On Tue, Sep 25, 2012 at 01:04:57PM +0200, Florian Lohoff wrote: > But still - This is all not a single reason for DS Light. CGN can be done > with a PPP Dual Stack session aswell. And BTW - I dont think that the > NAT in the CPE will be eliminated. If you do, you'll have another bunch > of problems like prefix delegation for IPv4 or eliminate PPP and use > proxy arp e.g. bridging. > > Another issue with eliminating the NAT in the CPE is that suddenly you > CGN address space shrinks very fast - You have a /10 - When you hand out > a /24 per subscriber you'll be able to support 2^14 subscribers per CGN > instance. 16K subscribers is not much - Todays linecards support > 16-64K Subscribers so you'll need up to 4 CGN instances per linecard, > and the big operations dont to CGN on the Edge but use a centralized > approach. I hear hundrets of MPLS VPNs creeping up to shovel Data from > the Edge to the CGN gateway. You are handing out the normal 192.168/16 space on the LAN side. You pass them on to the gateway without any NAT. I.e. default IPv4 route to 192.0.0.1 (and your device is 192.0.0.2). The AFTR can identify the interface by the public IPv6 address and the IPv4 address range only needs to be unique wrt RFC1918 behind the CPE. > And where do you hold the IPv4 State? At least for AAA purposes? The AFTR. The CPE just operates a v4-in-v6 tunnel to the AFTR and there you've got 192.0.0.0/24 on-link. But given that it's a point-to-point link it does not really matter what their IP addresses are. You just put your default route there and the AFTR sees the packets that are not destined to the local LAN and translates those. No need for prefix delegation or proxy ARP or bridging. But then any presentation of DS-lite would tell you that. :-) > As far as i understood the reasons for DS Light is licensing costs > in the mobile backhaul as those are per PDN context e.g. backhaul channel > to the mobile. Those are today not capable to do dual stack (Although > Standardised in 3GPP Version 8/9) so you'd need 2 PDN contexts, one for > IPv4 and one for IPv6. So Mobile Operators thought of DS Light so > they'll not need another context and simply switch UAs to v6 transport > only. That's a different problem of how to provide IPv4 connectivity to mobile devices which only support one single context that's either v4 or v6. > IMHO DSLight will be a niche market. With 3GPP Version9 we'll see Dual > Stack in the Mobiles and my guess is that we'll see v4/v6 dualstack, > later v4CGN/v6 Dualstack on DSL and FTTx. We're already seeing DS-lite deployment with cable modem deployments in Germany. Kabel Deutschland seems to do it. As long as you control the CPE and you tested it, it works. But people are crying about not getting a public legacy IP anymore. Kind regards Philipp Kern
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