unnumbered interfaces?

unnumbered interfaces?

[Mark Clayton]

I'm trying to understand unnumbered interfaces.  From 
searching the web, they seem to be point-to-point links 
that do not have IP numbers (hence the name).  This is
what alludes:

 1) How do you set a pair on linux boxes to do this? ppp? 
 2) How would a program send data across the link?  Via
sockets?  Or thru /dev/something0?
 3) Does it make sense that to use ethernet?  Not to me
but sometimes I'm wrong :)

I'm sure I'm missing the obvious.  I usually do.  Can
anyone shed some light on this topic?

Thanks,
Mark
--
Mark & Kathy Clayton
S/V Brown Pelican
http://www.brown-pelican.com/  

Re: unnumbered interfaces?

[Remco Post]

> 
> I'm trying to understand unnumbered interfaces.  From 
> searching the web, they seem to be point-to-point links 
> that do not have IP numbers (hence the name).  This is
> what alludes:
> 
>  1) How do you set a pair on linux boxes to do this? ppp? 
>  2) How would a program send data across the link?  Via
> sockets?  Or thru /dev/something0?
>  3) Does it make sense that to use ethernet?  Not to me
> but sometimes I'm wrong :)
> 
> I'm sure I'm missing the obvious.  I usually do.  Can
> anyone shed some light on this topic?
> 
> Thanks,
> Mark
> --
> Mark & Kathy Clayton
> S/V Brown Pelican
> http://www.brown-pelican.com/  
> 
> 
Hi,

AFAIK, unnumbered interfaces are used only on routers on serial links and 
things like pos. Basically one would then enter a route entry routing one or 
more ip-blocks via an interface, not via the ip of a neigbouring router, in 
stead of the ip address of the neigbouring router one enters the name of the 
interface to use for this route.

Since these interfaces have no ip address, they cannot be the source of ip 
packets. Applications that generate ip traffic on such a router will use a 
different ip address on that router a the source ip, even if the packet has to 
go out on an unnumbered interface.

Having said this, unnumbered interfaces are quite rare in ip networks, most 
backbones use ip addresses on all of the interfaces of their routers. (do a 
traceroute to anywhere, you'll find very few hops that show no ip address).


-- 
Met vriendelijke groeten,

Remco Post

SARA - Stichting Academisch Rekencentrum Amsterdam
High Performance Computing  Tel. +31 20 592 8008    Fax. +31 20 668 3167

"I really didn't foresee the Internet. But then, neither did the computer
industry. Not that that tells us very much of course - the computer industry
didn't even foresee that the century was going to end." -- Douglas Adams

Re: unnumbered interfaces?

[Dan Hollis]

On Thu, 1 Nov 2001, Remco Post wrote:
> Having said this, unnumbered interfaces are quite rare in ip networks, most
> backbones use ip addresses on all of the interfaces of their routers. (do a
> traceroute to anywhere, you'll find very few hops that show no ip address).

unnumbered interfaces are more common than you think -- most dialup ppp
servers use them. iirc the linux pppd supports them too.

-Dan
-- 
[-] Omae no subete no kichi wa ore no mono da. [-]

Re: unnumbered interfaces?

[Bernd Eckenfels]

In article <200111011522.QAA22531@zhadum.sara.nl> you wrote:
>> I'm trying to understand unnumbered interfaces.  From 
>> searching the web, they seem to be point-to-point links 
>> that do not have IP numbers (hence the name). 

It is Cisco Speak. In Linux you simply give the Interface an IP Address of
an exisiting Interface, and then you have an "unnumbered" interface. It
simply means it does not add an additional address.

Routing in modern operating systems is so easy and natural with interface
and host routes, dont worry about cisco legacy.

Greetings
Bernd

Re: unnumbered interfaces? - OT

[Bruce Ferrell]

Bernd Eckenfels wrote:
> 
> In article <200111011522.QAA22531@zhadum.sara.nl> you wrote:
> >> I'm trying to understand unnumbered interfaces.  From
> >> searching the web, they seem to be point-to-point links
> >> that do not have IP numbers (hence the name).

They are in fact, used for point-to-point links.  It allows someone to
build a kind of distributed router; Kind of like the old IBM remote
bridge arrangemets.  Those had either a token ring or ethernet card and
a WAN card of some kind (usually SDLC or X.25) connecting them
together.  Kind of cool in a weird, expensive sort of way.

> It is Cisco Speak. In Linux you simply give the Interface an IP Address of
> an exisiting Interface, and then you have an "unnumbered" interface. It
> simply means it does not add an additional address.
> 
> Routing in modern operating systems is so easy and natural with interface
> and host routes, dont worry about cisco legacy.
> 
> Greetings
> Bernd
> -
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