPv6:
Router (config) # ipv6 router eigrp  autonomous-system
Similar to what happens in EIGRP for IPv4, the autonomous-system value must be the same on all routers in the routing domain. According to the following scheme, the EIGRP routing process for IPv6 could not be configured until IPv6 routing was enabled with the ipv6 unicast-routing global configuration mode command.
R1 (config) # ipv6 router eigrp 2 
% IPv6 routing not enabled
R1 (config) # ipv6 unicast-routing 
R1 (config) # ipv6 router eigrp 2 
R1 (config-rtr) #

EIGRP ROUTER ID

As shown below, the eigrp router-id command is used to configure the router ID.
R1 (config) # ipv6 router eigrp 2 
R1 (config-rtr) # eigrp router-id 1.0.0.0 
R1 (config-rtr) #
EIGRP for IPv6 uses a 32-bit value for the router ID. To obtain that value, EIGRP for IPv6 uses the same process as EIGRP for IPv4. The eigrp router-id command takes precedence over any loopback address or IPv4 physical interface address. If an EIGRP router for IPv6 does not have any active interface with an IPv4 address, the eigrp router-id command is required.
The router ID must be a unique 32-bit number in the EIGRP routing domain for IP; otherwise, routing inconsistencies may occur.
By default, the EIGRP process for IPv6 is in the disabled state. The no shutdown command is required to activate the EIGRP process for IPv6, as shown below:
R1 (config) # ipv6 router eigrp 2 
R1 (config-rtr) # eigrp router-id 1.0.0.0 
R1 (config-rtr) # no shutdown
This command is not required for EIGRP for IPv4. Although EIGRP for IPv6 is enabled, you cannot send or receive updates from neighbor adjacencies or routing until EIGRP is activated on the appropriate interfaces.
The no shutdown command and a router ID are required for the router to establish neighbor adjacencies.
The following shows the EIGRP configuration for IPv6 complete for router R2.
R2 (config) # ipv6 unicast-routing 
R2 (config) # ipv6 router eigrp 2 
R2 (config-rtr) # eigrp router-id 2.0.0.0 
R2 (config-rtr) # no shutdown

IPV6 EIGRP INTERFACE COMMAND

EIGRP for IPv6 uses a different method to enable an interface for EIGRP. Instead of using the router's network configuration mode command to specify matching interface addresses, EIGRP for IPv6 is configured directly on the interface.
Use the following interface configuration mode command to enable EIGRP for IPv6 on an interface:
Router (config-if) # ipv6 eigrp  autonomous-system
Similar to the network command that is used in EIGRP for IPv4, the ipv6 eigrp interface command performs the following:

• Enable the interface to form adjacencies and send or receive EIGRP updates for IPv6.
• It includes the interface prefix (network) in the EIGRP routing updates for IPv6.

In above Image, the configuration to enable EIGRP for IPv6 on the interfaces of routers R1 and R2 is shown. Look at the message below the serial interface 0/0/0 on R2:
% DUAL-5-NBRCHANGE: EIGRP-IPv6 2: Neighbor FE80 :: 1 
(Serial0 / 0/0) is up: new adjacency
This message indicates that R2 formed an EIGRP-IPv6 adjacency with the neighbor at the link-local address FE80 :: 1. Because static link-local addresses were configured on all three routers, it is easy to determine that this adjacency is with router R1 (FE80 :: 1).

PASSIVE INTERFACE WITH EIGRP FOR IPV6

The same passive-interface command that is used for IPv4 is used to configure an interface as passive in EIGRP for IPv6. As shown below, the show ipv6 protocols command is used to verify the configuration.

EIGRP DUAL The Diffusion Update Algorithm Complete Concepts

EIGRP DUAL The Diffusion Update Algorithm 

Article will provide the complete concepts about EIGRP DUAL (The Diffusion Update Algorithm) and the EIGRP topology table are fully explained. You will also learn how the DUAL finite state machine (FSM) works and its use is exemplified.
EIGRP uses the DUAL convergence algorithm which helps the networks to avoid routing loops. Routing loops, even temporary ones, can be detrimental to network performance. Distance vector routing protocols, such as RIP, avoid routing loops with waiting timers and split horizon. Although EIGRP uses both techniques, it uses them somewhat differently; The main way in which EIGRP avoids routing loops is with the DUAL algorithm.
What is EIGRP DUAL Algorithm ?
EIGRP uses the diffusion update algorithm (DUAL) to provide the best route without loops and the best backup routes without loops. The DUAL algorithm is used to ensure that there are no loops in each instance through the computation of a route. In the context of DUAL several terms are used, which are analyzed in more detail in this section:

