Category Archives: EIGRP

Enhanced Interior Gateway Routing Protocol

EIGRP Metric Calculator

bw = 200000
delay = 2900
K1 = 1
K3 = 1
met = 256 * (int(K1 * 10**7 / bw) + K3 * delay / 10)
print met
bw = raw_input(“Bandwidth: “)
dly = raw_input(“Delay: “)
met = 256 * (int(K1 * 10**7 / bw) + K3 * delay / 10)

Use case of EIGRP

First we need to understand some of eigrp features.

Basic Manipulation
Maximum Path – router configuration command, up to 32 equal-cost entries can be in the routing table for the same destination. The default is four.
NOTE: Setting the maximum-path to 1 disables load balancing.
Split-horizon route advertisement is a method of preventing routing loops in distance-vector routing protocols by prohibiting a router from advertising a route back onto the interface from which it was learned.
R5#sh ip protocols
*** IP Routing is NSF aware ***

Routing Protocol is “eigrp 10”
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
Redistributing: eigrp 10
EIGRP-IPv4 Protocol for AS(10)
Metric weight K1=1, K2=0, K3=1, K4=0, K5=0

NSF-aware route hold timer is 240
Topology : 0 (base)
Active Timer: 3 min
Distance: internal 90 external 170
Maximum path: 4
Maximum hopcount 100
Maximum metric variance 1

Automatic Summarization: disabled
Maximum path: 4
Routing for Networks:
Routing Information Sources:
Gateway Distance Last Update 90 00:00:11 90 00:00:11
Distance: internal 90 external 170

For EIGRP network 2 routers play a key rule in determining the best path and the backup path. EIGRP is the only routing protocol that has a backup path to each destination.

EIGRP only advertise what’s in its local table.


1. Query chain become longer and then the neighbor adjacency dead timer could cause lots of problem with SIA(Never Converge).
2. Setting up your maximum-paths ex 8 and you build 32 alternate path everywhere. and you’ll advertising only to all only 8 paths. (set the path to all to stable EIGRP).

Note: theres no whitepaper that eigrp can be use indata center fabric. (maybe because ospf more preferred because they can do traffic engineering.

Use Cases of EIGRP as IGP.
1. Hub and Spoke (Data center fabric “leaf/spine”(havent seen)).
2. Campus Network.
3. Split horizon design features

In IPSEC SA – You don’t want spoke to spoke traffic split horizon help to put in blackhole.

What should be considered when scaling eigrp
Query Range/Scope – Important (Design Problem)
Stub / Filter / Summary and Summary Boundaries.
IP Address

Note: Don’t change the SIA timer up.(how long your’e willing to allow your network not to converge. it already set to maximum)

Bandwidth – Query?

Stub Router
1. Can’t be use as transit, only advertise connected and summary routes.
2. You can never query a stub router.

– Spoke01 will never know that spoke 01 is down.
– Spoke will not query the hub because they don’t know the changes.
– But hub query all the spoke because hub is aware of the change and none of the spoke configured as stub.
– Hub will not query the spoke since it’s configured as stub, But spoke will query the HUB if there a change on routing table.

EIGRP Neighbor Issue

6 Common issue of EIGRP Neighbor.

1. No multicast transport.
Solution: Set/use unicast.

2. Mismatched AS number.
Solution: Redistribution

3. Uni-directional link (one-way-neighborship).
Solution: verify #show ip eigrp neighbor

Smooth round-trip time (SRTT)—The number of milliseconds it takes for an EIGRP packet to be sent to this neighbor and for the local router to receive an acknowledgment of that packet

Retransmission timeout (RTO), in milliseconds—The amount of time that the software waits before retransmitting a packet from the retransmission queue to a neighbor

Q count—The number of EIGRP packets (Update, Query, and Reply) that the software is waiting to send

The Q count is not decrementing, which indicates that the router is trying to send EIGRP packets but no acknowledgement is being received. RTR B will retry 16 times to resend the packet; eventually, RTR B will reset the neighbor relationship with the log indicating RETRY LIMIT EXCEEDED, and the process starts again. Also, keep in mind that the 16 times retransmission of the same packet is done using unicast, not multicast. Therefore, the RETRY LIMIT EXCEEDED message indicates a problem with transmitting unicast packets over the link, and this is most likely a Layer 1 or Layer 2 problem.

