Namespace inet

Ieee8021qTagEpdHeader

class

This chunk represents an IEEE 802.1Q tag header without the TPID field and with the following EtherType Protocol Discrimination (EPD) in the packet. The reason for this shifted representation is that it's often easier to look at a 802.1Q tag this way during processing. The typeOrLength field contains the EtherType as defined in the section 9.2 EtherTypes of the IEEE Std 802-2014, IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture.

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-----+-+-----------------------+-------------------------------+ | PCP |D| VLAN ID | EtherType/Length | +-----+-+-----------------------+-------------------------------+

Extends

Name	Type	Description
FieldsChunk	(unknown -- not in documented files)

Fields

Name	Type	Description
chunkLength
pcp	uint8_t	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. Priority order lowest to highest: 1 0 2 3 4 5 6 7
dei	bool	Drop Eligible Indicator (DEI): a 1-bit field. May be used separately or in conjunction with PCP to indicate frames eligible to be dropped in the presence of congestion.
vid	uint16_t	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.
typeOrLength	uint16_t	This field contains the 16 bits immediately following the 802.1Q tag header TCI field: I. Tag Protocol Identifier (TPID) of the following tag header: 16-bit field specifying an EtherType value that is used to identify the frame as a tagged frame and to select the correct tag decoding functions. II. This two-octet field takes one of two meanings, depending on its numeric value. For numerical evaluation, the first octet is the most significant octet of this field. a) If the value of this field is less than or equal to 1500 decimal (05DC hexadecimal), then the Length/ Type field indicates the number of MAC client data octets contained in the subsequent MAC Client Data field of the basic frame (Length interpretation). b) If the value of this field is greater than or equal to 1536 decimal (0600 hexadecimal), then the Length/Type field indicates the Ethertype of the MAC client protocol (Type interpretation).

Packet operations (observed)

action	module
insertAtFront	Ieee8021qTagEpdHeaderInserter
peekAtFront	Ieee8021qTagEpdHeaderChecker
popAtFront	Ieee8021qTagEpdHeaderChecker

Source code

//
// This chunk represents an IEEE 802.1Q tag header without the TPID field and
// with the following EtherType Protocol Discrimination (EPD) in the packet.
// The reason for this shifted representation is that it's often easier to look
// at a 802.1Q tag this way during processing. The typeOrLength field contains
// the EtherType as defined in the section 9.2 EtherTypes of the IEEE Std 802-2014,
// IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture.
//
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-----+-+-----------------------+-------------------------------+
// | PCP |D| VLAN ID | EtherType/Length |
// +-----+-+-----------------------+-------------------------------+
//
class Ieee8021qTagEpdHeader extends FieldsChunk
{
chunkLength = B(4);
uint8_t pcp; // 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.
// Priority order lowest to highest: 1 0 2 3 4 5 6 7
bool dei; // Drop Eligible Indicator (DEI): a 1-bit field. May be used separately or in conjunction with PCP to indicate frames eligible to be dropped in the presence of congestion.
uint16_t vid; // 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.
uint16_t typeOrLength; // This field contains the 16 bits immediately following the 802.1Q tag header TCI field:
// I. Tag Protocol Identifier (TPID) of the following tag header: 16-bit field specifying an EtherType value that is used to identify the frame as a tagged frame and to select the correct tag decoding functions.
// II. This two-octet field takes one of two meanings, depending on its numeric value. For numerical evaluation,
// the first octet is the most significant octet of this field.
// a) If the value of this field is less than or equal to 1500 decimal (05DC hexadecimal), then the Length/
// Type field indicates the number of MAC client data octets contained in the subsequent MAC Client
// Data field of the basic frame (Length interpretation).
// b) If the value of this field is greater than or equal to 1536 decimal (0600 hexadecimal), then the
// Length/Type field indicates the Ethertype of the MAC client protocol (Type interpretation).
}

File: src/inet/linklayer/ieee8021q/Ieee8021qTagHeader.msg