• Successor
• Feasible distance (FD)
• Feasible Successor (FS)
• Published Distance (AD) or Notified Distance (RD):
• Feasible condition or Feasibility condition (FC)

These terms and concepts are essential in the DUAL loop prevention mechanism. EIGRP DUAL provides:

• Routes without loops
• Backup routes without loops that can be used immediately
• Fast convergence
• Minimal bandwidth usage with limited updates

EIGRP Successors and Feasible Distance?

In Image, the topology for this topic is shown. A successor is a neighboring router that is used for packet forwarding and is the least expensive route to the destination network. The successor's IP address is shown in a routing table entry just after the word via.

FD is the lowest metric calculated to reach the destination network. FD is the metric listed in the routing table entry as the second number within the square brackets. As in other routing protocols, this is also known as the “ route metric” .

Analyze the routing table for R2 in Image 2 and note that the best EIGRP route for the 192.168.1.0/24 network is through router R3 and that the feasible distance is 3 012 096. This is the metric that was calculated in the previous topic.

FEASIBLE SUCCESSORS, FEASIBILITY CONDITION AND DISTANCE REPORTED

DUAL can converge quickly after a change in the topology, because it can use backup routes to other networks without recalculating DUAL. These backup routes are known as " feasible successors " (FS).
An FS is a neighbor that has a backup route without loops to the same network as the successor and satisfies the feasibility condition (FC). The successor of R2 for the 192.168.1.0/24 network is R3, which provides the best route or the lowest metric to the destination network. Note in Figure 1 that R1 provides an alternative route, but is it an FS? Before R1 can be an FS for R2, it must meet the FC.
The FC is met when the notified distance (RD) from a neighbor to a network is less than the feasible distance from the local router to the same destination network. If the reported distance is shorter, it represents a route without loops. The reported distance is simply a feasible distance from the EIGRP neighbor to the same destination network. The reported distance is the metric that a router informs a neighbor about its own cost to that network.

EXAMPLES:  Feasible Successor 

In following figure, the feasible distance from R1 to 192.168.1.0/24 is 2 170 112.

• R1 informs R2 that its FD at 192.168.1.0/24 is 2 170 112.
• From the perspective of R2, 2 170 112 is the RD of R1.

R2 uses this information to determine if R1 meets the FC and therefore can be an FS.
As shown in following image, because the RD of R1 (2 170 112) is lower than the FD of R2 (3 012 096), R1 meets the FC.

R1 is now an FS for R2 to the 192.168.1.0/24 network.
If there is an error in the route from R2 to 192.168.1.0/24 through R3 (successor), R2 immediately installs the route through R1 (FS) in its routing table. R1 becomes the new successor for the route of R2 to this network, as shown in Image below.

EIGRP TOPOLOGY TABLE

The EIGRP topology table contains all known routes to each EIGRP neighbor. As an EIGRP router discovers routes from its neighbors, those routes are installed in its EIGRP topology table. If you want to learn about EIGRP Commands you can visit here.

As shown in Image 6, use the show ip eigrp topology command to view the topology table. The topology table includes all successors and FS to the destination networks calculated by DUAL. Only the successor is installed in the IP routing table.

SHOW IP EIGRP TOPOLOGY COMMAND 

As shown in Image, the first line in the topology table shows the following:

• P : route in passive state. When DUAL does not perform its broadcast counts to determine the route for a network, the route is in stable mode, known as " passive state ".

If DUAL recalculates or searches for a new route, the route is active, and an “A” is displayed. All routes in the topology table should be in the passive state for a stable routing domain.
192.168.1.0/24 : destination network, which is also found in the routing table.

• 1 successors : shows the number of successors for this network. If there are several routes of the same cost to this network, there are several successors.
• FD is 3012096 : FD is the metric of EIGRP to reach the destination network. This is the metric shown in the IP routing table.

