On 2008-08-04 17:25, Gregory M. Lebovitz wrote:
> At 07:17 PM 8/3/2008, Shin Miyakawa wrote:
>> oops. Let me correct.
>> Our Linksys box can assign same address for WAN and LAN interfaces.
>> But anyway ... Still I am wondering what's happening in this case...
>>
>> Shin
>>
>> > Brian, please explain, where does a packet from PC1 for 10.0.0.12 go
>> > in the following settings ? PC3 ? or CGN ?
>
> Shin,
> Assuming
> -that I've understood your question, and
> -that PC1, 2, & 3 are all in the same subnet...
>
> Unless I am missing something, according to basic host processing, a
> packet from PC1 to 10.0.0.12 will be sent directly to PC3 by PC1. The
> host processing should look like this:
> - PC1 IP stack receives datagram from upper layer, destined for 10.0.0.12
> - DST IP in same subnet as local interface
> - check local MAC learning table for entry associated with 10.0.0.12.
> - If entry, then create frame for that MAC and send frame on segment.
> - If no entry, then ARP for 10.0.0.12. Upon receiving MAC response,
> create frame for that MAC and send frame on segment.
Exactly. Perhaps another way to look at it, remembering that RFC 1918
introduced ambiguous address spaces that can *only* be distinguished
by context, is to label the contexts:
ADDRESS CONTEXT A : ADDRESS CONTEXT B : ADDRESS CONTEXT C
: :
[PC1]-----------+ : :
10.0.0.10A | : :
| : :
[PC2]-----------+-----------[NAT]--------------------------[CGN]----------------
10.0.0.11A | 10.0.0.1A : 10.0.0.20B 10.0.0.12B : Global Address
| : :
[PC3]-----------+ : :
10.0.0.12A : :
A NAT that doesn't treat the two address contexts as logically
disjoint is broken IMHO. Of course, 10.0.0.12B (like every
address in Context B) is totally inaccessible from Context A.
But the Context B side of the CPE NAT will use 10.0.0.12B
as its default router.
It's certainly horrible, but when you run out of addresses,
what else can you expect?
Brian
>
> Did I understand your question?
>
>> >
>> >
>> > [PC1]-----------+
>> > 10.0.0.10 |
>> > |
>> >
>> [PC2]-----------+-----------[NAT]--------------------------[CGN]----------------
>>
>> > 10.0.0.11 | 10.0.0.1 10.0.0.20 10.0.0.12
>> Global Address
>> > |
>> > [PC3]-----------+
>> > 10.0.0.12
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