CCNP Exam Prep Tips and Must Knows

studnet765016Things 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
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