Introduction - Understanding Basic Cisco Switching and Routing IT Part II

Here in part two of Understanding basic Cisco switching and routing information technology, we will gain an important insight into the primary roles and functions of network switches and routers. By presenting a simple Cisco style outline of what each device is and does, you can apply the same theory to most devices of like types. Even brands not manufactured by Cisco will be similar in many ways.

Network Switches

Switching technology is generally associated with OSI data link layer 2. All switches generally evolved from a need to concentrate a number of network connections together to form a group that could share resources. An earlier form of a similar device was a hub. A hub is a device that accepts several devices plugged into it and there is usually a main port connected to a server or resource link. A switch is similar, but switches have bi directional data port path capability they can use without concern of data collisions. Switches also have more intelligence than a hub. A hub is just essentially a data repeater, and repeaters are OSI physical layer 1 devices.

A great innovation of switches is they learn what MAC address of a device is on a particular port and save the information to a MAC address table. A MAC address is the hardware address of a device or resource. When a device wants to send data, the switch will look on the MAC address table for a specific path to a port that has the correct device address to send to. If the MAC address is unknown to the switch it will perform a broadcast to see if a helpful response is received in order to locate a device MAC address. If no information to locate the device is received or learned then a switch may forward the request to a default gateway or router. This will occur as a possibility if the switch has a default gateway option configured.

Switches often have various network options and enhancements that can be really helpful for some network environments. These might include VLAN, virtual local area networks or often there might be a need for STP, spanning tree protocol. These two switch enhancements may be useful in your network environment depending on how it’s designed or intended to function. Also vendors have different brands and flavors of these types of technologies. Switch enhancements may be fairly similar or something all their own idea, so look further into the details of manufacturer specific offerings if needed.

Network Routers

Routing technology is generally associated with the OSI network layer 3. Routers do quite nicely what they are named to do. They route network traffic to a certain path. These paths are stored in the routers route table. Through the routes data can be directed in a way to facilitate finding the proper place. It may take several paths through several routers to get the data where it’s going though. A router does not directly deal with hardware addresses. Being primarily an OSI layer 3 device it uses a layer 3 delivery protocol for the appropriate and reliable means of delivery. Most popular by far is the TCP/IP protocol. Other delivery protocols are available but they need to be supported by the receiving router. The reason for this is each router keeps a routing table of routes, and the table and routes are based on a protocol. If an unknown or outdated protocol is sent to a router that only understands TCP/IP, that router will drop the data because it doesn’t understand the unknown protocol. It is possible to have several tables with many routing protocols, but this must be considered carefully on an individual basis because more routing tables and protocols will use more router resources.

If we can see TCP/IP as a routing delivery protocol, then we can understand categorizing OSPF or EIGRP as topology protocols. Topology routing protocols support mapping out the routing resources of a network so they can efficiently route data. For example if a router goes offline EIGRP will have a replacement route waiting to go around the down router. In making these topology decisions topology routing protocols have a different capability than a delivery protocol because they can organize the routers into a group. The delivery protocol is still needed and important but does not make topology decisions in a direct way. The two popular protocols for most topologies are EIGRP which is a CISCO proprietary protocol where the equipment and devices used are Cisco. OSPF functions similar to EIGRP but can be used with many equipment brands and is a more open standard.

Other protocols may be useful for referencing topology outside an enterprise or private network. For example BGP may be used with a WAN solution provider for a specified reason. At this time we will just consider this because BGP is a more advanced subject and is only referenced here for further study.

WAN or wide area network links are used by routers and the data they work with is routed through a transfer system between routers till it arrives at the proper place. A large variety of WAN types may be used to provide network solutions. For an enterprise network it was common to use dial up systems for WAN and this was found to be rather slow in data transfer. Frame relay WAN solutions were offered by some providers and became popular for a time. Now many companies are looking into MPLS, multi protocol label switching. In this way they can use their own routers with a MPLS delivery system and add data encryption with VPN. If the right routing equipment is available this may be a great option but will require skilled administration to manage.

Evolving Technology

One noteworthy thing to mention is some routing is going virtual. Integration with virtualization applications like VMware is being done now. Cisco is using VMware with some models of switches. Virtual cable routing for example would not require someone to go to a switch and move a cable from one port to the next, because it could be assigned through software configuration without changing any physical wires to the switch.

We can see many exiting and new switching and routing technologies being used everyday. Networking is becoming more important in our lives, from home high speed internet to using the enterprise network at the office or town library. Switches and routers truly are great building blocks for wonderful networks of all kinds.

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