RE: [fw-wiz] NAPT - NAT Port selection
From: Bill Royds (broyds_at_rogers.com)
Date: 08/20/04
- Previous message: Kevin Sheldrake: "Re: [fw-wiz] Top Secret DOD Data over the Public Internet? Thoughts?"
- In reply to: ravivsn_at_www.rocsys.com: "[fw-wiz] NAPT - NAT Port selection"
- Next in thread: Orca: "RE: [fw-wiz] NAPT - NAT Port selection"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] [ attachment ]
To: <ravivsn@www.rocsys.com>, <firewall-wizards@honor.icsalabs.com> Date: Fri, 20 Aug 2004 11:33:14 -0400
If the destination IP address is different, a port forwarder on the receiving
end has your problem in reverse. It needs to translate the destination port on
one IP to a different port on the actual web server. As long as the combination
source_IP:Source_Port,Destination_IP:Destination_Port is unique, then you have a
unique TCP (or UDP) connection.
So (from your example)
Source_IP Destination_IP Protocol Source_Port Destination_Port
66.10.5.10 70.1.2.5 TCP 2000 80
66.10.5.10 70.1.5.6 TCP 2000 80
A port forwarding load balance on destination IP 70.1.2.5 and destination
70.1.2.6 could translate incoming traffic by changing your source ports as it
goes through their load balancer's NAT. Internally their servers would see
Source_IP Destination_IP Protocol Source_Port Destination_Port
66.10.5.10 192.168.20.5 TCP 32001 80
66.10.5.10 192.168.20.5 TCP 32002 80
Which leaves the sockets still unique. Their load balancer has the
responsibility of ensuring uniqueness within their internal network, not you.
The limit of 64K is for source ports per sourceaddress:destination IP:port
triplet, not just per source address. How do you think AOL supports millions of
customers on a fairly limited IP source address space?
-----Original Message-----
From: firewall-wizards-admin@honor.icsalabs.com
[mailto:firewall-wizards-admin@honor.icsalabs.com] On Behalf Of
ravivsn@www.rocsys.com
Sent: Thursday, August 19, 2004 11:36 PM
To: firewall-wizards@honor.icsalabs.com
Cc: ravivsn@rocsys.com
Subject: [fw-wiz] NAPT - NAT Port selection
Hi,
NAPT devices allow access to internet by internal machines having
private IP addresses using one or more public IP addresses.
We are vendors of security devices and these have NAPT feature
and we allow upto 63K TCP connections from internal machines at any
time. 63K limit comes from number of unique source ports that can be
assigned as NAT ports.
Our customer, who is one of small ISPs, wanted to use these devices. This
ISP gives private IP addresses to their customers and using NAPT provides
internet access to its customers. The ISP has limited number of public IP
addresses and it wants us to increase the number of TCP connection for each
public IP address to go from 63K to very high number.
Internally, among developers, we discussed this issue and we came out with
one suggestion - Reusage of NAT port in multiple sessions, as long as
atleast one of 5 tuples is different - Since source IP is same (public IP
address), destination IP or destination port has to be different.
It means that, on the Internet side, it is possible to have following
(example):
Source_IP Destination_IP Protocol Source_Port Destination_Port
66.10.5.10 70.1.2.5 TCP 2000 80
66.10.5.10 70.1.5.6 TCP 2000 80
One of our Engineers points out that, port forwarders on the receiving end
might be assuming that for a given source IP, source port would always
be different. His point is that, if both 70.1.2.5 and 70.1.5.6 belong to
same webhosting server and if a port-forwarder forwards traffic from
these two IP addresses to the same internal server, then internal server
might drop one connection.
Some of us feel that, this would be very rare condition and if it happens,
port forwarders are intelligent enough detect this and forward the
connection to next server and gracefullty shutdown second connection.
I solicit your feedback on this.
- Is it good for NAPT device to use same NAT port for different
sessions, if they are going to different destination (based on
Destination IP and Port)? Do you see any problems associated with
this apart one mentioned above?
- Any experiences?
Thanks in advance
Ravi
_______________________________________________
firewall-wizards mailing list
firewall-wizards@honor.icsalabs.com
http://honor.icsalabs.com/mailman/listinfo/firewall-wizards
_______________________________________________
firewall-wizards mailing list
firewall-wizards@honor.icsalabs.com
http://honor.icsalabs.com/mailman/listinfo/firewall-wizards
- Previous message: Kevin Sheldrake: "Re: [fw-wiz] Top Secret DOD Data over the Public Internet? Thoughts?"
- In reply to: ravivsn_at_www.rocsys.com: "[fw-wiz] NAPT - NAT Port selection"
- Next in thread: Orca: "RE: [fw-wiz] NAPT - NAT Port selection"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] [ attachment ]
Relevant Pages
|
