Re: [dhcwg] MTU option for DHCPv6?

"Templin, Fred L" <Fred.L.Templin@boeing.com> Thu, 28 July 2016 15:05 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Lorenzo Colitti <lorenzo@google.com>, Ian Farrer <ianfarrer@gmx.com>
Thread-Topic: [dhcwg] MTU option for DHCPv6?
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Cc: "<dhcwg@ietf.org>" <dhcwg@ietf.org>, "Bernie Volz \(volz\)" <volz@cisco.com>
Subject: Re: [dhcwg] MTU option for DHCPv6?
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Hi Lorenzeo,


Ø  Why doesn't the link use RAs?

It does use RAs, only not for configuration information; it uses DHCPv6 for all
configuration information. If the Client sends an RS to the router, it will get back
an RA the same as for any link. It’s just that the RA won’t be providing any
configuration information.

Thanks - Fred

From: dhcwg [mailto:dhcwg-bounces@ietf.org] On Behalf Of Lorenzo Colitti
Sent: Thursday, July 28, 2016 2:14 AM
To: Ian Farrer <ianfarrer@gmx.com>
Cc: <dhcwg@ietf.org> <dhcwg@ietf.org>rg>; Bernie Volz (volz) <volz@cisco.com>
Subject: Re: [dhcwg] MTU option for DHCPv6?

Ian,

please let's not rehash the arguments about putting routing into DHCPv6. Last time that happened the resulting controversy was substantial.

Why doesn't the link use RAs? It seems to me that MTU is just one of the parameters that are needed for link configuration. Other examples are be router lifetimes, or default router addresses for things like liveness detection using NUD or failover between multiple routers.

Cheers,
Lorenzo

On Thu, Jul 28, 2016 at 5:49 PM, Ian Farrer <ianfarrer@gmx.com<mailto:ianfarrer@gmx.com>> wrote:
Hi Bernie,

It sounds like Fred is looking for a DHCPv6 equivalent of DHCPv4 option 26 which (as I understand it) allows the DHCP server to tell the client the interface MTU to use on the link. Is this the same option as the one that you’re referring to?

I can also see a use for having this information being sent to the client as we plan to use large MTUs to clients. From my perspective, having this information inside the PIO would be most useful.

@Fred, if the MTU was carried as an option inside the PIO, and there was a way of putting the PIO into DHCP, would this work for you?


Ian


> On 28 Jul 2016, at 00:14, Bernie Volz (volz) <volz@cisco.com<mailto:volz@cisco.com>> wrote:
>
> I'm not sure I fully follow.
>
> The v4 MTU option is the client telling the server how much it can receive.
>
> I'm not sure why the client wouldn't just use a large buffer (64K) as it isn't likely to need many of these buffers? The server is often more restrictive since it might be processing many requests at once.
>
> And, why would you need to have the server send so much data that the client might not be able to receive it all?
>
> BTW: I think when this came up during the writing of 3315, it was thought that having the client use a 64K buffer wasn't really an issue.
>
> - Bernie
>
> -----Original Message-----
> From: Templin, Fred L [mailto:Fred.L.Templin@boeing.com<mailto:Fred.L.Templin@boeing.com>]
> Sent: Wednesday, July 27, 2016 5:24 PM
> To: Bernie Volz (volz) <volz@cisco.com<mailto:volz@cisco.com>>; <dhcwg@ietf.org<mailto:dhcwg@ietf.org>> <dhcwg@ietf.org<mailto:dhcwg@ietf.org>>
> Subject: RE: MTU option for DHCPv6?
>
> Hi Bernie,
>
> I'm operating on a link where I don't need to get any configuration information from RS/RA - everything comes from DHCPv6. So, ideally, I would like to see DHCPv6 provide an MTU option and a Prefix Information Option - then I would have everything I need so that I don't have to use a vendor-specific option. Would that be possible?
>
> Thanks - Fred
>
>> -----Original Message-----
>> From: Bernie Volz (volz) [mailto:volz@cisco.com<mailto:volz@cisco.com>]
>> Sent: Wednesday, July 27, 2016 2:02 PM
>> To: Templin, Fred L <Fred.L.Templin@boeing.com<mailto:Fred.L.Templin@boeing.com>>; <dhcwg@ietf.org<mailto:dhcwg@ietf.org>>
>> <dhcwg@ietf.org<mailto:dhcwg@ietf.org>>
>> Subject: RE: MTU option for DHCPv6?
>>
>> Hi Fred:
>>
>> Nothing has been proposed that I can recall. The issue really hasn't come up (to date).
>>
>> - Bernie
>>
>> -----Original Message-----
>> From: dhcwg [mailto:dhcwg-bounces@ietf.org<mailto:dhcwg-bounces@ietf.org>] On Behalf Of Templin, Fred
>> L
>> Sent: Wednesday, July 27, 2016 4:10 PM
>> To: <dhcwg@ietf.org<mailto:dhcwg@ietf.org>> <dhcwg@ietf.org<mailto:dhcwg@ietf.org>>
>> Subject: [dhcwg] MTU option for DHCPv6?
>>
>> Just curious - is there now (or has there ever been proposed) an MTU
>> option for DHCPv6 in the same way that DHCPv4 has an MTU option?
>>
>> Thanks - Fred
>>
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