The solution to this problem is to troubleshoot from a Layer 2 perspective. In this example, a call to the WAN provider is needed to find out why the circuit from RTR B to RTR A is broken. After the link between RTR B to RTR A is fixed, the problem will be resolved. Output from show ip eigrp neighbors in Example 7-2 shows that the neighbor relationship after the WAN link has been fixed.

4. Uncommon Subnet (mismatched IP Address/Subnet)
LOG MESSAGE: IP-EIGRP: Neighbor ip address not on common subnet for

5. K Values – If there’s a minipulation of K values on devices it can afftect the neighbor peer.

For EIGRP to establish its neighbors, the K constant value to manipulate the EIGRP metric must be the same. Refer to Chapter 6 for an explanation of the K values. In EIGRP’s metric calculation, the default for the K value is set so that only the bandwidth and the delay of the interface are used to calculate the EIGRP metric. Many times, the network administrator might want other interface factors, such as load and reliability, to determine the EIGRP metric. Therefore, the K values are changed. Because only bandwidth and delay are used in calculations, the remaining K values are set to a value of 0 by default. However, the K values must be the same for all the routers, or EIGRP won’t establish a neighbor relationship. Figure 7-8 shows an example of this case.’

For the network in Figure 7-8, K1 is bandwidth and K3 is delay. The network administrator changed the K values of RTR B to all 1s from K1 to K4, while RTR A retains the default value of K1 and K3 to be 1. In this example, RTR A and RTR B will not form EIGRP neighbor relationship because the K values don’t match. Example 7-5 shows the configuration for RTR B.

Example 7-5 Configuration for RTR B in Figure 7-8
RTR B#router eigrp 1
network xxxx
metric weights 0 1 1 1 1 0
RTR B’s configuration includes the extra metric weights command. The first number is the type of service (ToS) number, which, because it’s not supported, gets a value of 0. The five numbers after the ToS are the K1 through K5 values.

Troubleshooting this problem requires careful scrutiny of the router’s configuration. The solu-tion for this problem is to change all the K values to be the same on all the neighboring routers. In this example, in Router A, changing the K values to match the K value of Router B will solve the problem, as demonstrated in Example 7-6.

Example 7-6 Configuring the K Values on Router A to Match Router B
RTR A#router eigrp 1
network xxxx
metric weights 0 1 1 1 1 0

6. Stuck in active (SIA) – Network prefix goes from passive to active.

Log: %DUAL-3-SIA: Route network mask stuck-in-active state in IP-EIGRP AS. Cleaning up


EIGRP Packet Type

Describing EIGRP Packet Types (HA/U/Q/R/R)
1. Hello
– Used to recover/discover and to maintain EIGRP neighbor adjacencies.

– They do not require acknowledgement.

– EIGRP uses small hello packets to discover other EIGRP-enabled routers on
directly connected links.

– EIGRP Hello packets are sent as IPv4 or IPv6 multicast, and use RTP
unreliable delivery. This mean that the receiver does not reply with an
– The reserved EIGRP multicast address for ipv4 is
– The reserved EIGRP multicast address for IPv6 is FF02::A.

– EIGRP Hello packets are sent as multicast packet every 5 second.

However, on multipoint, nonbroadcast multiple access (NBMA) networks, such as X.25,Frame relay and Asynchronous transfer mode (ATM) interfaces with access links of T1(1.544 Mb/s) or slower. Hello packets are sent as unicast packet every 60 seconds.

EIGRP uses a Hold timer to determine the maximum time the router should wait to receive the next Hello before declaring that neighbor as unreachable.

1.a Acknowledgement
– Acks are always sent using a unicast address and contain a non-zero
acknowledgment number
– Acknowledgement is an EIGRP hello packet without data.
– EIGRP Ack packets are always sent as an unreliable unicast. (Unreliable
delivery makes sense, otherwise, there would be an endless loop of

NOTE: RTP uses reliable delivery for EIGRP update, query and reply packets.

