Network Layer Features
Routing takes place at the network layer. All wireless equipment currently available performs bridging; however, some models of wireless equipment also perform routing. Just as there is a wide range of routing features available with conventional (wired) routers, there is also a wide range of features available with wireless routers.
Later in this chapter, there is an additional discussion of the advantages and disadvantages of selecting wireless equipment that includes routing.
The following sections contain descriptions of some of the routing protocols and features that are often available in wireless routers.
Static IP Routing
Every wireless router includes static IP routing. Static routing enables you to configure permanent IP routes.
Dynamic IP Routing
Some wireless routers include dynamic IP routing. These routers support one or more dynamic routing protocols. The most common of these supported protocols include the following:
Routing Information Protocol (RIP) v1 and v2RIP is an interior routing protocol. It is a distance-vector metric protocol that routes packets based on the number of routing hops needed to reach the destination. RIP is relatively easy to implement, but it does not take into account the bandwidth of each hop.
Open Shortest Path First (OSPF)OSPF is also an interior routing protocol. It is a link-state metric protocol. OSPF routes packets based on the shortest distance, the least delay, and the most bandwidth available to reach the destination.
Dynamic Host Configuration Protocol Server
A Dynamic Host Configuration Protocol (DHCP) server allows the allocation and reuse of IP addresses as end users need them. The DHCP server allocates an address when a DHCP client logs on. When the client logs off, the IP address is returned to the address pool, ready to be reused when another client logs on.
Network Address Translation
Like DHCP, Network Address Translation (NAT) expands the pool of usable IP addresses. NAT allows the use of a pool of private nonroutable IP addresses within a network. When IP traffic needs to be routed over the Internet, NAT translates the nonroutable addresses to an Internet-routable address.
Point-to-Point Protocol over Ethernet
Point-to-Point Protocol over Ethernet (PPPoE) allows an ISP to authenticate end users. Some wireless routers support PPPoE by passing PPPoE packets to the PPPoE server.
Wireless equipment occasionally includes bandwidth management features. This allows the bandwidth available to and from each MAC or IP address to be throttled or limited to a specified level. This feature allows you to manage your total available bandwidth, to offer different service levels to different groups of end users, and to serve more end users. Some equipment allows end user bandwidth to be throttled at different speeds in different (downstream and upstream) directions.
Some wireless routers allow you to allocate bandwidth based on either the IP address of the end user or the MAC address of the end user.
Quality of Service (QoS)
Quality of service functionality is not one, but a set of features that work together to prioritize different service levels for different users. One use, for example, is to prioritize the handling and thereby reduce the latency for voice over IP (VoIP) packets.
Roaming is the ability of an end user to move from AP to AP within the same subnet while maintaining a network connection. 802.11b APs usually include roaming capabilities. The vast majority of wireless WANs provide service to fixed end user locations; therefore, roaming is not used. If you need to design or deploy a wireless WAN that includes roaming, you should evaluate the following:
Reassociation speedThe length of time it takes for an end user to be switched from one AP to another.
Tunable parametersAny other AP parameters that are designed specifically to enable smooth roaming.
Compatibility issuesAP-to-AP communication standards are not specified in 802.11b. If you anticipate building a network that supports roaming, you should plan to buy all of your APs from the same vendor.
Network Layer Security Features
The following network layer security features are often available on wireless routers.
IP Address Access Control Lists
Some wireless routers allow specific IP addresses to be included in an ACL. Addresses in the list can either be denied or allowed network access.
Wireless routers sometimes contain firewall features. These features allow traffic to flow outward from a local network to the Internet. Traffic flowing inward from the Internet to the local network is filtered or blocked.
Virtual Private Networks
Virtual private network (VPN) features include IP Security (IPSec) encryption capabilities and tunneling capabilities, such as the Point-to-Point Tunneling Protocol (PPTP).