REVISION
Cisco!
NETWORK COMPONENTS
PROTOCOL SUITES
TCP/IP PROTOCOL SUITE
ENCAPSULATION PROCESS
NETWORK ADDRESSES AND DATA LINK
ADDRESSES
The network layer and data link layer are
responsible for delivering the data from the sourc
device to the destination device.
IPV4 ADDRESS
A numerical label assigned to each device participating in a
computer network that uses the Internet Protocol for
communication.
32-bit binary number expressed using four decimal numbers
separated by dots (dotted decimal notation).
CLASSFUL IP ADDRESS
Originally IP addresses were divided into five
classes.
The initial bits determine which class an address
belongs to.
Classes A, B and C are the most important.
ROUTER
Connects multiple networks.
Has multiple interfaces.
Primary functions:
Determine the best path to send packets.
PACKET FORWARDING
Three packet forwarding mechanisms:
Process Switching
Fast Switching
Cisco Express Forwarding (CEF)
PROCESS SWITCHING
Each packet must be processed individually.
FAST SWITCHING
First packet of a flow is process-switched and flow
information added to the fast-switching cache to
be used by the following packets.
CISCO EXPRESS FORWARDING (CEF)
Builds Forwarding Information Base (FIB) and an
Adjacency Table to perform layer-3 switching in
hardware.
TYPES OF ROUTING
Two main types of routing:
Static routing
A static route is a route that is manually configured on
the router.
Dynamic routing
Dynamic routes are routes that a router learns by using
DYNAMIC ROUTING PROTOCOLS
Routing protocols are used to facilitate the
exchange of routing information between routers
Routing protocols allow routers to dynamically
learn information about remote networks and
automatically add this information to their own
routing tables.
CLASSIFICATIONS OF DYNAMIC ROUTING
PROTOCOLS
Routing protocols can be classified into dierent groups according to their
characteristics:
Purpose
Operation
Interior gateway protocol (IGP) or exterior gateway protocol (EGP).
Distance vector or link-state.
Behaviour:
IGP VS EGP
Autonomous system (AS) - a collection of routers under a
common administration.
IGP: used for exchanging routing information between routers
within an autonomous system.
Examples: RIP, EIGRP, OSPF, and IS-IS.
EGP: used for exchanging routing information between
autonomous systems.
DISTANCE VECTOR VS LINK-STATE
Distance vector routing protocols advertise route as vectors of
distance and direction between directly connected neighbours.
A router knows from which neighbour a route was learned,
but it does not know where that neighbour learned the route.
Link-state routing protocols advertise link-state information
throughout the link-state domain.
All routers know about the paths reachable by all other
CLASSFUL ROUTING VERSUS CLASSLESS
ROUTING PROTOCOL
Classful routing protocol do not send subnet mask
information with their routing updates.
Classless routing protocol include subnet mask
information with their updates.
ROUTING TABLE
Contains the information necessary to forward a packet along the best path
toward its destination.
Store route information about directly connected and remote networks.
The routing table contains network or next hop associations.
These associations tell a router that a particular destination can be
optimally reached by sending the packet to a specific router that
represents the next hop on the way to the final destination.
The next hop association can also be the outgoing or exit interface to
ROUTING TABLE SOURCES
Entries in the routing table can be added as:
Local route interfaces
Directly connected interfaces
Added when an interface is configured and active.
Static routes
Added when an interface is configured and active.
Added when a route is manually configured and the exit interface is active.
Dynamic routing protocols
Added when routing protocols are configured and networks identified.
BUILDING THE ROUTING TABLE
The main considerations while building the
routing table are:
Administrative distance
Metrics
ADMINISTRATIVE DISTANCE
Represents the reliability (trustworthiness) of a
routing protocol (or a route).
Used by router to select the best path when there
are two or more dierent routes to the same
destination from two or more routing protocols.
The smaller the administrative distance, the more
DEFAULT ADMINISTRATIVE DISTANCE
Route Source
Connected
Static
EIGRP summary route
External BGP
Internal EIGRP
OSPF
IS-IS
RIP
External EIGRP
Administrative Distance
0
1
5
20
90
110
115
120
170
ROUTING METRIC
A value generated by the routing algorithm for each path
through the network.
The best path to a network is the path with the lowest
metric.
Metrics can be based on either a single characteristic or
several characteristics of a path.
Dynamic routing protocols typically use their own rules and
ROUTING TABLE ENTRY:
REMOTE NETWORKS
ROUTING TABLE ENTRY:
DIRECTLY CONNECTED NETWORKS
