Network Definitions

IGMP Querier

When enabled, a network switch may act as a "querier" to coordinate multicast traffic such as sACN lighting levels. Its job is to send out a "query" at a regular interval  to ask all network devices if they are interested in multicast traffic such as sACN universes. A DMX Gateway, for example, will respond to a query with a simple Membership Report packet, instructing the network that it is interested in a universe such as universe 1. Switches that have IGMP snooping enabled between any source of universe 1 and that gateway will forward that universe's data to the DMX gateway port.

If there is multicast data on a network that has not been accounted for by IGMP, we enter the world of Unregistered Multicast.

IGMP Querier Election

Only one active IGMP Querier may be present on a network (or VLAN). The Querier is a feature that can be enabled and disabled on managed switches (depending on make/model). In a multiple network switch system, if Querier is only enabled on one switch, that switch will be the Querier. However, all switches in a network should have the querier enabled, in case the active querier fails. Since there can only be one active querier at a time, a system of switches must have a method to decide which switch will be the active querier at any given time. This process is called Election.

In Cisco switches provided by ETC, the switch with the lowest IP Address will be elected the Querier*. All other switches with Querier enabled will not output Querier messages. In the event the Querier is no longer seen on the network, the next lowest IP Address will take over as Querier and so on. 

If the lowest IP Addressed switch is not the desired Querier, it is recommended to change the IP Address of the desired switch so that it is the lowest. In the default ETC network scheme, 10.101.1.1 is the lowest IP address but it is recommended to leave this reserved if a router is needed in the future. 10.101.1.2 would be the next lowest IP address.

It is recommended to make the core switch or the switch closest to the center of the network (fewest hops to all other switches) be the IGMP Querier. This switch should also be easily accessible in the event of failure.

*Other switch manufacturers may implement IGMP Querier Election differently, if it is implemented at all. Multiple managed switches from different manufacturers (such as Cisco and Pathway) on the same network with IGMP Querier enabled may not correctly elect a querier, resulting in unpredictable multicast behavior!

IGMP Snooping

Allows switches to detect multicast groups based on the multicast traffic flowing through them. A switch with IGMP snooping enabled will process IGMP query responses from devices connected to the switch and forward multicast traffic accordingly. A switch without IGMP snooping enabled will treat all multicast traffic as unregistered.

IGMP - Membership Report (Join Group)

The message sent from a multicast receiver when it first connects to a network, when it needs to update which multicast groups it belongs to, or in response to an IGMP query. These messages are detected by switches with IGMP snooping enabled so that they can correctly forward multicast traffic.

A 4-port gateway assigned to sACN universes 1, 2, 3, and 4 will send a membership report when it connects to the network saying that it needs to have those universes forwarded to it--or, in other words, that it is part of the multicast group for those four universes. All switches on the network with IGMP snooping enabled will then work together to ensure that port receives those universes from any source on the network. It will send the same membership report each time it receives a query from the querier. If you reconfigure the gateway to receive sACN universes 2, 3, 4, and 5, it will send a new membership report immediately for those universes, as well as a leave group message for universe 1. The snooping switches will then stop sending universe 1 to that port and begin sending universe 5. The gateway will continue to respond to queries from the querier with the new report.

IGMP - Query Interval

This is the interval of time between General Membership Query packets transmitted by the IGMP Querier on a network. Typically this interval can occur anywhere between 30 seconds to 125 seconds. In order words, every X seconds, the querier sends out a packet asking if anyone is interested in multicast traffic. Note that while there is only ever one IGMP querier active on a network, it is still possible for other network switches to have querier enabled in the event that the designated querier goes offline.

All switches on the same network (that have querier enabled) must have the same query interval timers, or multicast traffic may become unstable if the querier goes offline.

IGMP - Robustness 

This is the quantity of General Membership Query packets transmitted at the given Query Interval. Typically this ranges from 1 to 10. As these packets are UDP, high robustness is beneficial as the querier has no way of knowing if a device did not receive a query packet.

IGMP - Leave Group

It is possible for a multicast receiver to notify the querier that it wishes to leave a multicast group. For example, if Port 1 on a DMX Gateway is changed from sACN Universe 1 to sACN Universe 2, the gateway transmits a Leave Group packet notifying the querier (and all snooping switches) that it no longer needs to listen to sACN Universe 1 (239.255.0.1). The switch hardware will then stop forwarding packets from that multicast address to the device (physical network port) that submitted the Leave Group request.

