Network Note For Debug

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This is my network note which record different linux and debug command

Debug Using tool

Nmap port scan

Scan port can use either:

nc -vz: quick, lightweight probe (good for QA spot checks).
nmap: more detailed: can scan ranges, detect service versions, OS fingerprints, etc.

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nmap -Pn -p 21 172.21.201.16

Scan port option:

-Pn: don’t ping first (treat host as alive)
-p 21: scan only port 21

Netcat: scan and send traffic

The nc command allow you to debug like send a small traffic or scan port just like nmap

Scan if a port is open like nmap

Syntax: nc -vz ip-add port

-v: verbose
-z: just scan for listening service (don’t send data)

  • scan http
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nc -vz 172.21.201.250 8080
  • scan ftp
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nc -vz 172.21.201.250 21 #ftp

Output tells you if the port is open, closed, or filtered.

Send traffic

If DUT NOT support FTP related command, when you want to debug field side issue, to make sure traffic is working or not. You can only use http , or ftp related potocol to verify it. Since use remote like ssh to debug, so the only method is use the nc command to check traffic work or not under ssh.

If you want to verify traffic you have to first run nf command on local pc, and use tcpdump on field side ssh server to make sure you pass traffic really psss. I

Environment might look like this:

CPE(send traffic ex: nf) <——>(Lan) CPE (Wan)<——->Internet<——–>SSH field Router(tcpdump)

send http

Netcat will try to connect to host 172.21.201.250 on TCP port 8080

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nc 172.21.201.250 8080

If something is listening there (like a web server), the connection opens and anything you type will be sent to it.
If nothing is listening, you’ll get a timeout or connection refused, aslo mean netrwork unreachable

Send ftp

I can use this command below to make ftp connection

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nc Ftp-IPaddress 21

Run server as listen

  • Host 1 as listen server
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nc -l -p 9090

Listens on TCP port 8080.
Any client that connects can send/receive text.

  • Host 2 connect and send traffic
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nc <Host 1 IP> 9090

Quick file transer

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# on Receiver
nc -l -p 9000 > file.txt
# On sender:
nc <IP> 9000 < file.txt

tcpdump capture packet

In the top we use the nc command to send traffic, you also need to see the packet flow to make sure it really pass.

TCP 3 hand shake: syn->syn/ack -> Ack

If the traffic really make connection success then your packet should see the three flow

Capture packet for 21 ftp

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tcpdump -i eth4_v0 -nn port 21

Save traffic as packet

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tcpdump -i eth1.1035 -s 0 -w /tmp/ap.pcap &

tcpdump -i br-lan.960 -s 0 -w /tmp/AP_vlan960.pcap &

tcpdump -i rax0 -s 0 -w /tmp/sta.pcap &

Curl

Some DuT uses a light weight curl, which mean not support ftp or other feature. You can use curl --version to check.

This mean even though you don;t have a ftp installed in your system, but you can use curl, however this version curl don’t even support ftp.

To use ftp right now is you need to use the nf command

Curl webpage

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curl http://localhost/test1234/test.html

Fetch a file and store in a local file [-o option]

Syntax: curl -o [name of output] [url name]

o: is rename another file

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curl -o test.html http://127.0.0.1/tt.html #download and rename to test.html
curl -o filename.tar.gz http://filename-4.0.1.tar.gz # download and rename

Curl ftp connection

  • username and password connection
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curl -u user:pass ftp://192.168.1.163/
  • Download anonymous account
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curl -u anonymous:anonymous -O http://192.168.3.181/iperfcommand.txt
curl -u anonymous:anonymous -O ftp://192.168.3.181/iperfcommand.txt
  • upload
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curl -u anonymous:anonymous -T [file name] [url]
curl -u anonymous:anonymous -T test.html  ftp://192.168.3.181/
multiple file upload:
curl -u anonymous:anonymous -T {file1,file2}  ftp://192.168.3.181/

tftp

  • linux or console
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#upload to lcoal side from console
tftp -l wan0-cap.pcap -p 192.168.5.104
  • window tftp might look different

Syntax: tftp -i [IP ADD] [PUT|GET][ FILE NAME]

-g: get file
-r: remote
-p: put file
-l: loca

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#download
tftp -i 192.168.1.55 PUT TLV43.cfg
#upload
tftp -i 192.168.1.55 GET TLV43.cfg

scp upload download file

scp

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#upload
scp filename username@192.188.4.21:/home/nrgnb/Downloads/
#download
scp username@host/var/gnb/log/collect/20220805.163658.log.tgz .

using sshpass without type password

sshpass bypass the interactive password prompt for scp (and ssh).

install: apt install sshpass

syntax:: sshpass -p 'server passw' scp <filename or path> <sshhostname>:<destinationPath>

  • Example
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sshpass -p 'nr@Gnb' scp l1app-0809 nrgnb@192.188.4.21:/home/nrgnb/Downloads/
sshpass -p scp nrgnb@192.188.4.21:/home/nrgnb/Desktop/chenchihFile/flow.pcapng .
  • script
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sshhostname="nrgnb@192.188.4.21"
echo -n "enter your local file name (source): "
read sourcePath
destinationPath="/home/nrgnb/Downloads/"
sshpass -p 'nr@Gnb' scp $sourcePath $sshhostname:$destinationPath

Ping command

Ping with timestamp

  • Linux
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$ ping linuxbuzz.com | while read pong; do echo "$(date): $pong"; done

Add into shell script

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#!/bin/bash
#Script will continuously ping NFS VIP and capture timestamp
DIR=/var/tmp/nfs-ping-pong
if [ -d $DIR ]
then
    echo "Directory Exists"
else
    mkdir -p $DIR
fi

ping 10.8.3.102 | while read pong; do echo "$(date): $pong" >> $DIR/nfs-ping-$(date +%Y-%m-%d)

Reference:

https://www.linuxbuzz.com/enable-timestamp-linux-ping-command

  • PowerShell
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ping.exe -t <IP> | Foreach{"{0} - {1}" -f (Get-Date -f "yyyyMMdd HH:mm:ss"),$_}
#or
ping.exe -t 8.8.8.8 | ForEach {"{0} - {1}" -f (Get-Date), $_}

CPU Busy

You can either use:

  • method1
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for i in 1 2 3 4; do while : ; do : ; done & done
  • method2
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sha1sum /dev/zero &

kill process: kill sha1sum

  • Script:
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#!/bin/bash
while :; do :; done

Change permission: chmod +x cpu_load.sh
Run Script: ./cpu_load.sh &

Reference:

https://dev.to/abstractmusa/how-to-simulate-high-cpu-usage-on-aws-ubuntu-instances-for-testing-and-performance-optimization-1f5f >> https://superuser.com/questions/443406/how-can-i-produce-high-cpu-load-on-a-linux-server