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UNIX Networking

UNIX Networking. Section Overview. TCP/IP Basics TCP/IP Configuration TCP/IP Network Testing Dynamic Host Config Protocol (DHCP) Wireless Networking. TCP/IP Protocol Stack. Application (FTP, HTTP, DNS). Transport Layer (TCP,UDP). Network Layer (IP). Link Layer (Device Drivers).

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UNIX Networking

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

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

  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

  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: 255.255.255.0 (255 = 11111111) • 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. Address Resolution Protocol Translates IP addresses to Ethernet (MAC) addresses • Translates IP addresses to Ethernet (MAC) addresses Who is 10.0.0.3? I am (1:2:3:7:8:9) 10.0.0.1 10.0.0.2 10.0.0.3 10.0.0.4 arp –a: View the cache

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

  14. RedHat Network Files • /etc/sysconfig/network HOSTNAME • /etc/sysconfig/network-scripts/ ifcfg-[interface] BOOTPROTO ONBOOT IPADDR GATEWAY USERCTL NETMASK NETWORK BROADCAST • ifup/ifdown [interface]

  15. Name Services • /etc/hosts • Local configuration • Localhost – 127.0.0.1 • /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 Root Server Non-Recursive 2 3 1 4 5 Recursive 8 7 6 host.domain.com dns.domain.com dns.iupui.edu dns.cs.iupui.edu

  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!) • 802.11b – 11 Mbps • 802.11g – 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 VPN Server Internet Application Server Virtual Private Network

  24. Point to Point Tunneling Protocol • Based on • Point to Point Protocol (PPP) • Generic Routing Encapsulation (GRE) IP Hdr Encrypted GRE Body GRE Hdr PPP Data IP TCP • Weaknesses • Poor Encryption • Session handshaking done in clear

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

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