1. Explain exactly how routers route packets.
The routers employ the use of packet switching whereby, packets are directed towards a specified route and the transit is logically addressed from their source towards the ultimate destinations through intermediate nodes. The routing process usually directs the forwarding of packets on the basis of routing tables which has a record of the routes to various network destinations. Most of the routing algorithms make use of only one network path at a time whereas the multipath routing techniques enable the use of multiple alternative paths. A router typically organises and controls data flow among the computers on the network and other network devices. The router is basically responsible for determining how information is passed in the most efficient manner. A router performs the routing process in the following ways:
Electronic messages which are sent inform of data packets between computer networks are first stored in the router as it determines all the possible paths to the specified destination. The router through a routing algorithm then chooses the best route based on the traffic load, distance cost algorithms. Once the best route has been established based on the investigations above, the data packet is then channelled to the final destination. A router has some rules that govern how computers from the outside network can connect to the computers inside the network.
The routing process employs the use of a traceroute which is a computer network diagnostic tool for displaying the route and for measuring the delay ossaf packets across an IP network. The traceroute is available on most operating systems but with different names. It displays the list of traversed routers together with the timing information. The traceroute will send a sequence of Internet Control Message Protocol (ICMP) packets which are addressed to a destination host. In order to determine the intermediate routers traversed, TTL (time to live) which is also known as hop limit internet protocol parameter needs to be adjusted. Usually this is done by starting with a value like 128 or 64 for windows and Linux respectively. The routers will then decrement this and discard a packet when the TTL value has reached zero thus returning the ICMP error message – ICMP time surpassed. The traceroute usually works by increasing the TTL value of each successive set of packets sent. Usually the first set will have a hop limit of 1 and the second a hop limit of 2 and it is the one that carries the error reply. This procedure continues until the destination host receives the packets and returns the error message.
2. Discuss ARP (Address Resolution Protocol).
The ARP is a computer networking protocol which is used for determining a network host’s link layer or the hardware address in situations whereby only the internet layer or the network layer is known. It uses a simple message format which contains one address resolution request or response.
ARP defines the exchanges that exist between network interfaces which are connected to an ethernet device so as to enable the mapping of an IP address to a link layer address upon request. The ARP can also be used for locating the Ethernet address which is associated with a desired IP address.
It exists mainly to connect together the IP and Ethernet networking layers. The ARP is responsible for defining the conversation by which IP capable hosts can exchange the mappings of their Ethernet and IP addressing. It hangs around most of the networks. It is very simple in terms of implementation and operation as compared to higher layer protocols.
An ARP request is usually transmitted in a broadcast Ethernet frame and its reply is a unicast response which contains the desired information which is sent to the link address of the requestor.
The packet structure of ARP is shown in the table below which illustrates the case of IPv4 networks running on Ethernet.
3. Troubleshooting with PING (command).
Trouble shooting with a PING command can be done using any of the following forms of PING. Extended PING, Standard PING and Record Route PING.
Extended PING – Is commonly used by the less knowledgeable professionals in tracking down latency. Different operating platforms have different set of commands. Linux uses ping –s and windows uses ping -t
Standard PING – This is the most common ways to do a PING. It is usually used to check for the availability of a host. It can be done from the command prompt on Windows, Linux and in Cisco routers by using the ping command – ping
Record Route PING – this is used in situations when there are few hops and when an additional host inforation about the routing path is needed.
4. Explain at least 5 advantages of switches.
It reduces the number of broadcast domains. This makes the network connections more and easily manageable thus make it simpler to implement.
Can assist in logical segmentation. This is achieved through the incorporation of VLAN’s. The Vlans are supported by the switches which can also be used in logical segmentation of ports and in splitting up the broadcast domains.
They are intelligent – the switches are more intelligent than the hubs. This enables them to perform routing activities and also perform port to MAC mapping.
They are more hardware oriented – This makes them less CPU intensive thus consuming lesser CPU resources.
When one considers the cost to the number of ports available, it is very good. A bigger switch with more ports is usually cheaper in terms of the cost per port. This makes it easier to expand your network without stretching your budget alot.