IGMP - General Membership Query

A message sent by the IGMP Querier to determine which multicast groups have any active members. If, for example, a querier sends this message and receives no response for sACN universe 500, the system knows that it does not need to forward traffic for that group or gather any details on its members.

IGMP - Group Specific Membership Query

A message sent by the IGMP Querier to determine if any particular multicast group has active members. For example, if a console starts outputting sACN universe 500, the querier may send this message to determine if any gateways need to receive that universe.

IP Address

A unique numerical identifier, sometimes colloquially referred to as "an IP," assigned to each logical device on a TCP/IP network. An IPv4 address is 32 bits, almost always represented as 4 octets in decimal form, delineated by periods.

For example, the default IP address for port 1 on an Ion is 10.101.100.101. 

IP addresses can be either static or dynamic.

• Static
  • set by an arbitrary means, usually set by a manufacturer or user-defined
  • Not meant to change, so they can be documented and relied on
  • Useful for infrastructural devices such as switches, dimmer racks, and processors
• Dynamic
  • Set by an application on the network such as a DHCP or BootP server
  • Can change at any time
  • Useful for devices we don't need to remember the IP of such as gateways and network fixtures

IPv6 has significantly larger IP addresses that are notated differently, but as of 2026, all ETC devices exclusively implement IPv4.

All devices on a LAN must have a unique IP address, or messages cannot be transmitted correctly, potentially between any  device on the network. A common troubleshooting step when diagnosing network communications issues is to ensure there are no duplicate IP addresses on the network.

IP Subnet

The devices on an IP network that may communicate with each other via unicast communication. Devices which are not in the same subnet will fail to communicate directly. The subnet for each device is defined by its subnet mask or prefix length and its own IP address.

Subnet Mask

A 32-bit value, represented as four octets delineated by periods, which defines a device's subnet. 

A subnet mask defines which bits of two addresses must match between two network interfaces' IP addresses in order to establish unicast communications. When comparing the two IP addresses, if a bit in the subnet mask has the value of 1, both the sending and receiving device must have the same value for that bit, either 1 or 0. If the bit in the subnet mask is 0, the corresponding bit in the IP addresses does not need to match. Subnet masks are generally a sequence of a certain number of 1s followed by 0s for the rest of the value, so it is also called a "prefix length."

That's a lot of low-level computing jargon, but in practical terms it is fairly simple. For most networks, a subnet mask will consist of either one, two, or three 255s in a row:

255.0.0.0 (or prefix length 8, represented as /8)
255.255.0.0 (/16)
255.255.255.0 (/24)

Four 255s would not be valid, because two devices would need the same IP to communicate, but two devices on the same network may not share an IP address. All 0s is not invalid, but is extremely unusual for LANs. 

When comparing the four-octet IP address of two devices, if their subnet mask has a 255, that octet must have the same value, and if it has a 0, the octet may have any value.

If you want to use an Ion XE as a client for an Apex, the Ion must be on the same physical network as the Apex, and it must be within the same subnet. The default IPs for port 1 of both devices are already set that way, so we can use them as an example.

Our Ion XE's port 1 IP address is 10.101.100.20. 
Our Apex's port 1 IP address is 10.101.191.101.

Both devices have a subnet mask of 255.255.0.0. This means that the first two octets must match for the devices to communicate, and because both IPs start with 10.101, they are in the same subnet and can establish unicast communications.

If you changed the Ion XE's port 1 subnet mask to 255.255.255.0 or changed its IP address to 192.168.100.20, the ports would no longer be in the same subnet and would fail to communicate.

IP Gateway

When a device wants to send an IP message to another device that is not within its own LAN, it sends the message to a gateway, which will pass (or route) that message along to another LAN or gateway to get it closer to its final destination. In the case of Internet traffic, gateways are the devices that are networked together across the world, routing messages in a mesh topology to get them to where they need to go. 

The default gateway is the IP address a network interface will (unless otherwise specified by the application) send packets to which have a destination outside of its subnet.

As lighting networks are generally not connected to the Internet, most do not have a gateway, though complex and specialized systems may have routed networks that utilize multiple LANs to manage traffic. Some devices and applications require a default gateway IP to be defined even if it will not be used.

ipconfig -all

Used in the Windows Command Prompt. Displays all IP settings, including DHCP lease times, DNS servers, etc of each network interface on your PC.

"ipconfig" without the "-all" flag will display only the IP address, Subnet Mask, and Default Gateway for currently active ports.

IPv4

The original standardization of the Internet Protocol, introduced in 1980.

