Network protocol learning -- lldp protocol learning

brief introduction

LLDP（Link Layer Discovery Protocol） Link Layer Discovery Protocol , The main purpose of protocol design is to announce information , Further, information about network topology and related management configuration can be obtained . This is a layer 2 protocol , It provides a standard way to discover the link connection relationship , So that a device connected to the network can transfer its main capabilities , Management address , Device identifier , Information such as interface identification is organized into different groups TLV（Type/Length/Value）, And it's packaged in LLDPDU(Link Layer Discovery Protocol Data Unit, Link layer discovery protocol data unit ) in , Sent to other devices connected to the same local area network .
We usually use LLDP Protocol to view , Which port of the switch is our device plugged into …… The colorful world , It's not easy to understand

working principle

LLDP agreement , In essence, it is an information discovery and Notification Protocol . In the equipment LLDP The entity maintains two MIB(Management Information Base) library , One is local system MIB, Used to maintain relevant information of local equipment ; One is remote system MIB, It is used to maintain the relevant information of the remote device .
LLDP By relating to MIB Library interaction to initialize and maintain local MIB, And announce it through local relevant information , Receive notification information from other devices at the same time , And update it to remote system MIB. In this way , You can get the neighbor information of the device . Users can use these two MIB Library to complete their own needs .
LLDP Message format
Packaging has a LLDPDU (lldp Protocol data unit of the protocol ) Message of , be called LLDP frame . There are two packaging formats ：Ethernet II and SNAP(Subnetwork Access Protocol, Subnet access protocol ). What we often use is Ethernet frame , So let's focus on... Based Ethernet II Of LLDP message .

Field	meaning
Destination MAC address	Purpose MAC Address , For fixed multicast MAC Address 0x0180-C200-000E.
Source MAC address	Source MAC Address , Is the port MAC Address or device bridge MAC Address （ If there is a port address, use port MAC Address , Otherwise, use the equipment bridge MAC Address ）
Type	Message type , Fixed for 0x88CC.
Data	data , by LLDPDU
FCS	Frame check sequence

among LLDPDU Is encapsulated in LLDP The data unit of the message data part . Just making up LLDPDU Before , The device will first encapsulate the local relevant information into TLV, Then add more TLV Combine into one LLDPDU, Packaged in LLDP The data part of the message is transmitted .
LLDPDU Format

Every LLDPDU You can carry at most 28 Kind of TLV,LLDP Message reservation ,Chasis ID TLV, Port ID TLV, TTL TLV and End TLV These four must be carried , The rest TLV It's optional .
Here is a basic TLV Of list:

TLV Format
TLV It's the composition LLDPDU Unit of , The basic format is as follows ：

among TLV Type and TLV Info String Length be called TLV Of header, The rest of the message is TLV The data part of , according to TLV Length Value of field , You can get the specific TLV data .
among TLV Type The definition and distribution of are as follows ：

among type 0-8 Basic TLV aggregate , among Mandatory Is necessary TLV, Must be included in lldp In the data message .
The above is from cloudman《 How to use LLDP Get network topology ？》

Method

There are two ways to get LLDP Information .
One is lldpad, The other is lldpd.
First check the network card information .

[[email protected] ~]# lspci | grep Eth 
1a:00.0 Ethernet controller: Intel Corporation Ethernet Connection X722 for 10GbE SFP+ (rev 09)
1a:00.1 Ethernet controller: Intel Corporation Ethernet Connection X722 for 10GbE SFP+ (rev 09)
1a:00.2 Ethernet controller: Intel Corporation Ethernet Connection X722 for 1GbE (rev 09)
1a:00.3 Ethernet controller: Intel Corporation Ethernet Connection X722 for 1GbE (rev 09)

When the network card is X722 perhaps 711 Type , Need a common configuration , Turn off the network card itself lldp

echo 'lldp stop' > /sys/kernel/debug/i40e/0000\:1a\:00.2/command

Just do it .

Then introduce two methods

lldpad

First installation
yum install lldpad

And then start the service
lldpad -d

Finally, configure and display

lldptool set-lldp -i eno3 adminStatus=rxtx
lldptool -T -i eno3 -V sysName enableTx=yes
lldptool -T -i eno3 -V portDesc enableTx=yes
lldptool -T -i eno3 -V sysDesc enableTx=yes
lldptool -T -i eno3 -V mngAddr enableTx=yes

Finally, check

[[email protected] ~]# lldptool -t -n -i eno3
Chassis ID TLV
        MAC: 5c:a7:21:b0:46:58
Port ID TLV
        Ifname: GigabitEthernet1/0/11
Time to Live TLV
        121
Port Description TLV
        GigabitEthernet1/0/11 Interface
System Name TLV
        H3C
System Description TLV
        H3C Comware Platform Software, Software Version 7.1.070, Release 6318P01
H3C S5130S-28TP-EI
Copyright (c) 2004-2020 New H3C Technologies Co., Ltd. All rights reserved.
System Capabilities TLV
        System capabilities:  Bridge, Router
        Enabled capabilities: Bridge, Router
Management Address TLV
        IPv4: 192.168.32.5
        Ifindex: 635
Port VLAN ID TLV
        PVID: 1
Link Aggregation TLV
        Aggregation capable
        Currently not aggregated
        Aggregated Port ID: 0
MAC/PHY Configuration Status TLV
        Auto-negotiation supported and enabled
        PMD auto-negotiation capabilities: 0x6c01
        MAU type: 1000 BaseTFD
Power via MDI TLV
        Bad Power Via MDI TLV: 0101011000000000
Maximum Frame Size TLV
        10240
End of LLDPDU TLV

You can see that the machine is plugged into the switch “GigabitEthernet1/0/11 Interface” On the mouth . Contains TLV That's a lot , What a naked child ----- What let you know .

lldpd

Install the software

yum install lldpd -y

Start the service

systemctl start lldpd.service

Call the command

[[email protected] ~]# lldpcli show neighbors
-------------------------------------------------------------------------------
LLDP neighbors:
-------------------------------------------------------------------------------
Interface:    eno3, via: LLDP, RID: 1, Time: 0 day, 00:00:51
  Chassis:     
    ChassisID:    mac 5c:a7:21:b0:46:58
    SysName:      H3C
    SysDescr:     H3C Comware Platform Software, Software Version 7.1.070, Release 6318P01
                  H3C S5130S-28TP-EI
                  Copyright (c) 2004-2020 New H3C Technologies Co., Ltd. All rights reserved.
    MgmtIP:       192.168.32.5
    Capability:   Bridge, on
    Capability:   Router, on
  Port:        
    PortID:       ifname GigabitEthernet1/0/11
    PortDescr:    GigabitEthernet1/0/11 Interface
    TTL:          121
-------------------------------------------------------------------------------

You can also see the connected network port , Switch information , Management port IP etc. .

C The method of language

You can also use socket Simulation mode , receive lldp agreement , The main function is

int  sock = socket(PF_PACKET, SOCK_RAW, htons(0x88CC));

The received Ethernet frame type is 0x88cc.

Source download

Conclusion

If it's true , That's really sinister