ROUTING PROTOCOLSPART IIIET4187/ET5187 Advanced Telecommunication Network

2Enhanced Interior Gateway Routing Protocol(EIGRP)

Enhanced Interior Gateway Routing Protocol (EIGRP)• Really just an enhanced version of IGRP • A Cisco proprietary routing protocol• Called a hybrid protocol, but really just an advanced distance vector

protocol.• Fast convergence• Variable length subnet masks• Partial updates - only when the metric for a route changes• Multiple network layer support - IP, IPX, and AppleTalk• A router running EIGRP stores all its neighbor’s routing tables so that it

can quickly adapt or alternate routes.

EIGRP Concepts

Every EIGRP router maintains a topology table for each configured network protocol.

All learned routes to a destination are maintained in the topology table.

Features of EIGRP Classless Routing Protocol (VLSM, CIDR) Faster convergence times and improved scalability Multiprotocol support: TCP/IP, IPX/SPX, Appletalk

– Rapid Convergence and Better handling of routing loops – (DUAL)

Efficient Use of Bandwidth– Partial, bounded updates: Incremental updates only to

the routers that need them. – Minimal bandwidth consumption: Hello packets and by

default uses no more that 50% of link’s bandwidth EIGRP packets.

PDM (Protocol Dependent Module)– Keeps EIGRP modular– Different PDMs can be added to EIGRP as new routed

protocols are enhanced or developed: IPv4, IPv6, IPX, and AppleTalk

IGRP & EIGRPThey work together and routes are redistributed

automaticallyRTB(config)# router igrp 2446RTB(config-router)#network 192.168.1.0RTB(config)#router eigrp 2446RTB(config-router)# network 10.1.1.0RTB(config-router)# network 172.16.1.0

Displaying Interface Values

shows reliability as a fraction of 255, for example (higher is better):

rely 190/255 (or 74% reliability)

rely 234/255 (or 92% reliability)

rely 255/255 (or 100% reliability)

Router> show interface s0/0Serial0/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec)<output omitted>

Bandwidth Delay

Reliability Load

shows load as a fraction of 255, for example (lower is better):

load 10/255 (or 3% loaded link) load 40/255 (or 16% loaded link) load 255/255 (or 100% loaded link)

EIGRP TerminologyTerm Definition

Neighbor table Lists adjacent routers (like adjacency DB in OSPF

Topology table Each router has one for each network protocol routed

Routing table Chooses routes from topology table – maintains one for each network protocol

Successor Route selected as the primary route to use to reach a destination

Feasible successor A backup route to above – multiple feasible successors for a destination can be kept in the topology table

Improvements from IGRP

1. Neighbor discovery & recovery– Use small “hello” packets to estab. adjacencies

– sent every 5 seconds– Dynamically learn routes that way

2. Reliable Transport Protocol (RTP)– A transport layer protocol that guarantees

delivery order– EIGRP is protocol independent, so has its own

guarantee (compare to TCP)

Improvements from IGRP3. Dual finite-state machine

– An algorithm that EIGRP uses to calculate routes– Tracks all routes advertised by neighbors and uses a

composite metric of each route to compare them

4. Protocol-dependent modules– Each module is responsible for all functions

related to its specific routed protocol– In other words, there is an IP PDM, an IPX PDM,

an AppleTalk PDM, etc.

EIGRP Technologies

Neighbor discovery and recovery Reliable Transport Protocol DUAL finite-state machine algorithm Protocol-dependent modules By forming adjacencies, EIGRP routers:

– Dynamically learn of new routes that join their network

– Identify routers that become either unreachable or inoperable

– Rediscover routers that had previously been unreachable

EIGRP Neighbor Table

•This table is the basis for all EIGRP routing updates & convergence•Has info about the neighbor routers•Smooth Round Trip Timer (SRTT) The average time it takes to send and receive packets from a neighbor.

•Queue count The number of packets waiting in queue to be sent.

EIGRP Topology Table

Each EIGRP router maintains a topology table for each configured network protocol.

This table includes the current routes (successors) and back-up routes (feasible successors).

P = Passive (good), A = Active (not ready, DUAL running) EIGRP uses its topology table to store all the information

it needs to calculate a set of distances and vectors to all reachable destinations.

