220.127.116.11 Class Activity – Join My Social Circle! (Instructor Version – Optional Class Activity)
Instructor Note: Red font color or gray highlights indicate text that appears in the instructor copy only. Optional activities are designed to enhance understanding and/or to provide additional practice.
Describe the impact of ARP requests on network and host performance.
Background / Scenario
Note: This activity can be completed individually in class or outside of class.
A lot of our network communication is in the form of email, messaging (text or instant), video contact, and social media postings.
For this activity, choose one of the following types of network communications and answer the questions in the Reflection section.
- Text or instant message
- Audio/video conference
- Online gaming
Instructor Note: This optional Modeling Activity is not intended to be a graded assignment. Its purpose is to encourage students to reflect on their perceptions of source and destination host identification as compared to social media. Students’ answers should generate discussion about how we are identified as we communicate through these types of networks.
- Recording capabilities (paper, tablet, etc.) so that reflective comments can be shared with the class.
1. Is there a procedure you must follow to register others and yourself so that you can form a communications account? Why do you think that a procedure is needed?
In each of these services, you are bringing the person you want to communicate with “directly into your network”. You are doing this in order to have contact with your friends and be able to communicate directly. You do not want to have an intermediary person relay messages between you and your friends in your network. By registering yourself and your friends to your contact list, you are building your own (social) communication network.
During the registration process, you as a person with a civil name are assigned a service-specific user identifier that identifies you in the particular communication service. When you add your friends to your contact list, you are looking for their service-specific user identifiers. This service-specific user identifier may have different formats:
– Email service: Has an email address
– ICQ accounts: Have a number
– Skype, LinkedIn, or Facebook accounts: Have a username
When you contact the person, you select their civil name in your contact list and the system contacts the user using the associated user identifier. A single person may have different user identifiers depending on how many social networks he or she subscribes to.
In communication networks, there is a similar process. Although a network node (for example, a PC) is a single entity, it may have several network interface cards (NICs). In IP networks, this would be a process of associating the peer’s IP address in the same network with its Layer 2 data-link layer address. On Ethernet and WiFi, IP uses a supporting protocol called Address Resolution Protocol (ARP) to perform this translation.
2. How do you initiate contact with the person or people with whom you wish to communicate?
The exact sequence of steps depends on the service you are using to communicate with your peer. However, there will always be common steps: First, decide within which network your peer is reachable. Second, look up the person’s contact in your contact list, and use it to send your peer a message. Depending on the service, the message will be received only by this person (email or instant messaging services) or it may be visible by other people in the recipient’s network (LinkedIn or Facebook message boards). However, there is no doubt who the intended recipient is.
When Node A needs to send a message to Node B in an IP network, it determines which network the peer (Node B) is located within. Node A performs a destination IP (or next-hop IP) into Layer 2 address translation in order to determine how to address Node B’s NIC. If there are switches on the path between Node A and B, Node A can send a message that can only be delivered to Node B’s NIC. If there are WiFi stations that can hear each other, Node A’s message to Node B can be seen by others.
3. How do you ensure that your conversations are received only by those with whom you wish to communicate?
The primary prerequisite is that the message is clearly addressed to a single intended recipient. This is the purpose of using a contact list that associates individual persons with their unique user identifiers. If we do not know the user identifier of the recipient, we have to send the message to everyone or not at all. In IP networks, this is accomplished by the resolution of the recipient (or next-hop) IP address into its unique Layer 2 address, using ARP or a similar mechanism. It is then up to the network technology to make sure that the message is sent only to the intended recipient.
Some technologies do not allow messages to be sent in a way that prevents third parties from seeing the message. For example, in Ethernet deployments using hubs or WiFi, the transmission is always visible to all nodes in the network. Only the intended recipient will process the message, but others can see it. This is similar to message boards on LinkedIn or Facebook where, although intended for a single recipient, many or all other users can see the messages.
Identify elements of the model that map to IT-related content:
- Different social network technologies correspond to different network technologies.
- User IDs for one particular person, depending on the social network the person is subscribed to, correspond to different Layer 2 addressing used by different network technologies.
- Contact lists correspond to tables where Layer 3-to-Layer 2 mappings are stored (e.g. ARP tables in Ethernet or IP/DLCI tables in Frame Relay).
- Subscribing to a social network corresponds to the process of obtaining access to a particular network and the related network technology.
- Looking up a person in one’s contact list corresponds to lookups in the L3/L2 mapping tables.