IEEE 802.1Q: Difference between revisions

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IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames. The standard also contains provisions for a quality-of-service prioritization scheme commonly known as IEEE 802.1p and defines the Generic Attribute Registration Protocol.

Portions of the network which are VLAN-aware (i.e., IEEE 802.1Q conformant) can include VLAN tags. When a frame enters the VLAN-aware portion of the network, a tag is added to represent the VLAN membership.^[a] Each frame must be distinguishable as being within exactly one VLAN. A frame in the VLAN-aware portion of the network that does not contain a VLAN tag is assumed to be flowing on the native VLAN.

The standard was developed by IEEE 802.1, a working group of the IEEE 802 standards committee, and continues to be actively revised with notable amendments including IEEE 802.1ad, IEEE 802.1ak and IEEE 802.1s. The 802.1Q-2014 revision incorporated the IEEE 802.1D-2004 standard.^[1]

Frame format

Insertion of 802.1Q tag in an Ethernet frame

802.1Q adds a 32-bit field between the source MAC address and the EtherType fields of the original frame. Under 802.1Q, the maximum frame size is extended from 1,518 bytes to 1,522 bytes. The minimum frame size remains 64 bytes, but a bridge may extend the minimum size frame from 64 to 68 bytes on transmission. This allows a tag to be popped without needing additional padding.^[2]^[3] Two bytes are used for the tag protocol identifier (TPID), the other two bytes for tag control information (TCI). The TCI field is further divided into PCP, DEI, and VID.^[4]

802.1Q tag format
16 bits	3 bits	1 bit	12 bits
TPID	TCI
TPID	PCP	DEI	VID

Tag protocol identifier (TPID)

A 16-bit field set to a value of 0x8100^[b] in order to identify the frame as an IEEE 802.1Q-tagged frame. This field is located at the same position as the EtherType field in untagged frames, and is thus used to distinguish the frame from untagged frames.

Tag control information (TCI)

A 16-bit field containing the following sub-fields:

Priority code point (PCP): A 3-bit field which refers to the IEEE 802.1p class of service (CoS) and maps to the frame priority level. Different PCP values can be used to prioritize different classes of traffic.^[5]
Drop eligible indicator (DEI): A 1-bit field. (formerly CFI^[c]) May be used separately or in conjunction with PCP to indicate frames eligible to be dropped in the presence of congestion.^[7]
VLAN identifier (VID): A 12-bit field specifying the VLAN to which the frame belongs. The values of 0 and 4095 (0x000 and 0xFFF in hexadecimal) are reserved. All other values may be used as VLAN identifiers, allowing up to 4,094 VLANs. The reserved value 0x000 indicates that the frame does not carry a VLAN ID; in this case, the 802.1Q tag specifies only a priority (in PCP and DEI fields) and is referred to as a priority tag. On bridges, VID 0x001 (the default VLAN ID) is often reserved for a network management VLAN; this is vendor-specific. The VID value 0xFFF is reserved for implementation use; it must not be configured or transmitted. 0xFFF can be used to indicate a wildcard match in management operations or filtering database entries.^[8]

For frames (other than 802.3 frames) using Subnetwork Access Protocol (SNAP) encapsulation with an organizationally unique identifier (OUI) field of 00-00-00 (so that the protocol ID field in the SNAP header is an EtherType as specified in RFC 1042), the EtherType value in the SNAP header is set to 0x8100 and the aforementioned extra 4 bytes are appended after the SNAP header.^[9] In other words the VLAN tag follows the SNAP header. For 802.3 frames in LLC-SNAP format, the order is opposite; the VLAN tag is placed before the LLC-SNAP header.

Because inserting the VLAN tag changes the frame, 802.1Q encapsulation forces a recalculation of the original frame check sequence field in the Ethernet trailer.

