[[nsp] 127.0.0.0/8 unroutable?]

[Jared Mauch]

On Tue, Nov 11, 2003 at 12:38:31PM -0500, 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 ;)

	btw, some cisco devices actually use this 127/8 internally
(eg: 6500)

(output of "sh ip cef")
127.0.0.0/8         attached             EOBC0/0
127.0.0.0/32        receive
127.0.0.12/32       receive
127.255.255.255/32  receive

	- jared

-- 
Jared Mauch  | pgp key available via finger from jared at puck.nether.net
clue++;      | http://puck.nether.net/~jared/  My statements are only mine.