IPv6

The most recent Internet Protocol standard, introduced in 1995 and ratified in 2017. Improves on the IPV4 standard in many ways, most notably by increasing from a 32-bit IP address to a 128-bit IP address, to account for the number of devices on the Internet which require unique addresses. As of 2026, it is generally used in the devices which make up the infrastructure of the Internet, but end-user-facing devices are beginning to implement it.

Daisy Chain Topology

In a daisy chain topology, each node connects to both the next and previous node in a contiguous line.

This topology works well for DMX, because each node is connected passively to the data line. This means that if the electronics of single device in the chain fail, the system as a whole remains functional.

Since Ethernet networking cannot be passive, a daisy chain topology with switches is not recommended, as each node is a potential failure point for the entire network.

Mesh Topology

A topology in which all nodes on a network may be connected to multiple other nodes. This means that there can be multiple (and sometimes many) valid paths for data to take to get from one point to another in the network. As a result, when one node can no longer pass data, it is still possible for data to pass through the network normally. The more connections in the network, the more resilient the network is to individual node failures. However, as the number of connections between nodes increases, the system becomes more complex. Depending on the type of communication being transferred across the network, this complexity may have consequences.

In Ethernet networking, a mesh network is only possible when there are rules for how data gets from one point to another. Without these rules, a network storm would prevent communications between any devices. Spanning Tree Protocol allows for a mesh network without a network storm.

Ring / Loop Topology

A ring or loop topology is similar to a daisy chain, as each node in the network is connected to the next and previous node in line. In a ring, the first and last nodes are also connected. If a single node on the network can no longer pass data, the network is still functional, but further failures are likely to quickly cause problems. However, a ring is simpler than a mesh, so its maintenance may not be as resource-intensive.

In Ethernet networking, a ring is easier to set up than a mesh, but it still requires STP to prevent network storms. All switches in a ring network will likely share bandwidth fairly equally.

Star Topology

Also called "hub and spoke." In a star topology, there is one node which all other nodes connect to and through which all data flows. Any number of the nodes at the outside of the star can fail without disrupting communication between any other nodes on the network, but if the node that all other nodes are connected to fails, the entire network fails.

In Ethernet networking, most small networks use star topology, with a switch at the center and other devices plugged into it. Networks of up to three switches can be considered star topology. In larger networks, the switch at the center of the star is a core switch that can handle much more traffic than the switches at the outside of the network.

PIM Dense Mode

coming soon

PIM Spare Mode

coming soon

sACN Discovery

This is a part of the sACN protocol described above. sACN Discovery uses multicast address 239.255.250.214. In order for sACN Discovery to work, both the transmitter and receiver must comply with this part of the standard. The concept of the Discovery packet is that the sACN source, in addition to sending out lighting levels, also transmits a packet alerted others on the network which universes it is sourcing. For example, if a source is transmitting universes 1, 2, and 3 then it would be transmitting lighting levels (typically over multicast) on multicast addresses 239.255.0.1, 239.255.0.2, and 239.255.0.3. If we wished to find out what the source was transmitting without guessing or subscribing to those universes (likely because we don't know what it is transmitting), the source would also transmit a packet at 239.255.250.214 (the Discovery packet) that contains a list of the universes it is sourcing). This is a very handy tool for troubleshooting and identifying different sACN sources and their respective universes on a network. Not all products that are capable of transmitting sACN support (or transmit) sACN Discovery packets.

sACN Priority 

This is a part of the sACN protocol described above. An mentioned above, each UDP packet that is transmitted (streamed) from it's source contains lighting level information for addresses 1-512 (much like a DMX universe). Embedded within each packet is a Priority number between 1-200. 1 is the lowest priority (least important) and 200 is the highest priority (most important). When multiple controls sources are present on a network, which ever source is transmitting lighting levels at a higher priority wins. If both sources are at the same priority then HTP usually wins (depends on the sACN receiver). Be careful as some sACN receivers do not support multiple sources or rather they do not interpret the priority embedded within the packet and may try to continuously switch between the two different lighting levels.

There also exists what is known as a sACN Priority packet. This is different than the Priority that is embedded within each sACN lighting level packet. A sACN Priority packet can list unique sACN priorities for each address in the universe. The embedded priority with a lighting level packet is a single priority for the whole universe. The separate sACN Priority packet is sometimes referred to "Priority-by-Address". Note that both the sACN source and sACN receiver need to support this in order for it to work. The sACN Priority packet uses a different start code than a lighting level packet. A standard sACN packet uses start code 0x00 and a priority packet uses 0xdd. If the receiver does not support sACN Priority it is likely that the 0xdd packet will be ignored.

