≡ Menu

Networking

Q. How do I configure default router or gateway IP address under Ubuntu Linux / Debian Linux? How do I change default router / gateway IP under Ubuntu Linux?
[click to continue…]

I know how to add additional IPv4 IP address using virtual IP address configuration under Debian Linux. How do I add additional IPv6 address (aliased IPv6 addresses) under Debian Linux server?
[click to continue…]

FreeBSD Configure NIC Jumbo Frames

Q.Under Linux I can set Jumbo Frames by modifying configuration file. How do I configure FreeBSD network card to enable Jumbo frames on all of my NIC for 1000 Mbps speed and make MTU configuration persistence?
[click to continue…]

Ubuntu Static IP

Q. I've Intel Corporation 80003ES2 LAN Gigabit Ethernet Controller. How do I set static IP address settings for my Ubuntu Linux as follows:

DEVICE name : eth0
Type: static
IP ADDR : 10.10.29.66
NETMASK : 255.255.255.192
Router IP: 10.10.29.65
Broadcast: 10.10.29.127

How do I setup static IP address under Ubuntu?
[click to continue…]

Q. How do I track and monitor connection for eth1 public network interface under Redhat Enterprise Linux (RHEL) 5 server?

A.You can use netstat command or tcptrack command. Both command can show established TCP connection and provides the ability to monitor the same.

netstat command

netstat command prints information about the Linux networking subsystem. It also works under UNIX and *BSD oses. It can display network connections, routing tables, interface statistics, masquerade connections, and multicast memberships etc.

netstat command to display established connections

Type the command as follows:
$ netstat -nat
Output:

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 127.0.0.1:2208          0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:52459           0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:10000           0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.1:8080          0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:1521            0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:53              0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:3128            0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.1:31323         0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.1:2207          0.0.0.0:*               LISTEN
tcp        0      0 192.168.1.100:59917     74.86.48.98:291         ESTABLISHED
tcp        0      0 127.0.0.1:3128          127.0.0.1:49413         TIME_WAIT
tcp        0      0 127.0.1.1:54624         127.0.1.1:1521          ESTABLISHED
tcp        0      0 127.0.1.1:1521          127.0.1.1:54624         ESTABLISHED
tcp        0      0 192.168.1.100:55914     74.125.19.147:80        ESTABLISHED
tcp        0      0 127.0.0.1:3128          127.0.0.1:42471         TIME_WAIT
tcp        0      0 192.168.1.100:56357     74.86.48.98:993         ESTABLISHED
tcp        0      0 192.168.1.100:56350     74.86.48.98:993         ESTABLISHED
tcp6       0      0 :::53                   :::*                    LISTEN
tcp6       0      0 :::22                   :::*                    LISTEN 

To display client / server ESTABLISHED connections only:
$ netstat -nat | grep 'ESTABLISHED'

tcptrack command

tcptrack command displays the status of TCP connections that it sees on a given network interface. tcptrack monitors their state and displays information such as state, source/destination addresses and bandwidth usage in a sorted, updated list very much like the top command.

Install tcptrack

Redhat (RHEL) / Fedora / CentOS user, download tcptract here. For example download RHEL 64 bit version:
# cd /tmp/
# wget http://dag.wieers.com/rpm/packages/tcptrack/tcptrack-1.1.5-1.2.el5.rf.x86_64.rpm
# rpm -ivh tcptrack-1.1.5-1.2.el5.rf.x86_64.rpm

Debian / Ubuntu Linux user use apt-get as follows:
$ sudo apt-get install tcptrack

How do I use tcptract to monitor and track TCP connections ?

tcptrack requires only one parameter to run i.e. the name of an interface such as eth0, eth1 etc. Use the -i flag followed by an interface name that you want tcptrack to monitor.
# tcptrack -i eth0
# tcptrack -i eth1

Redhat Enterprise Linux 5 / CentOS 5 monitor and track TCP connections on the network (eth0)
(tcptrack in action)

You can just monitor TCP port 25 (SMTP)
# tcptrack -i eth0 port 25

The next example will only show web traffic monitoring on port 80:
# tcptrack -i eth1 port 80

tcptrack can also take a pcap filter expression as an argument. The format of this filter expression is the same as that of tcpdump and other libpcap-based sniffers. The following example will only show connections from host 76.11.22.12:
# tcptrack -i eth0 src or dst 76.11.22.12

For further option please refer to man page of netstat and tcptrack command.

Ubuntu Linux Restart Network Service

I am a new Ubuntu Linux user and using it on my HP Laptop. Now, I need to restart my network service. How do I restart network under Ubuntu Linux? How can I restart networking service on Ubuntu LTS server? How do I successfully restart a network service without rebooting Ubuntu box?
[click to continue…]

I've recently installed Debian Linux 4.0 on my server and Ubuntu Linux 7.04 on Laptop. I would love to have a multiple IP address that I can use for verity of purposes. I would like to bind 4 IP's to the 'eth0' device or NIC. How do I achieve this?
[click to continue…]