I run Tor on Linux and tried setting it up as a bridge with obfs3 and obfs4 enabled. According to the log everything is ok, but Atlas shows a seemingly random ORPort in the higher ranges instead of port 443, which I defined in torrc. It is not any of the PTs ports. ExtORPort auto is enabled. There was traffic when the bridge was started but I think it was only server descriptors and keys being exchanged. So, what is this port on Atlas, what is it doing and should I open the firewall for incoming connections to it?

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To avoid giving out information about the bridge. If the ORPort was on some high numbered or unusual port, for example, then an adversary who knows the port could perform an internet-wide scan to discover Tor instances running on that port, confirm the bridges identity and block the bridge.

See ticket #19317: Sanitize TCP ports in bridge descriptors for more information on how this is performed.

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