1. Networking Colin Alworth May 26, 2006

2. Quick Review IP address: four octets Broadcast addresses –IP addresses use all 1’s for the host bits, and whatever network bits are needed –MAC addresses are all 1’s (FF:FF:FF:FF:FF:FF)

3. Packet Makeup Encapsulation (Ethernet, SLIP) –IPX –IPv4 (64k) TCP –http, ftp, icmp UDP DHCP ARP

4. OSI Model: All People Seem To Need Data Processing Application Presentation Session Transport Network Data Link Physical

5. Linux Uses this model Based on the BSD TCP/IP network stack

6. Linux Commands ifconfig – sets up interfaces route – defines routing information netstat – displays network statistics tcpdump – outputs the incoming packets

7. Adding Devices to a Network Any OS will need information like: –IP Address –Subnet Mask –DNS Server –Gateway Address

8. DHCP Dynamic Host Configuration Protocol Based on BOOTP – not so dynamic Gets all of the network info from a single server Can be different on every distro –Debian – edit the file /etc/network/interfaces –Another option – /etc/dhclient.conf, or the command dhclient

9. Looking at the kernel net directory holds the code for networking Why have networking code in the kernel?

10. Simple diagram

11. Complex Diagram

12. Kernel Issues IP –Checksums: done in software –Packet mangling, unmangling –net/ipv4/ip_input.c Security? –Root access needed for many operations –SSL, and tunneling

13. Example in UML Create a new interface Give user access to interface Run UML with eth0=tuntap,device No routing or connections to internet wget, ping

14. Making changes net/ipv4/ip_input.c:260 Avoiding mangled packets Testing, running

15. Next step: IPv6 IPv4 has 4.3×10 9 (4.3 billion) addresses IPv6 supports 3.4×10 38 addresses Bigger packet size limits (jumbograms) Routing performance Notation: eight groups of four hex digits Same network/host differences No broadcast – use flags instead

16. Bibliography http://user-mode- linux.sourceforge.net/networking.htmlhttp://user-mode- linux.sourceforge.net/networking.html http://lxr.linux.no/ http://www.tldp.org/HOWTO/NET3-4- HOWTO.htmlhttp://www.tldp.org/HOWTO/NET3-4- HOWTO.html http://cs.uml.edu/~cgould/#Networking http://cisco.netacad.net - name and password requiredhttp://cisco.netacad.net http://en.wikipedia.org/wiki/IPv6

17. Links to start with http://news.netcraft.com/archives/web_serv er_survey.htmlhttp://news.netcraft.com/archives/web_serv er_survey.html http://lxr.linux.no/