Networking / Computer Communications:

Refer to Figure 3.19a. Assuming that the network address is 192.168.1.x, explain the entries 192.168.1.255 ff-ff-ff-ff-ff-ff and 255.255.255.255 ff-ff-ff-ff-ff-ff in their meanings.

3.8 Address Resolution Protocol 3.8.1 Background Transportation of application data across subnetworks requires that switching (based on MAC addressing) and routing (based on IP addressing) go hand in hand. For this, the host's LAN port should have MAC and IP addresses coupled (see Figures 1.23 and 1.24) so that the IP address becomes a vehicle to forward packets between subnetworks (inter-networking) and the MAC address is used to move frames within a subnetwork (intra-networking). The ARP request is issued when the MAC address of a node (e.g., a host station, a router port) needs to be obtained based on its IP address. For instance, assurme that a source host (192.168.10.1) has to deliver a frame to a target host (192.168.10.2) within a subnetwork (192.168.10.x). In this situation of intra-networking, the frame should contain the target host's MAC address in the frame hcader for its delivery. If the source host finds the target host's IP and corresponding MAC addresses in its own ARP table (or ARP cache), the mapping between them becomes straightforward. CAWindows1system32cmdexe Interface: 192.168.1.4 0xc Internet Address 192.168.1.1 192.168.1.255 224.0.0.2 224.0.0.22 224.0.0.251 224.0.0.252 239.255.255.250 255.255.255.255 Physical Address 00-14-6c-4d-a6-82 01-00-5e-00-00-02 01-00-5c-00-00-16 01-00-5c-00-00-f 01-00-5e-00-00-fo 01-00-5e-f-ff-fa ype dynanic static stati static stati stati static stati Physical address 00-23-4C-6A-64-29 00-23-4C-6D-7B-EF 00-23-4C-2C-8A-DE Interface (port) Internet address 172.16.10.1 172.16.5.1 172.16.7.1 FastEthernet0/2 Figure 319 Sample ARP tables of (a) host and (b) router. Figure 319a shows a sample ARP table of a host obtained by the C.arp-acommand. From this figure, you can observe that the host computer's ARP table only contains IP addresses and corresponding MAC (or physical) addresses. The router's ARP table (see Figure 3.19b) has one more column that indicates the exit port (interface) of a target MAC address. This additional exit port information is required because, unlike the host station that belongs to only one subnetwork, the router is designed to connect several subnetworks simultaneously When the mapping information hetween an IP and a MAC address is not available in the ARP cache, the source node has to hroadcast an ARP request. Continuing the carlier cxample, the sourcc host (192.168.10.1) can broadcast an ARP request asking "Hello, what is the MAC address of the IP host 196.168.10.27" On receiving it, the target host (196.168.10.2) returns its MAC address to the requesting node (192.168.10.1). The source host, 192.168.10.1 then updates the mapping information on its ARP cache and dispatches the frame with the newly obtained MAC address in the destination address field Exercise 3.7 1. Refer to Figure 3.19. What is a key difference between the host's and the router's ARP tables? 2. Refer to Figure 3.19a. Assuning that the network address is 192.168.1x, explain the entries "192.168.1255 --T-r-r-l" and "255.255.255.255 T-T-IT-N-IT-fr" in their meanings 3. Refer to Figure 3.19b and answer the following questions: a. How many difTerent subnetworks the router is interconnecting? b. Can we tell from the ARP table if the router has a WAN connectionn? Why or why not? 4. Does the layer 2 switch need to maintain an ARP table for frame switching? Why or why not? 3.8 Address Resolution Protocol 3.8.1 Background Transportation of application data across subnetworks requires that switching (based on MAC addressing) and routing (based on IP addressing) go hand in hand. For this, the host's LAN port should have MAC and IP addresses coupled (see Figures 1.23 and 1.24) so that the IP address becomes a vehicle to forward packets between subnetworks (inter-networking) and the MAC address is used to move frames within a subnetwork (intra-networking). The ARP request is issued when the MAC address of a node (e.g., a host station, a router port) needs to be obtained based on its IP address. For instance, assurme that a source host (192.168.10.1) has to deliver a frame to a target host (192.168.10.2) within a subnetwork (192.168.10.x). In this situation of intra-networking, the frame should contain the target host's MAC address in the frame hcader for its delivery. If the source host finds the target host's IP and corresponding MAC addresses in its own ARP table (or ARP cache), the mapping between them becomes straightforward. CAWindows1system32cmdexe Interface: 192.168.1.4 0xc Internet Address 192.168.1.1 192.168.1.255 224.0.0.2 224.0.0.22 224.0.0.251 224.0.0.252 239.255.255.250 255.255.255.255 Physical Address 00-14-6c-4d-a6-82 01-00-5e-00-00-02 01-00-5c-00-00-16 01-00-5c-00-00-f 01-00-5e-00-00-fo 01-00-5e-f-ff-fa ype dynanic static stati static stati stati static stati Physical address 00-23-4C-6A-64-29 00-23-4C-6D-7B-EF 00-23-4C-2C-8A-DE Interface (port) Internet address 172.16.10.1 172.16.5.1 172.16.7.1 FastEthernet0/2 Figure 319 Sample ARP tables of (a) host and (b) router. Figure 319a shows a sample ARP table of a host obtained by the C.arp-acommand. From this figure, you can observe that the host computer's ARP table only contains IP addresses and corresponding MAC (or physical) addresses. The router's ARP table (see Figure 3.19b) has one more column that indicates the exit port (interface) of a target MAC address. This additional exit port information is required because, unlike the host station that belongs to only one subnetwork, the router is designed to connect several subnetworks simultaneously When the mapping information hetween an IP and a MAC address is not available in the ARP cache, the source node has to hroadcast an ARP request. Continuing the carlier cxample, the sourcc host (192.168.10.1) can broadcast an ARP request asking "Hello, what is the MAC address of the IP host 196.168.10.27" On receiving it, the target host (196.168.10.2) returns its MAC address to the requesting node (192.168.10.1). The source host, 192.168.10.1 then updates the mapping information on its ARP cache and dispatches the frame with the newly obtained MAC address in the destination address field Exercise 3.7 1. Refer to Figure 3.19. What is a key difference between the host's and the router's ARP tables? 2. Refer to Figure 3.19a. Assuning that the network address is 192.168.1x, explain the entries "192.168.1255 --T-r-r-l" and "255.255.255.255 T-T-IT-N-IT-fr" in their meanings 3. Refer to Figure 3.19b and answer the following questions: a. How many difTerent subnetworks the router is interconnecting? b. Can we tell from the ARP table if the router has a WAN connectionn? Why or why not? 4. Does the layer 2 switch need to maintain an ARP table for frame switching? Why or why not