In a sACN Priority packet, only the "patched" addresses are given priority levels. For those unpatched addresses, they are given a priority of 0. A priority of 0 is still a valid priority (between the range of 0-200). It is the lowest priority and essentially means "ignore me" and do not output any lighting levels associated with priority 0. In order for this to work, the sACN receiver must understand (support) that concept that 0 priority should be ignored and not output. If the receiver fails to interpret this, it will still output lighting levels at priority 0 if no other source exists on the network.

STP - BPDU

Bridge Protocol Data Unit is used in Spanning Tree to determine network topology. Spanning Tree is used when a network is set up in a ring or mesh topology. BPDUs are transmitted from each switch to it's neighbor switch to inform them them which physical ports on the switch are in which state (forwarding, listening, blocked, and so on). Think of it like a "Hello" message between neighboring switches. The neighboring switch uses that information to determine what state it should put its ports into and then transmits its own BPDU down the line. 

There are multiple pieces of information contained within the BPDU "Hello" packet regarding the switch. Some examples include:

• MAC Address
• IP Address
• Bridge Priority (Switch Priority)
• Network port and speed (physical port)

One of the purposes of the BPDU is to find the best path (or lowest cost path) to the root bridge. Eventually the root bridge will get the BPDU's from its neighboring switch and it will transmit a configuration message on all of its ports. BPDU's are transmitted in moderate frequency of about 1 message every 2 seconds. Note that in a Spanning Tree scenario, at the time of network convergence (when a switch or node is added to the network), ports do not immediately start data transmission immediately. Instead they navigate through many different BPDU states until it is proven that this port does not create a "loop" and is safe, then it will start transmitting data.

STP - BPDU Guard

This is a feature in some Cisco switch models. A BPDU Guard can be applied to physical ports of a network switch. The purpose of a BPDU Guard is to keep Spanning Tree and the network topology predictable. When a port on a network switch has BPDU Guard enabled, the device on the other end cannot influence Spanning Tree on that VLAN/network. If BPDU packets are detected on a network port that has BDPU Guard enabled, then the port is automatically disabled. The port would then have to be manually enabled again using the web interface or command line. This can be done in the Error Recovery Settings area of the network switch. 

This is an excellent tool in networks to prevent accidental changes in ring-topology when additional or temporary edge switches are added that may not be part of the permanent loop/ring topology. If BPDU Guard is enabled and a BPDU is detected, the BPDU Handling state for that port will show up as "Guarding" (Blocked State) in the switch webUI. Also the Operational Status of the port will say "Down (BPDU Guard)".

Note that BPDU Guard is used with ports that have PortFast enabled. PortFast still uses STP but allows traffic to flow immediately (port STP is set to "Forwarding State") instead of first waiting for the BPDU's to negotiate the Spanning Tree topology first ("Learning and Listening States", these states are bypassed). If PortFast is enabled and a BPDU packet is detected whilst BPDU Guard is also enabled, then the port immediately gets disabled.

STP - Bridge ID & Bridge Priority

Determines which bridge (or network switch) is elected the Root Bridge in a ring or mesh topology. A Bridge ID consists of the Bridge Priority--a value between 0 and 61400, in increments of 4096--and the port's MAC address. The network switch with the lowest Bridge ID is the root bridge. The Bridge Priority can be edited while the MAC Address cannot. The default Bridge Priority for a Cisco switch is 32768 in a range of 0-61440 (increments of 4096). If all Bridge Priorities are equal (for example, they are left at the defaults of 32768), then the MAC Address is the deciding factor in determining which switch becomes the root bridge. In that case, the switch with the lowest MAC Address becomes the root bridge.

STP - Edge Port

This is a feature in Cisco network switches related to Spanning Tree. Edge Port is the name of the feature in the WebUI, but in the switch configuration file or when using CLI this feature is called PortFast. Edge Port can be set to one of three states per port: Enable, Auto, and Disable. If Enabled, the port is set to a Forwarding State. This means that all traffic is allowed through this port in relationship to the Spanning Tree. This also means that BPDU exchange between switches will not force this port to change state to Blocking, Listening, or Learning. Those other states are what keep a Loop/Ring topology from sending traffic indefinitely ultimately resulting in a Broadcast Storm / Network Storm that could cause undesired behavior (lag, reboot, etc.) in network switches and edge devices (gateways, controllers, consoles).