UNDERSTANDING THE RESULT

As shown in Image, the first sub-entry in the result shows the successor:

• via 192.168.10.10 : address of the next hop of the successor, R3. This address is shown in the routing table.
• 3012096 : FD at 192.168.1.0/24. It is the metric shown in the IP routing table.
• 2816 : RD of the successor; It is the cost of R3 to reach this network.
• Serial 0/0/1 : output interface used to reach this network, which is also shown in the routing table.

ABSENCE OF FEASIBLE SUCCESSOR

To see how DUAL uses successors and FSs, examine the routing table of R1 based on the assumption that the network is convergent, as shown in the figure.

In the following result, a partial result of the show ip route command is shown on R1. The route to 192.168.1.0/24 shows that the successor is R3 through 192.168.10.6, with an FD of 2 170 112.
R1 # show ip route
<result omitted>
D 192.168.1.0/24 [ 90/2170112 ] via 192.168.10.6 ,
01:23:13, Serial0 / 0/1
The IP routing table only includes the best route, that is, the successor. To see if there is any FS, we must analyze the EIGRP topology table.
In the following topology table, only the successor 192.168.10.6 is shown, which is R3.
R1 # show ip eigrp topology
<result omitted>
P 192.168.1.0/24, 1 successors, FD is 2170112
 via 192.168.10.6 (2170112/2816), Serial0 / 0/1
There is no FS. When looking at the actual physical topology or the network diagram, it is obvious that there is a backup route for 192.168.1.0/24 through R2. R2 is not an FS, because it does not meet the FC. However, when observing the topology, it is obvious that R2 is a backup route, since EIGRP does not have a map of the network topology. EIGRP is a distance vector routing protocol and only knows the information of the remote network through its neighbors.

THE SHOW IP EIGRP TOPOLOGY ALL-LINKS COMMAND

DUAL does not store the route through R2 in the topology table. All links can be displayed using the show ip eigrp topology all-links command . This command shows the links, regardless of whether they meet the FC or not.
As shown in Image, the show ip eigrp topology all-links command shows all possible routes to a network, including successors, FSs and even non-FS routes. The FD of R1 at 192.168.1.0/24 is 2 170 112, through the successor R3. For R2 to be considered an FS, it must meet the FC. The RD from R2 to R1 to reach 192.168.1.0/24 must be lower than the current FD of R1. According to the illustration, the RD of R2 is 3 012 096, which is higher than the current FD of R1, of 2 170 112.

Although R2 looks like a possible backup route for 192.168.1.0/24, R1 does not know that the route is not a potential loop back through itself. EIGRP is a distance vector routing protocol, without the ability to view a topology map without complete network loops.
The DUAL method to ensure that a neighbor has a loopless route is that the neighbor's metric meets the FC. By ensuring that the neighbor's RD is lower than its own FD, the router can assume that that neighboring router is not part of its own announced route and, therefore, always avoid a potential loop.
R2 can be used as a successor if R3 fails, however, there is a longer delay before adding it to the routing table. Before R2 can be used as a successor, DUAL must carry out more processes.

DUAL FINITE STATE MACHINE (FSM)

The core of EIGRP are DUAL and its EIGRP route calculation engine. The real name of this technology is DUAL Finite State Machine (FSM). This FSM contains all the logic used to calculate and compare routes in an EIGRP network. The figure shows a simplified version of DUAL FSM.
An FSM is an abstract machine, not a mechanical device with moving parts. FSM defines a set of possible states that can be passed through, what events cause these states and what events are the result of these states. Designers use the WSF to describe the way in which a device, a computer program or a routing algorithm reacts to a set of input events.
The WFTUs exceed the scope of this course. However, the concept is used to examine some of the results of the EIGRP FSMs by using the debug eigrp fsm command . Use this command to analyze what DUAL does when a route is deleted from the routing table.

DUAL: FEASIBLE SUCCESSOR

Currently, R2 uses R3 as the successor to 192.168.1.0/24. In addition, R2 currently includes R1 as an FS, as shown in Image.

The result of show ip eigrp topology for R2 verifies that R3 is the successor and R1 is the FS for network 192.168.1.0/24.
R2 # show ip eigrp topology
P 192.168.1.0/24, 1 successors, FD is 3012096
 via 192.168.10.10 (3012096/2816), Serial0 / 
 0/1 via 172.16.3.1 (41024256/2170112), Serial0 / 0/0
To understand how DUAL can use an FS when the route used by the successor is not available, a link failure between R2 and R3 is simulated.

