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#Tshoot EIGRP Route Advertisement
Distribute-List - check if you have a distribute-list that is preventing prefixes from being advertised or installed in the routing table
    show run | section eigrp (the is distribute list)
Discontiguous Network - If EIGRP auto-summary is enabled you might end up with discontiguous networks
    show run | section eigrp (the is auto-summary)
Summarization - EIGRP auto-summary creates an entry to the null0 interface which might prevent the installation of summaries you receive from neighbor routers.
    show ip eigrp topology ip (Null0 is there)
Summary not advertised - You can’t advertise what you don’t have in your routing table.
Split Horizon - prevents the advertisement of a prefix out of the interface where we learned it on
    no ip split-horizon eigrp 123
Redistribution Sub-Optimal Routing - Change the administrative distance to change traffic patterns but be aware; In more complex topologies this can also cause routing loops.
    router rip | distance 175 192.168.13.3 0.0.0.0
Redistribution Seed Metric - When you redistribute something into EIGRP you need to configure seed metrics.
    router eigrp 12 | default-metric 1500 100 255 1 1500

#Reasons not to form neighbor: 
Uncommon subnet
K value mismatch
AS mismatch
Layer 2 issues
Access-list issues
NBMA -make sure multicast traffic can be forwarded

Autonomous system (AS)
A set of routers running the same routing protocol under a single realm of control and authority.

Successor route
The route with the lowest-path metric to reach a destination.

Successor
The first next-hop router for the successor route.

Feasible distance
The total distance to the destination
Total metric to get to the destination
The metric value for the lowest-metric path to reach a destination.

Advertised distance / Reported distance
The distance reported by a router to reach a prefix. 
The reported distance value is the feasible distance for the advertising router.
How far the destination is away for your neighbor.

Feasibility condition
The condition which says that for a route to be considered a backup route, 
the reported distance received for that route must be less than the feasible distance calculated locally. 
This logic guarantees a loop-free path.

Feasible successor
A route that satisfies the feasibility condition that is maintained as a backup route.

Topology table
A table used by EIGRP that maintains all network prefixes, advertising EIGRP neighbors 
for that prefix and path metrics for calculating the best path.

EIGRP classic configuration
An EIGRP configuration mode in which most of the configuration resides under the EIGRP process, 
but some settings are configured under the interface configuration submode.

EIGRP named mode configuration
An EIGRP configuration mode that provides a hierarchical configuration and stores settings 
in three subsections: address family, interface, and topology.

Passive interface
An interface that has been enabled with a routing protocol to advertise its associated interfaces 
into its RIB but that does not establish neighborship with other routers associated to that interface.

K values
A set of values that EIGRP uses to calculate the best path.

Wide metrics
A method of advertising and identifying interface speeds and delay that accounts for higher-bandwidth interfaces (20 Gbps and higher).

Variance value
With EIGRP, the feasible distance (FD) for a route multiplied by the EIGRP variance multiplier. 
Any feasible successor’s FD with a metric below the EIGRP variance value is installed into the RIB.

Hello packets
A packet that is sent out to detect neighbors for establishing adjacency and ensuring that neighbors are still available.

Hello timer
The amount of time between hello packets being advertised out an interface.

Hold timer
The amount of time required for a hello packet to be received for the neighbor to be deemed healthy. 
Upon receipt, the value resets and decrements towards zero.

stuck in active (SIA)
An event that occurs when an EIGRP query is sent to downstream neighbors and the router doesn’t receives a reply within 90 seconds.

Summarization
A method of reducing the routing table by advertising a less specific network prefix rather than multiple more specific network prefixes

EIGRP stub router
An EIGRP feature that advertises to all other neighbors that it is isolated and should not be queried when routes go active.

EIGPR stub site router/Feature
Page 163 of ENARSI 300-410 book

Split horizon
A routing loop-prevention mechanism that prevents a route from being advertised out of the same interface on which it was learned.

Offset list
A list used for increasing the delay for received or advertised EIGRP routes.

224.0.0.10
The multicast IPv4 address used by EIGRP routers to form neighbor adjacencies.

network command
A command used to enable the RIPv2, EIGRP for IPv4, and OSPFv2 routing processes on an interface

Key ID
The numeric value that identifies the key used for authentication.
Key string
The alphanumeric string of characters that is being used for authentication. This is not to be confused with the name of the keychain.
Keychain
A collection of one or more keys (that is, passwords) used for authentication, where each key has an associated key ID and key string.

Stub
A router running EIGRP that limits EIGRP DUAL algorithm computations and reduces the EIGRP query scope.

Autosummarization
A routing protocol feature in which a router that connects to more than one classful network advertises summarized routes 
for each entire classful network when sending updates out interfaces connected to other classful networks.

Classful
A convention for discussing and thinking about IP addresses by which Class A, B, and C default network prefixes (of 8, 16, and 24 bits, respectively) are considered.

Classless
A convention for IP addresses in which Class A, B, and C default network prefixes (of 8, 16, and 24 bits, respectively) are ignored and subnetting is performed.

Variance
With EIGRP, the feasible distance (FD) for a route multiplied by the EIGRP variance multiplier. 
Any feasible successor’s FD with a metric below the EIGRP variance value is installed into the RIB.

FF02::A
The multicast IPv6 address that EIGRP routers use to form neighbor adjacencies.

Maximum paths
The number of paths that a router can use to load balance traffic.

Named EIGRP
An EIGRP configuration approach that allows you to configure all EIGRP commands under a single hierarchical configuration.

Address family
A method of configuring IPv4 and IPv6 routing services under the same routing process. 
IPv4 address families are used for IPv4 routing, and IPv6 address families are used for IPv6 routing.