IPv4 Addresses. Network Layer. Types of IPv4 Addresses. IPv4 Address Classes (old) q 32 bits long q Identifier for host, router interface q Notation:

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1 IPv4 Addresses Network Layer q 32 bits long q Identifier for host, router interface q Notation: v Each byte is written in decimal in MSB order, separated by dots v Example: Types of IPv4 Addresses IPv4 Address Classes (old) q Unicast Address v Destination is a single host q Multicast address v Destination is a group of hosts q Broadcast address v v Destination is all hosts Class A B C D 0 Net 32 bits Type of Serv. Host 10 Net Host 110 Net Host 1110 Multicast address E Reserved 3 4 1

2 IP Address Classes q Class A: v For very large organizations v 16 million hosts allowed q Class B: v For large organizations v 65 thousand hosts allowed q Class C v For small organizations v 255 hosts allowed q Class D v Multicast addresses v No network/host hierarchy IP Address Hierarchy q Class A, B, C addresses support two levels of hierarchy q However, the host portion can be further split into subnets by the address class owner v more than 2 levels of hierarchy 5 6 Subnetting Subnet Masks Example Address: Example: Class B address with 8-bit subnetting 16 bits 8 bits 8 bits Network id Subnet id Host id Mask: Subnet masks allow hosts to determine if another IP address is on the same subnet or the same network 16 bits 8 bits 8 bits Network id Subnet id Host id

3 Subnet Masks (cont d) IP Addressing in network Assume IP addresses A and B share subnet mask M. Are IP addresses A and B on the same subnet? 1. Compute (A and M). 2. Compute (B and M). 3. If (A and M) = (B and M) then A and B are on the same subnet Example: A and B are class B addresses A = B = Same network? Same subnet? M = Problems with Class-based Routing q Too many small networks requiring multiple class C addresses q Running out of class B addresses, not enough nets in class A q Addressing strategy must allow for greater diversity of network sizes IP addressing: CIDR CIDR: Classless InterDomain Routing v subnet portion of address of arbitrary length v address format: a.b.c.d/x, where x is # bits in subnet portion of address subnet host part part /

4 CIDR Reducing Routing Table Size q An ISP can obtain a block of addresses and partition this further to its customers v Say an ISP has /24 address (256 addresses). He has another customer who needs only 4 addresses from then that block can be specified as /30 Without CIDR: service provider Routing table With CIDR: service provider /16 Routing table Hierarchical addressing: route aggregation Hierarchical addressing allows efficient advertisement of routing information: Organization /23 Organization /23 Organization /23 Organization /23. Fly-By-Night-ISP ISPs-R-Us Send me anything with addresses beginning /20 Send me anything with addresses beginning /16 Internet Hierarchical addressing: more specific routes ISPs-R-Us has a more specific route to Organization 1 Longest prefix match will be used to route IP packets Organization /23 Organization /23 Organization /23 Organization /23. Fly-By-Night-ISP ISPs-R-Us Send me anything with addresses beginning /20 Send me anything with addresses beginning /16 or /23 Internet

5 What do routers look like? What s inside a router Access routers e.g. ISDN, ADSL Core router e.g. OC48c POS Core ATM switch 18 Basic Components Forwarding Engine Packet Forwarding Table Routing Protocols Routing Table Switching Control Plane Datapath per-packet processing Destination Address payload header Router Routing Lookup Data Structure Forwarding Table Dest-network Port / / Outgoing Port /

6 Router Architecture Overview Input Port Functions Physical layer: bit-level reception Data link layer: e.g., Ethernet see chapter 5 Decentralized switching: q queuing: if datagrams arrive faster than forwarding rate into switch fabric Three types of switching fabrics Output Ports q Buffering required when datagrams arrive from fabric faster than the transmission rate q Scheduling discipline chooses among queued datagrams for transmission

7 Example Forwarding Table Longest prefix match Destination IP Prefix /8 Prefix length / / /19 7 IP prefix: 0-32 bits Longest prefix match / /16 Outgoing Port /19 q With CIDR, route entries are prefixes <prefix, CIDR mask> q Can be aggregated q We need to find the longest matching prefix that matches the destination address q Need to search all prefixes of all length (in order) and among prefixes of the same length / / / Prefixes can Overlap Key Network-Layer Functions Longest matching prefix / / / / / / Routing lookup: Find the longest matching prefix (the most specific route) among all prefixes that match the destination address. q forwarding: move packets from router s input to appropriate router output q routing: determine route taken by packets from source to dest. v Routing algorithms analogy: q routing: process of planning trip from source to destination q forwarding: process of getting through single interchange

