Network Services

Section Overview Client-Server Model Network Ports, Services and Daemons Network Protocols Viewing Active Ports Common Server Daemons

TCP/IP Protocol Stack Application (FTP, HTTP, DNS) Transport Layer (TCP,UDP) Network Layer (IP) Link Layer (Device Drivers) Physical Layer (media)

Client-Server Model Server Client Makes a request Request fulfilled Listens for incoming requests

Network Ports Enables processes to communicate with each other across a network 64K possible ports Privileged ports < 1024 reserved for system use only Correspond to well-known services /etc/services

/etc/services Service-name port/protocol aliases Examples: ssh 22/tcp smtp 25/tcp mail www 80/tcp http www-http imaps 993/tcp syslog 514/udp

Running Network Servers Stand-alone Daemon Each started via rc script Always running Listens (binds) to the service port Uses resources even when idle inetd “Super-daemon” Listens to many ports Starts daemon when request is received Daemon shuts down when finished /etc/inetd.conf

/etc/inetd.conf service_name: Service name sock_type: stream (tcp) dgram (udp) raw (direct IP) proto: protocol used (/etc/protocol) flags: wait, nowait user: User to run daemon as server_path: Full path to daemon program args: Command line arguments to daemon

Xinetd Replacement for inetd Enhancements Default: /etc/xinetd.conf Access Control Resource based limits Logging (Success and Failure) Default: /etc/xinetd.conf Service Specific: /etc/xinetd.d

/etc/xinetd.conf defaults { instances = 60 log_type = SYSLOG authpriv log_on_success = HOST PID log_on_failure = HOST cps = 25 30 } includedir /etc/xinetd.d

Example xinetd service /etc/xinetd.d/imaps: service imaps { disable = no socket_type = stream wait = no user = root server = /usr/local/sbin/imapd groups = yes flags = REUSE IPv6 }

Windows Service Management Microkernel – Everything a service Administrative tools -> Services Service Options Startup Type: Automatic, Manual, Disabled Log On: Which user to run service as Recovery: What to do on failure Dependencies: Which services does this one depend upon

Windows Service Recovery Settings for: First Failure Second Failure Subsequent Failures Counter Reset (Days) Options: Take no Action Restart the Service Run a program Restart the Computer

Network Protocols Service request/response syntax Often uses English commands Request For Comments (RFC) Documentation for protocols and practices Each revision its own number May have a second classification For Your Information (FYI) Best Common Practices (BCP) Standards (STD)

Viewing Active Ports netstat –a – Ports in use Source/destination addresses and ports Protocol used State LISTEN ESTABLISHED lsof –i :service – Process using port tcpdump – View network traffic

Resource Sharing Daemons Network File System (NFS) nfsd mountd Line Printing Daemon (lpd) Samba smbd – Microsoft file and print sharing nmbd – Microsoft name resolution

Internet Daemons telnetd – Remote Access ftpd – File transfer Berkeley-R Daemons sshd – Secure Shell Electronic Mail sendmail/postfix – Receiving email imapd, popd – Remote email access httpd – Web

Infrastructure Daemons named – DNS dhcpd – Dynamic Host Config Protocol nisd/ldapd – Directory Services fingerd – User information xntpd – System time synchronization routed/gated – Routing Firewall