[Re: [[nsp] 127.0.0.0/8 unroutable?]]

[joshua sahala]

Hank Nussbacher <hank at att.net.il> wrote:

> 
> 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

there is a cef entry (from a 7513 running 12.0(25)S1):

tricksy_router#sho ip route 127.0.0.1
% Network not in table
tricksy_router#sho ip cef 127.0.0.1
0.0.0.0/0, version 0, epoch 0, attached, default route handler
0 packets, 0 bytes
  via 0.0.0.0, 0 dependencies
    valid null adjacency
tricksy_router#

as to what the router does with it, i'm not sure, my bogon filters block
it before it gets to the router (don't yours? ;) ) 

it is an interesting question, will the router (lacking appropriate bogon
and spoofing filters) pass a packet source from 127.x.x.x to a valid
(or invalid) address on the other side of the router - sounds like 
something to play with....

/joshua



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