2. Update
– Propagates routing information to EIGRP neighbors. UPdate packets are sent
only when necessary. EIGRP contain only the routing information needed and
are sent only to those routers that require it.
– Sent with reliable delivery.
– Unicast or multicast.
– Trigger updates/Periodic updates, Send only when the state of a destination changes. This can include when a new network becomes available, an existing network becomes unavailable, or a change occurs in the routing metric for an existing network.

3. Query
– Looking information to get to the prefix.
– Sent with reliable delivery. Because queries use reliable delivery, the
receiving router must return an EIGRP acknowledgement. The acknowledgment
inform the sender of the quesry that it has received the query message.
– Unicast or multicast.

4. Replies
– Sent in response to an EIGRP query.
– Always sent in response to queries to indicate to the originator that it
does not need to go into Active state because it has feasible successors.
– Sent with reliable delivery
– Unicast

5. Requests
– Request packets are used to get specific information from one or more
– Request packets are used in route server applications.
– They can be multicast or unicast.
– Requests are transmitted unreliably.

Note: Update, Query and Reply require Ack’s.Update, query and reply packets require acknowledgement, whereas hello and ack do not require ack.

Neighborship reset occurs after a 16 retry limit is reached. Slow neighbors will be sent unicast updates instead.


EIGRP Name Mode

EIGRP Name Mode

1. Named Mode
– 64-bit mode
– Address Family (AF) mode
– Multi-Address Family (AF) mode

2. Consolidation of EIGRP configuration stanzas
3. Benefits
– 64-bit metric granularity (We can now differentiate multiple speed interface)
– SHA-256 authentication

How to Enable ‘Named Mode’:
– router eigrp [name]
– address-family [ipv4/ipv6] autonomous-system [#]

Hitless upgrade of existing EIGRP ‘Classic Mode’ Configuration
– eigrp upgrade-cli command

Supported Software Version (
1. IOS version 15.x

## Named mode configuration
(config)#router eigrp cisco
(config-router)#address-family ipv4 unicast autonomous-system 1

## Default passive
(config-router)#address-family ipv4 unicast autonomous-system 1
(config-router-af)#af-interface default

## Removing passive interface
(config-router)#address-family ipv4 unicast autonomous-system 1
config-router-af)#af-interface fastEthernet 1/1
config-router-af-interface)#no passive-interface

## Router ID / Network
(config-router)#address-family ipv4 unicast autonomous-system 1
(config-router-af)#eigrp router-id

R5#sh run | sec router eigrp
router eigrp regreased
address-family ipv4 unicast autonomous-system 1
af-interface default
af-interface FastEthernet1/1
no passive-interface
topology base
eigrp router-id
eigrp stub connected

Now we start to see the benefits! Logical layout in the config where we configure eigrp authentication under eigrp!! A side note that sha256 should also be available if you are running the newer code and md5 isnt considered the most secure anymore.
Now lets configure a legacy style stub on Old_Stub but inject a default from New into this stub area

Again nothing really new but note the name of the virtual router instance (weee/somethingelse) as no significance outside the local router and aren’t required to match.

## Upgrade Classic eigrp to named mode

R3#sh run | sec router eigrp
router eigrp 1

R3(config)#router eigrp 1
R3(config-router)#eigrp upgrade-cli

My final verdict:
There are 2 added few feature that will help interms of adding more secured authentication in neighbor formation and the 64bit metric granularity. But full advantage is the neatness and consolidation of the configuration unlike the classic/legacy mode.


EIGRP Stuck in active (SIA)

Q. What does the EIGRP stuck in active message mean?

A. When EIGRP returns a stuck in active (SIA) message, it means that it has not received a reply to a query. EIGRP sends a query when a route is lost and another feasible route does not exist in the topology table. The SIA is caused by two sequential events:
The route reported by the SIA has gone away.
An EIGRP neighbor (or neighbors) have not replied to the query for that route.
When the SIA occurs, the router clears the neighbor that did not reply to the query. When this happens, determine which neighbor has been cleared. Keep in mind that this router can be many hops away. Refer to What Does the EIGRP DUAL-3-SIA Error Message Mean? for more information.