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

[Chongfeng Xie <[e-mail]>]

Hi  Robert, Acee, 
 
From: Robert Raszuk
Date: 2024-03-18 23:08
To: Acee Lindem
CC: idr
Subject: Re: [Idr] MP-BGP Extension and the Procedures for IPv4/IPv6 Mapping Advertisement
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 ? 

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 interdomain. 

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. 

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.

[Chongfeng]: I generally agree with Robert's analysis here.  Based on our experience, mapping with an IPv6 prefix is an effective way to identify the location of IPv4 block in inter-domain network, so as to forward service data to the 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. 

[Chongfeng]:  Double-translation is a popular way for transition to IPv6-only, it has been even widely supported by terminal OS, such as IOS and Android. Double translation have deployed in the mobile networks of multiple operators.  In this case, double-translation is more suitable than encapsulation.  From the perspective of network operation, the extension to BGP should cover both cases, not only encapsulation, but also translation.
 

Cheers,
R.

PS. 


Best regards
Chongfeng

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.