Access Control List (ACL)
An access control list is a way to control network access. For example, an IP address or a list of IP addresses can be denied access to a server.
Auto MDI / MDI-X
A feature in network devices that allows the use of both crossover and straight-through Ethernet cables. For example, a connection between two PCs can be established using a straight-through cable if one of the network adapters supports Auto MDI/MDI-X.
Broadcast storm
Broadcast is when a packet is sent to all devices on a network. If these devices forward the packets after receiving them, a loop can occur (see Spanning Tree Protocol), also known as a broadcast storm.
Buffer
A buffer is a form of temporary storage for data. For example, if a router receives 100 packets on one port that must be sent out through another port, they are stored in the buffer until they have been transmitted.
Domain Name System (DNS)
DNS is a protocol that translates names into IP addresses. This is clear on the internet: all web addresses have an IP address, but instead of remembering IPs, we can use an address that is easier to remember than the IP itself. For example, we can type www.danbit.dk, after which the DNS server translates it to an IP address and directs us to Danbit’s server.
Gateway
A gateway is the device that connects one network to another network. For example, it can be a router connected to a cable modem that is connected to the internet. In that case, the router is the gateway for the network.
Jumbo Frame
Jumbo frames differ from standard frames by their size. A standard frame is 1500 bytes. Using jumbo frames can improve switch efficiency because it takes more effort to send six 1500-byte frames than to send one 9000-byte frame. Jumbo frames are only supported by certain Gigabit switches and Gigabit network adapters.
DHCP
DHCP is short for Dynamic Host Configuration Protocol. The DHCP protocol is part of the TCP/IP protocol suite and is responsible for managing and assigning IP addresses to computers in a TCP/IP network. A DHCP server on a local network provides clients with all the information about network structure, subnet, and gateways required for them to operate. The information is looked up based on the client’s unique Ethernet hardware address (often called the MAC address). On a local network, it is often a router that acts as the DHCP server.
MAC address
A MAC address is a unique ID that all network devices have. In principle, it is not possible to change the MAC address, as it must be unique compared to all other network devices in the world. The MAC address is used, among other things, in connection with DHCP, because the DHCP server uses the MAC address to send the network configuration.
Quality of Service (QoS)
QoS is a way to prioritize different packets. For example, QoS can be configured to prioritize packets from IP telephony so they are always first in the queue. This increases the delay for less important packets and helps ensure data quality for services with higher priority.
Service Set Identifier (SSID)
The SSID is the name of a wireless network. The SSID is unique within the coverage area of the access point. However, multiple access points can use the same SSID if they provide access to the same network. Some access points can broadcast multiple SSIDs; this is used together with VLAN. For example, VLAN 10 can use the first SSID and VLAN 20 the second SSID, and so on. This makes it possible to segment the network even if all wireless devices connect to the same access point.
Spanning Tree Protocol (STP)
Spanning Tree Protocol is a protocol used by switches to prevent loops. A loop is when a packet continues to circulate in the network. STP ensures there is only one active path for a packet; if that path fails, an alternative path is used. Rapid Spanning Tree Protocol (RSTP) is a successor to STP that is faster at selecting the preferred path. When a path fails, RSTP typically finds a new path in about 1 second, while STP can take 30–50 seconds.
Trunking
Trunking is a way to increase speed between switches by connecting multiple ports. For example, two Gigabit switches can be connected with three cables to achieve a total throughput of 3 Gbit/s.
Managed switch
Sometimes also called a “managed switch”. The term is typically used for switches with more advanced functions such as VLAN, spanning tree, bandwidth allocation, and more. These functions can be configured, for example, via a console interface through a serial port on the switch, or via a Telnet connection using TCP/IP. Many switches also include a built-in web server, which has become the most commonly used method.
VLAN (Virtual Local Area Network)
In a traditional local network, all switches and all ports are part of the same broadcast domain, so they can communicate with each other. However, there is often a need to divide the network into smaller domains. This can be done to limit network traffic or to improve security. This can be achieved by using separate cables and switches for each domain, but it is usually more practical to use network switches with VLAN functionality to achieve the same result in a much more flexible way. A VLAN switch can be configured internally so data can only be forwarded between selected groups of ports. From the outside, it appears as if there are multiple physically separate switches. Therefore, the method is called “port-based”.
IEEE 802.1Q is a standard that describes a more flexible method called “VLAN tagging”, where the switch can add 32-bit information to Ethernet frames that indicates which VLAN group the frame belongs to. This enables more advanced VLAN networks where groups can be distributed across multiple switches, as VLAN switches exchange traffic via “trunk links”. See more about VLAN in Danbit’s knowledge base under “support”.
All Danbit switches with VLAN support the IEEE 802.1Q standard, even if it is not mentioned on the product page.
WLAN / WiFi
WLAN (Wireless Local Area Network) refers to a wireless network that works like a wired network, using radio signals instead of cables between participants. See more about building wireless networks on the next page.
By default, a WLAN can be vulnerable and unprotected. To secure a WLAN, it can be protected with a password that is encrypted using a security algorithm (WEP, WPA, or WPA2). It is also possible to hide the name of the wireless network, also called the SSID (Service Set Identifier). This means users must know the name before they can connect to the wireless network.
A WLAN is defined by a set of standards called WiFi, based on the IEEE 802.11 standard, which has evolved over time. Common standards include 802.11g (data rates up to 54 MB/s) and 802.11n (up to 150 MB/s). To maintain a stable connection, devices automatically fall back to lower speeds when signal strength is insufficient.