EIGRPConcepts

woonsocketpoliticalNetworking and Communications

Oct 28, 2013 (3 years and 1 month ago)

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EIGRP
EIGRP Concepts
EIGRP Background
•Cisco proprietary
•Released in 1994
•Based on IGRP
•An advanced distance-vector routing
protocol

Relies on features commonly associated

Relies on features commonly associated
with link-state protocols
–Sometimes called a hybrid routing protocol
•Supports VLSM and CIDR
•Supports unequal-cost load balancing
–Like IGRP
–Unlike OSPF
EIGRP Metrics
•EIGRP uses a metriccalculated as a
function of:
–Bandwidth
–Delay

Reliability

Reliability
–Load
–MTU
•By default, EIGRP uses only bandwidth
and delay as metrics.
EIGRP Metric Calculation
•By default:
•K1 = 1
•K2 = 0

K3 = 1
•K1affects
Bandwidth

K3 = 1
•K4 = 0
•K5 = 0
= Bandwidth + Delay
•Actually, = Slowest
Bandwidth + Sum of All
Delays
Bandwidth
•K2affects Load
and Bandwidth
•K3affects Delay
•K4and K5affect
Reliability
Viewing EIGRP Metrics
bandwidth
delay
MTU
Viewing EIGRP K-Values
EIGRP and IGRP
•IGRP and EIGRP are compatible with
each other, although EIGRP offers
multiprotocol support and IGRP does
not.

EIGRP supports

EIGRP supports
–IP
–IPX
–AppleTalk
EIGRP and IGRP Route
Redistribution
•EIGRP and IGRP automatically redistribute
each other’s routes when using the same
Autonomous System number.
EIGRP and IGRP Automatic
Redistribution
•EIGRP routers keep route and topology
information readily available in RAM so
that they can react quickly to changes.
•EIGRP uses Successors and Feasible
Successors to determine routes and
backup routes.
EIGRP Terminology
•EIGRP keeps this information in several
tables, or databases.
–Neighbor table
–Topology table
–Routing table
EIGRP Neighbor Table
•Each EIGRP router maintains a neighbor
table that lists adjacent routers.
•This table is comparable to the adjacency
database used by OSPF.
•There is a neighbor table for each protocol
that EIGRP supports.
that EIGRP supports.
EIGRP Topology Table
•Every EIGRP router maintains a topology table for each
configured network protocol.
•This table includes route entries for all destinations that the
router has learned.
•All learned routes to a destination are maintained in the
topology table.
•Each EIGRP router maintains a topology table for each network
protocol.
EIGRP Routing Table
•EIGRP chooses the best routes to a
destination from the topology table and
places these routes in the routing table.
•Each EIGRP router maintains a routing table
for each network protocol.
Successor
•A successor is a route selected as the
primary route to use to reach a
destination.
•Successors are the entries kept in the
routing table.
routing table.
•Multiple successors for a destination
can be retained in the routing table.
Feasible Successor
•A feasible successor is a backup route.
•These routes are selected at the same
time the successors are identified, but
are kept in the topology table.

Multiple feasible successors for a

Multiple feasible successors for a
destination can be retained in the
topology table.
EIGRP Operation
•Routing tables are not exchanged on a
periodic basis.
•Uses Hello packets to create and
maintain neighbor relationships and
determine when a link is down
•When a change in topology occurs,
EIGRP does not flood updates like link
-
EIGRP does not flood updates like link
-
state protocols, but immediately sends
those changes to only its neighbors.
•Has speed and efficiency of routing
updates like a link-state protocol, along
with a topology database.
Hello Packets
•Multicast to 224.0.0.10
–Sent every 5 seconds, with a hold
timer of 15 seconds for links greater
than T1 speed (LAN)
–Sent every 60 seconds, with a hold
timer of 180 seconds for links less
than T1 speed (WAN)
timer of 180 seconds for links less
than T1 speed (WAN)
•Hold Timer specifies how long to wait
before considering a neighboring
router inaccessible
–3 times hello time, by default
EIGRP Neighbor Exchanges
Reliable Transport Protocol
•RTP (Reliable Transport Protocol)
–Transport-layer protocol
•EIGRP is protocol-independent
–Does not rely only on TCP/IP or IPX/SPX
to exchange routing information

EIGRP uses RTP to guarantee

EIGRP uses RTP to guarantee
delivery of routing information.
•RTP supports reliable and unreliable
delivery.
•RTP supports unicasting and
multicasting.
RTP Use
•Initial delivery of EIGRP messages is done
using multicast packets
–Data is sent to all neighbors on a segment, and
every neighbor is expected to acknowledge it
with a unicast Hello packet.
•After adjacency has been formed and added
to neighbor table, routers exchange routing
information which is stored in the topology
to neighbor table, routers exchange routing
information which is stored in the topology
table.
•RTP uses a mechanism of sequence numbers
and acknowledgements.
•RTP is used for EIGRP queries, updates and
replies.
•RTP is not used for EIGRP Hellos and ACKs.
The Diffusing Update
Algorithm
•The centerpiece of EIGRP is DUAL,
the EIGRP route-calculation engine.
–This engine contains all the logic
used to calculate and compare
routes in an EIGRP network.
routes in an EIGRP network.
–DUAL uses the neighbor table and
topology table to make decisions
about successors, feasible
successors, and other alternate
routes.