LINK FAILURE SIMULATION

Before simulating the failure, DUAL debugging must be enabled using the debug eigrp fsm command on R2, as shown in Image 14. The link failure is simulated by the shutdown command on the Serial 0/0/1 interface of the R2.

The debug result shows the activity generated by DUAL when a link is out of order. The R2 must inform all EIGRP neighbors of the lost link and also update their own routing and topology tables. In this example, only selected debug results are shown. Note in particular that the DUAL FSM searches for and finds an FS for the route in the EIGRP topology table.
The FS R1 now becomes the successor and is installed in the routing table as the new best route to 192.168.1.0/24. With an FS, this change in the routing table happens almost immediately.
R2 # show ip route
D 192.168.1.0/24 [90/41024256] via 172.16.3.1, 00:15:51, 
Serial0 / 0/0
As shown below, the topology table for R2 now shows R1 as the successor, and there are no new FS. If the link between R2 and R3 is activated again, R3 becomes the successor again and R1 becomes the FS once again.
R2 # show ip eigrp topology
P 192.168.1.0/24, 1 successors, FD is 41024256
 via 172.16.3.1 (41024256/2170112), Serial0 / 0/0

EIGRP Metric And K Values

EIGRP Metric And K Values

EIGRP Metric And K Values are important concepts for configuration of EIGRP on Cisco Router. This post also explains how neighbor adjacencies are formed and the purpose of the metrics in EIGRP. The objective of any dynamic routing protocol is to discover remote networks of other routers and achieve convergence in the routing domain. Before any EIGRP update package can be exchanged between routers, EIGRP must discover its neighbors. Neighboring EIGRP are other routers that run EIGRP on directly connected networks.

How EIGRP NEIGHBORS and ADJACENCY Form

EIGRP uses greeting packages to establish and maintain neighbor adjacencies. For two EIGRP routers to become neighbors, several parameters must match between them. For example, two EIGRP routers must use the same EIGRP metric parameters and both must be configured with the same autonomous system number. Each EIGRP router maintains a neighbor table, which contains a list of the routers in the shared links that have an EIGRP adjacency with that router. The neighbor table is used to track the status of these EIGRP neighbors.
The illustration shows two EIGRP routers that exchange initial EIGRP hello packets. When a router with EIGRP enabled receives a hello packet in an interface, it adds that router to its neighbor table.

1. A new router (R1) appears on the link and sends an EIGRP hello packet through all its configured EIGRP interfaces.
2. Router R2 receives the hello packet on an interface with EIGRP enabled. R2 responds with an EIGRP update package that contains all the routes included in its routing table, except those discovered through that interface (split horizon). However, neighbor adjacency is not established until R2 also sends an EIGRP hello packet to R1.
3. Once both routers exchange greetings, neighbor adjacency is established. R1 and R2 update their EIGRP neighbor tables and add the adjacent router as a neighbor.

EIGRP TOPOLOGY TABLE

EIGRP updates contain networks that can be reached from the router that sends the update. As EIGRP updates are exchanged between neighbors, the receiving router adds those entries to its EIGRP topology table.
Each EIGRP router maintains a topology table for each configured routing protocol, such as IPv4 and IPv6. The topology table includes the route entries for each destination that the router discovers from its directly connected EIGRP neighbors.
The illustration shows the continuation of the initial route discovery process on the previous page. Now, the topology table update is displayed.

When a router receives an EIGRP routing update, it adds the routing information to its EIGRP topology table and responds with an EIGRP acknowledgment.

1. R1 receives the EIGRP update from neighbor R2 and includes information about the routes announced by the neighbor, including the metric to each destination. R1 adds all update entries to its topology table. The topology table includes all destinations announced by neighboring (adjacent) routers and the cost (metric) to reach each network.
2. EIGRP update packages use reliable delivery; therefore, R1 responds with an EIGRP acknowledgment packet that informs R2 that it received the update.
3. The R1 sends an EIGRP update to the R2 in which it announces the networks it knows, except those discovered from the R2 (split horizon).
4. R2 receives the EIGRP update from neighbor R1 and adds this information to its own topology table.
5. The R2 responds to the EIGRP update package of R1 with an EIGRP acknowledgment.

EIGRP CONVERGENCE

In the illustration, the last steps of the initial route discovery process are shown.

