Module 2 - Design the Network Structure

Section 4 - Design a Network-Layer Addressing and Naming Model

Case Study: Pretty Paper Ltd.

• Because this is a closed network with the Cisco PIX in use for the Internet connection, private Internet addressing should be implemented. Use one of the Class B addresses defined in RFC 1918 Section 3 (172.16.0.0 to 172.31.255.255), say 172.16.0.0/24; in other words, 172.16.0.0 with a simple 255.255.255.0 mask that would then be divided with one network per site, perhaps as follows:

 
• 172.16.0.0 for the headquarters
• 172.16.1.0 through 172.16.9.0 for the WAN
• 172.16.10.0 through 172.16.99.0 for the sales offices
• 172-16.100.0 through 172.16.199 for the manufacturing/warehouses

 
• Within each network, the last octet can be used to identify the network nodes, which will provide 254 nodes for each of the facilities. With this solution the internal routers and PC/server nodes will support a simple 255.255.255.0 subnet mask. This solution is attractive because it provides simplicity for an administrative staff that is not experienced with routers. Use of a 255.255.255.0 mask on the WANs could be seen as a waste, but there are so many addresses available that the mask is not important.

 
• The nodes should then be grouped by class for ease of identification. This solution would involve something similar to the following:

 
• For communication equipment, select nodes 1 through 9
• For servers and hosts, select nodes 10 through 59
• For user nodes, select nodes 60 through 254

 
• Cisco's DNS/DHCP Manager should be installed on the HP9000 used to dynamically assign IP addresses to the user computers.

• It would probably be best to name the servers by location and type, which will allow for the possibility of servers being at locations other than headquarters. For example, the servers could be headquarters NW1, headquarters NW2, and headquarters BS1. These names might be suffixed with the last octet of the node address to aid in troubleshooting. The user nodes should be named with names that aid troubleshooting, such as the letters "PC" followed by a "hyphen" and the user's first initial and last name, such as PC-BSMITH.

 
• A naming scheme for routers should be devised that will aid in troubleshooting, such as by location and function. For example, the router attached to the Frame Relay at headquarters might be PARIS-FR and the Internet router might be PARIS-IN.

 
• To name the various devices, a single DNS with a single domain could be installed on the HP9000.

• IPX network numbers also need to be assigned. Because headquarters is on an Ethernet switch, it is logically "flat" and therefore a single IPX number will be assigned for the headquarters facilities, including the warehouse and manufacturing facilities. Each of the other facilities and each WAN link will have a unique IPX network number assigned.

 
• As always it will help in troubleshooting if there is some logic to the assignment of these numbers. For example, you might use two-digit network numbers for locations and three-digit numbers for WAN links and give meaning to the positions. For locations, the first digit might represent the type of network and the second the location identifier. For WAN links the second and third digits might represent the location being linked.

 

Network	IPX Network Number
Headquarters	AA
Sales Office #1	BA
Sales Office #2	BB
Sales Office #3	BC
Sales Office #4	BD
Sales Office #5	BE
Manufacturing #1	CA
Manufacturing #2	CB
WAN Link to Headquarters	DAA
WAN Link to Sales Office #1	DBA
WAN Link to Sales Office #2	DBB
WAN Link to Sales Office #3	DBC
WAN Link to Sales Office #4	DBD
WAN Link to Sales Office #5	DBE
WAN Link to Manufacturing #1	DCA
WAN Link to Manufacturing #2	DCB

 

• Likewise, AppleTalk zones need to be defined. The number of Macintosh nodes would suggest a single zone per location and one per WAN link. The zones should be given meaningful names for troubleshooting purposes. Names by location and names by link would be appropriate. For example:
 

Zone	Assigned Name
All of the headquarters facilities	Headquarters
Sales Office 1-5	SO1 - SO5
Manufacturing 1-2	MFG1 - MFG2
Headquarters WAN Link	Headquarters FR
Sales Office 1-5 WAN Links	SO1FR - SO5FR
Manufacturing 1-2 WAN Links	MFG1FR - MFG2FR

 

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