8 Interplay between routing and forwarding routing algorithm The Internet Network layer Host, router network layer functions: value in arriving packet s header local forwarding table header value output link Network layer Routing protocols path selection RIP, OSPF, BGP Transport layer: TCP, UDP forwarding table Link layer physical layer IP protocol addressing conventions datagram format packet handling conventions ICMP protocol error reporting router signaling The Internet Protocol (IP) q Provides delivery of packets from one host to any other host in the Internet q Internet packets are called datagrams and may be up to 64 kilobytes in length v although they are typically much smaller 31 IP datagram format IP protocol version number header length (bytes) type of data max number remaining hops (decremented at each router) upper layer protocol to deliver payload to how much overhead with TCP? q 20 bytes of TCP q 20 bytes of IP q = 40 bytes + app layer overhead ver 32 bits 16-bit identifier flgs time to live head. type of len service upper layer length offset header checksum 32 bit source IP address data (variable length, typically a TCP or UDP segment) fragment 32 bit destination IP address Options (if any) total datagram length (bytes) for fragmentation/ reassembly E.g. timestamp, record route taken, specify list of routers to visit. 32 8

9 IP Fragmentation & Reassembly IP Fragmentation and Reassembly q network links have MTU (max.transfer size) - largest possible link-level frame. v different link types, different MTUs q large IP datagram divided ( fragmented ) within net v one datagram becomes several datagrams v reassembled only at final destination v IP header bits used to identify, order related fragments reassembly fragmentation: in: one large datagram out: 3 smaller datagrams Example q 4000 byte datagram q MTU = 1500 bytes 1480 bytes in data field offset = 1480/8 length =4000 ID =x length =1500 fragflag =0 ID =x ID =x offset =0 One large datagram becomes several smaller datagrams length =1500 length =1040 ID =x fragflag =1 fragflag =1 fragflag =0 offset =0 offset =185 offset = IP Support Protocols q ARP q RARP q ICMP ARP q Address Resolution Protocol q Returns a MAC sublayer address or link layer address when given an Internet address q After a packet reaches a router, the link layer header needs to be added to reflect the destination host on that link q Need IP à MAC address translation Type Preamble S D 0x0806 ARP PACKET

10 ARP packet format ARP (cont d) ARP packet containing ? Proto=IPv4 0x0800 Oper=1 Sender H/W address Sender IP address Target H/W address target IP address ARP Source MAC address Source IP address Destination MAC address Destination IP address Protocol Type : IPv4 0x0800 Opcode ARP request:0 Opcode ARP reply:1 37 Ethernet Address: 05:23:f4:3d:e1:04 IP Address: Wants to transmit to Ethernet Address: 12:04:2c:6e:11:9c IP Address: Ignored Ethernet Address: 98:22:ee:f1:90:1a IP Address: Answered 38 RARP ICMP q Reverse Address Resolution Protocol q RARP performs the inverse action of ARP q RARP returns an IP address for a given MAC sublayer address q Need MAC address à IP address q Host have no permanent storage q On reboot? Need to figure IP address q Operationally, RARP is the same as ARP q Protocol for error detection and reporting tightly coupled with IP, unreliable q ICMP messages delivered in IP packets q ICMP functions: v Announce network errors v Announce network congestion v Assist trouble shooting v Announce timeouts

11 ICMP MSG IPV4 Header for ICMP IP header Source, Destination Address, TTL,... 1 ICMP MSG Message type, Code, Checksum, Data ICMP header Protocol Field value=1 ICMP: Internet Control Message Protocol Type Code description 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest host unreachable 3 2 dest protocol unreachable 3 3 dest port unreachable 3 6 dest network unknown 3 7 dest host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 route advertisement 10 0 router discovery 11 0 TTL expired 12 0 bad IP header

