Transcript Semester 4 Chapter 1 - Institute of Technology Sligo

Institute of Technology,
Sligo Dept of Computing
Cisco Semester 4
Chapter 1, version 2.1.3
Review
Overview
Chapter 1 is a review of the following
subjects:
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1.2 LAN Switching
1.2 Virtual LANs
1.3 LAN Design
1.4 Routing Protocols
1.5 Access Control Lists
and 1.6 IPX Routing
1.1 LAN Switching
1.1.1 Congestion and Bandwidth
As more people utilize a network to share
large files, access file servers and connect
to the Internet, network congestion occurs.
To relieve network congestion, more
bandwidth is needed or the available
bandwidth must be used more efficiently.
1.1 LAN Switching
1.1.2 Why Segment LANs?

By using segments in a network, less users &
devices are sharing the same bandwidth when
communicating within the segment.
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This process of creating smaller collision and
broadcast domains is referred to as
segmentation.
1.1 LAN Switching
1.1.3 Segmentation with LAN Switches

A LAN that uses a switched Ethernet topology
creates a network that behaves like it only has two
nodes - the sending node and the receiving node.
They share the 10Mbps bandwidth between them,
which means that nearly all the bandwidth is
available for the transmission of data.
1.1 LAN Switching
1.1.4 LAN Switching Overview

Switching increases the bandwidth available on
a network by creating dedicated network
segments and connecting those segments in a
virtual network within the switch. This circuit
exists only when two nodes need to
communicate.
1.1 LAN Switching
1.1.5 How a LAN Switch Learns Addresses
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Switches learn device addresses by:
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Reading the source address of each
packet transmitted
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Noting the port where the frame was
heard
1.1 LAN Switching
1.1.6 Symmetric Switching
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A symmetric switch provides switched
connections between ports with the same
bandwidth, such as all 10 Mbps or all 100
Mbps ports.
1.1 LAN Switching
1.1.7 Asymmetric Switching
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An asymmetric LAN switch provides
switched connections between ports of
unlike bandwidth, such as a combination
of 10 Mbps and 100 Mbps ports.
1.1 LAN Switching
1.1.8 Two Switching Methods
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Store and Forward - (entire frame is
received)
Cut-through - (destination MAC address
is read)
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Fast Forward - No error checking
and Fragment Free - Checks for collisions
1.2 Virtual LANs
1.2.1 Introduction to VLANs

VLANs logically segment the physical LAN
infrastructure so that broadcast frames are
switched only between ports within the same
VLAN.
1.2 Virtual LANs
1.2.2 and 1.2.3 Frame Filtering and
Frame Tagging
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Two ways to implement VLANs are:
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Frame filtering, which uses the MAC addresses
already within the frame to base switching
decisions, and
Frame tagging, in which extra information is added
to the frame to identify the VLAN the frame
belongs to.
1.2 Virtual LANs
1.2.4 VLANs Establish Broadcast
Domains
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Members of the same VLAN are members
of the same broadcast (but not collision)
domain. VLANs break up broadcast
domains. Regularly configured bridges
and switches segment collision domains.
1.2 Virtual LANs
1.2.5 Port-Centric Virtual LANs

