Networking, poverty breeds ingenuity

[John Smith <netman1@home.nl>]

Hi All,

	why is the subnet mask of interface lo in sarge defined as /8 
(or 255.0.0.0) as, according to TheBonsai on #tcpip

RFC3330, page 2
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,

it should be /32 (or 255.255.255.255)? This (/8) causes problems 
like lo reacting to "ping 127.0.0.2"

	Background: I was for the last four days in _the_ standalone
situation: no net. Not even a link. Poverty breeds ingenuitity, and
since I knew I would be in this situation beforehand and I would need
to do some work and would need some networked applications, I prepared.
I depend on ssh, bind9, ldap, cfengine and www. 

	We, in our company, define boxes with very strict names and 
only ssh access but application names are free, but defined as "an 
ip-address with a port, served by 1 application". So, for example, we 
define a box as z12amd128 with ip-address 1.2.3.4 and run a secondary 
ip-address 1.2.3.5 on the same interface with hostname ns1.services.local 
on which only port 53 is open and listened to with bind9. This gives us
for example the operturnity to move an application very fast to another box.

	Since my job mainly involves defining the configuration files,
I hate to change host names when moving from testing to production, so
I wanted all hostnames (read applications) to run locally with the 
same hostnames without network connection. I defined secondary ip-
addresss lo:1, lo:2, lo:3 ... and bound 127.0.0.x addresses to them
with the different hostnames and applications I needed on top.

	It all worked fine. Except for that tiny little bit of testing
wether ip-address and applications are up and running. Every address
in the range 127.0.0.0/8 reacted :-(

	Now I'm back on-line, start asking around and wind up with the
above mentioned RFC part.

	Why is the netmask on lo defined as /8, where can I change it,
(/etc/network/interface lo loopback \ netmask 255.255.255.255 does not
work) what unwanted side-effects would this change have and why does 
debian not follow the RFC?

Sincerely,

Jan.