Download CCNA 1 Module 10 Routing Fundamentals and Subnets

CCNA 1 v3.0 Module 10
Routing Fundamentals and
Subnets
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Objectives
Routed protocol
IP routing protocols
The mechanics of subnetting
Routed Protocol
Routable and Routed Protocols
A routed protocol allows the router to forward
data between nodes on different networks.
In order for a protocol to be routable, it must
provide the ability to assign a network number
and a host number to each individual device.
These protocols also require a network mask
in order to differentiate the two numbers.
The reason that a network mask is used is to
allow groups of sequential IP addresses to be
treated as a single unit.
IP as a Routed Protocol
IP is a connectionless,
unreliable, best-effort
delivery protocol.
As information flows
down the layers of
the OSI model; the
data is processed at
each layer.
IP accepts whatever
data is passed down
to it from the upper
layers.
Packet Propagation and
Switching Within a Router
Packet Propagation and
Switching Within a Router
As a frame is received at a router interface.
The MAC address is checked to see if the
frame is directly addressed to the router
interface, or a broadcast.
The frame header and trailer are removed
and the packet is passed up to Layer 3.
The destination IP address is compared to
the routing table to find a match.
The packet is switched to the outgoing
interface and given the proper frame header.
The frame is then transmitted.
Internet Protocol (IP):
Connectionless
The Internet is a gigantic, connectionless network
in which all packet deliveries are handled by IP.
TCP adds Layer 4, connection-oriented reliability
services to IP.
Telephone Calls: Connectionoriented
A connection is established between the
sender and the recipient before any data is
transferred.
Anatomy of an IP Packet
While the IP source and destination
addresses are important, the other header
fields have made IP very flexible.
The header fields are the information that
is provided to the upper layer protocols
defining the data in the packet.
IP Routing Protocols
Routing Overview
A router is a network layer device that uses one or
more routing metrics to determine the optimal path.
Routing metrics are values used in determining the
advantage of one route over another.
Routing protocols use various combinations of
metrics for determining the best path for data.
Routing Versus Switching
This distinction is routing and switching
use different information in the process of
moving data from source to destination.
Routing Versus Switching
Routed Versus Routing
A routed protocol:


Includes any network protocol suite that provides
enough information in its network layer address
to allow a router to forward it to the next device
and ultimately to its destination.
Defines the format and use of the fields within a
packet.
A routing protocol:


Provides processes for sharing route information.
Allows routers to communicate with other routers
to update and maintain the routing tables.
Path Determination
Path determination enables a router to compare
the destination address to the available routes in
its routing table, and to select the best path.
Routing Tables
Routers keep track of the following:
 Protocol type
 Destination/next-hop associations
 Routing metric
 Outbound interfaces
Routing Algorithms and
Metrics
Routing protocols have one or more of the
following design goals:
 Optimization
 Simplicity and low overhead
 Robustness and stability
 Flexibility
 Rapid convergence
IGP and EGP
IGPs route data within an autonomous system.
 RIP, RIPv2, IGRP, EIGRP, OSPF, IS-IS
EGPs route data between autonomous systems
 Border Gateway Protocol (BGP)
Link State and Distance Vector
Examples of distance-vector protocols:



Routing Information Protocol (RIP)
Interior Gateway Routing Protocol (IGRP)
Enhanced IGRP (EIGRP)
Examples of link-state protocols:


Open Shortest Path First (OSPF)
Intermediate System-to-Intermediate System
(IS-IS)
Routing Protocols
RIP
RIP v2
IGRP
EIGRP
OSPF
IS-IS
BGP
Mechanics of Subnetting
Classes of Network IP
Addresses
Introduction to Subnetting
Host bits must
are reassigned
(or
“borrowed”) as
network bits.
The starting
point is always
the leftmost
host bit.
3 bits borrowed allows 23-2 or 6 subnets
5 bits borrowed allows 25-2 or 30 subnets
12 bits borrowed allows 212-2 or 4094 subnets
Reasons for Subnetting
Provides addressing flexibility for the
network administrator.

Each LAN must have its own network or
subnetwork address.
Provides broadcast containment and lowlevel security on the LAN.
Provides some security since access to
other subnets is only available through the
services of a router.
Establishing the Subnet Mask
Address
Determines which part of an IP address is the network
field and which part is the host field.
Follow these steps to determine the subnet mask:




1. Express the subnetwork IP address in binary form.
2. Replace the network and subnet portion of the address
with all 1s.
3. Replace the host portion of the address with all 0s.
4. Convert the binary expression back to dotted-decimal
notation.
Establishing the Subnet Mask
Address
To determine the number of bits to be used, the
network designer needs to calculate how many
hosts the largest subnetwork requires and the
number of subnetworks needed.
The “slash format” is a shorter way of
representing the subnet mask:

/25 represents the 25 one bits in the subnet mask
255.255.255.128
Establishing the Subnet Mask
Address
Subnetting Class A and B
Networks
The available bits for assignment to the
subnet field in a Class A address is 22 bits
while a Class B address has 14 bits.
Calculating the Subnetwork With
ANDing
ANDing is a binary process by which the router
calculates the subnetwork ID for an incoming
packet.

1 AND 1 = 1; 1 AND 0 = 0; 0 AND 0 = 0
The router then uses that information to forward
the packet across the correct interface.
Packet Address
192.168.10.65
11000000.10101000.00001010.0
10
00001
Subnet Mask
255.255.255.224
11111111.11111111.11111111.1
11
00000
Subnetwork Address
192.168.10.64
11000000.10101000.00001010.0
10
00000