interior gateway routing protocol

8/3/2019 Interior Gateway Routing Protocol

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Interior Gateway Routing Protocol (IGRP)

Internetworking functions of the 3Network Layer include 'networkaddressing'and 'best path selection'for traffic.

'Network addressing'uses one part to identify the path used by the

router and one part for ports or devices on the net.

'Routed protocols'carry user traffic, while 'Routing protocols'work

between routers to maintain path tables.

Network discovery for 'Distance vector'involves exchange of routing

tables; problems can include 'slower convergence'.

For 'Link-state', routers calculate the shortest paths to other

routers; problems can include 'inconsistent updates'.

'Balanced hybrid'routing uses attributes of both link-state and

distance vector, applying paths to several protocols.

Network Layer (Path Determination)

Layer 3 functions to find the best path through the internetwork

Routing services use network topology information

Provides best effort end-to-end packet delivery services to its user,

the Transport layer

Sends packets from the source network to the destination networkbased on IP routing table

After the router determines which path to use, it can proceed with

'switching'the packet

Network Layer (Communicate Path)

Addresses represent the path of media connections

Provide a relay connection that interconnects independent networks

Consistent end-to-end addressing improves the use of bandwidth bypreventing unnecessary broadcasts

Routing Table (Destination Network Address & Next Hop pairs)

------------------------------------------------------------

[ Interface ][ Desirability ][ Next Hop ][ Destination ]

----------- -------------- ---------- -----------------

[ E0 ][ + ][ Router C ][ 111.222.333.444 ]


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[ E1 ][ - ][ Router B ][ 192.168.130.123 ]

[ S0 ][ * ][ Router D ][ Default Gateway ]

------------------------------------------------------------

IP routing specifies that IP datagrams travel through internetworks

one hop at a time At each stop, the next destination is calculated by matching the

datagrams destination network address with an outgoing interface

If no match is found, the datagram is sent to the Default router

Router 'path determination'function:

enables the router to select the most appropriate interface for

forwarding a packet.

Router 'switching'function:

allows a router to accept a packet on one interface and forward it on a

second interface.

Addressing ( Network & Host)

Network Addrress - Location part used by the router

Host Address - Specific port or device on the network

Destination Address AND Subnet Mast = Destination Network

During AND operation, the Host portion is removed

Network portion of address used to make path selections

Node portion refers to a specific device in the network

Routed vs Routing Protocols

Routed protocol

used between routers to carry user traffic (Ex. IP,IPX)

Routing protocol

used between routers to maintain tables (Ex. RIP,IGRP)

Routed protocol - Protocol that can be routed by a router. A router must be

able to interpret the logical internetwork as specified by that routedprotocol. Examples of routed protocols include AppleTalk, DECnet, and IP.

Routing protocol - Protocol that accomplishes routing through the

implementation of a specific routing algorithm. Examples of routing

protocols include IGRP, OSPF, and RIP.


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RIP (Routing Information Protocol) - IGP supplied with UNIX BSD

systems. The most common IGP in the Internet. RIP uses hop count as a

routing metric.

IGRP (Interior Gateway Routing Protocol) - IGP developed by Cisco toaddress the problems associated with routing in large, heterogeneous

networks.

EIGRP (Enhanced Interior Gateway Routing Protocol) -Advanced version

of IGRP developed by Cisco. Provides superior convergence properties and

operating efficiency, and combines the advantages of link state protocols

with those of distance vector protocols.

OSPF (Open Shortest Path First) - Link-state, hierarchical IGP routing

protocol proposed as a successor to RIP in the Internet community. OSPFfeatures include least-cost routing, multipath routing, and load balancing.

OSPF was derived from an early version of the ISIS protocol.

Network Layer (Protocol Operations)

Each router provides its services to support upper-layer functions

Routers pass traffic from all routed protocols over the internetwork

Adaptive to topology changes

Routing protocols maintains and distributes routing information Information used to select the best path for routing

Multiprotocol Routing:

routers that are capable of supporting multiple independent routing

protocols and maintaining routing tables for several routed protocols

concurrently. This capability allows a router to deliver packets from

several routed protocols such as IP and IPX over the same data links.

Static route:

a route that is explicitly configured and entered into the routing

table. Static routes take precedence over routes chosen by dynamic

routing protocols. Use a protocol route that a network administrator

enters into the router. Fixed route to address (as in a 'stub' network)

reflects administrators knowlege. Useful for controlling security and

reducing traffic.

Dynamic routing:


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routing that adjusts automatically to network topology or traffic

changes. Also called adaptive routing. Uses a route that a network

routing protocol adjusts automatically for topology or traffic changes.

The success of dynamic routing depends on two basic router

functions:

1. Maintenance of a routing table

2. Timely distribution of knowledge in the form of routing

updatesto other routers

Default route:

routing table entry (manually defined by the system administrator)

that is used to direct frames for which a next hop is not explicitly

listed in the routing table.

A routing protocol describes:

How updates are sent

What knowledge is contained in these updates

When to send this knowledge

How to locate recipients of the updates

Representing distances with Metrics:

Bandwidth- Data capacity of a link. For instance, normally, a 10-Mbps

Ethernet link is preferable to a 64-kbps leased line.

