|[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]|
Hi Simon, On 10/07/2012 18:50, Simon Perreault wrote:
I like this longer explanation. I agree that once I understand what you are trying to say the shorter explanation in the document makes sense. But it is a bit cryptic. (I don't have specific suggestions, so if you can't improve existing text, that is Ok with me.)On 07/03/2012 08:24 AM, Alexey Melnikov wrote:I found the justification for REQ-6 hard to read/understand. Why does access to servers being on the internal network need to go through CGN at all?Here's the thing: the server is not on the internal network. It's on the external network, but it is still managed by the ISP. The ISP's network includes the internal network and some part of the external network. Furthermore, in many cases an ISP may run multiple CGNs, so the ISP's network is actually multiple internal networks and some part of the external network. The servers in the external network are operated by the ISP and "know" the internal networks (have routes to them), and can reach them directly without translation. And since connections from subscribers to those servers may account for a lot of traffic, it is important to not spend NAT resources on them.
Now, I'm not sure how to alter the existing text to make it easier to understand. It seems to me that all the information is there, just not with the same order/emphasis as what I wrote above. If the above was useful for you to understand, could you please point out in the text below what change would have helped you understand?REQ-6: It MUST be possible to administratively turn off translation for specific destination addresses and/or ports. Justification: It is common for a CGN administrator to provide access for subscribers to servers installed in the ISP's network, in the external realm. When such a server is able to reach the internal realm via normal routing (which is entirely controlled by the ISP), translation is unneeded. In that case, the CGN may forward packets without modification, thus acting like a plain router. This may represent an important efficiency gain. Figure 2 illustrates this use-case. X1:x1 X1':x1' X2:x2 +---+from X1:x1 +---+from X1:x1 +---+ | C | to X2:x2 | | to X2:x2 | S | | l |>>>>>>>>>>>>| C |>>>>>>>>>>>>>>| e | | i | | G | | r | | e |<<<<<<<<<<<<| N |<<<<<<<<<<<<<<| v | | n |from X2:x2 | |from X2:x2 | e | | t | to X1:x1 | | to X1:x1 | r | +---+ +---+ +---+ Figure 2: CGN pass-through Thanks, Simon