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January 2020

How to Configure EIGRP Load Balancing for IPv4

How to Configure EIGRP Load Balancing for IPv4

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EIGRP is a Cisco proprietary routing protocol. Router-enabled EIGRP calculates the best route to a destination using the metric value based on the link bandwidth and delay. The protocol selects the shortest path and installs that path in the routing table. If the destination has more than one path with the same administrative distance and a metric value, all least-metric and same routes are installed in the routing table.

When there are several routes with equal metric values, by default, all dynamic routing protocols, including EIGRP, forward packets using load balancing. We can configure EIGRP to install multiple paths even if the metric is unequal. This is the only protocol that supports unequal cost load balancing. There are two types of load balancing:

Equal-cost load balancing

When a router has two or more paths to a destination with equal cost metrics, it forwards the packets using all paths equally, a process called equal-cost load balancing. When forwarding packets, the protocol should have an equal administrative distance to a destination. Using load balancing, the router uses network segments and bandwidth more efficiently.

By default, Cisco IOS Software can balance the load across four equal-cost paths. We can configure the EIGRP load balancing up to 16 equal-cost paths using the “maximum-path” in the router configuration mode. The router can keep up to 32 equal-cost routes in the routing table.

If we set the maximum-path value to 1, the equal-path load balancing is disabled on the router. The Cisco router uses two types for balancing the network load: per-destination basis and per-packet basis. The command syntax for equal-cost EIGRP load balancing configuration is:

Router(config-router)# maximum-paths value

We can verify the EIGRP load balancing using the “show ip protocols” command. The command displays the number of equal-cost paths currently configured on the router. Cisco IOS, by default, allows EIGRP load balancing for four equal-cost path routes. The output in Figure 1 illustrates the topology that we will use in this lesson, and Figure 2 illustrates that R1 is using the default equal-cost EIGRP load balancing.

Figure 3 illustrates the routing table of R1. The Router R1 has two successors for network 192.168.5.0/24 via 192.168.0.2 and 192.168.1.2. The metric for both routes is equal, so both are installed in the routing table. This is an example of equal-cost load balancing. EIGRP uses four routes with equal cost by default in the routing table.

Unequal Cost Load Balancing

If routing metrics are not equal, load balancing will not occur automatically. So a command called “variance” must be used to configure a load-balancing. This command makes EIGRP load balance on unequal metrics values. The command syntax for unequal load-balancing is:

Router(config-router)variance < Metric variance Multiplier>

The command will enable EIGRP to install multiple loop-free routes with unequal cost in a local routing table. A route learned through EIGRP should meet two criteria to be installed in the local routing table:

  • The route should be loop-free, being both a feasible successor (FS) and having a reported distance (RD) less than the total distance.
  • The route’s metric must be lower than the metric of the best route (the successor) multiplied by the variance configured on the router.

If the variance value is set to 1 on the router then only routes with the same metric are installed as the successor in the local routing table, this is called equal-cost load balancing. But if the variance is set to 2, any EIGRP-learned route with a metric less than 2 times the successor metric will also be installed in the local routing table as successor.

Figure 4 illustrates that the R1 has two unequal links to reach network 192.168.5.0. The links via R3 have 256 kb/s, and the links via R2 have a speed of 128 Kb/s. We know that the EIGRP installs the route with the lowest cost in the routing table. Let’s check the routing table of R1 in Figure 5.

Now, let’s configure R1 with the variance command. We know that the link with R2 is two times slower than the link with R3, so the variance value should be 2. The range of variance that we can configure is from 1 to 128.

Figure 7 illustrates the variance configuration and the routing table of R1 after the variance configuration. You can see that two routes are installed for the destination 192.168.5.0/24 network; even the metric is not equal. This is unequal load balancing.

We can also examine the topology table with the “show ip eigrp topology” to verify successor routes for this destination. Figure 7 illustrates the output of this command.

We can control the traffic among routes in case multiple routes for the same destination network have different costs. The “traffic-share balanced” command can distribute traffic proportionately to the cost ratio.

EIGRP Hello Protocol – Exclusive Explanation

EIGRP Hello Protocol – Exclusive Explanation

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Hello Intervals and Hold Times – EIGRP for IPv4

EIGRP uses the Hello protocol to establish and maintain a connection with its neighbor and monitor the established connection. It sends a Hello packet periodically to its neighbor. The rate at which EIGRP sends a Hello Packet is known as the Hello interval.