12 Specific uses of ICMP q Echo request reply v Can be used to check if a host is alive q Destination unreachable v Invalid address and/or port q TTL expired v Routing loops, or too far away Ping q Uses ICMP echo request/reply q Source sends ICMP echo request message to the destination address q Destination replies with an ICMP echo reply message containing the data in the original echo request message q Source can calculate round trip time (RTT) of packets q If no echo reply comes back then the destination is unreachable Ping (cont d) Traceroute Time A Echo request R1 R2 R3 Echo reply B q Traceroute records the route that packets take q A clever use of the TTL field q When a router receives a packet, it decrements TTL q If TTL=0, it sends an ICMP time exceeded message back to the sender q To determine the route, progressively increase TTL v Every time an ICMP time exceeded message is received, record the sender s (router s) address v Repeat until the destination host is reached or an error message occurs

13 Traceroute (cont d) Traceroute Examle Time A R1 R2 R3 TTL=1, Dest = B, port = invalid Te (R1) TTL=2, Dest = B Te (R2) TTL=3, Dest = B Te (R3) TTL=4, Dest = B Te = Time exceeded Pu = Port unreachable B 1 lcsr-gw ( ) ms ms ms 2 rucs-gw ( ) ms ms ms 3 transition2-gw ( ) ms ms ms 4 rutgers-gw.rutgers.edu ( ) ms ms Vl1000-sr02-hil l012-svcs.rutgers.edu ( ) ms 5 rutgers-gw.rutgers.edu ( ) ms ms ms ( ) ms ms ms 7 clev-nycm.abilene.ucaid.edu ( ) ms ms ms 8 ipls-clev.abilene.ucaid.edu ( ) ms ms ms 9 kscy-ipls.abilene.ucaid.edu ( ) ms ms ms 10 dnvr-kscy.abilene.ucaid.edu ( ) ms ms ms 11 snva-dnvr.abilene.ucaid.edu ( ) ms ms ms ( ) ms ms ms 13 BERK--SUNV.POS.calren2.net ( ) ms ms ms 14 pos1-0.inr-000-eva.berkeley.edu ( ) ms ms ms 15 vlan198.inr-201-eva.berkeley.edu ( ) ms ms ms 16 fast8-0-0.inr-210-cory.berkeley.edu ( ) ms ms ms 17 GE.cory-gw.EECS.Berkeley.EDU ( ) ms ms ms 18 gig8-1.snr1.cs.berkeley.edu ( ) ms ms ms 19 now.cs.berkeley.edu ( ) ms * ms Pu (B) IP addresses: bootstrap? Q: How does host get IP address? IP bootstrap & NAT q hard-coded by system admin in a file v Wintel: control-panel->network->configuration- >tcp/ip->properties v UNIX: /etc/rc.config q DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server v plug-and-play 52 13

14 DHCP (Ch 4.4) More Internet Protocols DHCP, NAT, IPv6 q DHCP stands for dynamic host configuration protocol q DHCP is client-server q DHCP offers a number of more features v Dynamic IP address allocation v IP addresses can be leased for a certain time v Useful where there are a limited number of IP addresses v Useful for temporary connections (testing, laptops, mobile networks) 54 DHCP (cont d) Address Allocation Modes q DHCP has two components: v A protocol for delivering bootstrap information from the server to the clients v An algorithm for dynamically assigning addresses to clients q DHCP supports three modes of allocation v Automatic allocation: Server assigns a permanent address to a host v Dynamic allocation: Server assigns a host an IP address with a finite lease v Manual allocation: Server assigns host an IP address chosen by the network administrator

15 IPV4 Header for DHCP 17 Source Port Destination port=67 DHCP PACKET Request=1 Reply=2 DHCP Packets (cont d) Hardware address Request/Reply Hardware type length in bytes Hop count Transaction ID Number of seconds Flags Client IP address Your IP address Server IP address Gateway IP address Client hardware address (16 bytes) Server hostname (64 bytes) 57 Boot filename (128 bytes) Options (312+ bytes) 58 Definitions of address fields DHCP Packet Fields q ciaddr Client IP address; only filled in if client is in BOUND, RENEW or REBINDING state and can respond to ARP requests. q yiaddr 'your' (client) IP address. The IP address, server is assigning to client q siaddr IP address of server to use in the netx step of the bootstrap process; returned in DHCPOFFER, DHCPACK by server. q giaddr Relay agent IP address, used in booting via a relay agent. q chaddr Client hardware address used for identification. q All fields are same as BOOTP except: v Flags: One flag currently defined Broadcast (bit 0): Clients can request that all DHCP server messages be broadcast to it v Options: All DHCP packets must use the DHCP message type option, which defines the type of DHCP message being sent: 1= DHCPDISCOVER 2= DHCPOFFER 3= DHCPREQUEST 4= DHCPDECLINE 5=DHCPACK 6=DHCPNACK 7=DHCP RELEASE 8=DHCP INFORM

