Re: [irtf-discuss] Why do we need to go with 128 bits address space ?

[Masataka Ohta <[e-mail]>]

Robert Raszuk wrote:

> To configure exit path selection such that you take optimal exit to 
> destination X vs destination Y you need mechanism to either
> passively or actively measure it. The entire point I am trying to
> make here is that sweet spot for such measurements is the edge of the
> network and not on each host, VM, container etc ....

As I wrote:

    Note that end to end multihoming works with the separation between
    inter domain BGP and intra domain routing protocols, if BGP routers,
    based on domain policy, assign external routes preference values
    (metric) of intra domain routing protocols.

BGP routers are at the edge.

> Of course even if I would carry selective destinations in IGP with 
> properly mapped metrics how would host learn about it when it has to 
> pick the src address from N available in end to end multi homing 
> principle ? Is the assumption again that hosts, VMs, LXCs
> participate now in the IGP ?

I know poor source address selection is a flaw of current IP (both
v4 and v6).

> And even if it would be a passive IGP listener how do you encode in 
> any IGP today which src address should be selected such that packets
> wil not be dropped due to uRPF check by the upstream provider ?

For the solution, read the draft:

    Any source address may be selected.

    However, to enable source address filtering to discard packets with
    source addresses not belonging to an ISP, it is useful to enable a
    host, not some intelligent intermediate router, select a source
    address compatible with an outgoing ISP.  For that purpose, intra
    domain routing protocols should maintain routing table entries with
    not only preference values of an external routes, but also proper
    prefixes to be selected for source addresses, if the entries are
    chosen by a host.

						Masataka Ohta