network

Network testing with netcat (nc)

In order to pest whether is network port accessible, either udp or tcp.

Can server listen on udp port 5000 ?

Example with UDP port!

Server side
ncat -ulp 5000

Client side
ncat -u XXX.XXX.XXX.XXX 5000

Add IP address to whitlist with fail2ban
Open config file

vim /etc/fail2ban/jail.conf

find a line
ingoreip =
add particular IP or subnet
Remember to keep a space between records

Show transceiver type on Arista switches

show inventory
show interfaces status

If you need to create manually network interface in centos6

Get to network interface folder
cd /etc/sysconfig/network-scripts/

copy one of current to create a new one
cp ifcfg-eth0 ifcfg-ethX

Chek for crc error on network interface
ethtool -S "interface" |grep crc
netstat -i
ip -s link show

Possible Causes of Ethernet Errors

Bond test
Switchnig between slaves

ifenslave -c bond0 ethX

Bond status
cat /proc/net/bonding/bond0

To set LACP bonding correctly add file
vim /etc/modprobe.d/bonding.conf
options bonding mode=4 xmit_hash_policy=1

Po vymene IP na bondu v Archlinuxu
modprobe -r bonding
nmctl start bond0

temporary
echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_all

permanent
vim /etc/sysctl.conf net.ipv4.icmp_echo_ignore_all=0

Ping mu
fping -g 192.168.100.1 192.168.100.100

Or whole subnet
fping -gar1 83.40.128.0/24 2> null

sudo lsof -i -P -n | grep LISTEN sudo netstat -tulpn | grep LISTEN sudo nmap -sTU -O IP-address-Here