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71# Exercise 1: Understanding the Impact of Network Dynamics on Routing
## Question 1.
### Which nodes communicate with which other nodes?
- 1~5
- 2~5
### Which route do the packets follow?
- 0->1->4->5
- 2->3->5
### Does it change over time?
- not change
## Question 2:
### What happens at time 1.0 and at time 1.2?
- route between node 1 and 4 disconnected at 1.0 and reconnected at time 1.2
### Does the route between the communicating nodes change as a result of that?
- not change
## Question 3:
### Did you observe any additional traffic as compared to Step 3 above?
- yes, it happens at the beginning and at time 1.0
### How does the network react to the changes that take place at time 1.0 and time 1.2 now?
- the route between node 1 and 4 is disconnected, so it change the route to 0->1->2->3->5
## Question 4: How does this change affect the routing? Explain why.
- the route change to 0->1->2->3->5 and 2->3->5
- because the cost between node 1 and 4 increased, so it is not the most opitimal route
## Question 5: Describe what happens and deduce the effect of the line you just uncommented.
- traffic from 2 to 5 takes two route, which are 2->1->4->5 and 2->3-5
- the line uncommented allowed take multi-route when the cost are equal
## Exercise 3: Understanding IP Fragmentation
## Question 1:
### Which data size has caused fragmentation and why?
- 2000 bytes and 3500 bytes
- because the MTU is 1500 bytes
### Which host/router has fragmented the original datagram?
- the source host
### How many fragments have been created when data size is specified as 2000?
- 2
## Question 2: Did the reply from the destination 8.8.8.8. for 3500-byte data size also get fragmented? Why and why not?
- yes
- three fragments can be seen in wireshark
## Question 3: Give the ID, length, flag and offset values for all the fragments of the first packet sent by 192.168.1.103 with data size of 3500 bytes?
ID | length | flag | offset
---|------------|------|--------
39 | 1480 bytes | MF=1 | 0
40 | 1480 bytes | MF=1 | 185
41 | 548 bytes | MF=1 | 370
## Question 4: Has fragmentation of fragments occurred when data of size 3500 bytes has been used? Why and why not?
- No
- it has 3 fragments, each with less than 1480 bytes
## Question 5: What will happen if for our example one fragment of the original datagram from 192.168.1.103 is lost?
- it will drop the whole package