Loop back address

Hi all,

The following is the definition of loop back address ,i saw in the
book tcp/ip guide

special range of addresses ,127.0.0.0 to 127.255.255.255 , is set
aside for loop back functionality.IP datagrams sent by a host to a
127.x.x.x loop back address are not passed down to the data link layer
for transmission,instead they loopback
to the source device at the IP level. In essence this short circuits
the normal protocol stack; data is sent by a device's layer 3 IP
implementation and immediately received by it.

This loopback range is used for testing the TCP/IP protocol
implementation on a host. since the lower layers are short
circuited ,sending to a loopback address allows you to isolate and
test the higher layers ,IP and above without interference from lower
layers. 127.0.0.1 is the address most commonly used for testing
purposes

now my question is as follows

1)This loopback range is used for testing the TCP/IP protocol
implementation on a host. since the lower layers are short
circuited ,sending to a loopback address allows you to isolate and
test the higher layers

can any one give example(s) for this or a situation where this is
used ?

Hi.

I'm using the loopback-IF to for e.q. to check, if my deamons (apache,
snmpd, ...) are locally running and if the right ports are in listenning
state (well, this can show netstat too ...).

regards


<(E-Mail Removed)> schrieb im Newsbeitrag
news:c1b928ea-2be6-41fd-817e-(E-Mail Removed)...
> Hi all,
>
> The following is the definition of loop back address ,i saw in the
> book tcp/ip guide
>
> special range of addresses ,127.0.0.0 to 127.255.255.255 , is set
> aside for loop back functionality.IP datagrams sent by a host to a
> 127.x.x.x loop back address are not passed down to the data link layer
> for transmission,instead they loopback
> to the source device at the IP level. In essence this short circuits
> the normal protocol stack; data is sent by a device's layer 3 IP
> implementation and immediately received by it.
>
> This loopback range is used for testing the TCP/IP protocol
> implementation on a host. since the lower layers are short
> circuited ,sending to a loopback address allows you to isolate and
> test the higher layers ,IP and above without interference from lower
> layers. 127.0.0.1 is the address most commonly used for testing
> purposes
>
> now my question is as follows
>
> 1)This loopback range is used for testing the TCP/IP protocol
> implementation on a host. since the lower layers are short
> circuited ,sending to a loopback address allows you to isolate and
> test the higher layers
>
> can any one give example(s) for this or a situation where this is
> used ?
>