Cisco Semester 4

Cisco Semester 4

Chapter 1, version 2.1.3Review

Overview

Chapter 1 is a review of the following subjects:

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.

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

Switches learn device addresses by: Reading the source address of each

packet transmitted Noting the port where the frame

was heard

1.1 LAN Switching

1.1.6 Symmetric Switching

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

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

Store and Forward - (entire frame is received)

Cut-through - (destination MAC address is read)• 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

Two ways to implement VLANs are:• 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

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: Users are assigned by port

VLANs are easily administered

Security between VLANs is maximized

Packets do not "leak" into other domains

VLANs and VLAN membership are easily controlled across the network

1.2 Virtual LANs

1.2.6 Static VLANs

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

General requirements of network design: Functionality -- It must work Scalability -- It must be able to grow Adaptability -- It must work with future

technologies Manageability -- It must be monitored

1.3 LAN Design

1.3.2 Design Methodology

Three steps describe a simple model that could be used in network design:• Analyze requirements

• Develop a LAN structure (topology)

• Set up addressing and routing

1.3 LAN Design

1.3.3 What Problem are you Trying to Solve?

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:

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

The topology design can be broken into three OSI categories:• 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

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

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

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

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

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

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

The success of dynamic routing depends on two basic router functions: Maintenance of a routing table Timely distribution of knowledge in the form

of routing updates to other routers


1.4.1 Dynamic Routing Operations

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


1.4.2 Representing Distance with Metrics

The metrics most commonly used are: Bandwidth, Delay, Load Reliability, Hop

count, Ticks and Cost Typically, the smaller the metric number,

the better the path.


1.4.3 Classes of Routing Protocols

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.


1.4.4 One Issue: Time to Convergence

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.


1.4.5 Distance Vector Concept

Distance vector based routing algorithms pass periodic copies of a routing table from router to router. Periodic updates between routers communicate topology changes.


1.4.6 Interior or Exterior Routing Protocols

Exterior routing protocols are used to communicate between autonomous systems. Interior routing protocols are used within a single autonomous system.


1.4.7 Interior IP Routing Protocols

Examples of IP routing protocols are: 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.


1.4.8 IGRP Overview

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.


1.4.9 IGRP Configuration

Router(config)# router igrp AS number selects IGRP as a routing protocol.

Router(config-router)# network number specifies any directly connected networks

to be included.

1.5 Access List Overview

1.5.1 What are Access Lists?

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.


1.5.2 How Access Lists Work 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.


1.5.3 A List of Tests: Deny or Permit

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.


1.5.4 How to Identify Access Lists

Some numbering conventions apply to ACLs:

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.


1.5.5 Testing Packets with Access Lists

For TCP/IP packet filters, Cisco IOS access lists check the packet and upper-layer headers.


1.5.6 How to Use Wildcard Mask Bits

A wildcard mask bit 0 means "check the corresponding bit value."

A wildcard mask bit 1 means "do not check (ignore) that corresponding bit value."


1.5.7 How to Use the Wildcard “Any”

"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.


1.5.8 How to Use the Wildcard “Host”

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.


1.5.9 Where to Place IP Access Lists

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

Cisco's routers offer the following features in Novell network environments: Access lists and filters for IPX, RIP, SAP, and

NetBIOS Scalable routing protocols, including

Enhanced IGRP and NLSP


Cisco's routers offer the following features in Novell network environments: Configurable RIP and SAP updates and

packet sizes Serverless LAN support

• Rich diagnostics, management, and troubleshooting features


1.6.2 Novell Netware Protocol Suite

Novell IPX has the following characteristics: • 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


1.6.3 Novell IPX Addressing

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.


1.6.4 Cisco Encapsulation Names

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.


1.6.4 Cisco Encapsulation Names

The default encapsulation types on Cisco router interfaces and their keywords are: Ethernet-novell-ether Token Ring-sap FDDI-snap


1.6.5 Novell Uses RIP for Routing

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).


1.6.6 SAP Service Advertisements

A powerful feature of NetWare networks is the use of SAPs to facilitate client-server transactions.

By default, service advertisements occur at 60-second intervals.


1.6.7 GNS Get Nearest Server Protocol

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.


1.6.8 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).


show ipx interface show ipx route show ipx servers show ipx traffic

debug ipx routing activity

debug ipx sap

1.6.9 Verifying IPX OperationOnce IPX routing is configured, you can monitor and troubleshoot it using commands such as:


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.

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Cisco Semester 4