Re: [Idr] MP-BGP Extension and the Procedures for IPv4/IPv6 Mapping Advertisement

[Robert Raszuk <[e-mail]>]

> but I don't know why it the advertisement/translation/routing wouldn't
work as long as the IPv4 blocks aren't private addresses.

Well you can only do reserved non globally routable IPv6 prefix for
embedding IPv4 address in them. Notice the first 4 zeros there ?

Cheers,
R.


On Mon, Mar 18, 2024 at 4:17 PM Acee Lindem <[e-mail]> wrote:

> Hi Robert,
>
> > On Mar 18, 2024, at 11:08 AM, Robert Raszuk <[e-mail]> wrote:
> >
> > Hi Acee,
> >
> > Apologies if this has already been covered but it was clear from
> yesterday’s IDR meeting chat  that I’m not the only one who questions the
> necessity of this BGP extension.
> >
> > Why can you just use one of the IPv6 addresses ranges reserved for
> embedded IPv4 addresses as described in section 2.2.5 of RFC 4291?
> >
> > You man 2.5.5 ?
>
> Yes - I had the right link but wrong reference.
>
> >
> > Well the issue here is that this section describes a special address
> block to be used for mapping and last time I checked is hardly routable
> interdomai
>
>
>
> >
> > Moreover the goal of "IPv4-mapped IPv6 address" as explained even better
> in RFC4038 is to provide a way to talk to IPv6 services itself for IPv4
> only sites/hosts. This proposal just aims to assist to interconnect IPv4
> only sites.
>
> I got that but I don't know why it the advertisement/translation/routing
> wouldn't work as long as the IPv4 blocks aren't private addresses.
>
>
>
> >
> > So authors here are proposing to signal arbitrary prefix within and
> overlay between interesting (typically non directly connected ASNs) which
> of their prefix should be used to reach remote IPv4 sites.
> >
> > I think from this perspective the proposal is sound.
> >
> > What is however questionable and what we have recently discussed with
> Ketan - why not do encapsulation instead of double translation ... to
> accomplish the very same.
>
> Agreed - and this is generally cheaper than translation in the data plane.
>
> Thanks,
> Acee
>
>
> >
> > Cheers,
> > R.
> >
> > PS.
> >
> > If you use these embedded IPv4 using the standard mappings there no
> reason to advertise explicit mappings. There is already precedence for
> doing this - https://datatracker.ietf.org/doc/rfc6992/
> >
> > This is intradomain only.
> >
>
>