2009/7/7 John Lauro <john.lauro@covenanteyes.com>:

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Reusing the original port is usually a bad idea. A notable example of things breaking is Netfilter connection tracking, which gets confused if you reuse the exact same endpoints for a different connection.

Technically they are not the exact same if you include the interface.  If it doesn't consider the interface then they would appear the same.

Well, you don't always have >1 interface. Consider WCCPv2 "cache on a stick" with only one upstream interface to the router redirecting it both the client and server traffic. Adrian