Cisco IGRP

	Internetworking Technologies Instructor: Prabul, CCNA
	Internetworking Technologies Instructor: Prabul, CCNA

5. IGRP

Top 10 Graphics:

Review:

Internetworking functions of the 3Network Layer include 'network addressing' 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 network based 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 by preventing unnecessary broadcasts


Routing Table (Destination Network Address & Next Hop pairs)
-------------------------------------------------------------
[ Interface ][ Desirability ][ Next Hop ][ Destination     ]
 -----------  --------------  ----------  -----------------
[    E0     ][       +      ][ Router C ][ 111.222.333.444 ]
[    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 routed protocol. 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.

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 to address 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. OSPF features 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:

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:

Maintenance of a routing table
Timely distribution of knowledge in the form of routing updates to 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. 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 called Bellman-Ford routing 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) Routing algorithm 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 an internetwork 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 such as Cisco's Interior Gateway Routing Protocol (IGRP) requires that you specify this unique, assigned autonomous system number in your configuration.

Exterior routing protocols: are 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 - Cisco’s 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:
- Select a routing protocol, RIP or IGRP.
- Assign IP network numbers without specifying subnet values.
Interface Configuration
- 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)
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
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 routing table.
The table contains a list of all known networks and subnets and the metrics associated with each entry.

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