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New Member

why loopback network 127.0.0.0??

Hi,

Why we need whole network for loopback 127.0.0.0????    

3 ACCEPTED SOLUTIONS

Accepted Solutions

Re: why loopback network 127.0.0.0??

Hi,

Why we need whole network for loopback 127.0.0.0????

Hi,

127.0.0.1 is the standard IP  address used for a loopback network connection. This means that if you try to connect to 127.0.0.1, you are immediately looped back to your own machine. 127.0.0.1 is also referred to as “localhost”, meaning ‘this computer’.127.0.0.0/8 - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host.

Making a connection with a 127.0.0.1 loopback address is the same as making a connection with any remote computer on the network, but avoiding the local network interface hardware. It is widely used by application developers and system administrators with the intention of testing software/applications.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

Hall of Fame Super Blue

Re: why loopback network 127.0.0.0??

From RFC3330 - Special-Use IPv4 addresses -

127.0.0.0/8 - This block is assigned for use as the Internet host
   loopback address.  A datagram sent by a higher level protocol to an
   address anywhere within this block should loop back inside the host.
   This is ordinarily implemented using only 127.0.0.1/32 for loopback,
   but no addresses within this block should ever appear on any network
   anywhere [RFC1700, page 5].

In other words the whole of the 127.0.0.0/8 network is reserved for looping back to the host but it is general practice to only use 127.0.0.1

Jon

Cisco Employee

Re: why loopback network 127.0.0.0??

Just to throw out one example where more than 127.0.0.1 is used is the Catalyst 6500. The different processors on the chassis communicate using the EOBC channel. Each processor is given an address in this pool. The numbering scheme depends on the individual card and which slot it is in. If you have a SUP720 in slot 5 then the SP will listen on 127.0.0.50. The RP will listen on 127.0.0.51. Here is the output when using the session command to an ACE module in slot 1:

switch#session slot 1 processor 0
The default escape character is Ctrl-^, then x.
You can also type 'exit' at the remote prompt to end the session
Trying 127.0.0.10 ... Open


7 REPLIES

Re: why loopback network 127.0.0.0??

Hi,

Why we need whole network for loopback 127.0.0.0????

Hi,

127.0.0.1 is the standard IP  address used for a loopback network connection. This means that if you try to connect to 127.0.0.1, you are immediately looped back to your own machine. 127.0.0.1 is also referred to as “localhost”, meaning ‘this computer’.127.0.0.0/8 - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host.

Making a connection with a 127.0.0.1 loopback address is the same as making a connection with any remote computer on the network, but avoiding the local network interface hardware. It is widely used by application developers and system administrators with the intention of testing software/applications.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

Hall of Fame Super Blue

Re: why loopback network 127.0.0.0??

From RFC3330 - Special-Use IPv4 addresses -

127.0.0.0/8 - This block is assigned for use as the Internet host
   loopback address.  A datagram sent by a higher level protocol to an
   address anywhere within this block should loop back inside the host.
   This is ordinarily implemented using only 127.0.0.1/32 for loopback,
   but no addresses within this block should ever appear on any network
   anywhere [RFC1700, page 5].

In other words the whole of the 127.0.0.0/8 network is reserved for looping back to the host but it is general practice to only use 127.0.0.1

Jon

Cisco Employee

Re: why loopback network 127.0.0.0??

Just to throw out one example where more than 127.0.0.1 is used is the Catalyst 6500. The different processors on the chassis communicate using the EOBC channel. Each processor is given an address in this pool. The numbering scheme depends on the individual card and which slot it is in. If you have a SUP720 in slot 5 then the SP will listen on 127.0.0.50. The RP will listen on 127.0.0.51. Here is the output when using the session command to an ACE module in slot 1:

switch#session slot 1 processor 0
The default escape character is Ctrl-^, then x.
You can also type 'exit' at the remote prompt to end the session
Trying 127.0.0.10 ... Open


New Member

Re: why loopback network 127.0.0.0??

I agree about this answer but I want to know this IP (127.0.0.10 or any) is given by dynamically or we have to set the IP and one more doubt how I can see the all loopback ip where and which ip set any command is there or??

Cisco Employee

Re: why loopback network 127.0.0.0??

In the 6500 example the IP addresses used in the 127 network are given automatically.
There is no way to change an individual address with the exception of changing the slot the card is installed.

I am not aware of any command to display all of the addresses given in the chassis for the EOBC.

New Member

Re: why loopback network 127.0.0.0??

how I can check the which loopback IP is given to which interface or internal device.

New Member

Re: why loopback network 127.0.0.0??

Hi,

Loopback ip address use to check the functionality of TCP/IP Protocol installed on the locolhost.

Ping results from 127.0.0.0/8 shows that TCP/IP protocol is working fine at the local machine and loopback ip address looped the locolhost and NIC port and gives the ping result.

This is a standard and reserved ip address classified for classes IP Address.

Regards

Vinod Agrahari

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