EIGRP
Brigham Young University- Idaho
CIT 340
EIGRP
EIGRP Concepts
EIGRP Configuration
Troubleshooting Routing Protocols
EIGRP Overview
Cisco proprietary protocol, advanced
version of IGRP
Hybrid Routing protocol (best of SPF
and Distance vector)
Supports CIDR/VLSM
Supports multiple routed protocols
independently
Uses DUAL (Diffusing Update Algorithm)
to calculate routes.
EIGRP vs. IGRP
Similarities
– Both developed by
Cisco
– Both calculate metrics
using bandwidth and
delay
– Use autonomous
system numbers
Differences
– EIGRP scales metric of
IGRP by a factor of 256
(EIGRP=32 bits,
IGRP=24 bits)
– Hop count, IGRP=255,
EIGRP=224
– EIGRP supports
CIDR/VLSM
– EIGRP offers multiprotocol support
IGRP and EIGRP: A migration
path
IGRP
EIGRP
Classful Routing Protocol
Classless Routing Protocol
• VLSM, CIDR
bandwidth =
(10,000,000/bandwidth kbps)
delay
= delay/10
24 bit metric for bandwidth and
delay
bandwidth =
(10,000,000/bandwidth kbps) * 256
delay
= (delay/10) * 256
32 bit metric for bandwidth and
delay
No differentiation between
internal and external routes.
Outside routes (redistributed) are
tagged as external routes.
Automatic redistribution between IGRP and EIGRP as long as “AS”
numbers are the same.
EIGRP Concepts and
Terminology
Like OSPF, EIGRP saves data in RAM in
one of several databases for fast
availability.
Three databases are:
– Neighbor table
– Topology table
– Routing table
Neighbor Table
• Lists adjacent routers. A table is created for each
protocol EIGRP supports. (IP, IPX)
• Neighbor routers Interface and address are
recorded.
• Hold time information received from HELLO
packets determine if route is still accessible or
route changes need to be made.
• Number of packets waiting to be sent.
Neighbor Table
The following fields are found in the
Neighbor Table
– Neighbor address
– Hold time
– Smooth Round-Trip Timer (SRTT)
– Queue count (Q Cnt)
– Sequence Number (Seq No)
Topology Table
• Made up of all EIGRP routing tables from
Autonomous system.
• DUAL uses this information to determine
the best routes to a destination.
(Successor Route)
• A separate topology table is created for
each network protocol supported.
Topology Table Contents
• Feasible Distance-the lowest calculated metric to each
destination.
• Route source-identification number of the router that
originally advertised that route. Only used routes
originated outside of EIGRP.
• Reported distance-the distance reported by an adjacent
neighbor
• Interface information – The interface through which the
destination is reachable
• Router Status- A (Active), P (Passive)
• Routing Protocol used
DUAL
DUAL finite-state machine
algorithm
Diffusing Update Algorithm is the EIGRP
route-calculation engine.
Tracks all the routes advertised by
neighbors, uses composite metrics to
compare them and determine if they are
loop-free.
Routing Table
Holds best routes to each destination.
Maintains separate table for each
supported protocol.
Successor routes- Route selected to
destination.
EIGRP Design Features
• Rapid convergence-DUAL provides Loopfree operation with all routers being updated
at same time.
• Efficient use of bandwidth-Sends PartialBounded updates only to those routers who
need updates.
• Supports multiple protocols-IP, IPX and
AppleTalk are supported through Protocoldependant Modules, PDM’s. Modules can
change but EIGRP can stay the same.
EIGRP Technologies
Neighbor discovery and recovery
Reliable Transport Protocol
DUAL finite-state machine algorithm
Protocol-dependent modules
Protocol-Dependent Modules
(PDMs)
Neighbor Discovery/Recovery
• Like OSPF, EIGRP establishes neighbor
relationships.
• Establish adjacencies by sending Hello
Packets
– 5 seconds-High-speed links >1.5MHz
(default)
– 60 Seconds-Low-speed links <1.5MHz
• Hello Packets are multicast to address
224.0.0.10
Establishing Adjacencies with
Neighbors
By forming adjacencies, EIGRP routers do the following:
Dynamically learn of new routes that join their network
Identify routers that become either unreachable or inoperable
Rediscover routers that had previously been unreachable
Neighbor Discovery/Recovery
EIGRP has a Hold-time used to determine
when Hello packets are no longer being
received.
