Re: [LARTC] Unnumbered

[Arthur van Leeuwen <arthurvl@sci.kun.nl>]

On Fri, 22 Jun 2001, M.F. PSIkappa wrote:

> On Fri, 22 Jun 2001, Arthur van Leeuwen wrote:
>
> > > > > it's posibility to make something similar to Cisco unnumber on Linux ?
> > > > > E. g.
> > > > > interface Serial0
> > > > >  ip unnumbered Ethernet0
> > > > > I don't want to assign to interface private IP.
> > > >
> > > > If I understand the ip unnumbered command correctly it allows you to share a
> > > > single IP address on multiple interfaces. This is trivial on Linux: just add
> > > > the same IP address to each of the interfaces with  ip addr add
> > > >
> > > > The routing effects I cannot correctly comment on, as I'm not sufficiently
> > > > versed in IOS to fully grasp the effects of  ip unnumbered
> > >
> > > No, it's incorrect, unnumberd allow you to connect 2 router without IP
> > > adresses.
> > >
> > > 192.168.0.1/24 [cisco]unnumbered-----unnumberd[cisco] 192.168.2.1/24
> > >
> > > It's special case of point-to-point connection. In linux if I make
> > > point-to-point connection I have to assign any IP on both endpoint of
> > > connection.
> >
> > What is the difference with
> >
> > 192.168.0.1/24 [linux] 192.168.0.1 ------- 192.168.2.1 [linux] 192.168.2.1/24
> >
> > if I may be so bold to ask? Yes, the routing effects may be different, and I
> > mentioned that might be a problem, but the unnumbered thing looks like a
> > cisco-specific hack...
>
> Difference is in traceroute. Unnumbered is invisible, if I assign IP I see
> it in traceroute, but I can make hack that make this connection invisible,
> but it's rfc break ...

Ah, but iptable's mangle module will let you play around with the TTL field
of packets being forwarded through a linux box. Yes, it takes some more
configuring, but the behaviour can be duplicated. And that is not considered
a hack. Besides, ever heard of masquerading? That is nowhere near RFC
compliance... and should theoretically be impossible, if I'm to believe
Jos Vos (one of the first implementers).

Doei, Arthur.

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