[[nsp] 127.0.0.0/8 unroutable?]

[Hank Nussbacher]

On Tue, 11 Nov 2003, joshua sahala wrote:

> Hank Nussbacher <hank at att.net.il> wrote:
> 
> > IOS 12.0(25)S2:
> >
> > ip route 10.0.0.0 255.0.0.0 FastEthernet1/0/0
> > ip route 127.0.0.0 255.0.0.0 FastEthernet1/0/0
> >
> > TAU-gp1#sho ip rou 127.0.0.0
> > % Network not in table
> > TAU-gp1#sho ip rou 10.0.0.0
> > Routing entry for 10.0.0.0/8
> >  Known via "static", distance 1, metric 0 (connected)
> >  Redistributing via ospf 378
> >  Routing Descriptor Blocks:
> >  * directly connected, via FastEthernet1/0/0
> >      Route metric is 0, traffic share count is 1
> >
> > Something magical that 127.0.0.0/8 can't be statically routed?
> >
> > -Hank
> 
> from rfc1700:
> (g) {127, <any>}
> 
>        Internal host loopback address.  Should never appear outside
>        a host.
> 
> from rfc 3330:
> 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].
> 
> so in this case, it looks like cisco is following the rfc ;)

Ok.  I'll bite: and if a crafted packet comes in with source 127.x.x.x or
even better - destined to 127.x.x.x and there is no route entry, no cef
entry, nada - what does IOS do with the packet?

-Hank

> 
> /joshua
> 
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> >
> 
> 
> 
> "Walk with me through the Universe,
>  And along the way see how all of us are Connected.
>  Feast the eyes of your Soul,
>  On the Love that abounds.
>  In all places at once, seemingly endless,
>  Like your own existence."
>    - Stephen Hawking -
> 
> 

Hank Nussbacher