Re: [dhcwg] MTU option for DHCPv6?

"Bernie Volz (volz)" <> Thu, 28 July 2016 13:52 UTC

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From: "Bernie Volz (volz)" <>
To: "" <>, Ian Farrer <>, "Templin, Fred L" <>
Thread-Topic: [dhcwg] MTU option for DHCPv6?
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Date: Thu, 28 Jul 2016 13:52:20 +0000
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Subject: Re: [dhcwg] MTU option for DHCPv6?
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OK. For some reason I was thinking of option 22 (max db assembly).

Thanks for providing that link Ole for presentation & draft-van-beijnum-multi-mtu. 

The minutes from 6man @ IETF-95 don't say much about this work:

Extensions for Multi-MTU Subnets, draft-van-beijnum-multi-mtu , Mikael
Abrahamsson, 10 min

Discussed at IETF 69, 71, and 78.

David Lamparter: suggest doing this for link-local addresses on the basis
of per-link-local-per-interface.

Mark Townsley: really need PMTUD, still have issues about header insertion.

So what is the status of this work?

And, note that Fred had indicated "I'm operating on a link where I don't need to get any configuration information from RS/RA - everything comes from DHCPv6." So, looks like at least he wants DHCPv6 option(s). I guess he can always propose this by writing a DHCPv6 draft to provide one or more of the various DHCPv4 MTU options (27, MTU Subnet, is not really applicable for IPv6):

24	MTU Timeout	4	Path MTU Aging Timeout	[RFC2132]
25	MTU Plateau	N	Path MTU Plateau Table	[RFC2132]
26	MTU Interface	2	Interface MTU Size	[RFC2132]
27	MTU Subnet	1	All Subnets are Local	[RFC2132]

- Bernie

-----Original Message-----
From: [] 
Sent: Thursday, July 28, 2016 5:06 AM
To: Ian Farrer <>
Cc: Bernie Volz (volz) <>om>; <> <>
Subject: Re: [dhcwg] MTU option for DHCPv6?

> 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?

If you want to solve the set of problems that Mikael outlined here:

Then the notion of an interface MTU might not be so helpful. MTU is really a path property between two end hosts.

Best regards,