16 DHCP Message types q DHCP message types v DHCP Discover: Client broadcasts to locate a server v DHCP Offer: Server responds with proposal of parameters v DHCP Request: Client broadcasts its choice of server. All other servers are implicitly declined. v DHCP ACK: Selected server responds to client with address v DHCP NAK: Selected server rejects the client s request v DHCP Decline: Client declines server s parameters v DHCP Release: Client releases its assigned address DHCP Protocol Server 1 Client Server 2 DHCPDISCOVER DHCPOFFER DHCPREQUEST Collects replies Selects server 2 DHCPDISCOVER DHCPOFFER DHCPREQUEST DHCPACK DHCP Protocol (cont d) DHCP Relay Agents q DHCP client broadcasts a DHCP Discover message v Client may specify preference of a lease and/or IP address q Many servers may respond with offers v Client chooses one server from them q Client broadcasts DHCP request with id of chosen server q Selected server sends DHCP ACK or NAK q Client begins using offered IP address once it receives ACK q If the client finds a problem, it sends a DHCP Decline message to the server and starts over again q Client may choose to release the address before lease expires by sending a DHCP Release message to the server q Similar to BOOTP Relay Agents q DHCP relay agents allow DHCP servers to handle requests from other subnets Client DHCP Relay Agent IP Gateway Router IP Gateway Router DHCP Server

17 Summary NAT: Network Address Translation q DHCP allow ignorant hosts to receive IP addresses (and more) at start-up time q IP addresses don t have to be manually configured into hosts rest of Internet local network (e.g., home network) / All datagrams leaving local network have same single source NAT IP address: , different source port numbers NAT: Network Address Translation 2: NAT router changes datagram source addr from , 3345 to , 5001, updates table 2 NAT translation table WAN side addr LAN side addr , , 3345 S: , 5001 D: , S: , 80 D: , : Reply arrives dest. address: , S: , 3345 D: , 80 1 S: , 80 D: , : host sends datagram to , : NAT router changes datagram dest addr from , 5001 to , NAT: Network Address Translation q Features: local network uses just one IP address as far as outside world is concerned: v range of addresses not needed from ISP: just one IP address for all devices v can change addresses of devices in local network without notifying outside world v can change ISP without changing addresses of devices in local network v devices inside local net not explicitly addressable, visible by outside world (a security plus)

18 NAT: Network Address Translation Recent Developments: IPv6 q 16-bit port-number field: v 60,000 simultaneous connections with a single LAN-side address! q NAT is controversial: v routers should only process up to layer 3 v violates end-to-end argument NAT possibility must be taken into account by app designers, eg, P2P applications v address shortage should instead be solved by IPv6 q IPv4 (the standard IP protocol) has limited address space q Most importantly, IP is running out of addresses. 32 bits are not enough. q Real-time traffic and mobile users are also becoming more common IP version 6 (Also called IPng, or IP next generation) IPv6: The Changes IPv6 header l Large address space: l 128-bit addresses (16 bytes) l Allows up to 340,282,366,920,938,463,463,374,607,431,768,211,456 unique addresses (3.4 x ) l Fixed length headers (40 bytes) l Improves the speed of packet processing in routers Version (4) Traffic Class (8) Flow Label (20) PayloadLen (16) Next Header (8) Hop Limit (8) Source Address Destination Address l 40 bytes header l Version field set to 6 l PayloadLen field gives the length in bytes of the packet excluding the header l Next Header value specifies the type of next header (if any ) that follows the IPv6 header 6 Is TCP, 17 is UDP 4 bytes

19 IPv6: The Changes (cont d) q Support for flows v Flows help support real-time service in the Internet v A flow is a number in the IPv6 header that can be used by routers to see which packets belong to the same stream v Guarantees can then be assigned to certain flows v Example: Packets from flow 10 should receive rapid delivery Packets from flow 12 should receive reliable delivery IPv6 Addresses l Classless addressing/routing (similar to CIDR) l Notation: x:x:x:x:x:x:x:x (x = 16-bit hex number) l contiguous 0s are compressed: 47CD::A456:0124 l IPv6 compatible IPv4 address: :: l First 96 bits are 0 l Global unicast addresses start with 001. l 2000::/3 prefix 73 19