lldpd is a daemon able to receive and send LLDP frames. The Link Layer Discovery Protocol is a vendor-neutral Layer 2 protocol that allows a network device to advertise its identity and capabilities on the local network.
lldpd also implements an SNMP subagent using AgentX protocol to interface to a regular SNMP agent like Net-SNMP. To enable this subagent, you need something like that in your snmpd.conf(5):
This daemon implements both reception and sending. It will collect various information to send LLDP frames to all Ethernet interfaces, including management address, speed and VLAN names.
The options are as follows:
Do not daemonize. If this option is specified, lldpd will run in the foreground. When specified one more time, lldpd will not log to syslog but only to stderr. Then, this option can be specified many times to increase verbosity. When specified four times, debug logs will be enabled. They can be filtered with -D flag.
- -D debug
This option allows the user to filter out debugging information by specifying allowed tokens. This option can be repeated several times to allow several tokens. This option must be combined with the -d flag to have some effect. Only debugging logs can be filtered. Here is a list of allowed tokens with their description:
Discovery of local interfaces.
LLDP PDU encoding/decoding.
EDP PDU encoding/decoding.
CDP/FDP PDU encoding/decoding.
SONMP PDU encoding/decoding.
Events management but for logs generated by libevent.
Retrieval of information related to the local chassis.
Management of the Unix control socket.
SNMP subagent but for logs generated by NetSNMP.
Generic PDU decoding.
Low-level serialization mechanisms.
Low-level allocation mechanisms.
Sending PDU to some interface.
Receiving PDU from some interface.
Smart filtering of different protocols on the same port.
- -p pidfile
Use the provided PID file to record lldpd PID instead of /var/run/lldpd.pid.
Disable advertising of kernel release, version and machine. Kernel name (ie: Linux) will still be shared, and Inventory software version will be set to 'Unknown'.
- -S description
Override system description with the provided description. The default description is the kernel name, the node name, the kernel version, the build date and the architecture (except if you use the -k flag described above).
- -P platform
Override the CDP platform name with the provided value. The default description is the kernel name (Linux).
Enable SNMP subagent. With this option, lldpd will enable an SNMP subagent using AgentX protocol. This allows you to get information about local system and remote systems through SNMP.
- -X socket
Enable SNMP subagent using the specified socket. lldpd will enable an SNMP subagent using AgentX protocol for the given socket. This option implies the previous one. The default socket is usually /var/agentx/master. You can specify a socket like tcp:127.0.0.1:705 for example. Since the process that will open this socket is enclosed in a chroot, you need to specify an IP address (not a hostname) when using a TCP or UDP socket.
Enable the support of CDP protocol to deal with Cisco routers that do not speak LLDP. If repeated, CDPv1 packets will be sent even when there is no CDP peer detected. If repeated once again, CDPv2 packets will be sent even when there is no CDP peer detected. If repeated once again (i.e.
-cccc), CDPv1 will be disabled and CDPv2 will be enabled. If repeated once again (i.e.
-ccccc), CDPv1 will be disabled and CDPv2 will be forced.
Enable the support of FDP protocol to deal with Foundry routers that do not speak LLDP. If repeated, FDP packets will be sent even when there is no FDP peer detected.
Enable the support of SONMP protocol to deal with Nortel routers and switches that do not speak LLDP. If repeated, SONMP packets will be sent even when there is no SONMP peer detected.
Enable the support of EDP protocol to deal with Extreme routers and switches that do not speak LLDP. If repeated, EDP packets will be sent even when there is no EDP peer detected.
Force to send LLDP packets even when there is no LLDP peer detected but there is a peer speaking another protocol detected. By default, LLDP packets are sent when there is a peer speaking LLDP detected or when there is no peer at all. If repeated, LLDP is disabled.
Receive-only mode. With this switch, lldpd will not send any frame. It will only listen to neighbors.
- -m management
Specify the management addresses of this system. As for interfaces (described below), this option can use wildcards and inversions. Without this option, the first IPv4 and the first IPv6 are used. If an exact IP address is provided, it is used as a management address without any check. If only negative patterns are provided, only one IPv4 and one IPv6 addresses are chosen. Otherwise, many of them can be selected. If you want to blacklist IPv6 addresses, you can use !*:*.
- -u file
Specify the Unix-domain socket used for communication with lldpctl(8).