• If Edge Port is set to Enabled; BPDUs are ignored and traffic will flow around the Loop/Ring indefinitely.
  • Use this setting for all ports with Edge Devices connected (gateways, controllers, consoles, anything that is not another network switch).
  • CLI Syntax:  spanning-tree portfast
• If Edge Port is set to Auto, The link will become active (Forwarding State) after 3 seconds of no BPDUs on the port, thus giving the port time for STP to resolve loops.
  • CLI Syntax:  spanning-tree portfast auto
• If Edge Port is set to Disabled, BPDUs are respected and STP issues are resolved.
  • Use this setting for all ports connected to other network switches.
  • CLI Syntax:  no spanning-tree portfast

STP - PortFast

(See Edge Port) - This is the Cisco CLI (command line interface) command for using the Edge Port feature. Edge Port is what it is called on the Web Interface of a network switch.

STP - Loopback Guard

This is a function related to Spanning Tree. Sometimes referred to as Loop Guard. This is applied to individual ports on a network switch. The function of a Loopback Guard is to protect network topology in the event that BPDUs are no longer received on a non-Designated Port. Designated Ports on a network switch transmit constant BPDUs to alert the switch on the other end of the segment about the state of network topology. 

In an example where fiber is used between switches, there are two connections that make up one segment (at each switch). There is a wire for transmit and a wire for receive which equals a pair of fiber cables. If, for example, the transmit wire was severed but the receive was in-tact, BPDUs would cease to be transmitted from Switch A to Switch B. Switch B would then transition its port state from Alternate to Designated. The Switch B port changes state sas a result of no longer receiving BPDU packets. Associated with BPDU is a max age time. When the max age time expires from the last BPDU the port transitions state (to Designated). When a port becomes Designated, it forwards network traffic. Hence we have now created a network loop. If Loopback Guard was applied, it would place the port that was Alternate into an Inconsistant State which would block all traffic.

In the event that copper was used instead of fiber and only a single copper cable is used between switches (no EtherChannel or LAGs), the Loopback Guard would be less important because it is more likely that the cable as a whole would be severed instead of individual pairs in the cable (example Cat5e). To summarize, if fiber is used between switches in a ring/loop topology, it would be recommended to apply Loopback Guard to all non-designated ports.

STP Path Cost

This is a function related to Spanning Tree. See also Root Path. The Root Path is determined by the Path Cost. A refresher that the Root Path is the "lowest cost path" from a given point on a network to the Root Bridge. The Path Cost is evaluated, in part, by the speed of the segment between two switches. The table below outlines Path Costs based on typical network speeds. It is important to note whether the switch ports can auto negotiate speeds at that will impact the Path Cost.

The Path Cost is applied to each segment connecting network switches together. For each segment between a given point in the network and the Root Bridge, the Path Costs are added together. The path with the lowest cost becomes the Root Path. In the example below, the Path Cost for Switch 2 to get to Switch 1 is 20,000. If Switch 2 were to get to Switch 1 by way of Switch 3, then the Path Cost would be 40,000 (segment between Sw2 and Sw3 (20,000) + segment between Sw3 and Sw1 (20,000) = 40,000). Therefore the lowest cost path, the Root Path is directly between Switch 2 and Switch 1.

STP Port Role

There are three main port roles; Root, Designated, and Alternate (Blocked). Every active port on a network switch will have a role in Spanning Tree. The individual port roles are explained in further detail below by name. The graphic below shows port roles a simple loop topology.

STP Port Role - Alternate Port

Sometimes called a Blocked Port. The Alternate Port is chosen by looking at the segment and deciding which switch has the lowest Bridge ID. The switch with the lowest Bridge ID will have its end of the segment (port) keep the Designated Port status and the higher Bridge ID will have its end of the segment (port) become an Alternate Port (Blocked Port). This is the where the loop is broken. §  This path is automatically disabled by Spanning Tree until such time as the network topology changes (addition or subtraction of a switch or segment) and this port has a lower Path Cost to the Root Bridge.

STP Port Role - Backup Port

In the event that two segments exists between the same two network switches, one port will be designated and the other will be called backup. The backup port will block traffic unless the designated port goes down. If only a single segment exists between two switches that backup port state does not apply.

STP Port Role - Designated Port

A Designated Port exists on at least one end of every segment connecting network switches together. On the Root Bridge, every port connecting to a non-Root network switch is a Designated Port. On non-Root network switches the port that is not the Root Port will become a Designated Port. 

