1. Review of IPv4 Routing Dr Ram P Rustagi, PESIT rprustagi@pes.edu Jun 06, 2013 http://ise.pesit.pes.edu/Workshops/CDoT/

2. 2 IPv4 Overview Resources 2

3. Network service model Q: What service model for “channel” transporting datagrams from sender to receiver? Can transport layer rely on n/w layer? Will the packets be in order? Will the time gap between two pkts be maintained? Will network provide any congestion information? Will network provide any time gurantees? will network provide any BW guarantees?

4. Network Layer 4-17 1 2 3 Datagram forwarding table IP destination address in arriving packet’s header routing algorithm local forwarding table dest address output link address-range 1 address-range 2 address-range 3 address-range 4 32213221 4 billion IP addresses, so rather than list individual destination address list range of addresses (aggregate table entries) src: Kurose & Ross

5. Review of IPv4 General IP Networking Overview –Network Configuration –IPv4 Addressing * 1981 IP was standardized * Dotted Decimal Notation * Classful addressing - wastage

6. IP Addressing  Classful addressing:  first byte value determines the class  Class A (unicast): first bit is 0. value of first byte 0 - 126  Class B (unicast): first 2 bits have value 10 value of first byte: 128 - 191  Class C (unicast): first 3 bits have value 110 value of first byte: 191 - 223  Class D (Multicast): First 4 bits have value: 1110 value of first byte: 224 - 239  Class E (Experimental) : First 4 bits have value: 1111 value of first byte: 240 - 255  Large part of address space is wasted

7. Growth of the Internet In 1985 (RFC 950) subnetting concept was introduced. In 1987 VLSM (RFC 1009) It uses longest prefix match It allows Route aggregation Subnet Address Hierarchy Extended-Network-Prefix

8. Growth of the Internet By 1992 IETF identified the exponential growth of the internet. Three serious problems - Exhaustion of Class B address space - Rapid growth of Backbone Routing tables - Exhaustion of 32 bit IPv4 address space In 1993 CIDR was officially documented - Supernetting - Extensively supports Route aggregation IETF started the IPng working group for IPv6

9. IP Addressing  IPv4 addresses are unique and universal  exceptions ?  IPv4 address is 32 bit long  total available addresses: 4,294,967,296  Uses Dotted Decimal Notation (DDN)  example: 119.82.126.182  Exercise:  Find the error in following addresses 119.082.126.182 119.82.126.182.80 119.82.126.282 119.01010010.126.82

10. Subnets  Identified by subnet masks  Defines one network  A router is needed to connect two networks  Masks for classful addresses  Class A: 255.0.0.0 or /8  Class B: 255.255.0.0 or /16  Class C: 255.255.255.0 or /24  Glassful addressing obsolete now  replaced with classless addressing (CIDR)  RFCs  RFC 1518: Architecture for IP addr allocation with CIDR  RFC 1466: Guidelines for IP addr space management  RFC 917: Internet subnets

11. Subnets  Few terms to understand  network portion and host portion  network number apply subnet mask to IP address (bitwise AND)  Broadcast address set all bits to 1 in host portion  network mask set all bits to 0 in host portion  first available address in the block value of host portion = 1  last available address in the block value of host portion = 2 n -2

12. Subnets  Exercise 1  a block of addresses is granted to a small organization. one of the address is 119.82.126.182/27. Find out the following: the network number subnet mask broadcast address first available address and last available address  Exercise 2 :  repeat the above exercise for address 192.168.100.200/18

13. Address Types  Unicast  Multicast  Broadcast  Anycast

14. Forwarding Table  Needs at least 4 entries in forwarding table  Network Address  Network Mask  Next Hop Address  Interface  Forwarding table principles  Each routers makes its decision independently  Different routers may have different information  Tells how to reach destination but not how to get back  Effect of Forwarding Table principles  Packets are forwarded on hop by hop basis  Packets from A to B go via path X but return via path Y

15. 223.1.1.1 223.1.1.3 223.1.1.4 223.1.2.2 223.1.2.1 223.1.2.6 223.1.3.2 223.1.3.1 223.1.3.27 223.1.1.2 223.1.7.2 223.1.7.1 223.1.8.2223.1.8.1 223.1.9.1 223.1.9.2 R1 R3 R2 Rest of Internet Exercise: Build the routing table for all the routers Note: Take subnet mask for all network as /24 Q: What should be routing table for PCs? Forwarding Table e1 e2 e3 e2 e1 e3 e2 e1 src: Kurose & Ross

16. Network Layer 4-53 Hierarchical addressing: route aggregation “Send me anything with addresses beginning 200.23.16.0/20” 200.23.16.0/23 200.23.18.0/23 200.23.30.0/23 Fly-By-Night-ISP Organization 0 Organization 7 Internet Organization 1 ISPs-R-Us “Send me anything with addresses beginning 199.31.0.0/16” 200.23.20.0/23 Organization 2...... hierarchical addressing allows efficient advertisement of routing information: src: Kurose & Ross

