liblldp_clif-vdp22 man page

clif_vsi,clif_vsievt,clif_vsiwait — Manipulate VDP IEEE 802.1 Ratified Standard Assocications


#include "include/clif.h"

int clif_vsi(struct clif *connp, char *ifname, unsigned int tlvid, char *cmd, char *reply, size_t *reply_len);

int clif_vsievt(struct clif *connp, char *reply, size_t *reply_len, int wait);

int clif_vsiwait(struct clif *connp, char *ifname, unsigned int tlvid, char *cmd, char *reply, size_t *reply_len, int wait);


The Virtual station interface Discovery Protocol is a protocol to manage the association and deassociation of virtual machine network interfaces (VSIs) between the station and an adjacent switch. VDP is typically used with the local switch in VEPA mode and the adjacent switch port in reflective relay (also called haripin) mode. This allows all traffic to be sent to the switch for processing. Reflective relay mode is negotiated via EVB TLVs (see lldptool-evb).

This man pages describes the IEEE 802.1 Qbg ratified standard dated from July 5th, 2012. This differs from the draft 0.2 which is implemented as well, see lldptool-vdp(8). For clarification in this man page the version complying to the ratified standard is called VDP22 and the version complying to the draft 0.2 is called VDP.

VSI Parameter

Each VDP22 TLVs contains a command mode, manager identifier, type identifier, type identifier version, VSI instance identifier, migiration hints and filter information. The fields are explained next:

Command Mode:

The command mode determines the type  of the VSI association to be established. It is an ascii string can be one of:


Create an VSI association.


Create an VSI preassociation. The association is only announced to the switch.


Create an VSI preassociation. The association is only announced to the switch and the  switch should reserve the resources.


Delete an VSI association.

Other strings are not recognized and return an error.

Manager identifier:

The manager identifier is a string of up to 16 alphanumeric characters. It can also be an UUID according to RFC 4122 with optional dashes in between.

Type Identifier:

The type identifier is a number in the range of 0 to 2^24 - 1.

Type Identifier Version:

The type identifer version is a number in the range of 0 to 255.

VSI Instance Identifier:

The VSI instance identifier is an UUID according to RFC 4122 with optional dashes in between.

Migration Hints:

The migiration hints is a string aiding in  migration of virtual machines:


No hints available.


The virtual machine is migriting away.


The virtual machine is migriting to.

Filter Information Data:

The filter information data can be supplied in four different formats:

vlan (1)

A vlan number only, also known as filter information format 1. The vlan identifier is a number in the range of 1 to 2^16 - 1. The high order 4 bits are used as quality of service bits. The vlan identifier can be zero, a vlan identifier is then selected by the switch. Refer to IEEE 802.1 Qbg ratified standard for details.

vlan-mac (2)

A vlan number and MAC address delimited by a slash ('-'), also known as filter information format 2. The MAC address is specified in the format xx:xx:xx:xx:xx:xx. The colons are mandatory. For vlan details see (1).

vlan-mac-group (4)

A vlan number, MAC address and group identifier,  each delimited by a slash ('-'), also known as filter information format 4. The group identifier is a 32 bit number. For vlan and MAC address details see (1) and (2).

vlan--group (3)

A vlan number and group identifier,  delimited by two slashes ('--'), also known as filter information format 3. For vlan and group details see (1) and (4).

Several filter information fields can be supplied. The have to be separated by comma (',') and must be of the same format.


This function sends a VSI command to lldpad(8). Parameter connp is a pointer to the connection information. This information is obtained by calling clif_open and clif_attach. Parameter ifname is the interface name lldpad (8) uses to send the VSI data. Paramenter tlvid is the number of the VSI request. Valid numbers are 1 (for Preassociation), 2 (for Preassociation with resource reservation) and 3 (for association), 4 (for Deassociation). Parameter cmd points to a character string containing the VSI command. The layout of the VSI command has been explained above. All VSI fields are concatenated together and separated to by commas (',') to form one large string. Parameter reply is a pointer to a character array to receive the reply from lldpad(8). Parameter reply_len holds the maximum number of characters available in the array  pointed to by reply. On successful return of the call, reply_len contains the number of characters stored by lldpad(8) as the response of the command.

The functions returns zero on success and the reply and reply_len parameters are set. Reply_len contains the number of bytes in the memory area pointed to by reply. Reply contains the same information and format as the cmd parameter with several exceptions:

Command Mode:

This field should be the same as in cmd parameter. If it contains deassoc then the command failed and the field ,igration hints contains an error numner.

Migration Hints:

This field contains the error number on why the command was not accepted by lldpad(8). This command failed to pass the lldpad(8) sanity checks. Note that the command was not even sent to the switch for processing. If no error occured, this field contains a dash ('-').

Filter Information Data:

If parameter cmd contained the a vlan identifier of value zero or a group identifier the switch is allowed to assign a  different vlan identifier, which is saved and returned in the reply buffer.

All the other fields should be returned unchanged.

The function returns zero when the command was accepted by lldpad(8). Otherwise it returns a positive number on why the command was not accepted.


After a successful return of clif_vsi, lldpad(8) has sent the command to the switch and waits for a response from the switch. The switch can still deny the request. Function clif_vsievt waits for parameter wait seconds for a reply from lldpad(8). Parameter reply_len specifies the maximum buffer size pointed to by parameter reply. If a response was received in wait seconds, the function returns zero and sets reply_len to the number of bytes received and reply contains the response. The format is the same as in clif_vsi.

Since the switch can disassociate an established VSI association any time, it is recommended to call clif_vsievt periodically to check for disassociate event messages from lldpad(8).

If the functions fails it returns


No attachment to lldpad(8) or wait is negative.


No message was received during the wait.


Message was received but could not be read.


Message was received but was not an event message.


This function combines clif_vsi and clif_vsievt into one function call.

Example & Usage

Code sample to create an VSI association on eth0:

int rc;
size_t ok_len = sizeof(ok);
char *cmd ="assoc,blabla,12345,1,00000000-1111-2222-3333-aabbccddeeff"
struct clif *tool_conn = clif_open();

if (!tool_conn) {
	 fprintf(stderr, "%s can not open connection to LLDPAD0,

/* Attach to the vdp22 module */
if (clif_attach(tool_conn, "80c4")) {
	fprintf(stderr, "%s can not attach to LLDPAD0, progname);
	tool_conn = NULL;

rc = clif_vsiwait(tool_conn, "eth0", 1, cmd, ok, &ok_len, 5);
if (!rc) {
	/* Parse the response in ok */

See Also

lldptool-vdp(8), lldptool-evb(8), lldptool-evb22(8), lldptool(8), lldpad(8)
IEEE 802.1Qbg (


Thomas Richter


February 2014 open-lldp Linux