LLDP Neigbor Discovery

_get_lldp_data(self) is called to read LLDP Neigbor info. We read this from the SNMP LLDP-MIB lldpRemTable with entries located in lldpRemEntry at .1.0.8802.1.1.2.1.4.1.1

Entry Indexing

These lldpRemEntry items are indexed by <lldpRemTimeMark>.<lldpRemLocalPortNum>.<lldpRemIndex>

As seen in the LLDP-MIB:

lldpRemEntry:
INDEX {
        lldpRemTimeMark,
        lldpRemLocalPortNum,
        lldpRemIndex
    }

lldpRemLocalPortNum is of type LldpPortNumber, and identifies the port on which the remote system information is received.

Again, from the MIB:

LldpPortNumber ::=
    "Each port contained in the chassis (that is known to the
    LLDP agent) is uniquely identified by a port number.

    A port number has no mandatory relationship to an
    InterfaceIndex object (of the interfaces MIB, IETF RFC 2863).
    If the LLDP agent is a IEEE 802.1D, IEEE 802.1Q bridge, the
    LldpPortNumber will have the same value as the dot1dBasePort
    object (defined in IETF RFC 1493) associated corresponding
    bridge port.  If the system hosting LLDP agent is not an
    IEEE 802.1D or an IEEE 802.1Q bridge, the LldpPortNumber
    will have the same value as the corresponding interface's
    InterfaceIndex object.

    Port numbers should be in the range of 1 and 4096 since a
    particular port is also represented by the corresponding
    port number bit in LldpPortList."

This means that lldpRemLocalPortNum is the Q-BRIDGE <port-id>, mapped back to the ifIndex from MIB-II in self.qbridge_port_to_if_index[port_id]

If Q-BRIDGE is NOT implemented, <port-id> = ifIndex, ie without the mapping.

lldpRemTimeMark and lldpRemIndex are irrelevant for our needs, but the combination of all 3 indeces is used as the ‘key’ to storing the NeighborDevice() object on an Interface()

Entry Attributes

Each lldpRemEntry entry is a sequence of attributes, all indexed as described above. We read and store the following:

lldpRemPortId is lldpRemEntry.7 - a value describing the remote connected port name. Interpretation of this field depends on the value of lldpRemPortIdSubType.

lldpRemPortIdSubtype is lldpRemEntry.6 - a value indicating how the interpret lldpRemPortId. We think we can interpret these as strings:: LLDP_PORT_SUBTYPE_INTERFACE_ALIAS, LLDP_PORT_SUBTYPE_MAC_ADDRESS, LLDP_PORT_SUBTYPE_NETWORK_ADDRESS, LLDP_PORT_SUBTYPE_INTERFACE_NAME For all other values, we set the remote port name field to empty “”

lldpRemPortDesc is lldpRemEntry.8 - the remote port’s description

lldpRemSysName is lldpRemEntry.9 - the remote system name

lldpRemSysDesc is lldpRemEntry.10 - the remote system description, frequently the firmware version or OS info.

lldpRemSysCapEnabled is lldpRemEntry.12 - a bit-mapped field showing the current enabled capabilities of the remote device. E.g. wifi, telephone, router/switch, etc.

lldpRemChassisIdSubtype is lldpRemEntry.4 - what the chassis id means, ie how to interpret the data, eg as a string, ethernet address, ipv4/6 address.

lldpRemChassisId is lldpRemEntry.5 - the remote chassis id.(see above)

Attribute Parsing

Parsing is handled in switches/connect/snmp/connector.py, function _parse_mibs_lldp() around line 2500.

If we receive the following SNMP data:

..code-block:: text

.1.0.8802.1.1.2.1.4.1.1.8.405.12.1 = “Uplink Port”

We parse .1.0.8802.1.1.2.1.4.1.1.8 to be lldpRemPortDesc. This then gives an index of 405.12.1

Per the above, this means the interface <port_id> = 12, which can be mapped to an Interface(). For that interface, we can then set the NeighborDevice().port_descr = <return value> = “Uplink Port”

This parsing is implemented for all attributes listed above.

Management Address

We may be able to read a device management address from lldpRemManAddrIfSubtype (.1.0.8802.1.1.2.1.4.2.1.3), i.e. this is lldpRemManAddrEntry.3

This entry is parsed in _parse_mibs_lldp_management(). This OID returned is a long entry starting with lldpRemManAddrIfSubtype, followed by the 3 digits “lldp index”.

This lldp-index then is followed by the OID representation of the management IP address. This consists of <address-type>.<length>.<ip address in dotted-decimal format>, identical to how this is encoded in the ARP/ND tables at ipNetToPhysicalPhysAddress

Example:

We read the OID .1.0.8802.1.1.2.1.4.2.1.3.0.142.1.1.4.10.128.8.66 = 2

This is lldpRemManAddrIfSubtype . <0.142.1> . <1> . <4> . <10.128.8.66>

Ie. the device with lldp-index “0.142.1” has an IPv4 (1) address of length 4, and value “10.128.8.66”

We then set NeighborDevice().management_address and .management_address_type accordingly!