8: IP Basics IP protocol Routing protocols addressing conventions - PDF document

The Internet Network layer Host, router network layer functions: Transport layer: TCP, UDP 8: IP Basics IP protocol Routing protocols •addressing conventions •path selection •datagram format Network •RIP, OSPF, BGP •packet handling conventions layer routing ICMP protocol table •error reporting Last Modified: •router “signaling” 3/5/2003 2:11:15 PM Link layer physical layer 4: Network Layer 4: Network Layer 4a-1 4a-2 Protocol stack: Internet Protocol packet forwarding ❒ The Internet is a network of heterogeneous networks: Host A Host B ❍ using different technologies (ex. different maximum packet sizes) Router R Router W HTTP ❍ belonging to different administrative authorities (ex. Willing HTTP to accept packets from different addresses) ❒ Goal of IP: interconnect all these networks so can send TCP TCP end to end without any knowledge of the intermediate IP IP networks IP IP ❒ Routers: machines to forward packets between heterogeneous networks ethernet link link ethernet ethernet ethernet 4: Network Layer 4: Network Layer 4a-3 4a-4 IP Addressing IP Address Per Interface ❒ IP address: 32-bit ❒ IP address: 223.1.1.1 identifier for host, ❍ 32 bits 223.1.2.1 router interface 223.1.1.2 ❍ network part (high order bits) 223.1.1.4 223.1.2.9 ❒ interface: connection ❍ host part (low order bits) between host and 223.1.2.2 ❍ Defined by class of IP address? 223.1.1.3 223.1.3.27 physical link ❍ Defined by subnet mask? ❍ router’s must have multiple interfaces ❍ host may have multiple 223.1.3.1 223.1.3.2 interfaces ❍ IP addresses (unicast addresses) associated with interface, not 223.1.1.1 = 11011111 00000001 00000001 00000001 host, router 223 1 1 1 4: Network Layer 4: Network Layer 4a-5 4a-6

IP Addressing IP Addresses (Classes) given notion of “network”, let’s re-examine IP addresses: How to find the 223.1.1.2 223.1.1.1 223.1.1.4 networks? “class-full” addressing 223.1.1.3 ❍ device interfaces with same network part of class IP address? 223.1.9.2 223.1.7.0 1.0.0.0 to A 0network ❍ can physically reach host 127.255.255.255 each other without Unicast 128.0.0.0 to B network 10 host intervening router? 191.255.255.255 223.1.9.1 223.1.7.1 192.0.0.0 to 223.1.8.1 223.1.8.0 C Interconnected 110 network host 223.255.255.255 system consisting 223.1.2.6 223.1.3.27 of six “networks” 224.0.0.0 to Multicast D 1110 multicast address 239.255.255.255 or one network 223.1.2.1 223.1.2.2 223.1.3.1 223.1.3.2 (223.1.*.*)? 240.0.0.0 to Reserved E reserved 1111 255.255.255.255 32 bits 4: Network Layer 4: Network Layer 4a-7 4a-8 Hosts per Class IP Address Space Allocation ❒ Class A has ~2 24 hosts (16777216) CAIDA 1998 ❒ Class B has ~2 16 hosts (65536) ❒ Class C has ~2 8 hosts (256) ❒ What class do you think everyone wants? ❍ Suppose you are a company/university etc. Do you expect to need 16777216 hosts? Do you expect to need more than 256? 4: Network Layer 4: Network Layer 4a-10 4a-9 Current Allocation IP addressing: CIDR ❒ Class-full addressing: ❒ Interesting to exam current IP address ❍ inefficient use of address space, address space exhaustion space allocation (who has class A’s ? Etc) ❍ e.g., class B net allocated enough addresses for 65K hosts, even if only 2K hosts in that network ❍ Who has A’s? ❒ CIDR: Classless InterDomain Routing ❍ Computer companies around during initial allocation (IBM, Apple) ❍ network portion of address of arbitrary length ❍ address format: a.b.c.d/x, where x is # bits in network ❍ Universities (Stanford, MIT) portion of address ❍ Have A and still use other IP address blocks? ❒ CAIDA has info on complete allocation host network part part 11001000 00010111 00010000 00000000 200.23.16.0/23 4: Network Layer 4a-11 4: Network Layer 4a-12

