Question

Explain why telnet traffic from other “users” could be observed when using a hub.

Explain why telnet traffic from other “users” could not be observed when using a switch.

Answer 1

1)   If we can telnet from one device to the other we have proven that the routing (layer 3) and the physical layer are working properly. Since telnet is an application layer utility it gives us confirmation that all 7 OSI layers are working correctly between the two devices.

A VLAN is a group of devices on one or more logically segmented LANs. All devices working on a VLAN will have same broadcast domain. Like routers, switches (Layer 2) have the ability to provide domain broadcast segmentation called a VLAN. Using VLAN technology, you can group switch ports and their connected users into logically defined communities of interest. A VLAN operating on a Catalyst switch limits transmission of unicast, multicast, and broadcast traffic to only the other ports belonging to that VLAN, thereby controlling broadcasts.

The benefits of VLANS include:

1. Easy Administration resulting in reduced administration costs,

2. Increased Security due to broadcast control, if you are using simple hub, you can observe traffic corresponding to any node by simply inserting a Network analyzer.

3. Grouping based on functional requirements irrespective of physical location of nodes,

4. Simplify moves, adds, changes,

5. Distribution of traffic thereby using the network bandwidth more efficiently.

2)The “show users” shows telnet/ssh connections to your router while “show sessions” shows telnet/ssh connections from your router (to other devices). The question asks about “your active Telnet connections”, meaning connections from your router so the answer should be

Even though there may be IP connectivity between a source and a destination, problems may still exist for a specific upper-layer protocols such as FTP, HTTP, or Telnet. These protocols ride on top of the basic IP transport but are subject to protocol-specific problems relating to packet filters and firewalls. It is possible that everything except mail will work between a given source and destination. Before troubleshooting at this level, it is important to first establish whether IP connectivity exists between the source and the destination. If IP connectivity exists, then the issue must be at the application layer.

The following could go wrong:

•A packet filter/firewall issue might have arisen for the specific protocol, data connection, or return traffic.

•The specific service could be down on the server.

•An authentication problem might have occurred on the server for the source or source network.

•There could be a version mismatch or incompatibility with the client and server software.