The Hold timer works just like the dead interval of OSPF. It is the maximum wait time that the router should wait to receive the next Hello packet before declaring that neighbor inaccessible or dead.

Both Hello intervals and Hold times are configurable values on a per-interface basis. The range of the Hello interval “second” value is range from “1 to 65535”. The command syntax to configure a Hello interval is:

Router(config-if)# ip hello-interval eigrp <as-number> <seconds>

Changing the Hello interval equal to the Hold time value or greater than the Hello interval is important. If not, neighbor adjacency will decrease after the Hold time expires and before the next Hello interval. The range of the Hello interval “second” value also ranges from “1 to 65535”. To configure the Hold time value, use the following command to configure:

Router(config-if)# ip hold-time eigrp <as-number> <seconds>

Figure 1 illustrates the EIGRP topology. We can configure the Hello interval and Hold timer for this topology. We know that the Hello Interval and Hold timer in EIGRP is a per-interface base configurable value. Therefore, the Hello interval time and Hold time do not need to match for two routers to form an EIGRP adjacency and we can configure the different values for different interfaces on the above topology.

Hello Protocol

For a faster link, we can configure less timing (in seconds); for a slower one, we can configure larger timing (in seconds) to reduce the extra network overhead.

The default Hello Interval for 1.544 Mbps or slower link is 60 seconds and for T1 link and Ethernet link is 5 seconds. The default hold down timer for 1.544 Mbps or slower link is 180 seconds and for T1 link and Ethernet links are 15 seconds. The configuration of Hello Interval and Hold timer on the link between R1 and R2 is the following:

Router R1

R1(config)# interface gigabitEthernet 0/0

R1(config-if)# ip hello-interval eigrp 100 80

R1(config-if)# ip hold-time eigrp 100 240

Router R2

R2(config)# interface gigabitEthernet 0/0

R2(config-if)# ip hello-interval eigrp 100 80

R2(config-if)# ip hold-time eigrp 100 240

This configuration will set the hello interval to 80 seconds and hold timer to 240 seconds between R1 and R2 link. We can reset the values to default using the “no” form of the above commands.

Hello Intervals and Hold Times – EIGRP for IPv6

EIGRP for IPv6 also uses the same Hello protocol, which includes the hello interval and Holds times. The command to configure the Hello interval and Hold timers is similar commands for IPv4 with little difference. The commands syntax are the following:

Router(config-if)# ipv6 hello-interval eigrp <as-number> <seconds>

Router(config-if)# ipv6 hold-time eigrp <as-number> <seconds>

EIGRP Bandwidth

How to Configure EIGRP Bandwidth

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EIGRP Bandwidth for IPv4

EIGRP utilizes 50 % of an interface’s bandwidth for EIGRP information by default. Utilizing a half interface bandwidth not allowing enough bandwidth for the routing of normal traffic and prevents the EIGRP process from over-utilizing a link.

We can change to default bandwidth utilization ratio using the command “ip bandwidth-percent eigrp”. This is an interface mode command which changes the percentage of bandwidth that can be used by EIGRP on an interface. The command syntax for changing the interface bandwidth is:

Router(config-if)# ip bandwidth-percent eigrp as-number percent

EIGRP Bandwidth

This command is useful, where the link speed is slow. If the link speed is slow then we can configure the bandwidth utilization for EIGRP. Figure 1 illustrates the link between R1 and R2 share a slow 128 kb/s link. So we required to configure the bandwidth usage limitation for EIGRP. The configuration for bandwidth limitation for EIGRP between the R1 and R2 is the following:

Router R1

R1(config)# interface gigabitEthernet 0/0

R1(config-if)#ip bandwidth-percent eigrp 100 25

Router R2

R2(config)# interface gigabitEthernet 0/0

R2(config-if)#ip bandwidth-percent eigrp 100 25

In the above example, EIGRP is limited to use up to 25 percent of the link’s bandwidth. So, EIGRP never uses more the 32 kb/s of the link’s bandwidth for EIGRP packet traffic. We can restore the default value, using the no form of the “ip bandwidth-percent” command.

EIGRP Bandwidth for IPv6

We can also configure the EIGRP for IPv6 bandwidth limitation also. The “ipv6 bandwidth-percent eigrp as-number percent” command can be used to configure the limitation for IPv6 EIGRP. The command should be used similarly in the interface configuration mode. We can restore the default value, using the no form of this command.

