Question 1
Question 2
Explanation
By default, Cisco routers do not forward broadcast address. So what will happen if your PC does not in the same LAN with DHCP Server? Your PC (also a DHCP Client) will broadcast a packet but it is dropped by the router -> Your PC cannot get the IP from DHCP Server. So the “ip helper-address” command enables the DHCP broadcast to be forwarded to the DHCP server. For example, the IP address of your DHCP Server is 10.10.10.254 then we can type in the interface connecting with the DHCP Client (fa0/0 in this case) this command: “ip helper-address 10.10.10.254″.
Note: When a client boots up for the first time, it transmits a DHCPDISCOVER message on its local physical subnet. Because the client has no way of knowing the subnet to which it belongs, the DHCPDISCOVER is an all-subnets broadcast (destination IP address of 255.255.255.255, which is a layer 3 broadcast address). The client does not have a configured IP address, so the source IP address of 0.0.0.0 is used.
Question 3
Explanation
Routers do not look to the destination MAC address to forward packet. It will find the next destination MAC address itself to replace the old destination MAC address of the received packet.
Hubs do not care about MAC addresses, it just flood the frames out of all its port except the port that sent it.
Therefore only three switches in the exhibit above use destination MAC address to determine the next hops.
Question 4
Explanation
The destination MAC address at point A must be the MAC address of the interface fa0/0 of Toronto router -> E is correct.
Question 5
Explanation
The simple syntax of static route:
ip route destination-network-address subnet-mask {next-hop-IP-address | exit-interface}+ destination-network-address: destination network address of the remote network
+ subnet mask: subnet mask of the destination network
+ next-hop-IP-address: the IP address of the receiving interface on the next-hop router
+ exit-interface: the local interface of this router where the packets will go out
+ subnet mask: subnet mask of the destination network
+ next-hop-IP-address: the IP address of the receiving interface on the next-hop router
+ exit-interface: the local interface of this router where the packets will go out
Therefore the purpose of this command is to send any packets with destination IP address in the range of 192.168.100.160/27 subnet to 192.168.10.2. In fact, answer C is a bit weird when saying “host 192.168.100.160″ because 192.168.100.160 is the network address in this case and it cannot be assigned to a host. But answer C is the most suitable answer for this question.
Question 6
Question 7
Explanation
After receiving a packet, the router will keep the source and destination IP addresses while change the source MAC address (to the MAC address of its outgoing interface) and the destination MAC address (to the MAC address of the next-hop interface). Therefore when the packet reaches host B, the source MAC address must be the MAC address of the outgoing interface of R1.
Question 8
Explanation
Host A knows the IP address of Host B but it does not know the MAC address of host B, so it have to create an ARP Request (which is a broadcast frame) to ask for the MAC address of host B. When Router1 receives this ARP Request, it answers with its own MAC address.
Question 9
Question 10
Explanation
Along the routing path, the source and destination IP address will not change so the source IP will always be 10.1.1.16.