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Networking Colin Alworth May 26, 2006
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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)
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Packet Makeup Encapsulation (Ethernet, SLIP) –IPX –IPv4 (64k) TCP –http, ftp, icmp UDP DHCP ARP
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OSI Model: All People Seem To Need Data Processing Application Presentation Session Transport Network Data Link Physical
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Linux Uses this model Based on the BSD TCP/IP network stack
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Linux Commands ifconfig – sets up interfaces route – defines routing information netstat – displays network statistics tcpdump – outputs the incoming packets
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Adding Devices to a Network Any OS will need information like: –IP Address –Subnet Mask –DNS Server –Gateway Address
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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
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Looking at the kernel net directory holds the code for networking Why have networking code in the kernel?
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Simple diagram
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Complex Diagram
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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
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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
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Making changes net/ipv4/ip_input.c:260 Avoiding mangled packets Testing, running
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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
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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
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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/
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