1. Cisco Confidential © 2013 Cisco and/or its affiliates. All rights reserved. 1 Cisco Networking Training (CCENT/CCT/CCNA R&S) Rick Rowe Ron Giannetti

2. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2 Operation of IP Data Networks Routers/Switches IP Routing Technologies Static vs Dynamic TCP/IP Transport and Applications Only talking about IPv4 for the next few sessions

3. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 TCP/IP Network Layer (3) Defines how to deliver IP packets over the entire trip Functions IP Routing The process of hosts and routers forwarding IP Packets, while relying on the underlying LANs and WANs to forward the bits IP Addressing Used to identify the packets source and destination hosts – organized into groups IP Routing Protocol A Protocol that dynamically learns the IP address groups to help deliver packets Other Utilities Other utilities that help the network layer (DNS, ARP, PING, etc)

4. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4

5. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5 Different Layer 2 Technologies Not Scalable

6. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6 What happens when there is no logical grouping of numbers?

7. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 7 IP provides common protocol IP provides unique addresses What if phone companies assigned the same number to two different phones? For communication to be possible, you need uniqueness Provides a structured addressing Allows grouping of common addresses

8. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 8 TCP/IP model dominates protocols Many have existed Two options – IPv4 and IPv6 Same kinds of Network layer functions, just different details IP focuses on routing data Not concerned with the physical transmission Relies on lower layers to do that dirty work Focuses on the logical details How packets travel end to end over a TCP/IP network Layer 3 = Packet Layer 2 = Frame

9. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9 Routers and computers (hosts) use TCP/IP software

10. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 10 A LAN includes all devices in the same broadcast domain To reduce CPU overhead on each device by reducing the number of devices that receive each broadcast frame To reduce security risks by reducing the number of hosts that receive copies of frames that the switches flood (broadcasts, multicasts, and unknown unicasts) To improve security for hosts that send sensitive data by keeping those hosts on a separate VLAN To create more flexible designs that group users by department, or by groups that work together, instead of by physical location To solve problems more quickly, because the failure domain for many problems is the same set of devices as those in the same broadcast domain To reduce the workload for the Spanning Tree Protocol (STP) by limiting a VLAN to a single access switch

11. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11 Moving Data Between VLANs (hint.. Layer 2 switches won’t)

12. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12 Where do I send it? PC1 does some basic analysis Is the destination host in my same logical grouping? (IP Network or IP subnet) If it isn’t, send it to my default router (default gateway) PC1 sends to the “next hop” via the data link layer (Layer 2) Use the destination link layer address Uses ARP to find the link layer address

13. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 13 All routers use the same general process to route packets Each router has an IP Routing table Table lists IP address Groupings (IP Networks or IP subnets) Router compares a packet’s destination address to the routing table Makes a match, entry tells where to forward the packet Last router uses the same logic, but instead delivers to the end host

14. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 14 Network Layer routing ignores the physical transmission details Routing process forwards the network layer packet from end to end Data link frame only takes a smaller part of the trip Each successive data link layer frame moves the packet to the next device ARP Each host and router must build a new data link headers and trailers ARP dynamically learns the data link address of an IP host connected to a LAN

15. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 15 IP defines network layer addresses that identify any host or router interface that connects to a TCP/IP network Just like the mail, if you expect to receive mail, you need a postal address. If you expect to receive an IP packet, you need an IP address TCP/IP groups IP addresses together so that IP addresses used on the same physical network are part of the same group (IP network or IP subnet) Same as the postal service, nearby addresses are in the same postal code (ZIP code), while all “nearby” IP addresses are in the same IP Subnet “Nearby” IP addresses share the same Network portion of an address

16. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 16 Both Hosts and Routers need to know about the internetwork Hosts need to know their default router Routers need to know routes so they can forward packets to each and every network and IP subnet

17. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 17 Static Routes are manually defined Dynamic Routes are dynamically learned

18. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 18 If a device wants to communicate using TCP/IP, it needs an address Any device that has at least one interface with an IP address can send and receive IP packets and is called a Host 32-bit number, usually written in dotted-decimal notation (DDN) Each byte (8 bits) of the 32-bit IP address is shown as its decimal equivalent 10101000 00000001 00000001 00000001 = 168.1.1.1 Each DDN has four decimal octets, separated by periods Octet = byte Each 8-bit octet can be a number between 0 and 255 Each network interface has a unique IP address

19. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 19 4,294,967,296 addresses

20. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 20 Grouping Original specification for TCP/IP grouped IP addresses into sets of consecutive addresses(IP networks). The addresses in a single IP network have the same numeric value in the first part of all addresses in a network All IP addresses in the same group must not be separated from each other by a router IP addresses separated from each other by a router must be in different groups Only (1) ip address group per VLAN

21. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 21 IPv4 address space includes all possible combinations of numbers for the 32-bit IPv4 address. 0.0.0.0 – 255.255.255.255 IP standards divide into classes, identified by the first octet Class A gets roughly half Class B gets ¼ Class C gets 1/8

22. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 22 Unicast Class A, B, and C define unicast addresses, meaning single host interface Mulitcast Class D define multicast addresses, used to send on packet to multiple hosts IPv4 uses classes to define different sizes

23. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 23 Identified by their Network IDs Class A – first octet Class B – first and second octet Class C – first, second, and third octet

24. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 24 Class ranges Note – classful IP network refers to any Class A, B, or C network

25. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 25 Defines methods of further subdividing the IPv4 address space into groups that are smaller than a single IP network Flexible way to take a single Class A, B, or C IP network and further subdivide into smaller consecutive IP addresses Instead of wasting addresses from a complete Class A, B, or C, you can use a smaller subset 5 networks using classful networks and no subnetting

26. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 26 Instead using basic subnetting to break the Class B network 150.9.0.0 into five subnets One group of the 254 addresses that begin with 150.9.1 One group of the 254 addresses that begin with 150.9.2 One group of the 254 addresses that begin with 150.9.3 Etc..

27. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 27 Hosts use some routing logic If the destination IP address is in the same IP subnet as I am, send the packet directly to that destination host Otherwise, send the packet to my default gateway(default router) – the router has an interface on the same subnet as the host

28. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 28 After receiving a data link frame addressed to the router Use the data link Frame Check Sequence (FCS) field to ensure that frame has no errors Discard old data link header and trailer, leaving the IP packet Compare the IP Packet’s destination IP address to the routing table, find the route that best matches the destination, the route identifies the outgoing interface, and possibly the next hop IP address Encapsulate the IP packet inside a new data link header and trailer, forward the frame

29. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 29 Goals Optimal Path Selection Loop-free routing Fast Convergence Scalable networks Limited administration

30. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 30 Easy to use in smaller networks Not Scalable Most common type is the “default route”

31. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 31 Primary tool for testing basic network connecitvity Ping Packet Internet Groper uses Internet Control Message Protocol (ICMP) Sends an ICMP Echo request to another IP address Device with that address should reply with an ICMP echo reply

32. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 32 Remember that Ethernet devices communicate using the MAC address If we’re using IP as our layer 3 protocol how do we translate this to a MAC address? Using ARP!

33. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 33 Address Resolution Protocol (ARP) maps IP addresses to MAC addresses Each computer maintains a ARP table which maps IP addresses to MAC addresses If the MAC address isn’t in the ARP table the computer broadcasts a message to find the address

34. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 34

35. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 35 “ Where is PC 2? ” PC 2 PC 1 Network

36. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 36 fffff … f 255.255.255.255 MAC DAProtocol DA Layer 2 Layer 3 Broadcast Frame Network Send Broadcast to Everyone Send Broadcast to Everyone on This Subnet PC 1 Sends a Broadcast to find PC 2 PC 1 192.168.1.2 What is the MAC address of the computer with this IP address?

37. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 37 Switch sends the broadcast frame out all the ports within the broadcast domain fffff … f 255.255.255.255 Broadcast Switch Sees ffffff As the Destination and Sends This Frame to Everyone PC 1

38. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 38 Server Request for PC 2 PC 1PC 2 All PCs see MAC address of FFFFFFFFFFFF so they all process the packet. PC2 responds with its IP and MAC address. PC1 uses this information to update it’s ARP table.

39. © 2013 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 39