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Dynamic routing protocols help the network
administrator overcome the time-consuming
and exacting process of configuring and
maintaining static routes.
The purpose of a dynamic routing
protocol is to:
Discover remote networks
Maintaining up-to-date routing information
Choosing the best path to destination
Ability to find a new best path if the current
Interior Gateway Routing Protocols (IGP)
-Used for routing inside an autonomous
system & used to route within the individual
-Examples: RIP, EIGRP, OSPF
Exterior Routing Protocols (EGP)
-Used for routing between autonomous
Do NOT send subnet
mask in routing
Do send subnet mask
A value used by a routing protocol to determine which
routes are better than others.
Metrics used in IP routing
AD VALUE FOR ROUTING PROTOCOLS
it is a numeric value that specifies the preference of a particular route
ROUTING INFORMATION PROTOCOL
The Routing Information Protocol (RIP) is an
intradomain routing protocol used inside an
autonomous system. It is a very simple protocol
based on distance vector routing.
A metric in RIP is called a hop count; distance;
defined as the number of links (networks) that have
to be used to reach the destination.
Distance vector algorithm.
Included in BSD-UNIX Distribution in
Router (config)# router rip
Router (config-router)# network_required network
Distance vector routing protocol.
Uses hop count as a path selection metric.
Three types of timers.
Multiple stability features.
Hop Count -- Fifteen Hop Limit
- Hop count is the sum of all the legs in a route.
-After 15 hops, the packet is discarded
Timers in RIP
Periodic timer : controlling the advertisements of
regular update messages
expiration timer : governing the validity of a route
the garbage collection timer : advertising the
failure of a route
RIPv2 is an extends RIPv1:
Subnet masks are carried in the route
Authentication of routing messages
Route information carries next-hop address
Exploites IP multicasting
Extensions of RIPv2 are carried in unused fields
of RIPv1 messages
Router (config)# router rip
Router (config)# ver 2
Router (config-router)# network_required network
Simplicity ; little to no configuration, just start
Passive version for hosts
If a host wants to just listen and update its
RIP takes a long time to stabilize
Even for a small network, it takes several
minutes until the routing tables have settled
after a change
RIP has all the problems of distance vector
algorithms, e.g., count-to-Infinity
RIP uses split horizon to avoid count-
The maximum path in RIP is 15 hops
OSPF (Open Shortest Path
The Open Shortest Path First (OSPF)
protocol is an intradomain routing protocol
based on link state routing. Its domain is also
an autonomous system
Dividing an AS(autonomous system) into
to handle routing efficiently and in a timely
Functional Requirements of OSPF
Faster Convergence and less
consumption of network resources
A more descriptive routing metric
value ranges between 1 and 65,535
no restriction on network diameters
a way to do load balancing
support large routing domains
Separate internal and external routes
Support of flexible subnetting schemes
route to arbitrary [address,mask]
combinations using VLSMs
Type of Service Routing
Is a collection of networks, hosts, and routers in AS
AS can be divided into many different areas.
All networks inside an area must be connected.
Routers inside an area flood the area with routing information.
Area Border Router
Summarizes the information about the area and sends it to
All of the areas inside an AS must be connected to the
Serving as a primary area
Consisting of backbone routers
Back bone routers can be an area border router
OSPF protocol allows the administrator to assign a
cost, called the metricc, to each route
Based on a type of service (minimum delay,
maximum throughput, and so on)
A router can have multiple routing tables, each based
on a different type of service.
Link State Routing
OSPF uses Link State Routing to update the routing
tables in an area
Each router shares its knowledge about its
neighborhood with every router in the area.
Types of Links
In OSPF terminology, a connection is called a
Routers are represented by nodes and the
link is represented by a bidirectional edge
connecting the nodes.
Each router has only one neighbor at the
other side of the link.
• Tranisent network:
is a network with several routers attached to
transient Link .
is a network that is connected to only one router
is a special case of transient network
The link is only one-directional, from the router to
When the link between two routers is broken,
the administration may create a virtual link
between them using a longer path
An internet with 7 networks and 6 routers
A classless version of IGRP.
EIGRP includes several features that are not commonly
found in other distance vector routing protocols like RIP
(RIPv1 and RIPv2) and IGRP.
These features include:
Reliable Transport Protocol (RTP)
Diffusing Update Algorithm (DUAL)
Neighbor and Topology Tables
Although EIGRP may act like a link-state routing protocol,
it is still a distance vector routing protocol.
Path Determination (1)
Traditional distance vector routing protocols such as RIP
and IGRP keep track of only the preferred routes; the best
path to a destination network.
If the route becomes unavailable, the router waits for
another routing update with a path to this remote network.
EIGRP's DUAL maintains a topology table separate from
the routing table.
including both the best path to a destination network and any
backup paths that DUAL has determined to be loop-free.
Loop-free means that the neighbor does not have a route
to the destination network that passes through this router.
Path Determination (2)
If a route becomes unavailable, DUAL will
search its topology table for a valid backup path.
If one exists, that route is immediately entered
into the routing table.
If one does not exist, DUAL performs a network
discovery process to see if there happens to be
a backup path that did not meet the requirement
of the feasibility condition.
Router (config)# router eigrp_PROCESS ID ( )
Router (config-router)# network _ required
BORDER GATEWAY PROTOCOL
Routing protocols used to route information
between multiple autonomous systems
BGP (Border Gateway Protocol) is a protocol for exchanging routing
information between gateway hosts (each with its own router) in a network
of autonomous systems. BGP is often the protocol used between gateway
hosts on the Internet. The routing table contains a list of known routers, the
addresses they can reach, and a cost metric associated with the path to
each router so that the best available route is chosen.
Router (config)#router bgp_PID1
Router (config)#Network directly connect
Router (config –router)# neighbor_ip of end
NOTE 1: Before applying this command apply
Dynamic routing on each router
NOTE 2: Each router has different Process ID
NOTE 3:Do not write directly attached IP of network.
All except directly attached IP will be treated as
NOTE 4: PID will be of current router only.