RouterB#show ip eigrp topologyIP-EIGRP Topology Table for process 44Codes: P - Passive, A - Active, U - Update, Q - Query, R -

Reply, r - Reply statusP 206.202.17.0/24, 1 successors, FD is 2195456 via 206.202.16.1 (2195456/2169856), Ethernet0P 206.202.18.0/24, 2 successors, FD is 2198016 via 192.168.0.2 (2198016/284160), Serial0 via 206.202.16.1 (2198016/2172416), Ethernet0

Successor – Current Route 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. Feasible Successor - A backup route These routes are selected at the same time the successors are

identified, but they are kept in the topology table. Multiple feasible successors for a destination can be retained

in the topology table.

FD=15FD=15

FD=20

RD=5

RD=5

RD=6

10

10

6

14

Few Terms

151520

Feasible distance (FD) is the minimum distance (metric) along a path to a destination network. (“This Router’s Distance”)

Reported distance (RD) is the distance (metric) towards a destination as advertised by an upstream neighbor. (“The Neighbor Router’s Distance”)

FD=15FD=15

FD=20

RD=5

RD=5

RD=6

10

10

6

14

Few Terms

151520

The Feasible Distance to a network is sent to other routers, as this router’s Reported Distance.

FDDI R ing

Router A

Router H

Router B

Router D Router E Router F

Router C

Router G

(10)

(20)

(100)

(1)

(100)

(10)

(10)

172.30.1.0/24RouterX’s FD = 30 to 172.30.1.0/24 (Sent as RD to RouterA)

FD = 31 172.30.1.0 is 31

via RouterY

RouterX

RouterY

RouterY’s FD = 21 to 172.30.1.0/24 (Sent as RD to RouterA)

RouterZ’s FD =220 to 172.30.1.0/24 (Sent as RD to RouterA)

Best Route

RouterZ

A neighbor meets the Feasible condition (FC) if the reported distance by the neighbor is smaller than the current feasible distance (FD) of this router.

A distance-vector routing protocol not allowing possible paths with loops paths.

"If a neighbors metric is less than mine, then I know the neighbor doesn't have a loop going through me."

A feasible successor (FS) is a neighbor whose reported distance (RD) is less than the current feasible distance (FD).

Feasible successor is one who meets the feasible condition (FC).

FDDI R ing

Router A

Router H

Router B

Router D Router E Router F

Router C

Router G

(10)

(20)

(100)

(1)

(100)

(10)

(10)

172.30.1.0/24

(Current) Successor: RD= 21

Feasible Successor: RD= 30, FC: RD30 < FD31

NOT a Feasible Successor: RD = 220, FC not met: RD220 > FD31

FD = 31 172.30.1.0 is 31

via RouterY

RouterX

RouterY

RouterZ

Select Routes

If a link goes down, DUAL looks for an alternative route path, or feasible successor, in the topology table.

If a feasible successor is not found, the route is flagged as Active, or unusable at present.

Query packets are sent to neighboring routers requesting topology information.

DUAL uses this information to recalculate successor and feasible successor routes to the destination.

DUAL – Diffusing Update AlgorithmThe centerpiece of EIGRP is DUAL fsm (finite state

machine), the EIGRP route-calculation engine. DUAL selects alternate routes quickly by using

the information in the EIGRP neighbor and topology table.

If a link goes down, DUAL looks for a feasible successor in its topology table.

Feasible successors provide the next lowest-cost path without introducing routing loops.

All other routers to the same destination, that also meet the feasible condition, meaning they are also loop-free, become feasible successors, or back-up routes.

Router# debug eigrp fsm

EIGRP Packet Types

Packet DefinitionHello - multicast Discovers, verifies,

rediscovers neighbor routers

Acknowledgement (unicast)

Indicates receipt of an EIGRP during a reliable packet

Update When a router discovers a new neighbor or a topology change

Query Needing specific info from a neighbor

Reply Response to a query

Data Structures

Looking for a New Route

X

QueriesReplies

RtrF

RtrC

RtrE

RtrD

RtrB

RtrA

RtrG

• If there are no Feasible Successors, the router must ask neighbors for help in hope of finding a new, loop-free path to the destination.

• Neighbor routers are compelled to reply to this query. If a neighbor has a route, it will reply with information about the successor(s). If not, the neighbor notifies the sender that it doesn’t have a route to the destination either.

EIGRP Routing Table

•Contains routes installed by DUAL FSM as the best loop-free paths•Can maintain up to 4 routes per destination•Maintains a separate routing table for each protocol