VLAN membership by port maximizes forwarding
performance because:
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Users are assigned by port
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VLANs are easily administered
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Security between VLANs is maximized
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Packets do not "leak" into other domains
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VLANs and VLAN membership are easily controlled across
the network
1.2 Virtual LANs
1.2.6 Static VLANs
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Static VLANs have the same
characteristics as static routes: they are
secure, easy to configure, and
straightforward to monitor, but they must
be setup by an administrator.
1.2 Virtual LANs
1.2.7 Dynamic VLANs
Dynamic VLANs are ports on a switch that
can automatically determine their VLAN
assignments.
More administration is required up front to
set up the database within the VLAN
management software.
1.3 LAN Design
1.3.1 LAN Design Goals
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General requirements of network design:
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Functionality -- It must work
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Scalability -- It must be able to grow
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Adaptability -- It must work with future
technologies
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Manageability -- It must be monitored
1.3 LAN Design
1.3.2 Design Methodology
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Three steps describe a simple model that
could be used in network design:
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Analyze requirements
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Develop a LAN structure (topology)
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Set up addressing and routing
1.3 LAN Design
1.3.3 What Problem are you Trying to
Solve?
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The decision to use an internetworking device
depends on which problems you are trying to
solve for your client.
1.3 LAN Design
Types of Problems Include:
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Media contention
Excessive broadcasts
Need to transport new payloads
Need for more bandwidth
Overloaded backbone
Network addressing issues
1.3 LAN Design
1.3.4 Developing a LAN Topology
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The topology design can be broken into three OSI
categories:
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Layer 1 - Physical Layer (wire media type)
Layer 2 - Data Link Layer (bridges & switches)
Layer 3 - Network Layer (routers and network
addressing)
1.3 LAN Design
1.3.5 Developing Layer 1 LAN
Topology
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The Physical layer controls the way data is
transmitted between nodes. The type of
media and topology selected will
determine how much and how fast data
can travel across the network.
1.3 LAN Design
1.3.6 Extended Star Topology
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In larger networks it is not unusual to have
more than one wiring closet. By creating
multiple wiring closets, multiple catchment
areas are created. The secondary wiring
closets are referred to as Intermediate
Distribution Facilities.
1.3 LAN Design
1.3.7 Developing Layer 2 LAN Topology
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The purposes of Layer 2 devices in the network
are to provide flow control, error detection and
correction, and to reduce congestion in the
network.
1.3 LAN Design
1.3.8 Layer 2 Switching
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By installing LAN switching at the MDF and IDFs
we can start to look at the size of the collision
domains and the speed for each horizontal cable
and vertical cable run.
1.3 LAN Design
1.3.9 Layer 3 Router for Segmentation
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Where there are multiple physical networks, all
data traffic from Network 1 destined for Network
2 has to go through the router. The router is the
central point in the LAN for traffic destined for
the WAN port.
1.3 LAN Design
1.3.10 Server Placement
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If servers are to be distributed around the
network topology according to function,
the networks Layer 2 and 3 must be
designed to accommodate this. The Layer
2 LAN switches must have high speed
ports allocated for these servers.
1.4 Routing Protocols
1.4.1 Dynamic Routing Operations
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The success of dynamic routing depends
on two basic router functions:
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Maintenance of a routing table
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Timely distribution of knowledge in the form of
routing updates to other routers
1.4 Routing Protocols
1.4.1 Dynamic Routing Operations
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Dynamic routing relies on a routing protocol to
share knowledge. A routing protocol describes:
 How updates are sent
 What is contained in these updates
 When to send this information
 How to locate recipients of the updates
1.4 Routing Protocols
1.4.2 Representing Distance with Metrics
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The metrics most commonly used are:
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Bandwidth, Delay, Load Reliability, Hop
count, Ticks and Cost
Typically, the smaller the metric number, the
better the path.
1.4 Routing Protocols
1.4.3 Classes of Routing Protocols
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Most routing protocols are based on one
of two routing algorithms: distance
vector or link state.
The balanced hybrid approach combines
aspects of the link-state and distance
vector algorithms.
1.4 Routing Protocols
1.4.4 One Issue: Time to
Convergence
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The concept of convergence - that is, the
time it takes all the routers in a network to
share a consistent view of the network - is
a key issue for evaluating the performance
of routing protocols.
1.4 Routing Protocols
1.4.5 Distance Vector Concept
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Distance vector based routing algorithms
pass periodic copies of a routing table
from router to router. Periodic updates
between routers communicate topology
changes.
1.4 Routing Protocols
1.4.6 Interior or Exterior Routing
Protocols
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Exterior routing protocols are used to
communicate between autonomous
systems. Interior routing protocols are
used within a single autonomous system.
1.4 Routing Protocols
1.4.7 Interior IP Routing Protocols
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Examples of IP routing protocols are:
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RIP- A distance vector routing protocol.
IGRP- Cisco's distance vector routing protocol.
OSPF- A link-state routing protocol.
Enhanced IGRP- A balanced hybrid routing protocol.
1.4 Routing Protocols
1.4.8 IGRP Overview
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A primary advantage of IGRP over RIP is
that IGRP can use 7 metrics to determine
best paths. Of course, the price of all of
this extra information is added complexity
in configuring and monitoring IGRP.
1.4 Routing Protocols
1.4.9 IGRP Configuration
Router(config)# router igrp AS number
