Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 1 Cisco Systems CCNA Version 3 Semester 1 Module 9 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 2 Students completing this module should be able to: Explain why the Internet was developed and how TCP/IP fits the design of the Internet. List the four layers of the TCP/IP model. Describe the functions of each layer of the TCP/IP model. Compare the OSI model and the TCP/IP model. Describe the function and structure of IP addresses. Understand why subnetting is necessary. Explain the difference between public and private addressing. Understand the function of reserved IP addresses. Explain the use of static and dynamic addressing for a device. Understand how dynamic addressing can be done using RARP, BootP and DHCP. Use ARP to obtain the MAC address to send a packet to another device. Understand the issues related to addressing between networks. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 3 Module Overview 9.1 Introduction to TCP/IP History and future of TCP/IP Application layer Transport layer Internet layer Network access layer Comparing the OSI model and the TCP/IP model Internet architecture 9.2 Internet Addresses IP addressing Decimal and binary conversion IPv4 addressing Class A, B, C, D, and E IP addresses Reserved IP addresses Public and private IP addresses Introduction to subnetting IPv4 versus IPv6 9.3 Obtaining an IP Address Obtaining an Internet address Static assignment of an IP address RARP IP address assignment BOOTP IP address assignment DHCP IP address management Problems in address resolution Address Resolution Protocol (ARP) Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 4 Overview Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide History and future of TCP/IP The Department of Defense (DoD) developed the TCP/IP reference model to provide a communication network that could continue to function in wartime. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Comparing the OSI model and the TCP/IP model Both have an application layer. Both have similar transport and network layers. Both assume packet-switched networks. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Application layer OSI layers 5, 6 & 7 are all rolled into the TCP Application Layer. Encoding Dialog Control Data Presentation Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 8 1.File Transfer Protocol (FTP) FTP is a reliable, connection-oriented service that uses TCP to transfer files between systems that support FTP. It supports bi-directional binary file and ASCII file transfers. 2.Trivial File Transfer Protocol (TFTP) TFTP is a connectionless service that uses the User Datagram Protocol (UDP). TFTP is used on the router to transfer configuration files and Cisco IOS images, and to transfer files between systems that support TFTP. It is useful in some LANs because it operates faster than FTP in a stable environment. 3.Network File System (NFS) NFS is a distributed file system protocol suite developed by Sun Microsystems that allows file access to a remote storage device such as a hard disk across a network. 4.Simple Mail Transfer Protocol (SMTP) SMTP administers the transmission ofover computer networks. It does not provide support for transmission of data other than plaintext. 5.Terminal emulation (Telnet) Telnet provides the capability to remotely access another computer. It enables a user to log in to an Internet host and execute commands. A Telnet client is referred to as a local host. A Telnet server is referred to as a remote host. 6.Simple Network Management Protocol (SNMP) SNMP is a protocol that provides a way to monitor and control network devices, and to manage configurations, statistics collection, performance, and security. 7.Domain Name System (DNS) DNS is a system used on the Internet for translating names of domains and their publicly advertised network nodes into IP addresses. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Transport layer There are only two protocols at the transport layer, TCP and UDP. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Transport layer TCP is responsible for: end-to-end communication flow control reliability of data delivery Note: The first line is not sent. The second line is the ACK line. TCP supports a logical connection between the sending and receiving hosts Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Transport layer Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Internet layer It provides control and messaging capabilities: eg. Ping, Destination Unreachable etc. ARP & RARP also act at the network layer (They relate MAC & IP addresses) The IP Protocol is responsible for: routing packets to remote hosts defining packets transferring data between the internet layer and the network access layer Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide History and future of TCP/IP IPv4 IPv6 In 1992 the standardization of a new generation of IP, often called IPng, was supported by the Internet Engineering Task Force (IETF). IPng is now known as IPv6. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Internet layer Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Network access layer SLIP Serial Line Internet Protocol PPP Point to Point Protocol FDDI Fiber Distributed Data Interface ATM Asynchronous Transfer Mode SMDS Switched Multimegabit Data Service (They relate MAC & IP addresses) A NETWORK ACCESS problem could be caused by any of these protocols. The Network Access Layer supports BOTH LAN and WAN technologies Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Network access layer The Network Access Layer is considered to be the host-to-network layer of the TCP/IP model. The data comes in to the NIC at the Physical Layer (Frame) and leaves at the Network Layer (packet). Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Comparing the OSI model and the TCP/IP model Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Internet architecture A network of networks is called an internet, indicated with the lowercase i. When referring to the networks that developed from the DoD on which the Worldwide Web (www) runs, the uppercase I is used and is called the Internet. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Internet architecture The router keeps a list of all networks, but leaves the local delivery details to the local physical networks. In this situation, the routers pass messages to other routers. Each router shares information about which networks it is connected to. This builds the routing table. