send infrequent or event triggered LSA packets
reflecting topology changes. Web Links Routing Protocols
- Link State http://www.firewall.cx/i ndex.php?c=link_state
Content 6.3 Routing Protocols
Overview 6.3.1 Path determination A router
determines the path of a packet from one data link to another,
using two basic functions: - A path determination
function
- A switching function
Path
determination occurs at the network layer. The path
determination function enables a router to evaluate the paths
to a destination and to establish the preferred handling of a
packet. The router uses the routing table to determine the best
path and proceeds to forward the packet using the switching
function. - The switching function is the internal process used
by a router to accept a packet on one interface and forward it
to a second interface on the same router. A key responsibility
of the switching function of the router is to encapsulate
packets in the appropriate frame type for the next data link.
Figure illustrates how routers use addressing for these routing
and switching functions. The router uses the network portion of
the address to make path selections to pass the packet to the
next router along the path.
Content
6.3 Routing Protocols Overview
6.3.2 Routing configuration Enabling an IP
routing protocol on a router involves the setting of both
global and routing parameters. Global tasks include selecting a
routing protocol, such as RIP, IGRP, EIGRP or OSPF. The major
task in the routing configuration mode is to indicate IP
network numbers. Dynamic routing uses broadcasts and multicasts
to communicate with other routers. The routing metric helps
routers find the best path to each network or subnet. The
router command starts a routing process. The
network command is required because it enables the
routing process to determine which interfaces participate in
the sending and receiving of routing updates. An example of a
routing configuration is: GAD(config)#router rip
GAD(config-router)#network 172.16.0.0 The network
numbers are based on the network class addresses, not subnet
addresses or individual host addresses. Major network addresses
are limited to Class A, B, and C network numbers. Lab
Activity e-Lab Activity: Routing Configuration In this lab,
the students will configure the routers to start a routing
process, then add the networks that will be advertised.
Content 6.3 Routing Protocols
Overview 6.3.3 Routing protocols At the
Internet layer of the TCP/IP suite of protocols, a router can
use an IP routing protocol to accomplish routing through the
implementation of a specific routing algorithm. Examples of IP
routing protocols include: - RIP – A distance
vector interior routing protocol
- IGRP – Cisco's
distance vector interior routing protocol
- OSPF
– A link-state interior routing protocol
- EIGRP
– Cisco’s advanced distance vector interior routing
protocol
- BGP – A distance vector exterior
routing protocol
Routing Information Protocol (RIP)
was originally specified in RFC 1058. Its key characteristics
include the following: - It is a distance vector routing
protocol.
- Hop count is used as the metric for path
selection.
- If the hop count is greater than 15, the
packet is discarded.
- Routing updates are broadcast
every 30 seconds, by default.
Interior Gateway
Routing Protocol (IGRP) is a proprietary protocol developed by
Cisco. Some of the IGRP key design characteristics emphasize
the following: - It is a distance vector routing
protocol.
- Bandwidth, load, delay and reliability are
used to create a composite metric.
- Routing updates are
broadcast every 90 seconds, by default.
Open
Shortest Path First (OSPF) is a nonproprietary link-state
routing protocol. The key characteristics of OSPF are as
follows: - It is a link-state routing protocol.
- Open standard routing protocol described in RFC 2328.
- Uses the SPF algorithm to calculate the lowest cost to a
destination.
- Routing updates are flooded as topology
changes occur.
EIGRP is a Cisco proprietary enhanced
distance vector routing protocol. The key characteristics of
EIGRP are as follows: - It is an enhanced distance
vector routing protocol.
- Uses load balancing.
- Uses a combination of distance vector and link-state
features.
- Uses Diffused Update Algorithm (DUAL) to
calculate the shortest path.
- Routing updates are
broadcast every 90 seconds or as triggered by topology
changes.
Border Gateway Protocol (BGP) is an
exterior routing protocol. The key characteristics of BGP are
as follows: - It is a distance vector exterior routing
protocol.
- Used between ISPs or ISPs and clients.
- Used to route Internet traffic between autonomous
systems.
Interactive Media Activity
Checkbox: Link-State and Distance Vector Routing Protocols
After completing this activity, the student will be able to
understand IP routing protocols. Web Links Introduction
to IP Routing http://www.cisco.com/en/US/tech/tk365/tech_topology
_and_network_serv_and_protocol_suite_home.html
Content 6.3 Routing Protocols
Overview 6.3.4 Autonomous systems and IGP
versus EGP Interior routing protocols are designed for use
in a network whose parts are under the control of a single
organization. The design criteria for an interior routing
protocol require it to find the best path through the network.
In other words, the metric and how that metric is used is the
most important element in an interior routing protocol. An
exterior routing protocol is designed for use between two
different networks that are under the control of two different
organizations. These are typically used between ISPs or between
a company and an ISP. For example, a company would run BGP, an
exterior routing protocol, between one of its routers and a
router inside an ISP. IP exterior gateway protocols require the
following three sets of information before routing can begin:
- A list of neighbor routers with which to exchange
routing information.
- A list of networks to advertise
as directly reachable.
- The autonomous system number of
the local router.
An exterior routing protocol must
isolate autonomous systems. Remember, autonomous systems are
managed by different administrations. Networks must have a
protocol to communicate between these different systems.
Autonomous systems have an identifying number, which is
assigned to it by the American Registry of Internet Numbers
(ARIN) or a provider. This autonomous system number is a 16-bit
number. Routing protocols such as Cisco’s IGRP and EIGRP
require that a unique, autonomous system number be assigned.
Interactive Media Activity Checkbox: IGP versus EGP
After completing this activity, the student will be able to
understand IGP and EGP. Web Links IGP
http://searchsecurity.techtarget.com/ sDefinition/0,,sid14_
gci214018,00.html
Content 6.3
Routing Protocols Overview 6.3.5 Distance
vector Distance vector algorithms (also known as
Bellman-Ford algorithms) call for each router to send all or