1 UNIX Networking

2 Section Overview TCP/IP Basics TCP/IP Configuration TCP/IP Network Testing Dynamic Host Config Protocol (DHCP) Wireless Networking

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

4 EIPT/U TCP/IP Packet Encapsulation UTP/PSTN Ethernet/PPP IP TCP/UDP Service Data Data T/UData IPT/UData E

5 Connecting to a Network Hostname and IP Address assignment Configuration of hardware Default route (gateway) assignment Name Service Configuration Testing and troubleshooting

6 Hostnames Uniquely identifies each system Fully Qualified Domain Name hostname.site.domain[.country] Country: 2 letter identifier for country Domain: Type of site (edu, com, org) Site: Unique name of organization Hostname: Unique name of system hostname : Display or set system name

7 IP Addresses Unique for each connection (interface) Consists of 4 octets (#.#.#.#) Network portion Host portion Special Addresses Network Address Broadcast Address

8 IP Address Classes Class 1 st Byte Format Total Hosts A 0 – 126N.H.H.H16 Million B128 – 191N.N.H.H64 Thousand C192 – 239N.N.N.H254 D224 – 239-(Multicast) E240 – 254-(Experimental)

9 Subnet Masks Splits networks into subnetworks Separates address into 2 parts 1’s – Network Portion 0’s – Host Portion Example: Class C Network Address: N.N.N.H Mask: (255 = ) CIDR Notation: N.N.N.H/24

10 Interface Configuration Hardware to connect to network Common interfaces Ethernet Modem Loopback ( lo ) Interface ifconfig – View/Configure interface

11 Ethernet Addressing Assigned by manufacturer (hardware) Must be absolutely unique Address format 6 octets in hex (#:#:#:#:#:#) First 3 octets: Manufacturer Identifier Last 3 octets: Card serial number Used for local network communication

12 Translates IP addresses to Ethernet (MAC) addresses Address Resolution Protocol Who is ? I am (1:2:3:7:8:9) arp –a : View the cache

13 Connects Networks together If destination not on local network, packets sent through gateway Default Gateways route : Display/configure routing

14 RedHat Network Files /etc/sysconfig/network HOSTNAME /etc/sysconfig/network-scripts/ ifcfg-[interface] BOOTPROTOONBOOT IPADDRGATEWAY USERCTLNETMASK NETWORKBROADCAST ifup/ifdown [interface]

15 Name Services /etc/hosts Local configuration Localhost – /etc/resolv.conf Domain Name Service (DNS) lookup search : domains to search if not FQDN nameserver (3): Nameservers to consult /etc/nsswitch.conf

16 DNS Name Resolution host.domain.comdns.domain.comdns.iupui.edudns.cs.iupui.edu Root Server Non-Recursive Recursive

17 Network Testing Localhost reachability Hostname reachability Local network reachability Internet network reachability DNS resolution

18 Network tools ping – Reachability test traceroute – Routing performance netstat – Network performance stats tcpdump – Packet sniffing nslookup/dig – DNS Queries Configuration tools (already discussed)

19 Dynamic Host Config Protocol Client broadcasts a request for an IP address and network information Server leases address to client Lease must be renewed periodically Easy to make global network changes Linux: BOOTPROTO=dhcp

20 Wireless Networks Extend the network Included in many devices now Laptops PDAs DSL/Cable Modems Bandwidth (YMMV!) b – 11 Mbps g – 54 Mbps Set Service Identifier (SSID) Shared “key” between clients and Access Point (AP) Automatically detected vs. assigned

21 Wireless Security Issues Sniffing / War Driving Bandwidth stealing Access to private resources Security Measures Non-broadcasting SSIDs MAC Access Control Lists (ACLs) WEP?

22 RedHat ifcfg- Additions TYPE=Wireless ESSID=[ssid name] CHANNEL=[1-11] MODE=[Auto|Managed|Ad-hoc] Can set manually with /sbin/iwconfig

23 Virtual Private Networks Virtual Private Network VPNServer ApplicationServer Internet

24 Point to Point Tunneling Protocol Based on Point to Point Protocol (PPP) Generic Routing Encapsulation (GRE) IP Hdr GRE Hdr Encrypted GRE Body PPPData TCPIP  Weaknesses  Poor Encryption  Session handshaking done in clear

25 IPSec Part of IPv6 Spec Authentication Header (AH) IPv4 Hdr Auth Hdr TCP/UDP Hdr & Data  Encapsulating Security Payload (ESP) IPv4 Hdr ESP Hdr Encrypted Payload Data TCP Hdr ESP Auth ESP Tlr  Modes: Transport and Tunnel