After receiving the EIGRP update packets from R2, R1 uses the information in the topology table to update its IP routing table with the best route to each destination, including the metric and router of the next hop.
In the same way as R1, R2 updates its IP routing table with the best routes to each network.
At this point, EIGRP is considered to be in convergent state on both routers.

EIGRP K Values & Metrics

By default, EIGRP uses the following values ​​in its composite metric to calculate the preferred route to a network:

• Bandwidth : the slowest bandwidth between all output interfaces, along the route from origin to destination.
• Delay : the accumulation (sum) of all interface delays along the route (in tens of microseconds).

The following values ​​can be used, but not recommended, because they usually result in frequent recalculations of the topology table:

• Reliability : represents the worst reliability between origin and destination, which is based on keepalives.
• Load : represents the worst load on a link between origin and destination, which is calculated based on the packet speed and the configured bandwidth of the interface.

While the MTU is included in the routing table updates, it is not a routing metric used by EIGRP.

EIGRP COMPOSITE METRIC

In Image 4, the compound metric formula that EIGRP uses is shown.

The formula consists of the values ​​K1 to K5, known as " EIGRP metric weights ". K1 and K3 represent bandwidth and delay, respectively. K2 represents load, and K4 and K5 represent reliability.
By default, K1 and K3 are set to 1, and K2, K4 and K5 are set to 0. As a result, only the bandwidth and delay values ​​are used in the calculation of the default composite metric. In EIGRP for IPv4 and EIGRP for IPv6 the same formula is used for the composite metric.
The method to calculate the metric (k values) and the EIGRP autonomous system number must match between EIGRP neighbors. If they do not match, the routers do not form an adjacency.
The default k values ​​can be changed with the metric weights command of the router configuration mode:
Router (config-router) # metric weights tos k1 k2 k3 k4 k5
Note : the modification of the value of metric weights is generally not recommended and exceeds the scope of this course. However, its importance is relevant to the establishment of neighborhood adjacencies. If one router modified the weights of the metric and another router did not, an adjacency is not formed.

VERIFICATION OF THE EIGRP K VALUES

The show ip protocols command is used to verify the k values. In Image 5, the result of the command for R1 is shown. Note that the k values ​​in R1 are set to the default setting.

INTERFACE VALUE ANALYSIS

The show interfaces command displays information about the interfaces, including the parameters used to calculate the EIGRP metric. The illustration shows the command show interfaces for the Serial 0/0/0 interface on R1.

• BW : interface bandwidth (in kilobits per second | kb / s = Kbit / sec ).
• DLY : interface delay (in microseconds | usec ).
• Reliability : interface reliability expressed as a fraction of 255 (255/255 is a 100% reliability), calculated as an exponential average for five minutes.

By default, EIGRP does not include its value when calculating the metric.

• Txload, Rxload : load transmitted and received through the interface expressed as a fraction of 255 (255/255 is completely saturated), calculated as an exponential average for five minutes. By default, EIGRP does not include its value when calculating the metric.

EIGRP BANDWIDTH METRIC

The bandwidth metric is a static value that some routing protocols, such as EIGRP and OSPF, use to calculate the routing metric .
The bandwidth is shown in kilobits per second (kb / s). Most serial interfaces use the default bandwidth value of 1544 kb / s or 1,544,000 b / s (1,544 Mb / s). This is the bandwidth of a T1 connection.

However, some serial interfaces use another default bandwidth value. In Image 7, the topology used in this section is shown. The types of serial interfaces and their associated bandwidths may not necessarily reflect the most frequent types of connections found in networks today.
Always verify bandwidth with the show interfaces command . (EIGRP Verification Commands Cisco)
The default bandwidth value may or may not reflect the actual physical bandwidth of the interface. If the actual bandwidth of the link differs from the default bandwidth value, the bandwidth value must be modified.
BANDWIDTH PARAMETER SETTING
On most serial links, the default bandwidth metric is 1544 kb / s. Because EIGRP and OSPF use bandwidth in default metric calculations, a correct value for bandwidth is very important for the accuracy of routing information.
Use the following interface configuration mode command to modify the bandwidth metric:
Router (config-if) # bandwidth  kilobits-bandwidth-value
Use the no bandwidth command to restore the default value.
The configuration used in the three routers to modify the bandwidth in the appropriate serial interfaces is shown below.
R1 (config) # interface s 0/0/0
R1 (config-if) # bandwidth 64
R2 (config) # interface s 0/0/0
R2 (config-if) # bandwidth 64
R2 (config-if) # exit
R2 (config) # interface s 0/0/1
R2 (config-if) # bandwidth 1024
R3 (config) # interface s 0/0/1
R3 (config-if) # bandwidth 1024

BANDWIDTH PARAMETER VERIFICATION

Use the show interfaces command to verify the new bandwidth parameters, as shown in Image. It is important to modify the bandwidth metric on both sides of the link to ensure proper routing in both directions.

