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

[Robert Raszuk <[e-mail]>]

> That you configure your BGP poorly

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 ....

>  proper IGP metric may be given by proper policy based on such knowledge

If you are proposing to redistribute BGP into IGP and apply proper metric
to each dst route then I think we already differ a little bit in a
perspective how to construct a network.

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 ?

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 will not be
dropped due to uRPF check by the upstream provider ?

Many thx,
RR.



On Wed, Aug 21, 2019 at 10:59 PM Masataka Ohta <
[e-mail]> wrote:

> Robert Raszuk wrote:
>
> >> IGP metric is used as route preference,
> >
> > And that's the issue. Neither IGP metric nor BGP path attributes today
> > reflect reality of true network paths.
>
> I'm afraid you are not familiar with BGP policy, where you don't have
> to blindly rely on path attributes.
>
> > When I look at my BGP table in NY I get path to Europe via Seattle just
> > because such path has 1 AS less in the AS-PATH and neglect the fact that
> > there is alternative path just next to it with +1 AS but shorter RTT of
> 150
> > ms.
>
> That you configure your BGP poorly does not mean others can't have
> better policy to favor the alternative path.
>
> As is written in the draft:
>
>      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.
>
> proper IGP metric may be given by proper policy based on such knowledge
> (not carried by BGP) as "with +1 AS but shorter RTT of 150ms".
>
>                                                 Masataka Ohta
>