Help me with my networking uni assignment :)

[hv0k]

Dear LTT, 

 

I know that I should know these answers and all, but I honestly don't know, I did manage to answer a few questions but there are some that I literally couldn't comprehend.

 

those are the following questions: 

 

Problem 2- IP Fragmentation

Consider sending 4000-bytedatagram into a link that has an MTU of 250 bytes. 

a)    How many fragments are generated? 

b)    What are their characteristics (i.e. what are the flags and offset values for each (Assume that the DF flag was not set : )
Solution: Assume that no optional fields of the IP header are in use (i.e. IP header is 20 bytes) 

c)     When a large datagram is fragmented into multiple smaller datagrams, where are these smaller datagrams reassembled?

d)   Explain how traceroute works. Include a traceroute to a host at least 9 hops away.

 

Problem3:CIDR -A router has the following (CIDR) entries in its routing table: 

 

Destination Gateway        Next hop 

137.46.56.0/21                Interface 0 

137.46.60.0/21                Interface 1 

196.53.40.0/22                 Router 1 

default Router 2

1. For each of the following IP address, what does the router do if packets with the following addresses arrive? 

(a) 137.46.63.10/21 

(b) 137.46.57.14/21

(c) 135.46.52.2 /22

(d) 196.53.40.7 /24

(e) 192.53.56.7/24

2. What is the relationship between the “gateway” and “interface” fields?

 

 

I would really appreciate any help any can give. thank you very much.

 

[Acedia]

3 hours ago, hv0k said:

d)   Explain how traceroute works. Include a traceroute to a host at least 9 hops away.

Let's go for the low hanging fruit first. Basically Traceroute is part of the icmp protocol and shows the different routers or hops a packet will take to it's destination. It does this by pinging with a decreasing TTL so every step a different router answers.

Quote

137.46.56.0/21                Interface 0 

137.46.60.0/21                Interface 1 

Are you sure about those numbers? Because those two are within the same /21 subnet.

[mtz_federico]

On 4/27/2019 at 2:15 PM, hv0k said:

Consider sending 4000-bytedatagram into a link that has an MTU of 250 bytes. 

a)    How many fragments are generated? 

I believe this one is just 4000/250=16

[Acedia]

3 hours ago, mtz_federico said:

I believe this one is just 4000/250=16

You are not accounting for the Header which is 20 bytes.

 

Unless I am missing something tcp wise it should be (4000+20x)/250=x OR 4000/(250-30)=x hence x=17,39

So the solution should be 18 fragments?

[mtz_federico]

17 hours ago, Acedia said:

You are not accounting for the Header which is 20 bytes.

 

Unless I am missing something tcp wise it should be (4000+20x)/250=x OR 4000/(250-30)=x hence x=17,39

So the solution should be 18 fragments?

Your right.

your equations look right but im not sure