10/13/2015© 2008 Raymond P. Jefferis IIILect 07 1 Internet Protocol

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 2 What is the Internet? A collection of separate networks Interconnected by routers and gateways –routers interconnect similar networks –gateways interconnect differing networks

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 3 Connectionless Functions Unicasting of datagrams each datagram routed from source to destination Multicasting of datagrams single datagram routed to many destinations

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 4 Internet Protocol (IP) A connectionless (datagram) service Supports connectionless transport (TCP) (TCP also supports connection-oriented transport)

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 5 Internet Protocol Routing Allows interconnection of subnetworks within a Local Area Network Allows interconnection of Local Area Networks

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 6 Subnet Interconnection

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 7 Router Interconnects subnets Many ports, each on separate subnet Operates at Network Layer Restricts traffic - only subnet traffic visible Can interconnect Local Area Networks (LANs)

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 8 Hub Interconnects hosts on subnet Many ports, all on same subnet Operates at Data Link Layer Does not restrict traffic (all traffic visible)

10/13/2015© 2008 Raymond P. Jefferis IIILect 07 9 LAN Interconnection

10/13/2015© 2008 Raymond P. Jefferis IIILect Larger Networks Wide Area Networks (WANs) May operate with different protocols Gateway couples these Internet is an example

10/13/2015© 2008 Raymond P. Jefferis IIILect WAN Interconnection

10/13/2015© 2008 Raymond P. Jefferis IIILect Effect on Application Data TCP adds header at transport layer IP adds header at network layer

10/13/2015© 2008 Raymond P. Jefferis IIILect TCP/IP Header Embedding

10/13/2015© 2008 Raymond P. Jefferis IIILect Addressing of Network Nodes Physical address (Ethernet address) –Medium Access Control (MAC) format 6 octets (uniquely assigned to hardware) Network address –Internet Protocol (IP) format 4 octets (assigned by agency) Translation –Address Resolution Protocol (ARP) –Reverse Address Resolution Protocol (RARP)

10/13/2015© 2008 Raymond P. Jefferis IIILect Physical (Hardware) Address MAC (Medium Access Control) address 6 octets (48 bits) Note: 2 48 = x10 14 –3 octets of vendor code (Assigned by IEEE) 1 octet of flag bits 2 octets of vendor number –3 octets of serial number (Assigned by vendor)

10/13/2015© 2008 Raymond P. Jefferis IIILect MAC Address Format

10/13/2015© 2008 Raymond P. Jefferis IIILect Network (IP) Address 4 octets (32 bits) Note: 2 32 = x10 9 Left octet(s) are Network address leftmost bits signify address class next bits are network address Right octets are Host address Host addresses may be subnetted left bits are Subnet rightmost bits are Host

10/13/2015© 2008 Raymond P. Jefferis IIILect Network Address Classes

10/13/2015© 2008 Raymond P. Jefferis IIILect Example Widener University - Class B address xxx.yyy

10/13/2015© 2008 Raymond P. Jefferis IIILect Addressing limits Class A (Super WAN - e.g. country) –2 7 networks, 2 24 hosts (3 octets) Class B (WAN/LAN) –2 14 networks, 2 16 hosts (2 octets) Class C (LAN) –2 21 networks, 2 8 hosts (1 octet) (Note: all address octets can be 0 to 255 )

10/13/2015© 2008 Raymond P. Jefferis IIILect Subnets Needed to make efficient use of addresses Reduce routing effort by assigning a single address to all the subnets Resolve local traffic locally; keep Intra-net traffic off the Inter-net Organize hosts into groups (LANs)

10/13/2015© 2008 Raymond P. Jefferis IIILect Example Class B Subnet Note that the Subnet divides the Host address space Subnet mask will contain 1s in Subnet space; 0s in Host space A 9-bit host space is assumed (510 hosts) A 7-bit subnet space remains (126 subnets) Note: Addresses 0 and 255 are reserved

10/13/2015© 2008 Raymond P. Jefferis IIILect Subnet Masks Router will AND mask with IP address and pass result through to local network –Example: 254 hosts (H) in subnet (S) IP address is:N.N.S.H subnet mask is: –Example: 510 hosts (H) in subnet (S) IP address is:N.N.S-H.H subnet mask is:

10/13/2015© 2008 Raymond P. Jefferis IIILect Subnet Calculators Simplify binary subnet calculations Are available free on the Internet Search on “subnet calculator” Example: –

10/13/2015© 2008 Raymond P. Jefferis IIILect Host Mask Design Procedure Specify expected number of hosts (N) –all computers –printers –network devices (hubs, routers, etc.) –add 2 (for reserved 0 and 255 addresses) Set k to next power of 2 giving at least N addresses Mask is 1s complement of 2 k -1

10/13/2015© 2008 Raymond P. Jefferis IIILect Address Translation IP to Hardware Address Resolution Protocol (ARP) Hardware to IP Reverse Address Resolution Protocol (RARP)

10/13/2015© 2008 Raymond P. Jefferis IIILect ARP/RARP Overview

10/13/2015© 2008 Raymond P. Jefferis IIILect ARP Request Packet

10/13/2015© 2008 Raymond P. Jefferis IIILect Address Translation Procedure Source computer to send Outgoing packet is put in queue Special ARP request packet is broadcast on network Target computer responds Target computer returns packet with missing address Note: its “target” is original “source” computer Source computer sends queued packet