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Internet architecture Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Internet architecture Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 22 Scale-Free Networks Scientific American May 2003 The internet somewhere in the N.E. US Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IP addressing Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IP addressing A device is not said to have an address, but that each of the connection points, or interfaces, on that device has an address to a network. 2 NIC cards 2 MAC addresses 2 IP addresses Does not pass data unless programmed to do so. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IP addressing These are consecutive numbers. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IPv4 addressing Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IPv4 addressing This number must be a unique number, because duplicate addresses would make routing impossible. The only time that the host numbers matter is when the data is on the local area network. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IPv4 addressing Classful Addressing. A multicast address is a unique network address that directs packets with that destination address to predefined groups of IP addresses. Therefore, a single station can simultaneously transmit a single stream of data to multiple recipients. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IPv4 addressing Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IPv4 addressing The first octet range for Class E addresses is to , or 240 to 255 Reserved for research by IETF All of these criteria identify the class of address. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Class A, B, C, D, and E IP addresses Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Class A, B, C, D, and E IP addresses You can use these addresses on any private LAN. You CANNOT use them on the internet. Internet routers will block them. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Class A, B, C, D, and E IP addresses Error ? Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Class A, B, C, D, and E IP addresses Error ? Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Reserved IP addresses An IP address that has binary 0s in all host bit positions is reserved for the network address. A router uses the network IP address when it forwards data on the Internet. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Reserved IP addresses An IP address that has binary 1s in all host bit positions is reserved for the broadcast address. Data that is sent to the broadcast address will be read by all hosts on that network Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Reserved IP addresses Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Reserved IP addresses Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Reserved IP addresses Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Reserved IP addresses Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Public and private IP addresses It is appropriate to use private addressing on the private side of routers. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Public and private IP addresses Originally, an organization known as the Internet Network Information Center (InterNIC) handled IP assignments. InterNIC no longer exists and has been succeeded by the Internet Assigned Numbers Authority (IANA). Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Public and private IP addresses Connecting a network using private addresses to the Internet requires translation of the private addresses to public addresses. This translation process is referred to as Network Address Translation (NAT). NAT is one solution to expand the number of public IP addresses. Two others are: classless interdomain routing IPv6 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Introduction to subnetting For communication to occur between different physical network segments: IP address of the local (RARP) and destination hosts must be obtained. Only then, is it possible to transfer data packets from one network segment to another to reach the destination host. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Introduction to subnetting Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Introduction to subnetting Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IPv4 versus IPv6 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Introduction to subnetting Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide IPv4 versus IPv6 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 50 Module Overview 9.1 Introduction to TCP/IP History and future of TCP/IP Application layer Transport layer Internet layer Network access layer Comparing the OSI model and the TCP/IP model Internet architecture 9.2 Internet Addresses IP addressing Decimal and binary conversion IPv4 addressing Class A, B, C, D, and E IP addresses Reserved IP addresses Public and private IP addresses Introduction to subnetting IPv4 versus IPv6 9.3 Obtaining an IP Address Obtaining an Internet address Static assignment of an IP address RARP IP address assignment BOOTP IP address assignment DHCP IP address management Problems in address resolution Address Resolution Protocol (ARP) Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Obtaining an Internet address A network host needs a globally unique address in order to function on the Internet. The physical or MAC address that a host has is only locally significant, identifying the host within the local area network. Since this is a Layer 2 address, the router does not use it to forward outside the LAN. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Obtaining an Internet address The Packet is removed from the Frame inside the NIC card. Usually a router. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Static assignment of an IP address Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Static assignment of an IP address Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Address Resolution Protocol (ARP) For any sending device to communicate with another local IP host, must have BOTH the IP address and MAC (ARP) address of the destination device. The RAM ARP table or cache contains the IP and MAC address of other devices on the same LAN. