Use both diagrams below to answer the next 2 questions. As depicted a packet wit
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Question
Use both diagrams below to answer the next 2 questions.
As depicted a packet with the header 0111 arrives at the first router. What answers below describes what will transpire in the router:
a. The router will request a forwarding table from other routers on the network before processing the packet.
b. The router will forward the packet out interface 2.
c. The router will forward the packet out interface 1.
d. The router will route the packet out interface
2. QUESTION 2 What does the bit pattern header arriving at the first router represent?
a. The bit pattern of the source address stored in the header of the packet
b. The specific IP address of the destination address
c. The error checking bits
d. The bit pattern of the prefix of the packet’s destination address stored in the header of the packet
routing algorithm local forwarding table header value output link 0100 3 0101 0111 1001 value in arriving packet's heade 0111Explanation / Answer
Solution:
Before answering the question I would like to describe about forwarding table:
Forwarding table:
When a router receives a packet from one of its attatched networks the packet is first decapsulated at data-link layer. The link-layer address ( also known as MAC address or physical address ) of the destination node is checked to verify whether it matches to the receiving router's link-layer address. If it matches then the packet is checked for the IP address. Here the IP address of the destination along with the subnet mask is needed to calculate the network address or in other words prefix( a network address is calculated by putting (32 - subnet mask) number of right most bits of the destination IP address to 0). At this point the router uses a decision table which helps the router to choose the correct interface to which the packet needs to be forwarded. This decision table is known as forwarding table.
A forwarding table contains network address/mask, next hop and interface. When the router gets a matching of the network address in the forwarding table it comes to know what should be the next hop to which the packet needs to be forwarded and the interface. It therefore adds header which contains the next hop's link layer address and encapsulates the packet before forwarding.
Question 1:
When the packet with header '0111' arrives at the first router , the router checks its forwarding table and it finds that the packet needs to be forwarded to interface 2( refer to the forwarding table ).
Therefore the correct answer is-
Option b: The router will forward the packet out interface 2.
Question 2:
As I described earlier in the forwarding table section that, the header contains the IP address of the destination address and subnet mask. From this the router comes to know what is the network address of the destination and it forwards the packet to the interface accordingly.
Therefore the correct answer is-
Option b: The specific IP address of the destination address.
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