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I see this error Message in log from Our ISP provider. I am not sure if this is from the Cisco switch at the ISP or the router at the customer. What does this error actually say?

The "ip" is for Our monitor server, which monitors the network service for the customer. Does this mean that either the Cisco router or the customer router is blocking Our monitor server from reaching any IP on the network?

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up vote 2 down vote accepted

It means that a TCP packet destined for 0.0.0.0:23 was blocked by access list number 120. It's not an error, it's just an informational report -- the rule was set to log.

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0.0.0.0 denotes blocking any IP address. :23 denotes port 23, which is the well-known port for the telnet protocol. –  jftuga Dec 10 '12 at 13:27

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