The IEEE 802.3ac standard increased the maximum Ethernet frame size from 1518 bytes to 1522 bytes to accommodate the four-byte VLAN tag. Some network devices that do not support the larger frame size will process these frames successfully but may report them as "baby giant" anomalies.^[10]

Double tagging

IEEE 802.1ad introduced the concept of double tagging. Double tagging can be useful for Internet service providers (ISPs), allowing them to use their VLANs internally while carrying traffic from clients that is already VLAN tagged. The outer (next to source MAC and representing ISP VLAN) S-TAG (service tag) comes first, followed by the inner C-TAG (customer tag). In such cases, 802.1ad specifies a TPID of 0x88a8 for service-provider outer S-TAG.

Insertion of 802.1ad double tag in an Ethernet frame

Other protocols

IEEE 802.1Q defines the Multiple VLAN Registration Protocol (MVRP), an application of the Multiple Registration Protocol, allowing bridges to negotiate the set of VLANs to be used over a specific link. MVRP replaced the slower GARP VLAN Registration Protocol (GVRP) in 2007 with the IEEE 802.1ak-2007 amendment.

The 2003 revision of the standard was the first to include the Multiple Spanning Tree Protocol (MSTP) which was originally defined in IEEE 802.1s.

Notes

^ VLAN membership is determined by the frame's port or the port/protocol combination, depending on whether port-based or port-and-protocol-based VLAN classification is being used.
^ The prefix 0x indicates hexadecimal notation
^ This field was formerly designated Canonical Format Indicator (CFI) with a value of 0 indicating a MAC address in canonical format. It is always set to zero for Ethernet. CFI was used for compatibility between Ethernet and Token Ring networks. If a frame received at an Ethernet port had a CFI set to 1, then that frame would not be bridged to an untagged port.^[6]

References

^ 802.1Q-2014 - Bridges and Bridged Networks
^ Per IEEE 802.1Q Annex G.2.3 Minimum PDU size
^ "Inter-Switch Link and IEEE 802.1Q Frame Format". Cisco Systems. Retrieved 2019-09-26.
^ IEEE 802.1Q-2011 clause 9.6
^ IEEE 802.1Q I.4 Traffic types and priority values
^ IEEE 802.1Q-2005 clause 9.6
^ IEEE 802.1Q-2011 clause 6.9.3
^ IEEE 802.1Q-2005, 9.6 VLAN Tag Control Information
^ IEEE 802.1Q-2011 clause 9.4 Tag Protocol Identifier (TPID) formats
^ Understanding Baby Giant/Jumbo Frames Support on Catalyst 4000/4500 with Supervisor III/IV (PDF), archived from the original (PDF) on 2015-04-02

Sources

IEEE Std. 802.1Q-1998, Virtual Bridged Local Area Networks, doi:10.1109/IEEESTD.1999.89204, ISBN 0-7381-1537-1
IEEE Std. 802.1Q-2003, Virtual Bridged Local Area Networks, 2003, doi:10.1109/IEEESTD.2003.94280, ISBN 0-7381-3663-8
IEEE Std. 802.1Q-2005, Virtual Bridged Local Area Networks, doi:10.1109/IEEESTD.2006.216285, ISBN 0-7381-3662-X
IEEE Std. 802.1Q-2011, Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks, doi:10.1109/IEEESTD.2011.6009146, ISBN 978-0-7381-6708-4
IEEE Std. 802.1BR-2012, Virtual Bridged Local Area Networks—Bridge Port Extension, doi:10.1109/IEEESTD.2012.6239543, ISBN 978-0-7381-7281-1
IEEE Std. 802.1Q-2014, Bridges and Bridged Networks, doi:10.1109/IEEESTD.2014.6991462, ISBN 978-0-7381-9433-2
- IEEE Std. 802.1Q-2014/Cor 1-2015, Corrigendum 1: Technical and editorial corrections, doi:10.1109/IEEESTD.2016.7374647, ISBN 978-1-5044-0112-8
"Inter-Switch Link and IEEE 802.1Q Frame Format". Cisco Systems. Retrieved 2019-01-10.

