Subject: RFC3484 and RFC1918 clarification

From: Rémi Denis-Courmont <[email-masked]>
Date: Thu, 13 Dec 2007 23:25:41 +0200

Hello,

I was wondering if RFC1918 addresses were, in RFC3484 sense, supposed to be 
considered of the same or of a smaller scope than public IPv4 addresses?

Say a dual-stack host has a private IPv4 with a default (NATted) route, and 
6to4 and/or Teredo IPv6 connectivity (no native)
If an implementation treats RFC1918 as differently scoped from public IPv4 
addresses, it will prefer the IPv6 pseudotunnels through the relays over the 
native IPv4 link. My personal take is that this is a bad idea (and it 
contradicts the statement I made last week), but I'd like to have other's 
opinion...

Regards,

-- 
Rémi Denis-Courmont
http://www.remlab.net/

---

From: Mohacsi Janos <[email-masked]>
Date: Fri, 14 Dec 2007 13:47:42 +0100 (CET)

Hi Remi,

In my opinion. The RFC1918 style private addresses has smaller scopes than 
global addresses. In IPv4 has similar concept of scoping of addresses like 
in IPv6.

host local: 127.0.0.0/8
link local: 169.254.0.0/16 - RFC 3927
~site addresses: 10.0.0.0/8 et al. - RFC 1918
global addresses: routable IPv4 addresses

However the implementation I see is slightly different: 
127.0.0.0/8 treated link local - scope 0x2
169.254.0.0/16 - scope 0x2
10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 treated as global - scope 0xE 
(althougt there is a remark: /* XXX: It should be 5 unless NAT */)

I think the implementation is correct. Actually almost everybody is using 
private addresses with NAT gateway as an outgoing connection.

Best Regards,

Janos Mohacsi
Network Engineer, Research Associate, Head of Network Planning and Projects
NIIF/HUNGARNET, HUNGARY
Key 70EF9882: DEC2 C685 1ED4 C95A 145F  4300 6F64 7B00 70EF 9882