Chapter 14TCP/IP and Routing Part #2

Unix System Administration

Roto-Routing

There are several routing protocols to meet specific needs RIP - Routing Information Protocol OSPF - Open Shortest Path First IGRP - Interior Gateway Protocol EGP - Exterior Gateway Protocol BGP - Border Gateway Protocol DVMRP - Distance Vector Multicast Routing

Protocol

Let’s All RIP One

RIP is commonly implemented in the routed or gated daemon

RIP uses hop count as its metricRIP is a resource hog due to its

heavy use of broadcastingRIP is good for small networks

without redundant paths or paths of varying bandwidth

Roger, Roger; What’s Your Vector Victor?

OSPF is an industrial strength routing protocol for large, complex networks

OSPF uses distance (hop count) and vector (cost/weight) as its metrics

OSPF handles multiple paths and varying bandwidth links better than RIP

OSPF is more complicated to administrate

IGRP Your EGP

IGRP is a proprietary routing protocol from Cisco system

EGP is an old routing protocol from the ARPANET (pre-Internet)

BGP is the preferred Internet routing protocol

Border Your Gateway

BGP expands on EGPBGP supports an arbitrarily complex

topology of autonomous systems.BGP is typically used if your

company want to use two different Internet Providers

Cheap Routing

ICMP Redirects Use with hosts that don’t understand

routing and only know how to send non-local packets to a smarter device (e.g. router).

If the default router isn’t the correct one, it the forwards packet to the appropriate router and sends back an ICMP redirect to the host for future use.

ICMP Redirect at Work

Let’s Catch A U-Boat With Our Subnet

Subnets is the further breaking down of a network in smaller parts

You subnet the portion of the IP address that is meant for hosts devices (not the part assigned to you)

Subnets let you control traffic and routing policies

The dreaded subnet mask is used to separate the host portion and subnet portion of the IP address

Subnet Mask Example

IP - 159.91.15.220 Mask - 255.255.248.0

Convert to binary and remove the periods

nnnnnnnnnnnnnnnn0000111111011100

nnnnnnnnnnnnnnnn1111100000000000

and together nnnnnnnnnnnnnnnn0000100000000000

separate subnet nnnnnnnnnnnnnnnnssssshhhhhhhhhhh

So IP 159.91.15.220 with subnet mask 255.255.248.0 is in subnet #1 and is host #2012

Subnet Mask Example #2

Assume you have a Class C address, say 192.168.1.0 and you want to create a subnet mask that will allow you to have 6 subnets with up to 26 hosts per subnet. What subnet mask should you use?

Since it is a class C, you only get to work with the last octet which is 8 bits.

How many bits do you need for 6 subnets? How many for 26 hosts?

The subnet mask must be 255.255.255.224

Route This!

Which subnet mask should you select if there are multiple solutions to the # subnets/hosts required?

What would you need to do if you can’t satisfy the number of subnet and hosts per subnet with your IP address class?