How to Propagate the Default Static Route using EIGRP

How to Propagate the Default Static Route using EIGRP

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The IP address 0.0.0.0/0 is reserved for the default static route. The default route is not routing protocol-dependent; we can use it with any currently supported routing protocol. Usually, the static default route is configured on the edge router, where a network is connected outside the EIGRP routing domain and propagates the default static route to other routers.

Figure 1 illustrates the topology configured with EIGRP, where R2 is the internet gateway for the EIGRP routing domain. The static default route is configured on R2, pointing to the ISP router. When the static default route is configured, it is necessary to propagate the default static route throughout the EIGRP domain to other EIGRP routers, in this example, R1 and R3.

So, we can propagate the default static route within the EIGRP routing domain using the “redistribute static” command in router configuration mode. This command adds static routes previously configured in EIGRP routing updates to other routers. The redistribution configuration on R2 is the following:

  • R2(config)#router eigrp 100
  • R2(config-router)# redistribute static
  • R2(config-router)#

Verifying the Propagated Default Route

Now, we can verify the configuration on R2 as well as on R1 and R3. We can use the “show ip protocols?” command to verify that R2 redistributes static routes within the EIGRP routing domain. Figure 2 illustrates the output of this command.

We can verify the static default route on R1 and R3, where we have not configured any default route. Figure 3 illustrates the routing table of R1 and R3. In the routing tables for R1 and R3, you can see the routing source and administrative distance for the default route learned using EIGRP. We can identify the EIGRP learned default route by the following parameters:

  • D– This means the route was learned from an EIGRP routing update.
  • *– The route is a candidate for a default route.
  • EX– The route is an external EIGRP route.
  • 170– This is the administrative distance of an external EIGRP route.

EIGRP for IPv6: Default Route

We can configure the IPv6 default router and propagate that default router separately from the IPv4 default route. Similarly to EIGRP for IPv4, a default static route is configured on the gateway router. In this example, R2 is the gateway router, as shown in Figure 1. To configure a default static route on R2:

R2(config)# ipv6 route ::/0 GigaEthernet 0/0

The::/0 is the default prefix and prefix length, equivalent to the 0.0.0.0 0.0.0.0 IP address and subnet mask used in IPv4. Both are all-zero addresses with a /0 prefix length. We can redistribute the IPv6 static default route into the EIGRP for IPv6 domain using the same “redistribute static” command.

Verifying Propagation of IPv6 Default Route

We can verify the IPv6 default route propagation by examining the IPv6 routing table of R1 and R2 using the “show ipv6 route” command.

How to Configure EIGRP Manual Summary Routes

How to Configure EIGRP Manual Summary Routes

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We can configure manual summary routes without enabling the auto-summary. We can also use a manual summary if auto-summary is enabled because EIGRP is a classless routing protocol. Classless routing protocol includes the subnet mask in the routing update; therefore we can configure manual summarization using the supernet routes. In supernetting, we can aggregate multiple routes in one major classful network address.

Configuring EIGRP Manual Summary Routes

Figure 1 illustrates the topology for manual summary route configuration. This is the same topology we have already used in EIGRP auto-summary configuration. R1 has four adjacent routes and R3 has also the four adjacent routes. We can manually summarize the routes.

We can examine the routing table of R1, R2, and R3 to verify the EIGRP routes in the routing table for network 10.10.10.0/30, 10.10.11.0/24, 10.10.12.0/24, 10.10.12.0/24, 172.16.0.0/30, 172.16.1.0/24, 172.16.2.0/24, and 172.16.3.0/24. Figure 2 illustrates the routing table of all three routers in the above topology, before the manual auto-summarization.

Steps for Determining Summary Route

To determine the summary route follow the steps below separately for networks that need to summarize.

  1. Write all the network’s binary format that needs to summarize.
  2. Start from for left to summarize all the networks.
  3. Find all the consecutive matching bits from left to right
  4. Mark all the matching bits in all networks in the column of bits to define the summary boundary.
  5. Count the number of matching bits, which in this example you can see in figure 3 shown in red and italic.
  6. To find the network address for summarization, copy the matching bits and add all 0 bits to the remaining positions to complete 32 bits address.