10/13/2015© 2008 Raymond P. Jefferis IIILect To Send This packet will be broadcast to every host on network (subnet) Only responds (unicast response)

10/13/2015© 2008 Raymond P. Jefferis IIILect Answers now has the hardware address it needs to build packets to

10/13/2015© 2008 Raymond P. Jefferis IIILect Name Translation Name to IP-Address (engr.widener.edu => ) Domain Name Server (DNS) –a hierarchy of database servers on the network –local resolution attempted first; then network –secondary (backup), usually available

10/13/2015© 2008 Raymond P. Jefferis IIILect IP Header

10/13/2015© 2008 Raymond P. Jefferis IIILect IP Header Fields Version (4 bits) –version number Header Length (4 bits) –in 32-bit words (5 is minimum) Type of Service (8 bits) –Precedence (bits 0-2)– Throughput (bit 4) –Delay (bit 3)– Reliability (bit 5) –bits 6 & 7 reserved for future use

10/13/2015© 2008 Raymond P. Jefferis IIILect IP Header Fields (Cont’d) Total length –length of datagram, including header [bytes] –design minimum: 576 bytes Identification –sequence number for fragments Flags (3 bits) –bit 0 = 0 (reserved) bit 2 = more fragments –bit 1 = don’t fragment

10/13/2015© 2008 Raymond P. Jefferis IIILect IP Header Fields (Cont’d) Fragment offset (13 bits) –location of fragment in datagram (8-byte units) Time to live [seconds] –each router must count down by one Protocol type –for higher level processing of datagram –(TCP = 6, UDP = 17)

10/13/2015© 2008 Raymond P. Jefferis IIILect IP Header Fields (Cont’d) Source address (32 bits) –IP address Destination address (32 bits) –IP address Options –all devices must implement –typical: security, upper level protocols, etc.

10/13/2015© 2008 Raymond P. Jefferis IIILect ICMP Internet Control Message Protocol Conveys return error messages to source from an IP network No retransmission if lost

10/13/2015© 2008 Raymond P. Jefferis IIILect ICMP Header Format

10/13/2015© 2008 Raymond P. Jefferis IIILect Some ICMP Types & Codes

10/13/2015© 2008 Raymond P. Jefferis IIILect Some ICMP Interpretations Destination unreachable (router can’t find route) Source quench (reduce source rate) Time exceeded (TTL decremented to zero by router)

10/13/2015© 2008 Raymond P. Jefferis IIILect Routing Methods Distance Vector Protocol (uses RIP - Routing Information Protocol) Bellman-Ford routing algorithm Link State Protocol (uses OSPF - Open Shortest Path First) SPF routing algorithm (Dijkstra) All routers know complete network

10/13/2015© 2008 Raymond P. Jefferis IIILect RIP - Routing Information Protocol A distance vector protocol Uses hop count as metric (1 - 16) Peer routers exchange distance vectors every 30 seconds Router considered off-line if timeout exceeded (180 seconds) Problematic above subnet level

10/13/2015© 2008 Raymond P. Jefferis IIILect RIP2 (RIP) Header Note: White area repeats for each router addressed.

10/13/2015© 2008 Raymond P. Jefferis IIILect RIP Commands Request:For all or part of routing table of target router (destination address - via next-hop) Response:All or part of routing table from target router - or update COMMANDDESCRIPTION 1Request 2Response

10/13/2015© 2008 Raymond P. Jefferis IIILect RIP Version Number

10/13/2015© 2008 Raymond P. Jefferis IIILect OSPF - Open Shortest Path First An internal link state routing protocol Hierarchical routing by “areas” Link State Protocol (LSP) packets advertise routes Routers can advertise 1-hop hosts as sets One router of broadcast LAN is the“designated” router; failover to “backup”

10/13/2015© 2008 Raymond P. Jefferis IIILect More OSPF Features Allows multiple route definitions –by service types –by costs –by load (allows load balancing) Secures router databases –all data exchanges authenticated –only authenticated data can be propagated

10/13/2015© 2008 Raymond P. Jefferis IIILect Weighted Digraph Representation Vertices –routers –networks Edges –paths to routers to networks –corresponding costs

10/13/2015© 2008 Raymond P. Jefferis IIILect OSPF Packet Format

10/13/2015© 2008 Raymond P. Jefferis IIILect OSPF Fields Version Number at present, always 1 Packet Type 1 = Hello 2 = Database Description 3 = Link State Request 4 = Link State Update 5 = Link State Acknowledgment

10/13/2015© 2008 Raymond P. Jefferis IIILect OSPF Fields (cont’d) Packet length, including header [bytes] Source router address (ID) Area ID –Note: packets usually cover only 1 hop Checksum (1s complement) Authentication type Authentication field (64-bit)

10/13/2015© 2008 Raymond P. Jefferis IIILect Link State Tables Destination ID Next Hop ID Distance Metric –delay –data rate –unit cost ($) –combination

10/13/2015© 2008 Raymond P. Jefferis IIILect Network Routing Diagram

10/13/2015© 2008 Raymond P. Jefferis IIILect SPF Routing Table for R2