CCNP Exam Prep Tips and Must Knows

Things You Need to Know about EIGRP:

EIGRP is a Cisco proprietary protocol that uses Diffusing Update Algorithm (DUAL) and includes these key features:

• Fast convergence
• Partial Updates
• Multiple network-layer protocol support
• Uses multicast and unicast for updates (uses 224.0.0.10 for multicast)
• VLSM support

EIGRP Tables:

• Neighbor Table
• Topology Table
• Routing Table

EIGRP Packet Types:

• Hello
• Update
• Query
• Reply
• ACK

To become EIGRP Neighbors, the following Hello parameters must match:

• AS Number
• Subnet
• K values
• Authentication type and keys (authentication is optional)

Dual Terminology:

• Advertised Distance (AD) – next hop router cost to destination network
• Feasible Distance (FD) – local router cost to destination network + AD
• Lowest cost = lowest FD
• Successor = next hop router with the lowest FD to destination network
• Feasible successor – next hop router with an AD that is less than the current successor FD

EIGRP Metric – metric components are:

• Bandwidth (K1)
• Delay (K3)
• Reliability (K4 & K5)
• Loading (K2)

Using Passive Interfaces with EIGRP

• EIGRP announces the directly connected network of an interface
• EIGRP does not try to form neighbor relationships over the interface

Using the IP Default-Network Command

• Any EIGRP major network residing in the local routing table can be flagged as a candidate default with this command

EIGRP Route Summarization

• Improves network scalability – smaller routing tables and fewer updates
• Is configured on the interface
• Automatic summarization occurs by default
• Summarization results in a route pointing to Null0

EIGRP Automatic Route Summarization

• Performed on major network boundaries
• Automatic summarization occurs by default
• Disable auto summarization with no auto-summary command (config-router)

EIGRP with Frame-Relay – Requires mapping from Layer 3 to Layer 2

• Dynamic mapping – Split horizon behavior disabled by default
• Static mapping – Split horizon behavior disabled by default

EIGRP over Frame-RelayMultipoint Subinterfaces

• EIGRP split horizon must be disabled on the interface of the Hub router

EIGRP unicast neighbors

• Interface through which EIGRP will exchange routing updates must be configured with neighbor statement
• EIGRP stops sending multicast packets on that interface

EIGRP Load Balancing

• Equal cost load balancing enabled by default
• Unequal cost load balancing is configurable
• Maximum load balancing of 6 paths for a single destination network enabled by default
• Maximum-paths is configurable

EIGRP Bandwidth Use across WAN Links

• Up to 50% of bandwidth is utilized by default and is configurable
• Point-to-point interfaces:
  • Treat bandwidth as T-1 by default
• Multipoint interfaces:
  • Bandwidth on the physical interface divided by the number of neighbors on that interface

Router Authentication for EIGRP

• EIGRP supports MD5 Authentication
• Multiple keys can be configured
• Keys are managed using key chains

Requirements for EIGRP Authentication:

• EIGRP AS numbers
• Authentication Mode
• One or more keys
• Optionally key lifetimes

EIGRP Queries

• Queries are sent when a route is lost and no feasible successor is available
• Route is put in an “active” state
• Queries are sent to all neighboring routers on all interfaces except the interface of the successor
• If neighbors have lost route information, they respond to query; otherwise they forward query to their neighbors

EIGRP Stub Routers

• This feature allows administrators to prevent the sending of queries to spoke routers

    Stub Options:

• Receive-only: prevents the stub from sending any type of route
• Connected: permits the stub to send connected routes
• Static: permits the stub to send static routes
• Summary: permits the stub to send summary routes
• Redistribute: permits the stub to send redistributed routes