Subject: Re: New Version Notification for draft-xu-virtual-subnet-04

From: Martin Pels <[email-masked]>
Date: Sat, 18 Jun 2011 15:34:29 +0200

Hi Xiaohu,

On Mon, 24 Jan 2011 15:09:53 +0800
Xu Xiaohu <[email-masked]> wrote:

> Hi all,
> 
> An updated version of Virtual Subnet
> (http://tools.ietf.org/html/draft-xu-virtual-subnet-04) has been
> submitted.
> 
> One major change is to describe the inter-subnet communication
> mechanism in more details, especially in the case where VRRP is
> deployed in the CE network. For more details, please see
> http://tools.ietf.org/rfcdiff?difftype=--hwdiff&url2=draft-xu-virtual-subnet
> -04.txt
> 
> Any comments are welcome.

I have a couple of questions and comments.

Section 3.4:

* Can you elaborate on how active-active multi-homing would work in the
  PE-CE broadcast domain?

  Obviously, the VRRP Master and Slave cannot advertise the virtual
  Router MAC address concurrently, since this would cause rapid station
  movement of said MAC address. So in this scenario the active-active
  multi-homing would be unidirectional only, with the Slave PE sourcing
  the traffic destined for the CE from its local MAC address rather
  than the Virtual Router MAC address. Correct?

* In case of a VRRP transition remote PEs will continue to send traffic
  to the old VRRP Master until the new Master creates CE host routes
  for all local CEs, and the old Master withdraws them. In order to
  facilitate a quick transition there should be a mechanism to do this
  without having to wait for each CE to send an ARP request.

Section 3.5:

* If a CE moves to a different VPN site it may still have an ARP cache
  filled with IP addresses mapped to the MAC address of the PE of the
  original VPN site. Would this not cause a lot of flooding, due to the
  CE sourcing frames with the MAC address of its old PE as their
  destination?

Section 5:

* Considering the impending IPv4 depletion, it would be wise to make
  IPv6 CE support an intrinsic part of this solution, rather than
  deferring it to a future document.

Kind regards,
Martin Pels

---

From: Xu Xiaohu <[email-masked]>
Date: Mon, 20 Jun 2011 12:23:44 +0800

Hi Martin,

Thanks a lot for your valuable comments. Please see my reply inline.

> -----邮件原件-----
> 发件人: Martin Pels [mailto:[email-masked]]
> 发送时间: 2011年6月18日 21:34
> 收件人: Xu Xiaohu
> 抄送: [email-masked]
> 主题: Re: New Version Notification for draft-xu-virtual-subnet-04
> 
> Hi Xiaohu,
> 
>   than the Virtual Router MAC address. Correct?

The active-active multi-homing is available for the incoming traffic of a
multi-homed site. For more details, please see page 10 of my latest .PPT as
follows:
http://www.nanog.org/meetings/nanog52/presentations/Wednesday/XU-Virtual%20S
ubnet(for%20NANOG52)v1.0.pdf

>   without having to wait for each CE to send an ARP request.

Actually the VRRP master and the VRRP slaver could advertise CE host routes
simultaneously.

>   CE sourcing frames with the MAC address of its old PE as their

Yes, your observation is correct. There does need more detailed
consideration and description on this point. How about running VRRP on the
PE routers at any time? In this way, both the old PE router and the new PE
router could return the same Virtual MAC in their own ARP responses. 

>   deferring it to a future document.

Good suggestion. After we have reached a rough consensus on the IPv4-based
solution, I will put more effort into the IPv6-based solution.

Thanks again for your insightful comments.

Best regards,
Xiaohu