2018-07-19-lldp协议笔记

lldpd代码中编译会生成server端即lldpd。还有一个client端，名为lldpcli。

可以通过lldpcli来配置lldpd。比如下面这些测试命令，具体可以man一下：

lldpcli show configuration
lldpcli show statistics
lldpcli show statistics ports eth0
lldpcli show statistics ports wlan0

sudo lldpcli configure system description "my little server"
sudo lldpcli unconfigure system description

sudo lldpcli pause
sudo lldpcli resume

lldpcli show neighbors ports eth0

lldpd启动的时候有对应的配置文件，默认为 /etc/lldpd.conf 和 /etc/lldpd.d 目录下的所有以 .conf 结尾的文件。这些配置文件其实 就是lldpcli命令的集合。每行就是一行lldpcli命令。比如当前我测试的配 置文件可以这样写：

# You can put lldpd configuration snippets into this directory.
# Upon start, lldpd will read each files in this directory and execute content
# as if they were passed as arguments to lldpcli
#
# Files should be suffixed by .conf and have content like:
#   configure system description 'my little server'
#
# See lldpcli(8) for more details.

configure system description 'my little server'

LLDP information is sent by devices from each of their interfaces at
a fixed interval, in the form of an Ethernet frame. Each frame
contains one LLDP Data Unit (LLDPDU). Each LLDPDU is a sequence of
type-length-value (TLV) structures.

LLDP消息定时从设备的每个网卡中发出。消息都是以太网的frame形式。每个
frame包含了一个LLDP的数据单元。每个LLDP数据单元是多个TLV结构的组合。

The Ethernet frame used in LLDP has its destination MAC address
typically set to a special multicast address that 802.1D-compliant
bridges do not forward.^[note 1] Other multicast and unicast
destination addresses are permitted. The EtherType field is set to
0x88cc.

目的地址一般都是特定的多播地址，以保证802.1D的网桥不会转发这些报文。其
它的多播或都单播地址都是允许的。EtheType这个区域填0x88cc。

TLV的结构如下：

结构化的TLV可以克服兼容性问题，高级版本中可能加入新type的TLV。低版本 碰到不认识的type后，直接跳过对应长度处理下一个TLV即可。