Re: IPv6 Link Local Addresses [was Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?]

[Ole Troan <[e-mail]>]

>> This means that link local addresses have a 10 bit prefix (1111111010) followed by 54 bits of zeros.  That is it, nothing more.   Address with different prefixes or with a 1111111010 prefix followed by non-zero 54 bits are not link local addresses.
>> 
>> This is not ambiguous.  
> 
> So if an application asks my implementation to send a packet addressed to fe80:1::1 out a particular link what should the implementation do with it? It seems like there are only 3 choices:
> 
>   1. Run ND on that link to see if it can find a neighbor there with that address to send the packet to.
> 
>   2. Send the packet to the current default router.
> 
>   3. Something else (what?).
> 
> I had though 1. was the answer since that is what is done with packets addressed to link-local unicast destinations (which is what that address is according to RFC4191 section 2.4), but that now seems to be ambiguous.

Let me illustrate with a typical per-interface FIB:

 fe80::/10 -> drop
 fe80::/64 -> glean
 fe80::abcd -> neighbor abcd

Cheers,
Ole