Re: [dhcwg] What triggers a DHCP Information Request?

Tim Chown <tjc@ecs.soton.ac.uk> Sun, 19 October 2014 22:51 UTC

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From: Tim Chown <tjc@ecs.soton.ac.uk>
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To: "Bernie Volz (volz)" <volz@cisco.com>
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Cc: dhcwg <dhcwg@ietf.org>, Ted Lemon <mellon@fugue.com>
Subject: Re: [dhcwg] What triggers a DHCP Information Request?
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Hi,

On 16 Oct 2014, at 16:42, Bernie Volz (volz) <volz@cisco.com> wrote:

> This might be a good issue to add in the 3315bis issues list - recommendations on when to initiate an Information-Request based on network changes.
> 
> I would guess that most clients trigger it when the refresh time (OPTION_INFORMATION_REFRESH_TIME option) expires or when some application request some data that hasn't been obtained (if the OS has this capability)?
> 
> Probably something (at least for the address selection policy table) that should have been covered in RFC 7078.
> 
> The text there is:
> 
>   The received information can be considered stale in several cases,
>   e.g., when the interface goes down, the DHCP server does not respond
>   for a certain amount of time, or the Information Refresh Time has
>   expired.
> 
> Of course, the list is just 'e.g.' so could include more.
> 
> And, there might be some rate limiting that is applicable in case there is flapping of the RA prefix information.

I agree with Bernie and Ted. 

It would make sense to fetch at the very least a (potentially) new policy table when a new prefix is advertised. 

With hindsight I wish we’d added, or proposed adding, “or a new prefix information is received” in the RFC 7078 text above while it was still in draft status, at least to flush out consensus on the question back then.  

But we should get a clear recommendation somewhere to maximise consistency in behaviour. If a 3315-bis is in the works, that seems as good a place as any, given that also obviously predates RFC 4242 on the refresh timer.

Tim

> - Bernie
> 
> -----Original Message-----
> From: dhcwg [mailto:dhcwg-bounces@ietf.org] On Behalf Of Ted Lemon
> Sent: Thursday, October 16, 2014 11:26 AM
> To: Timothy Winters
> Cc: dhcwg
> Subject: Re: [dhcwg] What triggers a DHCP Information Request?
> 
> On Oct 16, 2014, at 10:01 AM, Timothy Winters <twinters@iol.unh.edu> wrote:
>> 	 At the IOL I'm not aware of many DHCPv6 clients that trigger the DHCPv6 Information Request based on addresses being added.  I could see the case of when you lose all Global address (including ULA) a device might send one, but I would be surprised if they send when when new prefixes are found.   I can look closer into this to see what triggers it, give me a couple of days and I'll report back. 
> 
> That seems broken, because you probably want to refresh the source address selection policy table whenever you see a new prefix.
> 
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