STP Port Role - Root Port

A port with the designation "Root Port" implies that this port is the Root Path or "lowest cost path" to the Root Bridge. In a loop topology, there can only be one Root Bridge and only one path (Root Path) to that switch from any given point in the topology. This is a part of how Spanning Tree works.  A Root Port is the port on every non-Root network switch that has the lowest Path Cost to the Root Bridge. There can only be one Root Port on every non-Root Switch. Once the Root Bridge, Root Path, and Root Port have been declared, the network knows which segments in the loop to shutdown to prevent infinity loops. The Root Port designation is given to a port that is connected to another switch. Root Ports are not designated to ports with edge devices such as DMX Gateways, et cetera.

STP - Root Bridge

In a closed Ring / Loop Topology, Spanning Tree is required to prevent an infinity loop or Network Storm / Broadcast Storm of network traffic. Read Spanning Tree first to better understand Root Bridge. Root Bridge is the pre-determined "center" of the switches in a loop. Essentially a loop has no center switch or core switch so one switch has to be elected from which to reference distance between switches and ultimately shut down the furthest link from it to break the loop and prevent Network Storms from occurring.

In a system where all things are equal between the network switches; (cable type, switch port speed, Bridge Priority, et cetera), the network switch with the lowest MAC Address is elected the Root Bridge. It is possible to manually configure a switch to be the Root Bridge by altering its Bridge Priority (this will vary by switch and not all switches have the ability to alter this). Note that physical cable distance or length is not a factor in determining the Root Bridge in most systems.

From the Root Bridge, the Path Cost (STP Path Cost) is determined, and the path to the Root Bridge that has the highest cost will be shut down (the segment between two switches). The paths to the Root Bridge with the lowest costs will remain open for network traffic. If traffic has to travel between multiple switches to get to the Root Bridge, the path with the fewest switches to pass through will remain open (every switch passed through adds a cost to the path).

STP - Root Guard

This is a function related to Spanning Tree. Root Guard gets assigned to network switch port(s), mostly commonly the ports on the Root Bridge that connect to other switches. The function of the Root Guard is to prevent a Designated Port from becoming a Root Port if a new switch or mis-configured switch converges with the existing network. Root Guard is typically enabled on ports that are facing other switches that are not supposed to be the Root Bridge. In other words Root Guard is applied to ports with switch to switch connections, not for edge devices such as DMX Gateways, Console, Dimmer Racks, et cetera.

STP - Root Path 

This is a function related to Spanning Tree. See also STP Path Cost. The Root Path is the "lowest cost path" from a given point in the network topology to the Root Bridge. The path is predictable if the Root Bridge has been assigned manually and the network topology is known. If the Root Bridge is unknown, then investigation must occur to find the Root Path. This is typically done by accessing an interface for every switch in the network and documenting which port on each switch has Root Port (STP Root Port) designation.

STP States - 1) Blocking / Disregarding State - (Spanning Tree)

Upon network convergence, when a port link first comes up, the port is put into a Blocking state. In a Blocking state, the port will listen to BPDU packets from other switches but that is about it. It will not transmit any packets. This allows it to determine the root ID of the Root Bridge and get an idea of what the rest of the network topology looks like. While in this state all other traffic is disregarded. In normal Spanning Tree (not Rapid Spanning Tree RTSP), it can remain in this state for a maximum of 20 seconds. After the Root Bridge and topology are identified, it will move into a Listening State next.

STP States - 2) Listening State - (Spanning Tree)

After leaving Blocking State, the network port enters Listening State. This state determines if this port is permitted to forward network traffic. It will continue to listen to BPDU packets from other switches but it will now also start transmitting its own BPDU packets. By default this state will have a forwarding delay of 15 seconds. After the delay the port moves to a Learning State.

STP States - 3) Learning State - (Spanning Tree)

After leaving Listening State, the network port enters Learning State. In this state, the port learns and populates its VLAN and MAC address tables in preparation for forwarding traffic. This is the first state that learns MAC addresses (the only other state that will learn MACs is Forwarding). The port will also remain in this state for 15 seconds (forward delay) before moving to Forwarding State.

STP States - 4) Forwarding State - (Spanning Tree)

After leaving Learning State, the network port enters Forwarding State. In this state, the port is actively forwarding packets and it considered a part of the network. It continues to send and receive BPDU packets. This is the only state that will forward normal network traffic.

STP States - Disabled State - (Spanning Tree)

In this state the packet does not forward any traffic and it does not participate in spanning tree. All packets including BPDUs are ignored. This is the only state in which the port will not send BDPUs but it will continue to receive them (again, it will just ignore them).