1. Network Services

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

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

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

5. 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

6. /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

7. 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

8. /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

9. 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

10. /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

11. 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 }

12. 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

13. 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

14. 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)

15. 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

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

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

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