09-16-2003
Let's say that you have two computers connected by a network....let's call them Jenn and Ben. They both will have IP addresses: Jenn=192.168.30.1 and Ben=192.168.30.2
Let's say that you are on Jenn and you want to telnet to Ben. From Jenn, you can send packets to Ben by addressing them to 192.168.30.2. But how will Ben know what to do with them when they arrive? This is where port numbers come in.
On Jenn, you would run the telnet command. It will need a local port number and it just pick one. This kind of port is a high number...let's say it picks 5,327. It also looks up it's local IP address which is 192.168.30.1. This pair of numbers (192.168.30.1 and 5,327) will be one endpoint of the connection.
Now it looks up Ben's address which is 192.168.30.2. It knows that it wants to talk to a telnet server on Ben. By convention, a telnet server must use port 23. 23 is a well known port...these are low numbers.
Now the telnet program will establish a connection from (192.168.30.1 and 5,327) to (192.168.30.2 and 23). You need all 4 numbers to identify a connection.
Originally, the pair of numbers (ip address and port) were called a "socket". And it sometimes still is.
But in Unix, socket is also a system call that can be used to write network programs. A socket is also the data structure created by the socket() system. I have heard a few people speak in a way that suggests that they think that a socket is all 4 numbers in a connection. So it's hard to say exactly what a socket is.
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LEARN ABOUT DEBIAN
vlan-interfaces
VLAN-INTERFACES(5) File formats VLAN-INTERFACES(5)
NAME
/etc/network/interfaces (vlan) - vlan extensions for the interfaces(5) file format
DESCRIPTION
/etc/network/interfaces contains network interface configuration information for the ifup(8) and ifdown(8) commands. This manpage
describes the vlan extensions to the standard interfaces(5) file format.
Primary extensions exist to make and destroy vlan interfaces, secondary extensions exist for ipv4 interface manipulation which are gener-
ally needed when using (a lot of) vlans.
VLAN CREATION
Vlan interface definitions exist of the vlan interface name, and an optional 'raw-device' parameter. Vlan interfaces are numbered 1 to
4095. You have the option to have interface names zero-padded to 4 numbers, or just the plain digits without leading zero. The following
example shows four ways to create a vlan with id 1 on interface eth0. They all result in different names.
iface eth0.1 inet static
address 192.168.1.1
netmask 255.255.255.0
iface vlan1 inet static
vlan-raw-device eth0
address 192.168.1.1
netmask 255.255.255.0
iface eth0.0001 inet static
address 192.168.1.1
netmask 255.255.255.0
iface vlan0001 inet static
vlan-raw-device eth0
address 192.168.1.1
netmask 255.255.255.0
# We don't have br support out of the box
iface br0.2 inet static
vlan-raw-device br0
address 192.168.1.1
netmask 255.255.255.0
# Aliases are ignored
iface br0.2:1 inet static
address 192.168.1.1
netmask 255.255.255.255
EXTRA IFACE OPTIONS
Usually someone who uses vlans also wants to do some other manipulations with the ip stack or interface.
vlan-raw-device devicename
Indicates the device to create the vlan on. This is ignored when the devicename is part of the vlan interface name.
ip-proxy-arp 0|1
Turn proxy-arp off or on for this specific interface. This also works on plain ethernet like devices.
ip-rp-filter 0|1|2
Set the return path filter for this specific interface. This also works on plain ethernet like devices.
hw-mac-address mac-address
This sets the mac address of the interface before bringing it up. This works on any device that allows setting the hardware address
with the ip command.
AUTHOR
This manpage was adapted from interfaces(5) by Ard van Breemen <ard@kwaak.net>
SEE ALSO
vconfig(8) interfaces(5)
vlan September 30 2007 VLAN-INTERFACES(5)