[1] VLAN membership is determined by the frame's port or the port/protocol combination, depending on whether port-based or port-and-protocol-based VLAN classification is being used.

[6] The prefix 0x indicates hexadecimal notation

[9] This field was formerly designated Canonical Format Indicator (CFI) with a value of 0 indicating a MAC address in canonical format. It is always set to zero for Ethernet. CFI was used for compatibility between Ethernet and Token Ring networks. If a frame received at an Ethernet port had a CFI set to 1, then that frame would not be bridged to an untagged port.^[6]

[2] 802.1Q-2014 - Bridges and Bridged Networks

[3] Per IEEE 802.1Q Annex G.2.3 Minimum PDU size

[4] "Inter-Switch Link and IEEE 802.1Q Frame Format". Cisco Systems. Retrieved 2019-09-26.

[5] IEEE 802.1Q-2011 clause 9.6

[7] IEEE 802.1Q I.4 Traffic types and priority values

[8] IEEE 802.1Q-2005 clause 9.6

[10] IEEE 802.1Q-2011 clause 6.9.3

[11] IEEE 802.1Q-2005, 9.6 VLAN Tag Control Information

[12] IEEE 802.1Q-2011 clause 9.4 Tag Protocol Identifier (TPID) formats

[13] Understanding Baby Giant/Jumbo Frames Support on Catalyst 4000/4500 with Supervisor III/IV (PDF), archived from the original (PDF) on 2015-04-02

[a]

[1]

[2]

[3]

[4]

[b]

[5]

[c]

[7]

[8]

[9]

[10]

[6]