Recall: How to get an IP How to get lots of IP Address? Addresses? Internet Registries RIPE NCC (Riseaux IP Europiens Network Coordination Centre) for Europe, Middle-East, ❒ Answer 1: Normally, answer is get an IP address Africa from your upstream provider APNIC (Asia Pacific Network Information Centre ) ❍ This is essential to maintain efficient routing! for Asia and Pacific ❒ Answer 2: If you need lots of IP addresses then ARIN (American Registry for Internet Numbers) for you can acquire your own block of them. the Americas, the Caribbean, sub-saharan Africa ❍ IP address space is a scarce resource - must prove you Note: Once again regional distribution is important have fully utilized a small block before can ask for a for efficient routing! larger one and pay $$ (Jan 2002 - $2250/year for /20 Can also get Autonomous System Numbers (ASNs) and $18000/year for a /14) from these registries 4: Network Layer 4a-13 4: Network Layer 4a-14 How to get a block of IP Classful vs Classless addresses?From upstream provider Network (network portion): ❒ Class A = /8 ❒ get allocated portion of ISP’s address space: ❒ Class B = /16 ❒ Class C = /24 ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20 Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23 Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23 Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23 ... ….. …. …. Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23 4: Network Layer 4a-15 4: Network Layer 4a-16 Hierarchical addressing: more specific Hierarchical addressing: route aggregation routes Hierarchical addressing allows efficient advertisement of routing information: ISPs-R-Us has a more specific route to Organization 1 Organization 0 Organization 0 200.23.16.0/23 200.23.16.0/23 “Send me anything Organization 1 with addresses “Send me anything 200.23.18.0/23 beginning Organization 2 with addresses . 200.23.16.0/20” beginning 200.23.20.0/23 Fly-By-Night-ISP Organization 2 . . . 200.23.16.0/20” . 200.23.20.0/23 Fly-By-Night-ISP . . Internet . . . Organization 7 . Internet . Organization 7 200.23.30.0/23 200.23.30.0/23 “Send me anything ISPs-R-Us with addresses “Send me anything ISPs-R-Us beginning 199.31.0.0/16 with addresses Organization 1 or 200.23.18.0/23” beginning 200.23.18.0/23 199.31.0.0/16” 4: Network Layer 4a-17 4: Network Layer 4a-18

IP addresses: how to get one? IP Address Allocation One more time ☺ ❒ CIDR is great but must work around existing ❒ Hard-coded by system admin in a file allocations of IP address space ❍ Long with subnet mask, default gateway and DNS ❍ Company 1 has a /20 allocation and has given out sub portions of it to server other companies ❍ University has a full class B address ❒ DHCP: Dynamic Host Configuration Protocol: ❍ Company 2 has a /23 allocation from some other class B dynamically get network identity and neighborhood ❍ ALL use the same upstream ISP – that ISP must advertise routes to all these blocks that cannot be described with a simple CIDR network ID and info dynamically, “plug-and-play” mask! ❒ Estimated reduction in routing table size with CIDR ❍ If IP addresses reallocated, CIDR applied to all, IP addresses reallocated based on geographic and service provider divisions that current routing tables with 10000+ entries could be reduced to 200 entries [Ford, Rekhter and Brown 1993] ❍ How stable would that be though? Leases for all? 4: Network Layer 4a-19 4: Network Layer 4a-20 DHCP Finding the DHCP server? ❒ Wouldn’t be big improvement if had to ❒ Automated configuration of IP addresses configure each host with address of DHCP ❒ DHCP server hands out IP addresses to server! hosts in a administrative domain ❍ A little better because at least every machine ❒ Relieves burdens of system administrators in a local network gets same info - major factor in lifetime cost of computer ❒ Hosts send special DHCPDISCOVER systems! message to the special IP address 255.255.255.255 ❒ Runs over UDP (ports 67 and 68) ❍ This is a special IP broadcast address and all ❒ RFC 2131 other nodes on that network will receive ❍ We’ll see more about special addresses like this 4: Network Layer 4a-21 4: Network Layer 4a-22 DHCP Discover/Offer DHCP server on every network? ❒ Host broadcasts “DHCP discover” msg ❒ If there is a DHCP server on the local network to receive the broadcast, then it ❍ Sent to 255.255.255.255 from 0.0.0.0 ❍ Contains a client ID to uniquely identify the client in that can respond the host with its IP address, network its default router, etc. ❍ Usually use MAC address ❒ Alternatively, can have a DHCP relay agent ❍ DHCP server can be configured with a “registered list” of MAC addresses to accept on each network that knows the address of ❒ DHCP server responds with “DHCP offer” msg the DHCP server and will forward the ❍ Sent from IP address of DHCP server to DHCPDISCOVER message 255.255.255.255 ❍ Includes ip address, subnet mask, DNS servers, default gateway, length of lease 4: Network Layer 4a-23 4: Network Layer 4a-24