The,Operational,Intricacies,Re technology The Operational Intricacies of Remote Monitoring Technology
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Assume that the network security policy allows internal hosts to initiate remote sessions with external hosts. There is an attempt to set up remote monitoring rules to implement this policy. You can see that you do not know the destination port number because this is set dynamically by the remote protocol. If you allow the host to call any one of the ports for the remote “call back” from the server, a program written with evil intent can probe any of the internal network hosts if it originates a call from port 20. This is clearly undesirable.One way to solve the problem is to use the TCP ACK flag to identify legitimate incoming connections and to block connections to the internal host’s standard service ports (usually less than 1024). They show the redesigned remote monitoring rules for a remote session. Filter rule 1 allows calls to the external host from any port from the internal network. Filter rule 2 blocks calls to ports less than 1024. This is safe for remote operation because the local call-back port is greater than 1024 in standard remote. Filter rule 3 only allows ACK packets from port 20 on the external host.The remote server has sent the entire file as a TCP message segment for transmission to the TCP layer. The remote server then server-announces its intention to break the data connection when file transfer is completed. A reply code indicates that the data connection will close at end of file transfer. Many experts have proposed the use of a command that does not require a modification to the remote protocol, but a modification to the remote clients. The remote protocol says that, by default, all data transfers should be over a single data connection. The remote server does an active open from TCP port 20 to a local dynamic port on the remote client, which does a passive open on this local port.Most current remote clients do not behave that way. They assign a new local port for each transfer and announce this through the PORT command. If the remote client sends a command to the remote server, the server does a passive TCP open on a random port and informs the client of the port number. The client can initiate an active open to establish the connection using a random local port. This mechanism avoids the remote server call-back to a service port on the remote client. The remote client initiates an active open to an external host, and this is usually not a problem with most organizations’ network security policies. Article Tags: Remote Monitoring, Remote Protocol, Filter Rule, Remote Server, Data Connection, Active Open, Remote Client
The,Operational,Intricacies,Re