Delay- Length of time required to move a packet from source to

destination.

Load- Amount of activity on a network resource such as a router or

link.

Reliability- Usually refers to the error rate of each network link.

Hop count- Number of routers a packet must pass through.

Ticks- Delay on a data link using IBM PC clock ticks (approximately 55

milliseconds).

Cost- Arbitrary value, usually based on bandwidth, dollar expense, or

other measurement, that is assigned by a network administrator.

Distance vector routing algorithm- Class of routing algorithms that iterate

on the number of hops in a route to find a shortest-path spanning tree.


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Distance vector routing algorithms call for each router to send its entire

routing table in each update, but only to its neighbors. Distance vector

routing algorithms can be prone to routing loops, but are computationally

simpler than link state routing algorithms. Distance vector algorithms do not

allow a router to know the exact topology of an internetwork. Also calledBellman-Fordrouting algorithm.

Distance Vector Routing:

Pass periodic copies of routing table to neighbor routers and

accumulate distance vectors

Routers discover the best path to destination from each neighbor

Updates proceed step-by-step from router to router

Link state routing algorithm- (also called Shortest Path First) Routingalgorithm in which each router broadcasts (floods) or multicasts information

regarding the cost of reaching each of its neighbors to all nodes in the

internetwork. Link state algorithms create a consistent view of the network

and are therefore not prone to routing loops, but they achieve this at the

cost of relatively greater computational difficulty and more widespread

traffic (compared with distance vector routing algorithms).

Convergence- The speed and ability of a group of internetworking devices

running a specific routing protocol to agree on the topology of aninternetwork after a change in that topology.

Convergence occurs when all routers use a consistent perspective of

network topology (When all routers in an internetwork are operating

with the same knowledge)

After a topology changes, routers must recompute routes, which

disrupts routing

The process and time required for router reconvergence varies in

routing protocols

Autonomous System (AS)- consists of routers, run by one or more

operators, that present a consistent view of routing to the external world.

(Routers under a common administration). The Internet Network

Information Center (InterNIC) assigns a unique autonomous system to

enterprises. This autonomous system is a 16-bit number. A routing protocol


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such as Cisco's Interior Gateway Routing Protocol (IGRP) requires that you

specify this unique, assigned autonomous system number in your

configuration.

Exterior routing protocolsare used to communicate between autonomous systems.

Interior routing protocols

are used within a single autonomous system.

Interior IP Routing Protocols:

RIP- A distance vector routing protocol.

IGRP- Ciscos distance vector routing protocol. (supports multipath

routing)

OSPF- A link-state routing protocol. Enhanced IGRP- A balanced hybrid routing protocol.

IP Routing configuration tasks:

Global Configuration:

o Select a routing protocol, RIP or IGRP.

o Assign IP network numbers without specifying subnet values.

Interface Configuration

o

Assign network/subnet addresses and subnet mask

Dynamic Routing configuration

Router(config)# router-protocol [keyword]

Defines an IP routing protocol (starts a routing process)

protocol - RIP,IGRP,OSPF,EIGRP

keyword - autonomous system

Router(config-router)# network network-number

The network subcommand is a mandatory configuration command for

each IP routing process (allows the routing process to determine

which interfaces will participate in the sending and receiving of

routing updates)


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network-number - specifies a directly connected network (must be

based on the NIC network numbers, not subnet numbers or individual

addresses)

Configuring IGRP

IGRP is a distance vector routing protocol developed by Cisco. IGRP sends

routing updates at 90-second intervals that advertise networks for a

particular autonomous system.

Composite metric selects the path

Speed is the primary consideration

Supports multi-path routing

Supports Equal-cost and Unequal-cost load balancing

Versatility to automatically handle indefinite, complex topologies. Flexibility for segments having different bandwidth and delay

characteristics.

Scalability to function in very large networks.

Variables IGRP uses include:

Bandwidth

Delay

Load Reliability

Maximum transmission unit (MTU)

MTU (Maximum transmission unit)- Maximum packet size, in bytes,

that a particular interface can handle.

Router(config)# router igrp autonomous-system

Defines/selects IGRP as an IP routing process/protocol autonomous-system (AS) - Identifies the IGRP router processes that

will share routing information

Router(config-router)# network network-number

Specifies any participating attached networks


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network-number - Specifies a directly connected network: a network

number, not a subnet number or individual address

EXAMPLE:

Router(config)# router igrp 109

Selects IGRP as the routing protocol for AS 109.

Router(config-router)# network 1.0.0.0

Specifies a directly connected network.

Router(config-router)# network 2.0.0.0

Specifies a directly connected network.

Router> show ip protocol

show ip protocol - Displays IP routing protocol, routing timers and

network information associated with the entire router. The algorithm

used to calculate the routing metric for IGRP is also shown as well as

information about routing metrics (like hop count) and routing filters.

Router> show ip route

show ip route - Command that displays the contents of an IP routingtable.

The table contains a list of all known networks and subnets and the

metrics associated with each entry.

interior gateway routing protocol

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