Modifying the bandwidth value does not change the actual bandwidth of the link. The bandwidth command only modifies the bandwidth metric that routing protocols use, such as EIGRP and OSPF.

EIGRP DELAY METRIC

The delay is the measure of the time it takes for a package to cross the route.
The delay metric (DLY) is a static value determined based on the type of link to which the interface is connected and is expressed in microseconds.
Delay is not measured dynamically. In other words, the router does not really track the time it takes for packets to reach the destination. The delay value, like the bandwidth value, is a default value that the network administrator can modify.
When used to determine the EIGRP metric, the delay is the accumulation (sum) of all interface delays along the route (measured in tens of microseconds).

In the table in Image, the default delay values ​​for various interfaces are shown. Note that the default value is 20,000 microseconds for serial interfaces and 10 microseconds for GigabitEthernet interfaces.

Use the show interfaces command to verify the delay value on an interface, as shown in Image 10.

While an interface with multiple bandwidths may have the same default delay value, Cisco recommends not changing the delay parameter, unless the network administrator has a specific reason for doing so.

HOW TO CALCULATE THE EIGRP METRIC

While EIGRP automatically calculates the routing table metric used to choose the best route, it is important that the network administrator understand how these metrics were determined.
The figure shows the composite metric used by EIGRP. By using the default values ​​for K1 and K3, the calculation can be simplified to the slowest bandwidth (or minimum bandwidth), plus the sum of all delays.

In other words, by analyzing the bandwidth and delay values ​​for all output interfaces on the route, we can determine the EIGRP metric as follows:

• Step 1 . Determine the link with the slowest bandwidth. Use that value to calculate the bandwidth (10 000 000 / bandwidth).
• Step 2 . Determine the delay value for each exit interface on the way to the destination. Add the delay values ​​and divide by 10 (sum of the delays / 10).
• Step 3 . Add the calculated bandwidth and delay values ​​and multiply the sum by 256 to obtain the EIGRP metric.

The result of the routing table for R2 shows that the route to 192.168.1.0/24 has an EIGRP metric of 3,012,096.

2.6. EIGRP METRIC CALCULATION
In Image , the topology of the three routers is shown. This example illustrates how EIGRP determines the metric shown in the R2 routing table for the 192.168.1.0/24 network.

EIGRP BANDWIDTH

EIGRP uses the slowest bandwidth in the calculation of its metric. The slowest bandwidth can be determined by analyzing each interface between R2 and the destination network 192.168.1.0.
The Serial 0/0/1 interface on R2 has a bandwidth of 1024 kb / s. The GigabitEthernet 0/0 interface on R3 has a bandwidth of 1 000 000 kb / s. Therefore, the slowest bandwidth is 1024 kb / s and is used in the calculation of the metric.
EIGRP divides a reference bandwidth value of 10,000,000 by the value in kb / s of the interface bandwidth. As a result, higher bandwidth values ​​receive a lower metric, and lower bandwidth values ​​receive a higher metric. 10 000 000 is divided by 1024.
If the result is not an integer, the value is rounded down. In this case, 10 000 000 divided by 1024 is equal to 9765.625. Decimals (625) are discarded, and the result is 9765 for the bandwidth portion of the composite metric, as shown in Image.

EIGRP TIME DELAY

As shown in Image, the same output interfaces are used to determine the delay value.

EIGRP uses the sum of all delays to the destination. The Serial 0/0/1 interface on R2 has a delay of 20,000 microseconds. The Gigabit 0/0 interface on R3 has a delay of 10 microseconds. The sum of these delays is divided by 10.
In the example, (20,000 + 10) / 10, results in a value of 2001 for the delay portion of the composite metric.

METRIC CALCULATION

Finally, use the calculated values ​​for the bandwidth and the delay in the metric formula. The result is a metric of 3,012,096, as shown in Image.

This value matches the value shown in the routing table for R2.