@@ Line 1: / Line 1: @@
+{{short description|IEEE networking standard supporting VLANs}}
-'''IEEE 802.1Q''' is the [[computer network|networking]] standard that supports [[Virtual LAN]]s (VLANs) on an [[Ethernet]] network. The standard defines a system of '''VLAN tagging''' for [[Ethernet frame]]s and the accompanying procedures to be used by [[Bridging (networking)|bridges]] and [[Network switch|switches]] in handling such frames. The standard also contains provisions for a [[quality of service]] prioritization scheme commonly known as [[IEEE 802.1p]] and defines the [[Generic Attribute Registration Protocol]].
+'''IEEE 802.1Q''', often referred to as '''Dot1q''', is the [[computer network|networking]] standard that supports [[virtual local area network]]ing (VLANs) on an [[IEEE 802.3]] [[Ethernet]] network. The standard defines a system of '''VLAN tagging''' for [[Ethernet frame]]s and the accompanying procedures to be used by [[Network bridge|bridges]] and [[Network switch|switches]] in handling such frames. The standard also contains provisions for a [[quality of service|quality-of-service]] prioritization scheme commonly known as [[IEEE 802.1p]] and defines the [[Generic Attribute Registration Protocol]].
-Portions of the network which are ''VLAN-aware'' (i.e., IEEE 802.1Q conformant) can include VLAN tags.  Traffic on a ''VLAN-unaware'' (i.e., IEEE 802.1D conformant) portion of the network will not contain VLAN tags.  When a frame enters the VLAN-aware portion of the network, a tag is added to represent the VLAN membership of the frame's port or the port/protocol combination, depending on whether port-based or port-and-protocol-based VLAN classification is being used.  Each frame must be distinguishable as being within exactly one VLAN.  A frame in the VLAN-aware portion of the network that does not contain a VLAN tag is assumed to be flowing on the native (or default) VLAN.
+Portions of the network which are VLAN-aware (i.e., IEEE 802.1Q conformant) can include VLAN tags.  When a frame enters the VLAN-aware portion of the network, a tag is added to represent the VLAN membership.{{efn|VLAN membership is determined by the frame's port or the port/protocol combination, depending on whether port-based or port-and-protocol-based VLAN classification is being used.}}  Each frame must be distinguishable as being within exactly one VLAN.  A frame in the VLAN-aware portion of the network that does not contain a VLAN tag is assumed to be flowing on the '''native VLAN'''.
-The standard was developed by [[IEEE 802.1]], a [[working group]] of the [[IEEE 802]] standards committee and continues to be actively revised with notable revisions including [[IEEE 802.1ak]], [[IEEE 802.1Qat]] and [[IEEE 802.1Qay]].
+The standard was developed by [[IEEE 802.1]], a [[working group]] of the [[IEEE 802]] standards committee, and continues to be actively revised with notable amendments including [[IEEE 802.1ad]], [[IEEE 802.1ak]] and [[IEEE 802.1s]]. The 802.1Q-2014 revision incorporated the [[IEEE 802.1D|IEEE 802.1D-2004]] standard.<ref>[http://www.ieee802.org/1/pages/802.1Q-2014.html 802.1Q-2014 - Bridges and Bridged Networks]</ref>
-==Applications==
-[[Network virtualization]] solutions, such as [[Open vSwitch]] rely on VLAN tags<ref>{{cite web |url=http://openvswitch.org/support/config-cookbooks/vlan-configuration-cookbook/ |title=VLANs - Open vSwitch | quote = Your physical switch(es) must be capable of forwarding VLAN tagged traffic and the physical switch ports should be VLAN trunks |accessdate=18 January 2014}} </ref>.
 ==Frame format==
-[[Image:Ethernet 802.1Q Insert.svg|center|thumb|950px|Insertion of 802.1Q Tag in an Ethernet frame]]
+{{wide image|Ethernet 802.1Q Insert.svg|1328px|Insertion of 802.1Q tag in an Ethernet frame}}