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selects IGRP as a routing protocol.
Router(config-router)# network number
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specifies any directly connected networks
to be included.
1.5 Access List Overview
1.5.1 What are Access Lists?
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Access lists allow an administrator to
specify conditions that determine how a
router will control traffic flow. Access
lists are used to permit or deny traffic
through a router interface. The two main
types of access lists are standard and
extended.
1.5 Access List Overview
1.5.2 How Access Lists Work
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Access lists express the set of rules that
give added control for packets that enter
inbound interfaces, packets that relay
through the router, and packets that exit
outbound interfaces of the router. Access
lists do not act on packets that originate in
the router itself.
1.5 Access List Overview
1.5.3 A List of Tests: Deny or Permit
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Access list statements operate in sequential, logical
order. They evaluate packets from the top down. If
a packet header and access list statement match,
the packet skips the rest of the statements. If a
condition match is true, the packet is permitted or
denied.
1.5 Access List Overview
1.5.4 How to Identify Access Lists
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Some numbering conventions apply to ACLs:
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1-99 are standard IP, 100-199 extended IP,
600-699 Apple Talk, 800-899 standard IPX,
900-999 extended IPX, 1000-1099 IPX SAP.
1.5 Access List Overview
1.5.5 Testing Packets with Access Lists
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For TCP/IP packet filters, Cisco IOS access lists
check the packet and upper-layer headers.
1.5 Access List Overview
1.5.6 How to Use Wildcard Mask Bits
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A wildcard mask bit 0 means "check the
corresponding bit value."
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A wildcard mask bit 1 means "do not check
(ignore) that corresponding bit value."
1.5 Access List Overview
1.5.7 How to Use the Wildcard “Any”
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"Any" is an IOS shortcut for 0.0.0.0
255.255.255.255 in an access list statement. It
might be used to permit all traffic in one
statement, preceding a statement where some
specific network traffic is denied.
1.5 Access List Overview
1.5.8 How to Use the Wildcard “Host”
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Another IOS shortcut is the "host"
command, which replaces 0.0.0.0 as a
wildcard mask - meaning all bits must be
checked and must match for the access-list
statement to be true.
1.5 Access List Overview
1.5.9 Where to Place IP Access Lists
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A design rule for placing ACLs is: put the
extended ACL as close as possible to the source
of traffic denied. In the case of standard ACLs,
they can only filter using source address, so they
should be put as close to the destination as
possible.
1.6 IPX Routing Overview
1.6.1 Cisco Routers in Netware
Networks
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Cisco's routers offer the following
features in Novell network environments:
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Access lists and filters for IPX, RIP, SAP,
and NetBIOS
Scalable routing protocols, including
Enhanced IGRP and NLSP
1.6 IPX Routing Overview
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Cisco's routers offer the following
features in Novell network environments:
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Configurable RIP and SAP updates and
packet sizes
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Serverless LAN support
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Rich diagnostics, management, and
troubleshooting features
1.6 IPX Routing Overview
1.6.2 Novell Netware Protocol Suite
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Novell IPX has the following characteristics:
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It is a connectionless protocol that does not require
acknowledgments for each packet (best effort
delivery)
It is a Layer 3 protocol that defines internetwork and
internode addresses
1.6 IPX Routing Overview
1.6.3 Novell IPX Addressing
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Novell IPX addressing uses a two-part
address, the network number and the node
number. The IPX network number can be up
to 8 hexadecimal digits in length. This number
is assigned by the network administrator.
1.6 IPX Routing Overview
1.6.4 Cisco Encapsulation Names
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When you configure Cisco IOS software for
Novell IPX, use the Cisco name for the
appropriate encapsulation. If you do not
specify an encapsulation type when you
configure the router for IPX, the router will
use the default encapsulation type on its
interfaces.
1.6 IPX Routing Overview
1.6.4 Cisco Encapsulation Names
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The default encapsulation types on Cisco
router interfaces and their keywords are:
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Ethernet-novell-ether
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Token Ring-sap
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FDDI-snap
1.6 IPX Routing Overview
1.6.5 Novell Uses RIP for Routing
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Novell RIP is a distance vector routing protocol.
Novell RIP uses two metrics to make routing
decisions: ticks (a time measure) and hop count
(a count of each router traversed).
1.6 IPX Routing Overview
1.6.6 SAP Service Advertisements
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A powerful feature of NetWare networks is the
use of SAPs to facilitate client-server
transactions.
By default, service advertisements occur at 60second intervals.
1.6 IPX Routing Overview
1.6.7 GNS Get Nearest Server Protocol
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GNS is a broadcast that comes from a client using
SAP. The nearest NetWare file server responds with
a GNS reply. From that point on, the client can log in
to the target server, make a connection, set the
packet size, and proceed to use server resources.
1.6 IPX Routing Overview
1.6.8 Novell IPX Configuration Tasks

Four major tasks for configuring IPX exist: enable
the IPX routing process, enable load-sharing if
appropriate, assign unique network numbers to
each router interface, and finally set the IPX
encapsulation type if it is different from the default
Ethernet_II (arpa).
1.6 IPX Routing Overview
1.6.9 Verifying IPX Operation
Once IPX routing is configured, you can
monitor and troubleshoot it using
commands such as:
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show ipx interface
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show ipx route
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show ipx servers
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show ipx traffic
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debug ipx routing
activity
debug ipx sap
1.6 IPX Routing Overview
Summary

This chapter is a review of semester 3,
whose focus is on LANs. In the
forthcoming chapters, you will shift your
focus to WANs. And your case study tasks
will shift to WANs as well.