Subject: [mif] Issue: lifetime 32bit or 16bit ? draft-ietf-mif-dhcpv6-route-option-04

From: Alexandru Petrescu <[email-masked]>
Date: Tue, 27 Mar 2012 14:01:55 +0200

Dear participants in MIF WG,

Currently draft-ietf-mif-dhcpv6-route-option-04 specifies that the
lifetime of a route (and implicitely of a default route) is to be 32bit
length field.

On another hand, the currently implemented default routes are
implemented according to ND Neighbor Discovery, which uses route_r_
lifetime on 16bit (RFC 4861 search "Router Lifetime").

I think this is an issue.  It generates additional work to the
implementer.  If one agrees that it is good to store the DHCP default
route in the existing ND data structures, then one notices a conversion
is needed.  If these lifetime fields were expressed in the same number
of bits (preferably 16bit, because that exists already) then the
implementer would be relieved from conversion work.

I wanted to ask the oppinion of the WG about this issue.

Yours,

Alex

---

From: Ted Lemon <[email-masked]>
Date: Tue, 27 Mar 2012 15:37:33 +0000

> I think this [16 bit vs 32 bit lifetimes] is an issue.  It generates additional work to the

> I wanted to ask the oppinion of the WG about this issue.

You already asked the working group this question, and got responses at least from me.   Has something changed since you last asked that encourages you to ask again, or are you just hoping for a different answer this time?

---

From: William Herrin <[email-masked]>
Date: Tue, 27 Mar 2012 11:54:20 -0400

> I wanted to ask the oppinion of the WG about this issue.

I'm new to the questions surrounding DHCPv6, so my apologies if this
has already been discussed.

It's common practice to issue IPv4 DHCP lifetimes in excess of 24
hours (86400 seconds). I have to think that supporting common
configurations outweighs preserving ND data structures.

However... why would DHCP issue a router lifetime which is different
from the overall lifetime anyway? What's the use case for different
components of the DHCP message having different lifetimes?

Thanks,
Bill

-- 
William D. Herrin ................ [email-masked]  [email-masked]
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

---

From: Alexandru Petrescu <[email-masked]>
Date: Tue, 27 Mar 2012 19:47:56 +0200

Le 27/03/2012 17:37, Ted Lemon a écrit :
>> I think this [16 bit vs 32 bit lifetimes] is an issue.  It
>> generates additional work to the implementer.  If one agrees that
>> it is good to store the DHCP default route in the existing ND data
>> structures, then one notices a conversion is needed.  If these
>> lifetime fields were expressed in the same number of bits
>> (preferably 16bit, because that exists already) then the
> You already asked the working group this question, and got responses
> at least from me.

What do the others think?

> Has something changed since you last asked that encourages you to ask
> again, or are you just hoping for a different answer this time?

We need to fix this in Paris.

Alex

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 29 Mar 2012 13:43:26 +0200

Le 27/03/2012 17:54, William Herrin a écrit :
>> lifetime of a route (and implicitely of a default route) is to be
>> 32bit length field.
>>
>> implemented according to ND Neighbor Discovery, which uses
>> route_r_ lifetime on 16bit (RFC 4861 search "Router Lifetime").
>>
>> implementer.  If one agrees that it is good to store the DHCP
>> default route in the existing ND data structures, then one notices
>>  a conversion is needed.  If these lifetime fields were expressed
>> in the same number of bits (preferably 16bit, because that exists
>> already) then the implementer would be relieved from conversion
>> work.
>>

Bill,

The ND use of Router Lifetime is sometimes to distinguish among multiple
default routers.  I.e., if the Host has two default routes each with a
different lifetime, it may prefer the one with longer lifetime.

Also, the Router Lifetime has distinctive treatment of the value '0'.
Depending on it the Router is considered good as default or not.

This semantics is there already, but I wonder how it applies to the
lifetime 32bit communicated by DHCP.

One may wonder how that default route is inserted in the existing
data structures and what happens when the lifetime expires - should it
issue an RS or a DHCP Request?

Alex

> Thanks, Bill