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Barracuda CloudGen Firewall

Linux Networking Commands

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To help you find and solve networking problems, this article describes some Linux utilities and their commonly used options and parameters. Usage examples for the utilities are also provided. For more information on any of the following utilities, see their man pages.


The ip tool is a TCP/IP interface configuration and routing utility. Use it to configure and view routing, devices, policy routing, and tunnels. You can also use it to configure network interfaces. To display all the options for this command, enter ip at the CLI.

ip a

Displays the list of used network interfaces (physical and virtual) with their assigned MAC addresses.

[root@winix:/]# ip a 1: lo: <loopback> mtu 16436 qdisc noqueue link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet brd scope host lo:loop 2: tap0: mtu 1500 qdisc noqueue link/ether fe:fd:00:00:00:00 brd ff:ff:ff:ff:ff:ff inet brd scope host tap0:fw 3: tap1: <broadcast> mtu 1500 qdisc noqueue link/ether fe:fd:00:00:00:00 brd ff:ff:ff:ff:ff:ff inet brd scope host tap1:vpn inet scope global tap1:aux1 4: tap2: mtu 1500 qdisc noqueue link/ether fe:fd:00:00:00:00 brd ff:ff:ff:ff:ff:ff inet brd scope host tap2:vpnpers inet scope global tap2:aux2
ip r g

Displays information about the device that is bound to the specified IP address.

[root@winix:/]# ip r g local dev lo src cache <local> mtu 16436 advmss 16396
ip a a dev

Adds an IP address to the specified device.

The IP address is removed again when the network or the Barracuda CloudGen Firewall is restarted. A device route is only added if a netmask has been given with the IP address.

[root@winix:/]# ip a a dev eth2
ip a d dev

Deletes an IP address from the specified device.

[root@winix:/]# ip a d dev eth2

If you use this command to remove a server or box IP address, the Control daemon will take action and reintroduce the deleted IP addresses.


To inspect packets, use the tcpdump utility. It is a sniffer tool that captures packets off a network interface and interprets them. It prints out the headers of packets on a network interface that match the Boolean expression. It understands all basic Internet protocols. It can also be used to save entire packets for later inspection.


Use the following options to specify which network interfaces you want to inspect: 

  • -i [interface] | any
    Specifies an interface name. To execute  tcpdump  on all available interfaces, use  any . To combine multiple devices, use  and/or .

  • host
    Specifies a host IP address. To combine multiple hosts, use  and/or .
  • port
    Specifies a queried port. To combine multiple ports, use  and/or .
[root@winix:/]# tcpdump -i eth0 -nnn -s0 host and host and port 801 [root@winix:/]# tcpdump -v -vv -n -nn -s0 -i any host and and port 443 [root@winix:/]# tcpdump -v -vv -n -nn -s0 -i any -w /tmp/dump.cap host and and port 443


If HDD/MEM tests are passing without errors, use the fsck utility with the following options to check and repair file systems:

fsck -A -y

These options solve most of the possible errors after a power outage because the utility checks all file systems and attempts to fix most detected file system corruption.


To check the kernel module architecture, use the rpm utility with the following options:

rpm -q --qf="%{arch}" kernel

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