The resultant summary network address and mask for the network of router R1 are 10.10.8.0/21 and for the network of the router, R2 is 172.16.0.0/22.

Configure EIGRP Manual Summarization

Now we have found the summary routes for the networks of both routers. To configure EIGRP manual summarization on a specific EIGRP interface, the interface mode command syntax is “Router(config-if)# ip summary-address eigrp <as-number> <network-address> <subnet-mask> “. So let’s configure the EIGRP summary route on both R1 and R2.

Router R1

R1(config)#interface serial 0/0/0

R1(config-if) ip summary-address eigrp 10.10.8.0 255.255.248.0

R1(config-if)#

Router R2

R2(config)#interface serial 0/0/1

R2(config-if) ip summary-address eigrp 192.168.0.0 255.255.252.0

R2(config-if)#

The configuration on R1 will propagate the route 10.10.8.0/21 network on serial 0/0/0 interface. In the router R2, the configuration will propagate the summary route on serial 0/0/1 interface of R2.

Verifying Manual Summary Routes

We can verify the summary router configuration by showing the routing table for R2 because both summary routes are propagated towards R2. Figure 4 illustrates the routing table of R2 after the summary route is configured. The routing tables of R2 has no longer include the individual route or R1 and R3. Instead, the routing table of R2 displays a single summary route of 172.16.0.0/22 and 10.10.8.0/21.

More router decrease the routing table lookup process efficiency, but summary routes decrease the number of routes in routing tables which increases the efficiency. Summary routes also utilize less bandwidth for the routing updates, so a single route can be sent instead of multiple individual routes.

How to EIGRP automatic summarization

How to EIGRP automatic summarization

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Route summarization is the most common tuning method of EIGRP. It allows a router to group multiple networks and advertises them as one large group using a single, summarized route. The capability to summarize routes is very important due to the rapid growth of networks.

Route summarization reduces the number of routes in a larger network with many subnets and the traffic used for routing updates. We can summarize the routes by automatic summarization or manual summarization. The auto summarization feature is enabled by default on EIGRP. Using default auto summarization, routes are summarized to classful addresses at network boundaries in the routing updates.

EIGRP will check for any subnets that fall within the range of your network command, and if found, it will advertise the classful A, B, or C network to its neighbors. The default auto-summary only summarizes routes from subnets on its interfaces, not the routes learned from other routers.

How to EIGRP automatic summarization

Figure 1 illustrates the process of route summarization. Routers R1, R2, and R3 are configured using EIGRP for IPv4 with automatic summarization. R1 has four subnets in its routing table: 10.10.10.0/30, 10.10.11.0/24, 10.10.12.0/24 and 10.10.13.0/24. These subnets are all considered part of a larger class A network, 10.0.0.0/8. Because automatic summarization is enabled on router R1, it summarizes all subnets as a single network of 10.0.0.0/8. Summarization reduces the number of routing updates sent and the number of entries in R2’s IPv4 routing table. Traffic destined for the three subnets 10.10.11.0/24, 10.10.12.0/24, and 10.10.12.0/24 travels across one common path. R2 never maintains routes to individual subnets.

Configuring EIGRP Automatic Summarization

Before Cisco IOS Release 15.0(1)M and 12.2(33), automatic summarization was enabled by default. However, after the release of these IOS versions, automatic summarization is disabled by default. Therefore, we should configure automatic summarization in the latest IOS release.

How to EIGRP automatic summarization

Figure 2 illustrates the output of the “show ip protocols” command on R1. The figure illustrates that the automatic summarization is disabled on R1. This is because the router running IOS Version 15.1(4)M4 therefore, automatic summarization is disabled

Figure 3 shows the current routing table for R2, the edge router for R1 and R2. Notice that the EIGRP IPv4 routing table for R2 contains all of the networks and subnets within the EIGRP routing domain. We can enable automatic summarization for EIGRP using the “auto-summary” command in router configuration mode.

R1(config)# router eigrp 100

R1(config-router)# auto-summary

Use the same commands for automatic summarization on all routers. “100” is the autonomous system number of the EIGRP domain. We can negate automatic summarization using the router configuration mode’s “no auto-summary” command.

Verifying Auto-Summary

We can verify the auto-summary configuration by using the command “show ip protocols.” Figure 4 illustrates the output of this command, which enables the auto-summary on R1.

