The previous answers were real world and quite detailed and appreciated answers....oddly enough in my CCNP studies this morning I ran across this (below). I always like real world answers better, but I know during test, sometimes they want rediculous text book answers. Text below taken from howtonetwork.net btw...http://www.howtonetwork.net/members/LAN_Switching_Fundamentals.cfm.
The Differences between Switches and Routers
In modern-day networks, Multilayer switches, such as the Cisco Catalyst 6500 series switches, merge router and switch functionality. Because of this blurred line, it becomes even more important for network engineers to have a solid understanding of the differences between LAN switches and network routers when it comes to addressing the following design concerns:
- Network loops
- Network convergence
- Broadcast traffic
- Inter-subnet communication
- Network security
- Media dependence
LAN switches use the Spanning Tree Protocol (STP) to prevent Layer 2 loops. This is performed by the Spanning Tree Algorithm (STA), which places redundant links in a blocked state. Although this does prevent network loops, it also means that only a subset of the network topology is used for forwarding data. Routers, on the other hand, do not block redundant network paths; instead, they rely on routing protocols in order to use the optimum path and to prevent loops.
A switched network is said to be converged when all ports are in a forwarding or blocking state, while a routed network is said to be converged when all routers have the same view of the network. Depending on the size of the switched network, convergence might take a very long time. Routers have the advantage of using advanced routing protocols, such as OSPF, that maintain a topology of the entire network, allowing for rapid convergence.
By default, LAN switches will forward Broadcast Multicast and unknown Unicast frames. In large networks with many of these types of packets, the LAN can become saturated quickly, resulting in poor performance, packet loss, and an unpleasant user experience. Because routers do not forward Broadcasts by default, they can be used to break up Broadcast domains.
Although multiple physical switches can exist on the same LAN, they provide connectivity to hosts on the assumption that they are all on the same logical network. In other words, Layer 2 addressing assumes a flat address space with universally unique addresses. Routers can use a hierarchical addressing structure, which allows them to associate a logical addressing structure to a physical infrastructure so that each network segment has an IP subnet. This provides a routed network a more flexible traffic flow because routers can use the hierarchy to determine optimal paths depending on dynamic factors, such as bandwidth, delay, etc.
Both LAN switches and routers can provide network security, but this is based on different information. Switches can be configured to filter based on many variables pertaining to Data Link Layer frames. Routers can use Network and Transport Layer information. Multilayer switches have the capability of providing both types of filtering.
When designing switched internetworks, it is imperative to ensure that network hosts use the MTU representing the lowest common denominator of all the switched LANs that make up the internetwork. When using switches, however, this results in poor performance and limits throughput, even on fast links. Unlike LAN switches, however, most Layer 3 protocols can fragment packets that are too large for a particular media type, so routed networks can accommodate different MTUs, which allow them to maximize throughput in internetworks.
Table 1-1 below lists the minimum and maximum frame size for common types of media that may be found within internetworks:
Table 1-1. Frame Size for Common Media Types
Media Type | Minimum Valid Frame Size | Maximum Valid Frame Size |
|---|
Ethernet | 46 bytes | 1500 bytes |
Token Ring | 32 bytes | 16 KB theoretical, 4 KB normal |
Fast Ethernet | 46 bytes | 1500 bytes |
FDDI | 32 bytes | 4468 bytes |
Serial HDLC | 14 bytes | No limit, 4.5 KB normal |
The Advantages of Using LAN Switches
LAN switches provide several advantages over bridges. These advantages include increased bandwidth to users via microsegmentation and supporting VLANs, which increase the number of Broadcast domains while reducing their overall size. In addition to these advantages, Cisco Catalyst switches also support Automatic Packet Recognition and Translation (APaRT).
Cisco's APaRT technology recognizes and converts a variety of Ethernet protocol formats into industry-standard CDDI and FDDI formats. Not all switches can provide these functions.
The Advantages of Using Routers
Even within switched LANs, the importance of routers cannot be ignored. Routers, or Multilayer switches, provide the following critical functions in switched LANs:
- Broadcast and Multicast control
- Media transition
- Network segment services
By default, routers do not forward Broadcast or Multicast packets. Instead, routers control Broadcast and Multicast packets via the following three methods:
- By caching the addresses of remote hosts and responding on behalf of remote hosts
- By caching advertised network services and responding on behalf of those services
- By providing special protocols, such as IGMP and PIM
Both routers and Multilayer switches can be used to connect networks of different media types, such as Fiber, Ethernet, and Token Ring, for example. Therefore, if a requirement for a switched campus network design is to provide high-speed connectivity between different media, these devices play a significant part in the design.
Routers are also responsible for providing Broadcast services, such as Proxy ARP, to a local network segment. When designing the switched LAN, it is important to consider the number of routers that can provide reliable services to a given network segment or segments.
As far as the VLAN answer, thats a good question....