-.1Q does not actually encapsulate the original frame. Instead, for [[Ethernet frame]]s, it adds a 32-bit field between the source [[MAC address]] and the [[EtherType]]/Length fields of the original frame, leaving the minimum frame size unchanged at 64 bytes (octets) and extending the maximum frame size from 1,518 bytes to 1,522 bytes (For the payload a 42 octet minimum applies when 802.1Q is present, when absent, a 46 octet minimum applies. IEEE 802.3-2005 Clause 3.5). Two bytes are used for the tag protocol identifier (TPID), the other two bytes for tag control information (TCI). The TCI field is further divided into PCP, DEI, and VID.<ref>IEEE 802.1Q-2011 clause 9.6</ref>
+.1Q adds a 32-bit field between the source [[MAC address]] and the [[EtherType]] fields of the original frame. Under 802.1Q, the maximum frame size is extended from 1,518 bytes to 1,522 bytes. The minimum frame size remains 64 bytes, but a bridge may extend the minimum size frame from 64 to 68 bytes on transmission. This allows a tag to be popped without needing additional padding.<ref>Per IEEE 802.1Q Annex G.2.3 ''Minimum PDU size''</ref><ref>{{cite web |url=https://www.cisco.com/c/en/us/support/docs/lan-switching/8021q/17056-741-4.html |title=Inter-Switch Link and IEEE 802.1Q Frame Format |publisher=[[Cisco Systems]] |access-date=2019-09-26}}</ref> Two bytes are used for the tag protocol identifier (TPID), the other two bytes for tag control information (TCI). The TCI field is further divided into PCP, DEI, and VID.<ref>IEEE 802.1Q-2011 clause 9.6</ref>
 {| class="wikitable" width=400px
+|+802.1Q tag format
 |-
 ! width=50%|16 bits
@@ Line 30: / Line 28: @@
 |}
+;Tag protocol identifier (TPID)
-* ''Tag Protocol Identifier (TPID)'': a 16-bit field set to a value of 0x8100 in order to identify the frame as an IEEE 802.1Q-tagged frame.  This field is located at the same position as the [[EtherType]]/Length field in untagged frames, and is thus used to distinguish the frame from untagged frames.
+:A 16-bit field set to a value of 0x8100{{efn|The prefix ''0x'' indicates [[hexadecimal]] notation}} in order to identify the frame as an IEEE 802.1Q-tagged frame.  This field is located at the same position as the EtherType field in untagged frames, and is thus used to distinguish the frame from untagged frames.
+;Tag control information (TCI)
+:A 16-bit field containing the following sub-fields:
+:;Priority code point (PCP)
+::A 3-bit field which refers to the [[IEEE 802.1p]] [[Class of service|class of service (CoS)]] and maps to the frame priority level. Different PCP values can be used to prioritize different classes of traffic.<ref>IEEE 802.1Q ''I.4 Traffic types and priority values''</ref>
+:;Drop eligible indicator (DEI)
+::A 1-bit field. (formerly CFI{{efn|This field was formerly designated ''Canonical Format Indicator (CFI)'' with a value of 0 indicating a MAC address in [[MAC address#Bit-reversed notation|canonical format]]. It is always set to zero for Ethernet. CFI was used for compatibility between Ethernet and [[Token Ring]] networks. If a frame received at an Ethernet port had a CFI set to 1, then that frame would not be bridged to an untagged port.<ref>IEEE 802.1Q-2005 clause 9.6</ref>}}) May be used separately or in conjunction with PCP to indicate frames eligible to be dropped in the presence of congestion.<ref>IEEE 802.1Q-2011 clause 6.9.3</ref>
+:;VLAN identifier (VID)
+::A 12-bit field specifying the VLAN to which the frame belongs.  The values of 0 and 4095 (0x000 and 0xFFF in [[hexadecimal]]) are reserved.  All other values may be used as VLAN identifiers, allowing up to 4,094 VLANs.  The reserved value 0x000 indicates that the frame does not carry a VLAN ID; in this case, the 802.1Q tag specifies only a priority (in PCP and DEI fields) and is referred to as a ''priority tag''. On bridges, VID 0x001 (the default VLAN ID) is often reserved for a [[network management]] VLAN; this is vendor-specific. The VID value 0xFFF is reserved for implementation use; it must not be configured or transmitted. 0xFFF can be used to indicate a wildcard match in management operations or filtering database entries.<ref>IEEE 802.1Q-2005, 9.6 VLAN Tag Control Information</ref>
