Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Mapping Phy to Logical Address: RARP, BOOTP, and DHCPReverse Address Resolution Protocol (ARP)Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 3621.1Chapter 21Network Layer: Address Mapping,Error Reporting, and MulticastingCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.21.221-1 ADDRESS MAPPING21-1 ADDRESS MAPPINGThe delivery of a packet to a host or a router requires The delivery of a packet to a host or a router requires two levels of addressing: two levels of addressing: logicallogical and and physicalphysical. We need . We need to be able to map a logical address to its correspondingto be able to map a logical address to its correspondingphysical address and vice versa. This can be done by physical address and vice versa. This can be done by using either static or dynamic mapping.using either static or dynamic mapping.Mapping Logical to Physical AddressMapping Physical to Logical AddressTopics discussed in this section:Topics discussed in this section:21.3Figure 21.1 ARP operation21.4ARP can be useful if the ARP reply is cached (kept in cache memory for a while).Note21.5Figure 21.2 ARP packet21.6Figure 21.3 Encapsulation of ARP packet21.7Figure 21.4 Four cases using ARP21.8An ARP request is broadcast;an ARP reply is unicast.Note21.9A host with IP address 130.23.43.20 and physical address B2:34:55:10:22:10 has a packet to send to another host with IP address 130.23.43.25 and physical address A4:6E:F4:59:83:AB. The two hosts are on the same Ethernet network. Show the ARP request and reply packets encapsulated in Ethernet frames.SolutionFigure 21.5 shows the ARP request and reply packets. Note that the ARP data field in this case is 28 bytes, and that the individual addresses do not fit in the 4-byte boundary. That is why we do not show the regular 4-byte boundaries for these addresses.Example 21.121.10Figure 21.5 Example 21.1, an ARP request and reply21.11Figure 21.6 Proxy ARP21.12Mapping Phy to Logical Address: RARP, BOOTP, and DHCPA diskless station just booted.An organization does not have enough IP addresses to assign to each station.21.13Reverse Address Resolution Protocol (ARP)A machine can use the phy address to get the logical address using RARP.A RARP messages is created and brodcast on the local network.The machine on the local network that knows the logical address will respond with a RARP reply.Broadcasting is done at data link layer.Broadcast requests does not pass the boundaries of a network.21.14Figure 21.7 BOOTP client and server on the same and different networks21.15DHCP provides static and dynamic address allocation that can bemanual or automatic.Note21.1621-2 ICMP21-2 ICMPThe IP protocol has no error-reporting or error-The IP protocol has no error-reporting or error-correcting mechanism. The IP protocol also lacks a correcting mechanism. The IP protocol also lacks a mechanism for host and management queries. The mechanism for host and management queries. The Internet Control Message Protocol (ICMP)Internet Control Message Protocol (ICMP) has been has been designed to compensate for the above two deficiencies. designed to compensate for the above two deficiencies. It is a companion to the IP protocol.It is a companion to the IP protocol.Types of MessagesMessage FormatError Reporting and QueryDebugging ToolsTopics discussed in this section:Topics discussed in this section:21.17Figure 21.8 General format of ICMP messages21.18ICMP always reports error messages to the original source.Note21.19Figure 21.9 Error-reporting messages21.20Important points about ICMP error messages:❏ No ICMP error message will be generated in response to a datagram carrying an ICMP error message.❏ No ICMP error message will be generated for a fragmented datagram that is not the first fragment.❏ No ICMP error message will be generated for a datagram having a multicast address.❏ No ICMP error message will be generated for a datagram having a special address such as 127.0.0.0 or 0.0.0.0.Note21.21Figure 21.10 Contents of data field for the error messages21.22Figure 21.11 Redirection concept21.23Figure 21.12 Query messages21.24Figure 21.13 Encapsulation of ICMP query messages21.25Figure 21.14 shows an example of checksum calculation for a simple echo-request message. We randomly chose the identifier to be 1 and the sequence number to be 9. The message is divided into 16-bit (2-byte) words. The words are added and the sum is complemented. Now the sender can put this value in the checksum field.Example 21.221.26Figure 21.14 Example of checksum calculation21.27We use the ping program to test the server fhda.edu. The result is shown on the next slide. The ping program sends messages with sequence numbers starting from 0. For each probe it gives us the RTT time. The TTL (time to live) field in the IP datagram that encapsulates an ICMPmessage has been set to 62. At the beginning, ping defines the number of data bytes as 56 and the total number of bytes as 84. It is obvious that if we add 8 bytes of ICMP header and 20 bytes of IP header to 56, the result is 84. However, note that in each probe ping defines the number of bytes as 64. This is the total number of bytes in the ICMP packet (56 + 8).Example 21.321.28Example 21.3 (continued)21.2921.3021.31Figure 21.15 The traceroute program operation21.32We use the traceroute program to find the route from the computer voyager.deanza.edu to the server fhda.edu. The following shows the result:Example 21.4The unnumbered line after the command shows that the destination is 153.18.8.1. The packet contains 38 bytes: 20 bytes of IP header, 8 bytes of UDP header, and 10 bytes of application data. The application data are used by traceroute to keep track of the packets.21.33The first line shows the first router visited. The router is named Dcore.fhda.edu with IP address 153.18.31.254. The first round-trip time was 0.995 ms, the second was 0.899 ms, and the third was