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Premium member Presentation Transcript PowerPoint Presentation: TCP/IP Protocol Suite 1 Chapter 7 Upon completion you will be able to: ARP and RARP Understand the need for ARP Understand the cases in which ARP is used Understand the components and interactions in an ARP package Understand the need for RARP ObjectivesPowerPoint Presentation: TCP/IP Protocol Suite 2 Figure 7.1 ARP and RARPPowerPoint Presentation: TCP/IP Protocol Suite 3 Figure 7.2 Position of ARP and RARP in TCP/IP protocol suite Notice that ARP and RARP are supplemental to IP.PowerPoint Presentation: TCP/IP Protocol Suite 4 7.1 ARP ARP associates an IP address with its physical address. On a typical physical network, such as a LAN, each device on a link is identified by a physical or station address that is usually imprinted on the NIC. Logical address to physical address translation can be done statically (not practical) or dynamically (with ARP).PowerPoint Presentation: TCP/IP Protocol Suite 5 Figure 7.3 ARP operationPowerPoint Presentation: TCP/IP Protocol Suite 6 Figure 7.4 ARP packet Hardware Type - Ethernet is type 1 Protocol Type- IPv4=x0800 Hardware Length:length of Ethernet Address (6) Protocol Length:length of IPv4 address (4)PowerPoint Presentation: TCP/IP Protocol Suite 7 Figure 7.5 Encapsulation of ARP packet The ARP packet is encapsulated within an Ethernet packet. Note: Type field for Ethernet is x0806PowerPoint Presentation: TCP/IP Protocol Suite 8 Figure 7.6 Four cases using ARPPowerPoint Presentation: TCP/IP Protocol Suite 9 A host with IP address 18.104.22.168 and physical address B2:34:55:10:22:10 has a packet to send to another host with IP address 22.214.171.124 and physical address A4:6E:F4:59:83:AB (which is unknown to the first host). The two hosts are on the same Ethernet network. Show the ARP request and reply packets encapsulated in Ethernet frames. Example 1 See Next SlidePowerPoint Presentation: TCP/IP Protocol Suite 10 Solution Figure 7.7 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. Also note that the IP addresses are shown in hexadecimal. For information on binary or hexadecimal notation see Appendix B. Example 1 (Continued) See Next SlidePowerPoint Presentation: TCP/IP Protocol Suite 11 Figure 7.7 Example 1PowerPoint Presentation: TCP/IP Protocol Suite 12 Figure 7.8 Proxy ARP A proxy ARP, running in a router, can respond to an ARP request for any of its proteges. The proxy ARP replies with its own MAC address. When the packet arrives, the router delivers it to the appropriate host.PowerPoint Presentation: TCP/IP Protocol Suite 13 7.2 ARP PACKAGE In this section, we give an example of a simplified ARP software package to show the components and the relationships between the components. This ARP package involves five modules: a cache table, queues, an output module, an input module, and a cache-control module. The topics discussed in this section include: Cache Table Queues Output Module Input Module Cache-Control ModuleThe Cache Table: TCP/IP Protocol Suite 14 The Cache Table If ARP just resolved an IP address, chances are a few moments later someone is going to ask to resolve the same IP address When ARP returns a MAC address, it is placed in a cache. When the next request comes in for the same IP address, look first in the cachePowerPoint Presentation: TCP/IP Protocol Suite 15 Figure 7.9 ARP componentsThe Cache Table Contents: TCP/IP Protocol Suite 16 The Cache Table Contents State: FREE, PENDING, RESOLVED Hardware type: same as ARP field Protocol type: same as ARP field Hardware length: same as ARP field Protocol length: same as ARP field Interface number: port number (m0,m1, m2)The Cache Table Contents: TCP/IP Protocol Suite 17 The Cache Table Contents Queue number: which queue the ARP request is sitting in Attempts: how many times have you tried to resolve this address? Time-out: how long until this address is tossed out (need the room in cache) Hardware address: destination hardware address Protocol address: destination IP addressHow Does the Cache Work?: TCP/IP Protocol Suite 18 How Does the Cache Work? The output module waits for an IP packet with a request Checks the cache for an existing entry If entry found and state RESOLVED, we already have this MAC address If entry found and state PENDING, packet waits until