+For frames (other than 802.3 frames) using [[Subnetwork Access Protocol]] (SNAP) encapsulation with an [[organizationally unique identifier]] (OUI) field of 00-00-00 (so that the protocol ID field in the SNAP header is an EtherType as specified in {{IETF RFC|1042}}), the EtherType value in the SNAP header is set to 0x8100 and the aforementioned extra 4 bytes are appended after the SNAP header.<ref>IEEE 802.1Q-2011 clause 9.4 Tag Protocol Identifier (TPID) formats</ref>  In other words the VLAN tag follows the SNAP header.  For 802.3 frames in LLC-SNAP format, the order is opposite; the VLAN tag is placed ''before'' the LLC-SNAP header.
-* ''Tag Control Information (TCI)''
-** ''Priority Code Point (PCP)'': a 3-bit field which refers to the [[IEEE 802.1p]] priority. It indicates the frame priority level. Values are from 0 (best effort) to 7 (highest);  1 represents the lowest priority. These values can be used to prioritize different classes of traffic (voice, video, data, etc.).  ''See also [[Class of Service]] or [[Class of Service|CoS]].''
-** ''Drop Eligible Indicator (DEI)'': a 1-bit field. (formerly CFI<ref group="note">This field was formerly designated ''Canonical Format Indicator (CFI)'' with a value of 0 indicating a MAC address in [[MAC address#Bit-reversed_notation|canonical format]]. It is always set to zero for Ethernet. CFI was used for compatibility between Ethernet and [[Token Ring]] networks. If a frame received at an Ethernet port had a CFI set to 1, then that frame would not be bridged to an untagged port.</ref><ref>IEEE 802.1Q-2005 clause 9.6</ref>) May be used separately or in conjunction with PCP to indicate frames eligible to be dropped in the presence of congestion.<ref>IEEE 802.1Q-2011 clause 6.9.3</ref>
-** ''VLAN Identifier (VID)'': a 12-bit field specifying the VLAN to which the frame belongs.  The hexadecimal values of 0x000 and 0xFFF are reserved.  All other values may be used as VLAN identifiers, allowing up to 4,094 VLANs.  The reserved value 0x000 indicates that the frame does not belong to any VLAN; in this case, the 802.1Q tag specifies only a priority and is referred to as a ''priority tag''.   On bridges, VLAN 1 (the default VLAN ID) is often reserved for a management VLAN; this is vendor-specific.
+Because inserting the VLAN tag changes the frame, 802.1Q encapsulation forces a recalculation of the original [[frame check sequence]] field in the Ethernet trailer.
-For frames using [[IEEE 802.2]]/[[Subnetwork Access Protocol|SNAP]] encapsulation with an OUI field of 00-00-00 (so that the protocol ID field in the SNAP header is an EtherType), as would be the case on LANs other than Ethernet, the EtherType value in the SNAP header is set to 0x8100 and the aforementioned extra 4 bytes are appended after the SNAP header.{{Citation needed|date=February 2010}}<!-- 802.1Q Annex C. C.3.2.1.3 showed VLAN TAG before LLC(SNAP) header. EtherType in SNAP header should not a TPID(0x8100).-->
+The IEEE 802.3ac standard increased the maximum Ethernet frame size from 1518 bytes to 1522 bytes to accommodate the four-byte VLAN tag. Some network devices that do not support the larger frame size will process these frames successfully but may report them as "baby giant" anomalies.<ref>{{citation |url=http://www.cisco.com/image/gif/paws/29805/175.pdf |title=Understanding Baby Giant/Jumbo Frames Support on Catalyst 4000/4500 with Supervisor III/IV |archive-url=https://web.archive.org/web/20150402195656/http://www.cisco.com/image/gif/paws/29805/175.pdf |archive-date=2015-04-02}}</ref>
-Because inserting the VLAN tag changes the frame, 802.1Q encapsulation forces a recalculation of the original [[Frame Check Sequence|FCS]] field in the Ethernet trailer.
-The IEEE 802.3ac standard increased the maximum Ethernet frame size from 1518 bytes to 1522 bytes to accommodate the four-byte VLAN tag. Some network devices that do not support the larger frame size will process the frame successfully but may report them as a "baby giant" anomalies.<ref>[http://www.cisco.com/application/pdf/paws/29805/175.pdf Understanding Baby Giant/Jumbo Frames Support on Catalyst]</ref>
 ===Double tagging===
