Subject: [Softwires] GI-DS-lite Review

From: "Lee, Yiu" <[email-masked]>
Date: Fri, 25 Feb 2011 20:52:10 +0000

Hi authors,

I was asked to do a review on the GI-DS-lite draft, this is my review.

The draft is well written and is ready to publish.

P.3:  If e.g., a GRE based
   encapsulation mechanisms is chosen, it allows the network between the
   access gateway and the "NAT" to be either IPv4 or IPv6

Suggest to change NAT to AFTR.

P.4:       AFTR: Address Family Transition Router (also known as "Large Scale
      NAT (LSN)" or "Dual-Stack lite Tunnel Concentrator", or "Carrier
      Grade NAT").  An AFTR combines IP-in-IP tunnel termination and
      IPv4-IPv4 NAT.

Suggest to remove "(also known as "Large Scale
      NAT (LSN)" or "Dual-Stack lite Tunnel Concentrator", or "Carrier
      Grade NAT"). "

P.4: TID: Access Tunnel Identifier.  The interface identifier of the
      point-to-point access tunnel.

In the GI-DS-lite context, my understanding is the GW is a L3 device, the TID (e.g. SID of the PPPoE) could be used to map to a CID. The two usages I can think of in the draft is mapping the SID to the GRE-key and SID to the IPv6-Flow-Label. But since MPLS-VPN and IP-in-IP are using AD's source IP address for the CID, the TID won't be used. In case of WiMAX, no TID will be assigned to the AD. This isn't discussed clearly in the draft. Do you think we should write a session to capture this?

P.4: The combination of CID and SWID
   (potentially along with other traffic identifiers such as e.g. interface, VLAN, port, etc.) serves as common context between Gateway
   and AFTR to uniquely identify flows associated with an access device.

Suggest to rewrite to: "The combination of CID and SWID must be unique between gateway and AFTR to identify the flows associated with an AD."

P.5: The outer/
   external IPv4 address of a NAT-binding at the AFTR is either assigned
   autonomously by the AFTR from a local address pool…..

Suggest to rewrite to: "The NAT binding of the AD's address could be assigned autonomously by the AFTR from a local address pool….."

P.8:  Softwire identification is supplied
      by the endpoints of the GRE tunnel.  The GRE-key serves as CID.

Suggest to rewrite to "SWID is the source address of the GRE tunnel from the GW.  The CID is the GRE-key assigned to the AD.

P.7: MPLS VPN: Softwire identification is supplied by the VPN
      Identifier of the MPLS VPN.  The IPv4-address serves as CID.  The
      IPv4-address within a VPN has to be unique.

Suggest to rewrite to "SWID is the MPLS VPN label. The AD's IPv4-address is the CID.  Give a MPLS VPN label, the AD's IPv4 address must be unique.

P.7:  Softwire identification is supplied by the
      endpoints of the IP-in-IP tunnel.  Either the inner IPv4-address
      serves as CID (in which case the IPv4-address has to be unique) or
      the IPv6-Flow-Label serves as CID (which obviously only applies to
      cases where IPv6 transport is used).  Note that when using the IP-
      Flow-Label as CID additional scaling considerations might apply
      given that the CID is to only 20 bits wide in this case.  Also one
      should ensure sufficient randomization in this case to for example
      avoid interference with other uses of the IP-Flow-Label, such as
      ECMP.

I think it would be more clear to separate the discussion for IPv4-in-IPv4 and IPv4-in-IPv6.

Suggest to rewrite to:

"IPv4-in-IPv4: SWID is the outer IPv4 source address. The AD's IPv4 address is the CID. Given an outer IPv4 source address, the AD's IPv4 address must be unique.

IPv4-in-IPv6: SWID is the outer IPv6 source address. If the AD's IPv4 address is the CID, the AD's IPv4 address must be unique. If the IPv6-Flow-Label [RFC3697] is the CID, the AD's IPv4 address may be overlapped. IPv6-Flow-Label is 20-bit wide which is shorter than the recommended 32-bit CID. In addition,  one should ensure sufficient randomization to avoid possible interference with other uses of the IP-Flow-Label, such as ECMP."

P.9: May want to update Figure 3 to separate the two IP-in-IP cases.

Regards,
Yiu