How to EIGRP automatic summarization

We can examine and verify the summarization from R2’s routing table. Using the “show ip route eigrp” command, we can display R2’s routing table for the EIGRP domain. Figure 5 illustrates R2’s routing table after auto-summary configuration.

How to EIGRP automatic summarization

As indicated in Figure 3, R1 summarizes the 192.168.10.4/30 and 192.168.10.8/30 subnet. It forwards the summarized address of 192.168.10.0/24 to its neighbors on its Serial 0/0/0 and GigabitEthernet 0/0 interfaces. Because R1 does not have any EIGRP neighbors on its GigabitEthernet 0/0 interface, the summarized routing update is only received by R2.

Verifying Auto-Summary from Topology Table

In Figure 6, routers R1 will send R2 a summarized EIGRP routing update of 172.16.0.0/16. Routing tables for R1, R2, and R3 contain the 172.16.0.0/16 network subnets, so all routers send the summary advertisement across a different major network.

How to EIGRP automatic summarization

We can verify the auto-summary configuration on the R2 and R3 topology table. This will verify that R2 and R3 have received the 172.16.0.0/16 summary route. We can use the all-links parameter with the “show ip eigrp topology” to show all received updates.

Null Interface

Figure 5 shows the routing table for R2. The highlighted entries use an exit interface of Null0. EIGRP automatically adds a summary route to Null0 for two classful networks: 10.0.0.0/8 and 172.16.0.0/16. It is an IOS virtual interface route to nowhere, also known as “the bit bucket.” Packets that match a route with a Null0 exit interface are discarded.

The Null0 summary route prevents routing loops for destinations integrated into the summary but not in the routing table. EIGRP for IPv4 automatically includes a Null0 summary route in the following conditions:

  • In the case of one subnet that was learned via EIGRP.
  • In the case of two or more network EIGRP router configuration mode commands.
  • Automatic summarization is enabled.

Notice – Automatic summarization is unavailable for IPv6 because classful addressing does not exist in IPv6.

Topology Table – Exclusive Introduction

Topology Table – Exclusive Introduction

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The EIGRP topology table contains all of the information about all known routes received from EIGRP neighbors. As an EIGRP router learns routes from its neighbors, those routes are stored in its EIGRP topology table. If a neighbor is advertising a possible route, it has to be using that route to forward packets to the destination network.

The topology stores all possible routes in the topology table database. It also provides the information used to select the best possible route, which is copied into the routing table. Topology tables are stored in Random Access Memory (RAM) and are re-created whenever a router starts up. Routing tables update all routing information from the topology table.

The “show ip eigrp topology” command illustrates the topology table as shown in figure 1. The topology table displays lists of all successors and Feasible Successors (FSs) calculated by DUAL. Only the successor with the lowest metric value is installed into the IP routing table. We should explain the entries marked in the red rectangle.

  • P– This parameter shows that the route is in the passive state. All routes in the topology table must be in the passive state for a stable routing domain. If the DUAL recalculates for a new path, the routes become is an active state and the parameter has changed to display A instead of P.
  • 168.2.0/24 – This is the destination network which is displayed just after the P or A. The address will also be displayed in the routing table if the route becomes the successors.
  • 1 successors– This parameter displays the number of successors for this network. If multiple equal-cost paths found to this network, there will be multiple successors.
  • FD is 258816– FD (Feasible Distance), It is the EIGRP metric to reach the destination network. This is the metric value we have calculated earlier. The metric is also displayed in the routing table.

Figure 2 illustrates the entries of the next hop of the successor router.

  • via 10.10.10.2– This field identifies the Next-hop address of the successor, 10.10.10.2 is the IP address of successor router. The IP address is also shown in the routing table.
  • 258816– FD to 192.168.2.0/24, the metric value is shown in the IP routing table.
  • 5120– This is the Reported Distance (RD) of the successor router and is R3’s cost to reach this network.
  • GigabitEthernet 0/1– This is the outbound interface of the local router to reach this network, also shown in the routing table.

