Subject: Re: [savi] Conclusion on SAVI device configuration with prefixes

From: Christian Vogt <[email-masked]>
Date: Thu, 1 Jul 2010 15:09:52 -0700

Folks:

Thank you also for the good discussion on explicit validation of IP
address prefixes in SAVI.  The discussion was useful to understand an
important analogy between SAVI for SLAAC and SAVI for DHCP:  In both
cases, there is an entity on the link which is responsible for assigning
at least part of an IP address.  In the case of SAVI for DHCP, this
entity is the DHCP server.  In the case of SAVI for SLAAC, this entity
is the first-hop router.  DHCP servers are responsible for assigning
full IP addresses, while in a SLAAC environment, first-hop routers are
responsible for assigning IP address prefixes.

Jean-Michel and I are now concluding this discussion with the following
conclusions:

- No explicit validation for IP address prefixes in SAVI for DHCP.  DHCP
  servers are in charge of full IP addresses, hence adding special
  validation of DHCP-assigned IP address prefixes in SAVI could break
  more than it would benefit.

- Explicit validation of IP address prefixes in SAVI for SLAAC.  Like
  SAVI-for-DHCP devices are configured with trusted ports through
  which they learn about DHCP-assigned IP addresses, SAVI-for-SLAAC
  devices will be configured with trusted ports through which they
  learn about IP address prefixes declared by first-hop routers.  To
  this extent SAVI-for-SLAAC devices listen for Router Advertisement
  messages on trusted ports, and retrieve IP address prefixes from
  those messages.

- SAVI-SLAAC devices expedite the recovery of IP address prefix state
  after state loss by issuing Router Solicitation messages.

Authors, please revise your documents accordingly.

- Christian, for Jean-Michel and Christian

On Jun 24, 2010, Christian Vogt wrote:

> Guang and all:
> 
> I understand Guang's comparison between the authority of DHCP servers
> versus first-hop routers.  But the benefit-cost tradeoff is different
> in the two cases, and so I think we should consider them separately:
> 
> The model of SAVI for DHCP is inherently based on the authoritativeness
> of DHCP servers over full addresses.  And I don't see extra benefit in
> giving SAVI devices an authority as well.  While it is true that
> misbehavior of a DHCP server could lead to disruption, extra
> configuration of SAVI devices to penalize such misbehavior wouldn't
> mitigate the problem.  Given that such extra configuration would also go
> against the working group objective of keeping its standards simple, I
> advise against the extra configuration in the case of SAVI for DHCP.
> 
> The model of SAVI for SLAAC is based on the authoritativeness of
> first-hop routers over address prefixes.  And an argument could be made
> to have SAVI devices learn address prefixes from first-hop routers, just
> as they learn full addresses from DHCP servers in the case of SAVI for
> DHCP.  But in that case, the learning should happen automatically in my
> opinion, i.e., without extra configuration of SAVI devices.
> 
> - Christian

---

From: "Jun Bi" <[email-masked]>
Date: Fri, 2 Jul 2010 12:08:00 +0800

Dear WG Chairs,

Although personally I intend to keep the prefix configuration for dhcp as a 
optional function, but I am OK to remove this at savi-dhcp solution. If 
there is more requirement rising, then we could consider it at the 
savi-framework.

Best Regards,
Jun Bi

--------------------------------------------------
From: "Christian Vogt" <[email-masked]>
Sent: Friday, July 02, 2010 6:09 AM
To: "SAVI Mailing List" <[email-masked]>
Cc: "Jean-Michel Combes" <[email-masked]>
Subject: Re: [savi] Conclusion on SAVI device configuration with prefixes

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