Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem

Mark ZZZ Smith <markzzzsmith@yahoo.com.au> Wed, 30 October 2013 19:40 UTC

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Date: Wed, 30 Oct 2013 12:39:50 -0700 (PDT)
From: Mark ZZZ Smith <markzzzsmith@yahoo.com.au>
To: Nick Hilliard <nick@inex.ie>, Lorenzo Colitti <lorenzo@google.com>
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Subject: Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem
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----- Original Message -----
> From: Nick Hilliard <nick@inex.ie>
> To: Lorenzo Colitti <lorenzo@google.com>
> Cc: "v6ops@ietf.org WG" <v6ops@ietf.org>
> Sent: Thursday, 31 October 2013 5:14 AM
> Subject: Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft:	draft-liu-bonica-v6ops-dhcpv6-slaac-problem
> 
> On 30/10/2013 13:07, Lorenzo Colitti wrote:
>>  Find me an medium or large enterprise deployment that doesn't have two
>>  routers on every LAN segment. I'll bet almost all of them do, because 
> they
>>  know that if one crashes or they want to take it down for maintenance, they
>>  have an outage, and nobody likes outages.
> 
> no need to bet - using multiple routers on a LAN is standard procedure
> where uptime matters.
> 
> The question is why would someone use RA for multiple gateway announcement
> when you'll get much better operational performance from a FHRP + single
> gateway address?  And why use RA for addressing when you'll get finer
> grained operational host control using dhcp?

It's been said a number of times in this thread. You can have client specific RAs that solve that problem. This is not a missing capability that duplicating RA functionality in DHCPv6 would then provide.


> Or when you need to use dhcp
> anyway in order to make your hosts do what they need to do?  Or on server
> farms when most of your hosts are statically addressed and it doesn't make
> sense to have multiple gateways with different addresses - and you'll get
> better uptime by not using RA?
> 
> I'm not proposing to take away the option of using RAs if that's what 
> you
> want to do.  I'm only suggesting that for many situations, it makes more
> sense to have a single static gateway address (optionally with multiple
> routers using a FHRP if you need reliability) and that consequently the
> idea of periodically announcing a selection of arbitrary gateways via RA is
> operationally second rate.
> 

I'd really like to know specific details of these many situations, and what specific benefits switching off RAs would have. I've been in many situations in many networks, and when I consider my IPv4 experience (and also compare it to my Novell IPX and Appletalk experiences), I see a lot of value in having RAs provide default gateway(s) (VRRP/HSRP or not) information and other layer 3 parameters to directly attached hosts from the directly attached router(s). This is in comparison with the IPv4 alternative effort of enabling and configuring a heavier and more resource consuming stateful DHCP server on either the first hop routers, or enabling DHCP relays and then having to have a redundant DHCP infrastructure somewhere else in the network.

It could be argued that DHCP could be enabled and configured by default, but that is also obviously the case with RAs, and they've been enabled by default since day one. The ability to automate the configuration of DHCP doesn't inherently make DHCP better than RAs.

Regards,
Mark.

> 

> Nick
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