Dragon0x40
asked on
Port address translation
How does PAT work?
Can you only use less the 65,000 hosts per one real ip address?
My understanding is this.
One external address for example 11.11.11.11 and two internal addresses of 10.10.10.10 and 10.10.10.11
Both internal clients want to go to yahoo.com on port 80
So one client sends packet destination 67.195.160.76:80 source 10.10.10.10:1500 and the other client sends packet destination 67.195.160.76:80 source 10.10.10.11:1501
Router performing PAT keeps the destinations 67.195.160.76:80 but changes the source to 11.11.11.11:1500 and 11.11.11.11:1501
When yahoo replies the destination is 11.11.11.11:1500 and 11.11.11.11:1501 but the source is 67.195.160.76:1503 and 67.195.160.76:1504
Our external router sees destination ports of 1500 and 1501 and knows which internal hosts to send to?
Where is the port translation? It seems that the ports remain the same but only the source ip address changes?
Would a better name be SAT? Source address translation?
The 65,000 limit comes from the fact that there are less than 65,000 unique source ports.
Or maybe I don't understand what is actually happening in PAT?
Can you only use less the 65,000 hosts per one real ip address?
My understanding is this.
One external address for example 11.11.11.11 and two internal addresses of 10.10.10.10 and 10.10.10.11
Both internal clients want to go to yahoo.com on port 80
So one client sends packet destination 67.195.160.76:80 source 10.10.10.10:1500 and the other client sends packet destination 67.195.160.76:80 source 10.10.10.11:1501
Router performing PAT keeps the destinations 67.195.160.76:80 but changes the source to 11.11.11.11:1500 and 11.11.11.11:1501
When yahoo replies the destination is 11.11.11.11:1500 and 11.11.11.11:1501 but the source is 67.195.160.76:1503 and 67.195.160.76:1504
Our external router sees destination ports of 1500 and 1501 and knows which internal hosts to send to?
Where is the port translation? It seems that the ports remain the same but only the source ip address changes?
Would a better name be SAT? Source address translation?
The 65,000 limit comes from the fact that there are less than 65,000 unique source ports.
Or maybe I don't understand what is actually happening in PAT?
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If one host client source is 10.10.10.10:1505 and the other host client source is 10.10.10.11:1505 then one source port will have to be "translated" to 1506 or some other port?
This is because if both hosts use source port of 1505 then yahoo will respond back to both requests streams with the destination address of 11.11.11.11:1505 and the external translating router would not be able to determine which packets should be sent to 10.10.10.10 or 10.10.10.11?