Donato Ba*aglino Lorenzo Bracciale

Transcription

1 IP Donato Ba*aglino Lorenzo Bracciale

2 Outline why IP (mo:va:on) IP architecture (router, LAN) IP addressing Sta:c IP (CIDR, host + net) DHCP Rou:ng IP ARP

3 Why IP? There are many different LAN technologies (Wifi, Ethernet ) because there are many different needs: wireless connec:vity: UMTS, WiFi, WiMax high speed cable data transfer: FDDI Cheap cable data transfer: Ethernet Low energy consump:on: bluetooth, zigbee How different hosts on different LAN can communicate? Needs a common language! Inter Net Protocol

4 Internet Protocol Internet Protocol Mission: allow hosts on different network to interoperate, disregarding the specific network tecnology adopted on each network LAN LAN WiFi LAN Internet Ethernet LAN LAN LAN

5 IP Architecture Every host must have an unique address (IP Address) Communication among IP Hosts is carried inside an IP Packets IP Packet is composed by an IP-Header and a Payload Inside the IP header is specified the source and the destination IP of the packet There is (at least) one Router inside each LAN that forward IP Packet depending from the packet destination

6 IP Architecture (example) If host want to communicate with host : generates an IP packet The IP packet is sent to a Router using the specific LAN technology Router read IP header field and forward to next-hop, according to a routing table

7 IP packet Format

8 Pra:ce: view an IP packet

9 Pra:ce: Traceroute traceroute to ( ), 64 hops max, 40 byte packets ( ) ms ms ms 2 tovrt8.net.uniroma2.it ( ) ms ms ms ( ) ms ms ms 4 ru uniromaii rt rm1.rm1.garr.net ( ) ms ms ms 5 rt rm1 rt rm2 l1.rm2.garr.net ( ) ms ms ms 6 so edge1.Paris1.Level3.net ( ) ms ms ms 7 ae ebr2.Paris1.Level3.net ( ) ms ae ebr2.Paris1.Level3.net ( ) ms ms 8 ae ebr1.Frankfurt1.Level3.net ( ) ms ms ms 9 ae csw4.Frankfurt1.Level3.net ( ) ms ae ebr1.Frankfurt1.Level3.net ( ) ms ms 10 ae csw1.Frankfurt1.Level3.net ( ) ms ae csw4.Frankfurt1.Level3.net ( ) ms ae 3 89.edge3.Frankfurt1.Level3.net ( ) ms ( ) ms ( ) ms ( ) ms ( ) ms ( ) ms ms ( ) ms ( ) ms ms ( ) ms ms ( ) ms ( ) ms ( ) ms ms 16 fx in f106.google.com ( ) ms ms ms

10 Subnets Every host inside each LAN belong to an IP subnet In each IP subnet hosts IP Address belong to a specific range so that: The first part of the address (net part) is the same for all the hosts The second part (host part) must be different for all the host Network part Host part SUBNET

11 IP Address and network Mask Every IPv4 machine must have: An IP address 32 bit long Ofen represented by do*ed nota:on : 4 byte separed by a point. Just for human convenience! Must be unique in all the IP Network A network Mask 32 bit long : first X se*ed 1, others to 0 Can be represented in do*ed nota:on Or by prefix nota:on /22

12 IP Address In each subnet there are two reserved addresses: Host part with all 0 is the network address Host part with all 1 is the broadcast address Routers must have an IP Address/Netmask for each interface they have

13 Gelng an IP address How to get an IP address: Manual configura:on Automa:cally assigned, permanent random IP address Dynamically assigned Auto assigned

14 DHCP, the Dynamic Host Configura:on Protocol DHCP, evolu:on of BOOTP protocol Goal of DHCP: full configura:on of a Host, assign of: IP Address, Subnet Mask, gateway IP address DNS server SMTP server <xxx> server (extensible protocol) Client/Server Model (UDP datagrams)

15 DHCP in a nutshell

16 Rou:ng All router forward IP Packets according to a ROUTING TABLE: At every line of the table there are: A des:na:on nework A subnet mask of the des:n:on network The next hop (i.e. the router to send the IP packet to) Des;na;on Nwk Mask Next HOP RULE: if the des*na*on IP Address of a packet matches a specific des*na*on network, route the packet to the related next hop

17 Rou:ng Example ? Des;na;on Nwk Mask Next HOP

18 Routers Do NOT learn from packet ( different from switch) Rou:ng tables can be filled automa:cally by rou:ng protocol (e.g. RIP, BGP, OSPF ) IP Addressing/Rou:ng depends from the place IP is not well suited for Mobility

19 Longest Prefix Match e Default GW Where to send packet with DST ADDR ?: Des;na;on Nwk Mask Next HOP RULE: if more entries are matched, apply the lines of the table with the greater Mask (longest prefix) Des;na;on Nwk Mask Next HOP Default Gateway: always matched, not always used!

20 Pra:ce: View the Rou:ng table pippo:/home/lorenzo# route n Kernel IP rou:ng table U eth UG eth UG eth U eth UG eth UG eth0

21 The bond between LAN and IP IP packet sent to physical network interface by encapsula:ng them in a Datalink frame using Datalink addresses (opera:on performed hop by hop) Datalink Addresses (MAC Addresses): local on specific subnet IP Addresses: global on Internet How to dynamically map IP addresses to Datalink addresses (e.g. Ethernet Addresses) without a priori knowledges?

22 The solu:on: ARP (Address Resolu:on Protocol) Dynamic mapping o not a concern for applica:on & user o not a concern for system administrator Not IP specific Not a Datalink layer protocol Need Datalink with broadcas:ng capability ARP NOT strictly necessary: may have IP MAC mapping 32 bit IP addresses ARP RARP 48 bit Ethernet address

23 The ARP idea Features: Stateless protocol: request response send broadcast request receive unicast respone how to show my ARP cache? C:\arp a ~$ arp -a so; state entries: storage of IP Datalink entries in a cache (the ARP cache ) for a fixed amount of :me