The second subentry as shown in figure 3 is the entry for Feasible Successor, if there is not a second entry, then there is no Feasible Successor

  • via 10.10.10.6– This is the Next-hop address of the Feasible Successor, 10.10.10.6 is the IP address of R1.
  • 1660928– R1’s new Feasible Distance to 192.168.2.0/24, if R2 became the new successor. The entry would also be displayed in the IP routing table.
  • 5376– Reported Distance of the Feasible Successor.
  • GigabitEthernet 0/0 – This is the outbound interface used to reach a Feasible Successor if this router becomes the successor.
Successor, Feasible Successor and Feasible Distance

Successor, Feasible Successor and Feasible Distance

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Successor -A successor route is the best route to a destination network. EIGRP uses the successor route to forward traffic to a destination. This is the router which is stored in the routing table. A successor route is based on the advertised distance from the neighbor. A successor route is a least-cost route to the destination network. A feasible successor is the backup route for a successor route.

Feasible Distance – Feasible Distance is the lowest calculated metric to reach the destination network. It is the metric planned in the routing table entry as the second number inside the brackets. The Feasible Distance is also known as the metric for the route.

Now examine the topology that we have used in the previous article in figure 1 and routing table for R1 in Figure 2, you can see that EIGRP’s best path for the 192.168.2.0/24 network is through router R3, and the feasible distance for network 192.168.2.0/24 is 258816. This is the metric that was calculated in the previous lesson.10.10.10.2 is the IP address of Gig 0/1 interface of R3.

Feasible Successor
Feasible Successor

Feasible Successors (FS), Feasibility Condition, and Reported Distance

Feasible Successor – The FS route is an alternative route to a particular network. It can be used instantly if the successor route fails for any reason. We can use the feasible successor route without causing a routing loop. For using the feasible successor the feasibility condition is required to match. The feasible successor route is stored in the EIGRP topology table.

Feasible Successor is the loop-free backup path to the same network as the successor, and it satisfies the Feasibility Condition. R2’s successor for the 192.168.2.0/24 network is R3, providing the path with the lowest metric to the destination network. You can see that R2 is providing an alternative path, but is it and Feasible Successor? For a Feasible Successor, R2 must first meet the Feasibility Condition.

The feasibility condition included when neighbor’s reported distance to a network is less than the local routers feasible distance to the same destination network. The reported distance is the metric that a router reports to a neighbor about its own cost to that network. If the condition met, it provides a loop-free path. If the FS is stored in the topology table, the DUAL converged quickly after a change in the topology, because the backup path has no need for recomputing.

What is DUAL?

What is DUAL?

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The diffusing update algorithm (DUAL) is the algorithm used by EIGRP routing protocol to make sure that a given route is recalculated globally whenever it might cause a routing loop. It is guarantees loop-free and backup paths throughout the routing domain. EIGRP store all available backup routes using diffusing update algorithm and then adapt the route when needed. There are several terms uses in diffusing update algorithm, which are:

  • Successor
  • Feasible Distance (FD)
  • Feasible Successor (FS)
  • Reported Distance (RD) or Advertised Distance (AD)
  • Feasible Condition or Feasibility Condition (FC)

DUAL is the algorithm used by EIGRP for convergence. Convergence is important to a network for avoiding routing loops. Routing loops are very damaging to network performance.  EIGRP uses a hold-down timer and split horizon to prevent routing loops.

The primary way that EIGRP prevents routing loops is with the DUAL algorithm. It provides loop-freedom at every instance throughout a route calculation. The DUAL allows all routers in a topology change to synchronize at the same time. Routers not affected by the topology changes are not part of recalculation.  DUAL EIGRP is the way of faster convergence than other distance vector routing protocols.

The DUAL Finite State Machine (FSM) is the decision process for all route computations. Finite State Machine (FSM) is a workflow model containing a limited number of states, transitions between those states, and FSM Operation.

The diffusing update algorithm FSM tracks all routes use EIGRP metrics to select efficient, loop-free paths and identify the routes with the least-cost path to be inserted into the routing table.

EIGRP avoids recalculation whenever possible because recalculation is processor-intensive. EIGRP avoid recalculation by maintaining a list of backup routes that DUAL has previously found for loop-free. If the primary route in the routing table not working, the best backup route is straight away added to the routing table.

DUAL

DUAL Finite State Machine (FSM)

The DUAL Finite State Machine (FSM) is EIGRP route-calculation engine. This FSM contains logic to calculate and compare routes in an EIGRP network. It is an abstract machine, not a mechanical device with moving parts. It classifies the different state of possibilities states that something can go through, what proceedings cause those states, and what proceedings result from those states. FSMs are not included in the scope of CCNA. But, the concept is used to examine some of the output from EIGRP’s FSM using the “debug eigrp fsm” command.

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