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If Norton blocks an apparent Symantec address, that sounds serious. But there is some doubt possible, as to its really being a Symantec address.
Port 54 is sometimes attacked by the MuSka52 Trojan, and is an odd port for a legitimate service to be requesting, even if it were symantec requesting it - it is the XNS (Xerox Network Service) Clearinghouse port.
I advise you to disregard this port being blocked, unless Symantec complains about it. Symantec software should know what it is doing - and this (port 54) is not a legitimate port for it to be requesting, in any obvious way. To open that port would be to invite trouble in, and I do not advise it - unless your Symantec software is recommending it.