-With the IEEE standard [[802.1ad]], double-tagging can be useful for Internet service providers, allowing them to use VLANs internally while mixing traffic from clients that are already VLAN-tagged.  The outer (next to source MAC and representing ISP VLAN) S-TAG (service tag) comes first, followed by the inner C-TAG (customer tag).  In such cases, [[802.1ad]] specifies a TPID of 0x88a8 for service-provider outer S-TAG.
+[[IEEE 802.1ad]] introduced the concept of double tagging. Double tagging can be useful for [[Internet service provider]]s (ISPs), allowing them to use their VLANs internally while carrying traffic from clients that is already VLAN tagged.  The outer (next to source MAC and representing ISP VLAN) S-TAG (service tag) comes first, followed by the inner C-TAG (customer tag).  In such cases, 802.1ad specifies a TPID of 0x88a8 for service-provider outer S-TAG.
-[[Image:TCPIP 802.1ad DoubleTag.jpg|center|thumb|950px|Insertion of 802.1ad DoubleTag in an Ethernet frame]]
+{{wide image|TCPIP 802.1ad DoubleTag.svg|1328px|Insertion of 802.1ad double tag in an Ethernet frame}}
+==Other protocols==
-Non-standard triple-tagging is also possible. The third tag of 4 bytes allows extended addressing and also a small hop-count. The 66-bit addressing plan now uses a fixed (non-stacking) QinQinQ format. The result is three 32-bit tags plus the 16-bit [[EtherType]]/Length for a total of 112 bits. The two 48-bit (MAC) address fields add another 96 bits. The total header is 208-bits compared to a 320-bit IPv6 header. The 66-bit addressing is 18+48. The 18-bits are encoded 6-bits per 32-bit tag in the 12-bit VID fields. The 16-bit [[EtherType]]/Length field can contain the Payload Size or an [[EtherType]] for Payloads that contain their own Length, such as IPv4.
+IEEE 802.1Q defines the [[Multiple VLAN Registration Protocol]] (MVRP), an application of the [[Multiple Registration Protocol]], allowing bridges to negotiate the set of VLANs to be used over a specific link. MVRP replaced the slower [[GARP VLAN Registration Protocol]] (GVRP) in 2007 with the IEEE 802.1ak-2007 amendment.
+The 2003 revision of the standard was the first to include the [[Multiple Spanning Tree Protocol]] (MSTP) which was originally defined in [[IEEE 802.1s]].
-{| class="wikitable"
-|-
-! 16 bits
-! 3 bits
-! 1 bit
-! 12 bits
-|-
-| TPID0
-| PCP
-| DEI
-| VID0
-|-
-| TPID1
-| CONTENT RATING
-| DEI
-| VID1
-|-
-| TPID2
-| HOP
-| DEI
-| VID2
-|}
-The contents of TPID0+TPID1+TPID2 contain the 48-bit MAC Address of the Source Device.
-==Trunk ports and the native VLAN==
-The terminology of ''trunk ports'' and ''native VLAN''s is non-standard.  Annex D to the 1998 802.1Q standard uses the concept of trunk links, but the current standard does not use the terms "trunk" or "native."
-Some vendors (most notably [[Cisco]]) use the concepts of a) trunk ports and b) native VLAN. The proprietary term ''native VLAN'' is similar to the 802.1Q ''PVID'' (port VLAN Identifier), which is used "to associate a VID with untagged and priority-tagged received frames." A ''trunk port'' can refer a port that sends and receives tagged frames on all VLANs, except the native VLAN, if one is configured. The term ''trunk'' may also be used to refer to a connection using [[link aggregation]].
-Frames belonging to the native VLAN do not carry VLAN tags when sent over the trunk. Conversely, if an untagged frame is received on a trunk port, the frame is associated with the native VLAN configured on that port.
-For example, if an 802.1Q port has VLANs 2, 3 and 4 assigned to it, with VLAN 2 being the native VLAN, frames on VLAN 2 that are sent from the aforementioned port are not given an 802.1Q header (i.e. they are plain Ethernet frames). Frames that are received on that port and have no 802.1Q header are assigned to VLAN 2. Tagging of frames sent to or received from VLANs 3 & 4 is the same as if no native VLAN had been configured – all frames on those VLANs must carry tags to identify their VLAN membership.