If Hello packets are being received, EIGRP
assumes route is available. Marked a
Passive.
If hold-time is past, EIGRP must rediscover
route. Marked as Active.
Hello packets are sent unreliably
EIGRP Data Structure
The five EIGRP packet types are:
– Hello
– Acknowledgment
– Update
– Query
– Reply
Acknowledgement Packets
• EIGRP is Routed-protocol independent.
• Reliable Transport Protocol (RTP) provides
acknowledgement of all packets sent.
• Acknowledgement packets are Hello packets
without data.
• Acknowledgement packets are Unicast.
Reliable Transport Protocol
EIGRP is protocol-independent; that is, it doesn’t rely on TCP/IP to
exchange routing information the way RIP, IGRP, and OSPF do.
To stay independent of IP, EIGRP uses the transport-layer protocol to
guarantee delivery of routing information: RTP.
RTP supports:
– Reliable delivery: Delivery guaranteed and in order, Cisco proprietary
algorithm known as reliable multicast, and are Acknolwedged
– Unreliable delivery
RTP supports unicasting and multicasting (224.0.0.10)
– Neighbors that receive a reliable multicast packet unicasts an
acknowledgement
Reliable RTP is used for EIGRP queries, updates and replies
(usually meant when referred to using RTP)
Unreliable RTP is used for EIGRP Hello’s and Ack’s
If any packet is reliably multicast and an ACK is not received from a
neighbor, the packet will be retransmitted as a unicast to that
unresponding neighbor.
If an ACK is not received after 16 of theses unicast transmissions, the
neighbor will be declared dead.
Update Packets
• Update packets are used when a new
neighbor is located or when the topology
changes.
• New neighbor packets are Unicast
• Topology changes are Multicast.
• Update packets are sent reliably.
Query Packets
• Query packets are used to gain specific
information from a neighbor.
• If a router loses it’s successor route and
cannot determine a feasible successor,
query packets are multicast to all
neighbors searching for a new route.
Reply Packets
• Reply packets are responses to query
packets.
• If a router receives a query from a router
looking for a new route, it must send a
reply, indicating a new route or that no info
is available.
• Replies are Unicast.
Configuring EIGRP
router(config)#router eigrp autonomous-systemnumber
Router(config)#router eigrp 101
•
Autonomous system number indicates all
routers belonging to the Internetwork. Must be
the same for IGRP and EIGRP to share
information
Configuring EIGRP
•
router(config-router)#network network-number
router(config-router)# network 10.0.0.0
Network 192.168.15.0
•
Network addresses are written in a
classful manner
Configuring EIGRP
•
router(config-if)#bandwidth kilobits
router(config-if)# bandwidth 64
•
Should be configured on Serial links so
that convergence happens quickly.
Mismatched bandwidth will cause
network problem
Configuring EIGRP
•
router(config-if)#eigrp log-neighbor-changes
•
This command enables the logging of
neighbor adjacency changes to monitor the
stability of the routing system and to help
detect problems.
EIGRP Summarization
EIGRP summarizes networks at the
Classful boundary.
This may be a problem in discontinuous
networks.
Auto-summarization can be turned off
with the following command.
router(config-router)#no auto-summary
Summarizing EIGRP Routes:
no auto-summary
EIGRP automatically summarizes routes
at the classful boundary, the boundary
where the network address ends as
defined by class-based addressing.
Summarizing EIGRP Routes:
no auto-summary
In the presence of discontiguous subnetworks, automatic
summarization must be disabled for routing to work properly.
To turn off auto-summarization, use the following command:
Router(config-router)#no auto-summary
Verifying EIGRP
Show IP EIGRP neighbor
– Displays neighbor table
Show IP EIGRP Interfaces
– Displays EIGRP info for all interfaces
running EIGRP
Show IP EIGRP Topology
– Displays feasible successors
Troubleshooting EIGRP
Verify EIGRP configuration with the
following commands:
– show running-configuration
– show ip protocols
– show ip eigrp neighbors