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Determine / Find ethernet connection speed

Q. How do I determine my Ethernet connection speed under Debian Linux 4.0 server?

A. You need to use ethtool command todisplay or change ethernet card settings. It is used for querying settings of an ethernet device such as
=> Link speed

=> Autonegotiation

=> Coalescing settings

=> Change the rx/tx ring parameters

=> Setup new speed and much more

Most intelligent network devices use an autonegotiation protocol to communicate what media technologies they support, and then select the
fastest mutually supported media technology.

How do I determine ethernet connection speed?

Type the following command to get speed for eth0:
$ ethtool eth0 | less
$ ethtool eth0 | grep -i speed

Bash Grep Subdirectories (Recursively)

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Q. I need to get the IP address assigned to eth0 Linux interface. How do I find out IP address only? I don't want other information displayed by Linux ifconfig command.

A. For shell script or may be for other cause you may need the IP address only. You can use ifconfig command with grep and other filters.

Default output of /sbin/ifconfig command is all interfaces:
$ /sbin/ifconfigOutput:

lo        Link encap:Local Loopback
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:69527 errors:0 dropped:0 overruns:0 frame:0
          TX packets:69527 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:41559546 (39.6 MiB)  TX bytes:41559546 (39.6 MiB)
eth0      Link encap:Ethernet  HWaddr 00:17:9A:0A:F6:44
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::217:9aff:fe0a:f644/64 Scope:Link
          RX packets:227614 errors:0 dropped:0 overruns:0 frame:0
          TX packets:60421 errors:0 dropped:0 overruns:0 carrier:0
          collisions:272 txqueuelen:1000
          RX bytes:69661583 (66.4 MiB)  TX bytes:10361043 (9.8 MiB)
ra0       Link encap:Ethernet  HWaddr 00:50:56:C0:00:01
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::250:56ff:fec0:1/64 Scope:Link
          RX packets:1024 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1320 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

Now you just select eth0 as follows:
$ /sbin/ifconfig eth0

Now you just wanted the IP address, use grep to get the IP:
$ /sbin/ifconfig eth0| grep 'inet addr:'Output:

inet addr:  Bcast:  Mask:

To get IP address from use cut command:
$ /sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2Output:  Bcast

Finally remove Bcast with awk
$ /sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}'

See how to read UNIX/Linux system IP address in a shell script

Restrict ssh access using tcpd (TCPWrapper)

tcpd is use to access control facility for internet services. The tcpd program can be set up to monitor incoming requests for telnet, finger, ftp, exec, rsh, rlogin, tftp, sshd and other services that have a one-to-one mapping onto executable files. Your sshd server must be configuring (compiled with) to support tcpd.

You can find out tcpd (tcpwrapper) support easily with following command:

# strings $(which sshd)| grep libwrap

libwrap refuse returns

If you get output libwrap (as above) then you can use tcpd as follows. Open file /etc/hosts.deny in text editor. This file list of hosts/IPs that are not allowed to access the system. In your case you will block sshd (port 22). Let us say you would like to deny access to IPs
# vi /etc/hosts.deny Add/append following line to file:sshd: and exit to shell prompt. Next make sure your rules are correct with the following command:
# tcpdchk -v

Using network configuration file: /etc/inetd.conf
>>> Rule /etc/hosts.deny line 20:
daemons:  sshd
access:   denied

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