-Note that unexpected results may occur if the native VLAN configuration is not the same on all sending and receiving ports on a link. Continuing the above example, if VLAN 2 is not configured as the native VLAN on some other 802.1Q port, that port will send tagged frames on VLAN 2. When the local port, on which VLAN 2 is configured as the native VLAN, receives these unexpectedly tagged frames, it will still assign them to VLAN 2, but it will send only untagged frames for VLAN 2. On receipt, the distant port will either associate the untagged frames with a different VLAN ID (the one locally configured as the native VLAN) or it will discard the untagged frames if it has no native VLAN configured. (Symmetrically, this remote port will send only untagged frames on its configured native VLAN, which will be associated with a different VLAN ID by the local port.)
-==Multiple VLAN Registration Protocol==
-In addition, IEEE 802.1Q defines the [[Multiple VLAN Registration Protocol]] (MVRP), an application of the [[Multiple Registration Protocol]], allowing bridges to negotiate the set of VLANs to be used over a specific link.
-MVRP replaced the slower [[GARP VLAN Registration Protocol]] (GVRP) in 2007 with the IEEE 802.1ak-2007 amendment.
-==Multiple Spanning Tree Protocol==
-The 2003 revision of the standard included the [[Multiple Spanning Tree Protocol]] (MSTP) which was originally defined in [[IEEE 802.1s]].
-==Notes==
-{{reflist|group=note}}
 ==See also==
+* [[Cisco Inter-Switch Link]] (ISL), an older Cisco proprietary VLAN management protocol
+* [[Dynamic Trunking Protocol]] (DTP), a Cisco proprietary protocol to negotiate trunking between two VLAN-aware devices
+* [[Time Sensitive Networking]] (TSN), a suite of enhancements to 802.1Q for realtime and time-critical data streaming
 * [[VLAN Trunking Protocol]] (VTP), a Cisco proprietary VLAN management protocol
-* [[Cisco Inter-Switch Link]] (ISL), an older VLAN trunking protocol that is proprietary to [[Cisco]]
-* [[Dynamic Trunking Protocol]] (DTP), another Cisco proprietary networking protocol.
-==Sources==
+==Notes==
+{{notelist}}
-* {{Cite book|title=IEEE Std. 802.1Q-2003, Virtual Bridged Local Area Networks|isbn=0-7381-3663-8|url=http://standards.ieee.org/getieee802/download/802.1Q-2003.pdf|format=PDF; 3.5&nbsp;MiB}}
-* {{Cite book|title=IEEE Std. 802.1Q-2005, Virtual Bridged Local Area Networks|isbn=0-7381-3662-X|url=http://standards.ieee.org/getieee802/download/802.1Q-2005.pdf|format=PDF; 2.3&nbsp;MiB}}
-* {{Cite book|title=IEEE Std. 802.1Q-2011, Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks|isbn=978-0-7381-6708-4|url=http://standards.ieee.org/getieee802/download/802.1Q-2011.pdf|format=PDF; 6.0&nbsp;MiB}}
-* [http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094665.shtml ISL & 802.1q Frame Formats]
 ==References==
 {{reflist}}
-==External links==
+==Sources==
+* {{Citation |title=IEEE Std. 802.1Q-1998, Virtual Bridged Local Area Networks |doi=10.1109/IEEESTD.1999.89204 |isbn=0-7381-1537-1}}
+* {{Citation |title=IEEE Std. 802.1Q-2003, Virtual Bridged Local Area Networks|doi=10.1109/IEEESTD.2003.94280 |isbn=0-7381-3663-8|year = 2003}}
+* {{Citation |title=IEEE Std. 802.1Q-2005, Virtual Bridged Local Area Networks|doi=10.1109/IEEESTD.2006.216285 |isbn=0-7381-3662-X}}
+* {{Citation |title=IEEE Std. 802.1Q-2011, Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks|doi=10.1109/IEEESTD.2011.6009146 |isbn=978-0-7381-6708-4 }}
+* {{Citation |title=IEEE Std. 802.1BR-2012, Virtual Bridged Local Area Networks—Bridge Port Extension  |doi=10.1109/IEEESTD.2012.6239543 |isbn=978-0-7381-7281-1}}
+* {{Citation |title=IEEE Std. 802.1Q-2014, Bridges and Bridged Networks|doi=10.1109/IEEESTD.2014.6991462|isbn=978-0-7381-9433-2}}
+** {{Citation |title=IEEE Std. 802.1Q-2014/Cor 1-2015, Corrigendum 1: Technical and editorial corrections |doi=10.1109/IEEESTD.2016.7374647 |isbn=978-1-5044-0112-8}}
+* {{cite web|url=https://www.cisco.com/c/en/us/support/docs/lan-switching/8021q/17056-741-4.html|title=Inter-Switch Link and IEEE 802.1Q Frame Format|publisher=[[Cisco Systems]]|access-date=2019-01-10}}
 {{IEEE standards}}
@@ Line 115: / Line 81: @@
 [[Category:IEEE 802]]
 [[Category:Ethernet standards]]
+[[Category:Link protocols]]