When the infrastructure grows and expands to multiple locations, it becomes hard to maintain up to date static network diagrams. Thus, NetCrunch topology maps are automatically updated when a new node is added, or port connection changes. Additionally, the maps display each device's status, while connections between switches show actual bandwidth usage.
NetCrunch uses SNMP (v1,v2c, or v3) to retrieve data from switches. It also supports CDP, STP and LLDP protocols.
The map shows connections on each switch port. Each line on the map presents current in/out traffic on the port. You can click on the line to see a real-time traffic graph of a given port, or you can open traffic history.
@@img:segment-map.png Segment Map
In the case when multiple devices are connected to a single port and NetCrunch can't access switch or router data, the program draws a static map without traffic data and port information.
This often happens when we discover non-manageable software switches.
@@img:static-port-map.png Static Port Map
Layer 2, also known as the Data Link Layer, is the second level in the seven-layer OSI reference model for network protocol design. Layer 2 is equivalent to the link layer (the lowest layer) in the TCP/IP network model. Layer 2 is the network layer used to transfer data between adjacent network nodes in a wide area network or between nodes on the same local area network.
Layer 2 switching (or Data Link layer switching) uses devices’ MAC addresses on a LAN to segment the network. Switches and bridges are used for Layer 2 switching. They break up one large collision domain into multiple smaller ones.
In a typical LAN, all hosts are connected to a single central device. In the past, the central device was usually a hub. But hubs had many disadvantages, such as not being aware of traffic that passes through them, creating one large collision domain, etc. To overcome some of the problems with hubs, bridges have been created. They were better than hubs because they created multiple collision domains, but they had a limited number of ports. Finally, switches have been created and are still widely used today.
Switches have more ports than bridges, can inspect incoming traffic, and make forwarding decisions accordingly. Each port on a switch is a separate collision domain.