Frequently Asked Questions (FAQ)

1:	What is the difference between a router and a switch?
A1:	Routers "think" before forwarding; switches just forward. When a switch receives a datagram (frame) on one of its ports, the switch tries to find the destination device (host) by looking up the MAC address in its Content Addressable Memory (CAM) table, and forwards the frame out of the appropriate port. The destination device must reside on the same local area network because a switch will not send datagrams to hosts on different network segments. When a router receives a datagram (packet), the router tries to find the destination device (host) by looking up the network address (for example, the IP address) in its routing tables (built by the routing protocol). If the destination computer is not on the same network segment or LAN, the router tries to determine where the intended host is located and then sends the datagram to that network (with the attached destination host).
2:	How much can a WAN port be oversubscribed?
A2:	A port can be oversubscribed without causing too high a risk to your application performance. There is no hard and fast recommended ratio because it all depends on the traffic characteristics. It is common to find that in many applications, a ratio concentration of 2:1 or 4:1 is acceptable and causes few application issues because most data applications are bursty, not requiring 100 percent of the bandwidth at all times. To determine an appropriate oversubscription rate, it is necessary to measure network usage. Measurements and related performance data can be collected from CSU/DSUs, WAN probes, the NSP, or from the WAN router itself.
3:	Does network architecture require core, distribution, and access layers?
A3:	Yes. The lines between these three hierarchical layers can be blurred, for example a router or switch can perform both access and distribution services. The three-tiered hierarchical model defines the services a network device needs to perform, depending on where the device is placed within the network architecture.