Re: [v6ops] MAC table shortage in IPv6 networks caused by multiple IPv6 prefixes/addresses//FW: New Version Notification for draft-liu-v6ops-running-multiple-prefixes-01.txt

[Andrew Yourtchenko <[e-mail]>]

Hi Leo,

On Fri, 11 Jul 2014, Liubing (Leo) wrote:

> Hi Andrew,
>
>>> Now there are some enterprise/campus networks under real use or
>>> considering using L2 networks. Some are aiming at better user isolation
>>> through VLANs (some even consider QinQ mechanism); while some are
>>> aiming less configuration/management than the traditional L3 networks.
>>> So there would be thousands of hosts aggregated to the core switch
>>> (normally there are two core switches stacked together, but only share one
>> cache space).
>>> As IPv6 is beginning real use, for example, some of the campus networks
>>> are already dual-stack, and the majority of the hosts are Win 7, we
>>> once observed in one campus that DHCPv6/SLAAC are both enabled, each
>>> Win 7 host had 4 IPv6 addr (SLAAC+DHCPv6+Privacy+link-local)+1 IPv4 addr.
>>
>> If the majority of the hosts are Win 7, and are under the control of the
>> administrator, this looks more like a misconfiguration rather than anything
>> else: clear the "A" bit on the prefix, and they'll half the address usage - down
>> to just link-local and DHCPv6-based.
>
> [Bing] I can hardly say SLAAC and DHCPv6 co-existing is a misconfiguration,

Note, I said "for this specific case". If you control your devices *and* 
devices are DHCPv6-capable *and* you want to minimize the number of 
addresses using SLAAC is not ideal.

> but I agree DHCPv6-only deployment can partly relieve the problem.
> However, even DHCPv6-only would have 2 IPv6 addr+1 IPv4 addr, which 
> would cause approximately 5~8 times cache space than IPv4-only.

You can work towards turning off IPv4.

Past that - it's just protocol's properties.

--a