Extreme Networks ExtremeWare XOS 11.3, Manual

Page: 148 / 698

Link Layer Discovery Protocol
ExtremeWare XOS 11.3 Concepts Guide
148
You configure LLDP per port, and each port can store received information for a maximum of four
neighbors.
NOTE
LLDP runs with load sharing.
LLDP Messages
You configure the device to transmit messages, to receive messages, or both. This section covers the
following topics:
●
LLDP Packets on page 148
●
Transmitting LLDP Messages on page 149
●
Receiving LLDP Messages on page 149
LLDP Packets
LLDP is enabled and configured per port.
Multiple advertisements messages (or TLVs) are transmitted in one LAN packet, the LLDPDU
(
Figure 4 ). The LLDP packet contains the destination multicast address, the source MAC address, the
LLDP EtherType, the LLDPDU data, and a frame check sequence (FCS). The LLDP multicast address is
defined as 01:80:C2:00:00:0E, and the EtherType is defined as 0x88CC.
Figure 4: LLDP packet format
The following characteristics apply to LLDP packets:
●
They are IEEE 802.3 Ethernet frames.
●
The frames are sent as untagged frames.
●
The frames are sent with a link-local-assigned multicast address as destination address.
●
The Spanning Tree Protocol (STP) state of the port does not affect the transmission of LLDP frames.
The length of the packet cannot exceed 1500 bytes. As you add TLVs, you increase the length of the
LLDP frame. Once you reach 1500 bytes, the remaining TLVs are dropped. Extreme Networks
recommends that you advertise information regarding only one or two VLANs on the LLDP port, to
avoid dropped TLVs. If the system drops TLVs because of exceeded length, the system logs a message
to the EMS and the
show lldp statistics
commands shows this information under the
Tx Length
Exceeded
field.
LLDP_Multicast
Address
Source MAC
Address
88-CC LLDPDU
Data + Pad Ethertype SA DA
1500 2 4 Octets 6 6
FCS
XOS005