1 TCP/IP Networking Yue Cui 06/13/02

2 Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines

3 Introduction TCP/IP and the Internet A brief history ARPARNET(1969 by DARPA) Internet Management ICANN IETF ISOC Standards and Documentation RFCs, FYIs, STDs and BCPs

4 Introduction TCP/IP protocol suite IP – routes data packets from one machine to another ICMP – provides lower-level support for IP, including error messages, routing assistance and debugging help ARP – translates IP address to hardware address (a.k.a. MAC address) UDP and TCP – deliver data to specific applications on the destination machine

5 Introduction TCP/IP family

6 Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines

7 Packets and Encapsulation Packet Header—tells where the packet came from and where it’s going Payload—actual data to be transferred

8 Encapsulation Layer M H4H4 M H4H4 H4H4 H3H3 H3H3 H2H2 M M M H4H4 M H4H4 H4H4 H3H3 H3H3 H2H2 M M source machine destination machine

9 Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines

10 IP Addresses Historical Internet address classes IP addresses were grouped into “classes” Class A,B and C denote regular IP addresses. Class D and E are used for multicasting and research purpose. Subnet masks Part of the host portion of an address is “borrowed” to extend the network portion. Use ifconfig command to configure IP address and subnet masks

11 IP Addresses IP address crisis We were going to run out of class B addresses by mid-1995 The routing tables of Internet backbone sites were growing so large that they would not fit in the memory of available routers IP addresses were being allocated with no locality of reference

12 IP Addresses Solution to the IP address crisis CIDR (Classless Inter-Domain Routing) A short-term solution Manage the existing 4-byte address space that uses the available addresses more efficiently and allows routing tables to be simplified by taking numerical adjacencies into account IPv6 A long-term solution A revision of the IP protocol that expands the address space to 16 bytes

13 Routing Meaning Looking up a network address in the routing table to forward a packet toward its destination Building the routing table in the first place Configure netstat route get (on BSD-based system)

14 Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines

15 ARP, DHCP and PPP ARP: Address Resolution Protocol Discovers the hardware address(MAC address) associated with a IP address Usage: Redhat% /sbin/arp –a xor.com( ) at 08:00:20:77:5E:A0[ether] on eth0 earth.xor.com( ) at 00:50:DA:12:4E:E5[ether] on eth0

16 ARP, DHCP and PPP DHCP: Dynamic Host Configuration Protocol Dynamically assigns network parameters to hosts Leasable parameters include: IP addresses and netmasks Gateways(default routes) DNS name servers Syslog hosts WINS servers, proxy servers TFTP servers(for loading a boot image)

17 ARP, DHCP and PPP PPP: Point-to-Point Protocol Serial line encapsulation protocol that specifies how IP packets must be encoded for transmission on a slow serial line Sometimes used with home technologies such as Dial-up, DSL and cable modem

18 ARP, DHCP and PPP System Commands Config files Red Hat /usr/sbin/pppd /etc/ppp/options /usr/sbin/chat /etc/ppp/ppp.conf /etc/ppp/allow Free BSD /usr/sbin/pppd /etc/ppp/options /usr/sbin/chat /etc/ppp/options.ttyserver /etc/ppp/chat.ttyserver PPP-related commands and configuration files example

19 Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines

20 Security Issues IP forwarding ICMP redirects Source routing Broadcast pings and other forms of directed broadcast UNIX-based firewalls Virtual private networks(VPN) IPSEC: secure IP (Refer to Chapter 21 for details)

21 Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines

22 Addition of machines Basic steps Assign an IP address and hostname Set up the new host to configure its network interfaces at boot time Set up a default route Point to a DNS name server, to allow access to the rest of the Internet

23 Assign an IP address and hostname /etc/hosts file Example from text book localhost lollipop.xor.com lollipop loghost chimchim-gw.xor.comchimchim-gw ns.xor.com ns licenses.xor.com license-server hostname command Assigns a hostname to a machine Typically runs at boot time

24 Configure network interface ifconfig command Common form: ifconfig interface address options… up/down For example: Ifconfig en netmask up Options Netmask Sets the subnet mask for the interface Broadcast Specifies the IP broadcast address for the interface

25 Configure static routes route command Format: route [-f] op [type] destination gateway [hop-count] Options Add, delete, (get, change, flush, monitor) Default routes route add default gateway-IP-address

26 Configure DNS /etc/resolv.conf file All systems require to modify it Sample: Search cs.colorado.edu colorado.edu Nameserver Nameserver Nameserver

27 Configure DNS “service switch” file Some systems do not use DNS by default, these systems use “service switch” file to resolve hostname-to IP- address mapping Service switch files by system SystemSwitch filesDefault for hostname lookups Solaris/etc/nsswitch.confnis [NOTFOUND=return] files HP-UX/etc/nsswitch.confdns [NOTFOUND=return] nis [NOTFOUND=return] files Red Hat/etc/nsswitch.conf /etc/host.conf db files nisplus dns hosts, bind FreeBSD/etc/host.confhost,bind

28 Thank you! Questions?