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Obtaining an Internet address IP protocol is a hierarchical addressing scheme that allows individual addresses to be associated together and treated as groups. These groups of addresses allow efficient transfer of data across the Internet. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide RARP IP address assignment Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Obtaining an Internet address 1.Hardware Type - this is 1 for Ethernet. 2.Protocol Type - the protocol used at the network layer. 3.Hardware Address Length - this is the length in bytes, so it would be 6 for Ethernet (MAC). 4.Protocol Address Length - For TCP/IP the value is 4 bytes. 5.Operation Code - ARP Request (1), ARP Response (2), RARP Request (3) RARP Response (4). 6.Senders Hardware Address - hardware address of the source node. 7.Senders Protocol Address - layer 3 address of the source node. 8.Target Hardware Address - used in a RARP request, the response carries both the destination's hardware and layer 3 addresses. 9.Target Protocol Address - used in an ARP request, the response carries both the destination's hardware and layer 3 addresses. The Ethernet Type/Length field has the value 0x0806 to indicate an ARP Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 59 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide :e0:18:f4:95:9d 00:00:00:00:00: x806 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide :e0:18:f4:95:9d 00:06:5b:1c:35: x806 1 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide :e0:18:f4:95:9d 00:00:00:00:00: x :e0:18:f4:95:9d 00:06:5b:1c:35: x :e0:18:f4:95:9d 00:06:5b:1c:35: :e0:18:f4:95:9d 00:06:5b:1c:35: ARP Request ARP Response RARP Request RARP Response x8035 The Op Code tells what kind of transaction it is. The missing information is shown as all 0s Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide RARP IP address assignment :e0:18:f4:95:9d 00:00:00:00:00: x8035 RARP binds a known MAC address to an IP unknown address. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 64 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide RARP IP address assignment Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide RARP IP address assignment Not used in BOOTP Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor BOOTP requires the administrator to set up a static IP and MAC address table in the BOOTP server. DHCP uses the same message structure. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide RARP IP address assignment Not used in BOOTP Usually a router Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide BOOTP IP address assignment Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide BOOTP IP address assignment Only one bit of 16-bit Flags has been defined Left-most flag bit =1 ? Servers, please reply using IP broadcast address Servers by default send hardware unicast response Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 70 The major advantages of DHCP over BOOTP are: 1.It allows user to be mobile. 2.It does not require fixed profiles to assign IP addresses. Servers with a dynamically assigned IP address would be difficult to locate on a network. Therefore they should have IP addresses assigned statically by a network system administrator. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 71 Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 72 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 73 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 74 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 75 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 76 Vendor specific field renamed to options Size increased to 312 bytes (from 64 bytes) Option type 53 specifies the "type of the message" Vendor specific area: Magic cookie: First 4 octets = Type-length-value: describes the option Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 77 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 78 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 79 Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 80 Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 81 Once DHCP is finished, some operating systems send out an ARP to prevent duplicate IP addresses on a local area network. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Problems in address resolution A datagram on a local-area network must contain both a destination MAC address and IP address. These addresses must match the destination MAC and IP addresses of the host device. If it does not match, the datagram will be discarded by the destination host. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Problems in address resolution Communications between two LAN segments have an additional task. IP and MAC addresses are needed for both the destination host AND the intermediate routing device. TCP/IP has a variation on ARP called Proxy ARP that will provide the MAC address of an intermediate device for transmission outside the LAN to another network segment. Proxy ARP For any messages outside your LAN, use my MAC address. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Address Resolution Protocol (ARP) The MAC address for this outside network is the Router interface MAC Each device on a network maintains its own ARP table. When a network device wants to send data across the network, it uses information provided by the ARP table. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Address Resolution Protocol (ARP) The default gateway is a HOST option where the IP address of the router interface is stored in the network configuration of the host. The HOST compares IP addresses to determine if the destination is located on the same segment. If it is not, the host sends the data using the destination IP address routers MAC address. It learned the routers MAC address from the ARP table by looking up the GATEWAY IP. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide Address Resolution Protocol (ARP) If the default gateway on the host OR the proxy ARP feature on the router is NOT configured, no traffic can leave the local area network. One or the other is required to have a connection outside of the local area network. Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 87 Summary Nov-03 Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 St. Lawrence College Cornwall Campus, ON, Canada Clark slide 88 FIN