- -I interfaces
Specify which interface to listen and send LLDPDU to. Without this option, lldpd will use all available physical interfaces. This option can use wildcards. Several interfaces can be specified separated by commas. It is also possible to blacklist an interface by suffixing it with an exclamation mark. It is possible to whitelist an interface by suffixing it with two exclamation marks. A whitelisted interface beats a blacklisted interface which beats a simple matched interface. For example, with eth*,!eth1,!eth2 lldpd will only use interfaces starting by eth with the exception of eth1 and eth2. While with *,!eth*,!!eth1 lldpd will use all interfaces, except interfaces starting by eth with the exception of eth1. When an exact match is found, it will circumvent some tests. For example, if eth0.12 is specified, it will be accepted even if this is a VLAN interface.
- -C interfaces
Specify which interfaces to use for computing chassis ID. Without this option, all interfaces are considered. lldpd will take the first MAC address from all the considered interfaces to compute the chassis ID. The logic of this option is the same as for -I flag: you can exclude interfaces with an exclamation mark and use globbing to specify several interfaces. If all interfaces are blacklisted (with !*), the system name is used as a chassis ID instead.
- -M class
Enable emission of LLDP-MED frame. Depending on the selected class, the standard defines which set of TLV should be transmitted. See section 10.2.1. Some devices may be strict about this aspect. The class should be one of the following value:
Generic Endpoint (Class I)
Media Endpoint (Class II). In this case, the standard requires to define at least one network policy through lldpcli.
Communication Device Endpoints (Class III). In this case, the standard requires to define at least one network policy through lldpcli.
Network Connectivity Device
Disable LLDP-MED inventory TLV transmission. lldpd will still receive (and publish using SNMP if enabled) those LLDP-MED TLV but will not send them. Use this option if you don't want to transmit sensible information like serial numbers.
- -H hide
Filter neighbors. See section Filtering Neighbors for details.
- -L lldpcli
Provide an alternative path to lldpcli for configuration. If empty, does not use lldpcli for configuration.
- -O configfile
Override default configuration locations processed by lldpcli at start. If a directory is provided, each file contained in it will be read if ending by .conf. Order is alphabetical.
Show lldpd version. When repeated, show more build information.
In a heterogeneous network, you may see several different hosts on the same port, even if there is only one physically plugged to this port. For example, if you have a Nortel switch running LLDP which is plugged to a Cisco switch running CDP and your host is plugged to the Cisco switch, you will see the Nortel switch as well because LLDP frames are forwarded by the Cisco switch. This may not be what you want. The -H hide parameter will allow you to tell lldpd to discard some frames that it receives and to avoid to send some other frames.
Incoming filtering and outgoing filtering are unrelated. Incoming filtering will hide some remote ports to get you a chance to know exactly what equipment is on the other side of the network cable. Outgoing filtering will avoid to use some protocols to avoid flooding your network with a protocol that is not handled by the nearest equipment. Keep in mind that even without filtering, lldpd will speak protocols for which at least one frame has been received and LLDP otherwise (there are other options to change this behaviour, for example
When enabling incoming filtering, lldpd will try to select one protocol and filter out neighbors using other protocols. To select this protocol, the rule is to take the less used protocol. If on one port, you get 12 CDP neighbors and 1 LLDP neighbor, this mean that the remote switch speaks LLDP and does not filter CDP. Therefore, we select LLDP. When enabling outgoing filtering, lldpd will also try to select one protocol and only speaks this protocol. The filtering is done per port. Each port may select a different protocol.
There are two additional criteria when enabling filtering: allowing one or several protocols to be selected (in case of a tie) and allowing one or several neighbors to be selected. Even when allowing several protocols, the rule of selecting the protocols with the less neighbors still apply. If lldpd selects LLDP and CDP, this means they have the same number of neighbors. The selection of the neighbor is random. Incoming filtering will select a set of neighbors to be displayed while outgoing filtering will use the selected set of neighbors to decide which protocols to use: if a selected neighbor speaks LLDP and another one CDP, lldpd will speak both CDP and LLDP on this port.
There are some corner cases. A typical example is a switch speaking two protocols (CDP and LLDP for example). You want to get the information from the best protocol but you want to speak both protocols because some tools use the CDP table and some other the LLDP table.
The table below summarize all accepted values for the -H hide parameter. The default value is 15 which corresponds to the corner case described above. The filter column means that filtering is enabled. The 1proto column tells that only one protocol will be kept. The 1neigh column tells that only one neighbor will be kept.
Unix-domain socket used for communication with lldpctl(8).
Configuration file for lldpd. Commands in this files are executed by lldpcli(8) at start.
Directory containing configuration files whose commands are executed by lldpcli(8) at start.
lldpctl(8), lldpcli(8), snmpd(8)
The lldpd program is inspired from a preliminary work of Reyk Floeter.
The lldpd program was written by Pierre-Yves Ritschard ⟨email@example.com⟩, and Vincent Bernat ⟨firstname.lastname@example.org⟩.