Ftp tcp ports9/17/2023 ![]() ![]() (note that Java / Tomcat is listening on port 8009 but that port is DROPped by the firewall) Sshd 3804 root 3u IPv4 7830 TCP *:ssh (LISTEN) Here's an lsof launched on the server: # lsof -i -nĬOMMAND PID USER FD TYPE DEVICE SIZE NODE NAME I really don't get why I have 2043 closed ports: Not shown: 2043 closed ports Here's the nmap output: # nmap -PN 94.xx.yy.zz -p1-2048 If it's normal to see 21, as "filtered", then why aren't all the other ports appearing as "filtered" too!? I expected to see only 22 and 80 as "open". My question is: why do port 21, appear as "filtered" and the 2043 other ports do not appear as filtered? However a few ports appear as "filtered". The result of nmap on the first 2048 ports gives 22 and 80 as open, as I expect. The only type of NEW packets allowed are TCP packets on port 22 and 80 and that's it (no HTTPS on that server). FTP uses and relies on TCP to ensure all the packets of data are sent correctly and to the proper destination.I'm scanning a server which should have a pretty simple firewall using iptables: by default everything is DROPped besides RELATED and ESTABLISHED packets. When an FTP client requests to connect to an FTP server, a TCP connection is being established using the application layer within TCP and ports 20 and 21. Link Layer: separate from the other layers, this layer describes protocols that exist only through one link that a host is connected to. Internet Layer: takes the network packets from the transport layer and sends them to the proper destinations based on their IP addresses. Transport Layer: creates and delivers the data packets passed on from the application layer to the appropriate host devices by adding source and destination port numbers and maintaining the end-to-end network connections. Protocols include: FTP, HTTP, IMAP, SMTP, SSH ![]() TCP and IP use the four-layer model that separates the protocols based on their functions.Īpplication Layer: standardizes the communication for data exchange between programs or devices and uses ports to pass data along to the transport layer. This frees up network paths for more requests since they are all considered unique connections and can be used continuously. Once the server has completed the request from the client, the connection is dissolved. IP: addresses and routes the packets of data to make sure they reach the right destination and device within the network.īased on the “end-to-end” and “client/server” communication models, TCP/IP features are separated based on functions into layers where one program or device (the client) can request a service from another program or device (the server). TCP: creates the link that allows the devices to connect and determines how data is packaged into smaller packets before being transmitted, and then reassembled after transfer. The Internet Protocol Suite, better known as TCP/IP, is a set of communications rules that allow two or more network devices to communicate. ![]()
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