multiple routing tables review patch ready for simple testing.

[Bruce M. Simpson]

Bruce M. Simpson wrote:
>>
>> Wouldn't it make sense to treat each alias as on a separate
>> logical interface?  Then each logical interface belongs to
>> exactly one FIB.  On input you decide which logical inteface
>> a packet arrived on by looking at its destination MAC
>> address.  That reduces confusion quite a bit, at least in my
>> mind!  What does doing more than this buy you?
>>   
>
> It doesn't buy anything because there is still no 1:1 mapping -- the 
> link-layer destination address maps to an ifp, and multiple aliases 
> exist on the ifp.

Let me qualify that further: You are talking about splitting network 
layer addresses onto their own logical interfaces, with the goal of 
having a 1:1 mapping for FIB resolution.

This doesn't buy anything, because in IP, the previous hop never encodes 
the next-hop address it sends to -- it merely performs a lookup and 
forwards to you; your MAC address is the same for every IP address you 
have on the link, therefore it is not a unique identifier.

UNLESS you use a separate MAC address for every IP alias which you add, 
in which case, you are merely pushing the mapping elsewhere in the 
stack; it actually adds more complexity in this case.