17. Route Aggregation 200.23.16.0/23 11001000 00010111 00010000 00000000 200.23.18.0/23 11001000 00010111 00010010 00000000 200.23.20.0/23 11001000 00010111 00010100 00000000 200.23.22.0/23 11001000 00010111 00010110 00000000 200.23.24.0/23 11001000 00010111 00011000 00000000 200.23.26.0/23 11001000 00010111 00011010 00000000 200.23.28.0/23 11001000 00010111 00011100 00000000 200.23.30.0/23 11001000 00010111 00011110 00000000

18. Exercise: Summary Route Summary Route ?

19. Design the subnetting/routing N/w given: 192.168.0.0/24 -Each LAN has 10 hosts -serial link n/w needs two addresses -LAN of R3-R7-R6 needs 3 addresses

20. Answer: subnetting exercise 9 LANs of 10 hosts 1 LAN of 3 addresses 8 Serial links of 2 addresses

21. Using Routing Table  For a given packet  take the destination address  repeat the following for each entry in routing table  apply the netmask  match the computed n/w number with routing table entry  if matches forward the packet to next-hop on listed interface exit  else continue to next entry  when no match found (assuming 0.0.0.0/0 not defined) drop the packet

22. Network Layer 4-55 IP addressing: the last word... Q: how does an ISP get block of addresses? A: ICANN: Internet Corporation for Assigned Names and Numbers http://www.icann.org/  allocates addresses  manages DNS  assigns domain names, resolves disputes

23. ARP - Address Resolution Protocol  Packet delivery to a host requires two addresses Logical address - IP Address Physical address - MAC address  Need to find mapping from logical to physical ARP is used - RFC 826 Fig Src: Forouzan - Data Communication and Networking, SIE

24. ARP - 4 cases Src: Forouzan

25. ARP  ARP Request and Reply  ARP Request is broadcast  ARP Reply is Unicast  Other forms of ARP  Proxy ARP (RFC 1027)  Reverse ARP (RFC 903)  Gratuitous ARP

26. Proxy ARP  Router (Proxy ARP Server) replied to all requests  Used when  splitting a network w/o changing hosts netmask  Taking care of statically configured m/c  Mobile IP Src: Forouzan

27. Reverse ARP  Reverse ARP (RARP)  RFC 903  Used for diskless stations  Organization does not have enough IP Address  Target as MAC Bcast does not cross the router  Needs one RARP server for each subnet  BOOTP  Improvement over RARP  Has a relay agent to forward across network  has static mapping of MAC to IP manageability issues  DHCP - replaces BOOTP

28. Gratuitous ARP  Ref: http://wiki.wireshark.org/Gratuitous_ARP  Gratuitous ARP Request  both src and dstn IP is set to that of m/c  dstn MAC is broadcast i.e. ff:ff:ff:ff:ff:ff  Ordinarily, no reply will occur normally if a m/c exists, it may respond  Gratuitous ARP Reply  a reply to which no request has occurred

29. Gratuitous ARP  Why Gratuitous ARP  help detect IP conflicts if a m/c receives G-ARP req which is its own, implies IP conflict  helps in updating other m/cs ARP tables used in clustering solutions, when IP is moved  helps inform the switch to update its port table  each time an i/f comes up (after down), sends G- ARP  Practice: use send_arp to perform gratuitous arp

30. Network Setup We are not using the backbone network - better delete the address 172.16.3.x/21 –These are backbone addresses (College network) with default gateway of 172.16.3.1 Should we not use commands like ifconfig, route, arp etc. –These are deprecated commands, use commands from iproute2 pkg. ip addr [options] ip route [options] ip neigh [options]

31. Utilities/Tools wireshark/tcpdump nc ping arping

32. Wireshark It is a network packet analyser In late 1997 Gerald Combs started writing Ethereal for his use 1998 version 0.2.0 was released later several patches, plug-ins were added In 2006 it is renamed as wireshark Users - Administrators - Security Engineers - Developers - Ordinary users

33. Wireshark Main window: Main menu bar The main toolbar The filter toolbar (Display filter) The packet list pane The packet details pane The packet byte pane The status bar

34. Wireshark capture

35. Utilities/Tools Go to capture option Specify the interface Specify the capture filter (otherwise you will get too much traffic) Examples of good capture filters –for capturing a traffic for a given network or networks net 172.16.1.0/24 or 172.16.2.0/24 –for capturing specific source and/or destination src 172.16.1.201 and dst 172.16.3.201 –for capture specific protocol or applications or TCP/UDP port no http port 80 or port 8080

36. Utilities/Tools Difference between the capture filter and the display filter –Capture filters are used for capturing only relevant packets –display filters are used for displaying selected packets from what is captured. these may be used to analyze a subset of packets e.g. –packets on a TCP Connection –looking at only TCP SYN/RST packets etc We can save captured data and analyse To check the connectivity we can use ping command with –c N option

37. 37 Utilities/Tools netcat ( nc ) –to send packets on the network –supports both udp and tcp –can act as a client and server as well –data is to be specified by the user can be piped from other programs (or files) –example of connecting using UDP –example of connecting using TCP 37

38. Summary Growth of internet IPv4 addressing IPv4 Routing Building IPv4 network Analysis

39. Thank You