Netgear Router WGR614 V4 User Manual

Network, Routing, Firewall, and Basics B-1
December 2003
Appendix B
Network, Routing, Firewall, and Basics
This chapter provides an overview of IP networks, routing, and networking.
Related Publications
As you read this document, you may be directed to various RFC documents for further 
information. An RFC is a Request For Comment (RFC) published by the Internet Engineering 
Task Force (IETF), an open organization that defines the architecture and operation of the Internet. 
The RFC documents outline and...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
B-2 Network, Routing, Firewall, and Basics
December 2003
Routing Information Protocol
One of the protocols used by a router to build and maintain a picture of the network is the Routing 
Information Protocol (RIP). Using RIP, routers periodically update one another and check for 
changes to add to the routing table.
The WGR614 v4 router supports both the older RIP-1 and the newer RIP-2 protocols. Among 
other improvements, RIP-2 supports subnet...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
Network, Routing, Firewall, and Basics B-3
December 2003 Figure 7-1:  Three Main Address Classes
The five address classes are:
• Class A 
Class A addresses can have up to 16,777,214 hosts on a single network. They use an eight-bit 
network number and a 24-bit node number. Class A addresses are in this range: 
1.x.x.x to 126.x.x.x. 
• Class B 
Class B addresses can have up to 65,354 hosts on a network. A Class B address uses a 16-bit 
network...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
B-4 Network, Routing, Firewall, and Basics
December 2003
This addressing structure allows IP addresses to uniquely identify each physical network and each 
node on each physical network.
For each unique value of the network portion of the address, the base address of the range (host 
address of all zeros) is known as the network address and is not usually assigned to a host. Also, 
the top address of the range (host address of all ones) is not...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
Network, Routing, Firewall, and Basics B-5
December 2003
Subnet addressing allows us to split one IP network address into smaller multiple physical 
networks known as subnetworks. Some of the node numbers are used as a subnet number instead. 
A Class B address gives us 16 bits of node numbers translating to 64,000 nodes. Most 
organizations do not use 64,000 nodes, so there are free bits that can be reassigned. Subnet 
addressing makes use of...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
B-6 Network, Routing, Firewall, and Basics
December 2003
The following table lists the additional subnet mask bits in dotted-decimal notation. To use the 
table, write down the original class netmask and replace the 0 value octets with the dotted-decimal 
value of the additional subnet bits. For example, to partition your Class C network with subnet 
mask 255.255.255.0 into 16 subnets (4 bits), the new subnet mask becomes 255.255.255.240.
The...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
Network, Routing, Firewall, and Basics B-7
December 2003
• So that hosts recognize local IP broadcast packets
When a device broadcasts to its segment neighbors, it uses a destination address of the local 
network address with all ones for the host address. In order for this scheme to work, all devices 
on the segment must agree on which bits comprise the host address. 
• So that a local router or bridge recognizes which addresses are local and...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
B-8 Network, Routing, Firewall, and Basics
December 2003
The following figure illustrates a single IP address operation.
 
Figure 7-3:  Single IP Address Operation Using NAT
This scheme offers the additional benefit of firewall-like protection because the internal LAN 
addresses are not available to the Internet through the translated connection. All incoming 
inquiries are filtered out by the router. This filtering can prevent intruders from...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
Network, Routing, Firewall, and Basics B-9
December 2003
If a device sends data to another station on the network and the destination MAC address is not yet 
recorded, ARP is used. An ARP request is broadcast onto the network. All stations on the network 
receive and read the request. The destination IP address for the chosen station is included as part of 
the message so that only the station with this IP address responds to the ARP request. All...

Reference Manual for the 54 Mbps Wireless Router WGR614 v4
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December 2003
IP Configuration by DHCP
When an IP-based local area network is installed, each PC must be configured with an IP address. 
If the PCs need to access the Internet, they should also be configured with a gateway address and 
one or more DNS server addresses. As an alternative to manual configuration, there is a method by 
which each PC on the network can automatically obtain this...