# Solutions to Practice Problems RB RA RD

```Solutions to Practice Problems
Practice Problem 16.1
Consider the network below. How would the routing table evolve using distance vector routing?
RB
4
2
RA
RD
RC
5
B
C
D
RA
4 (B)
5 (C)
∞
RB
4 (A)
∞
2 (D)
A
C
D
2
A
B
D
RC
5 (A)
∞
2 (D)
A
B
C
RD
∞
2 (B)
2 (C)
A
B
D
RC
5 (A)
4 (D)
2 (D)
A
B
C
RD
6 (B)
2 (B)
2 (C)
Everyone shares table with neighbors.
Solution:
B
C
D
RA
4 (B)
5 (C)
6 (B)
RB
4 (A)
4 (D)
2 (D)
A
C
D
But what if Router C was evil and began to falsify information about its link to Router A; how would the
routing table change?
RB
4
2
RA
RD
RC
1
B
C
D
RA
4 (B)
5 (C)
∞
A
C
D
RB
4 (A)
∞
2 (D)
2
A
B
D
RC
1 (A)
∞
2 (D)
A
B
D
RC
1 (A)
4 (D)
2 (D)
A
B
C
RD
∞
2 (B)
2 (C)
Everyone shares table with neighbors.
Solution:
B
C
D
RA
4 (B)
5 (C)
6 (B)
A
C
D
RB
4 (A)
4 (D)
2 (D)
2
A
B
C
RD
3 (C)
2 (B)
2 (C)
What does this mean for all of Router D’s traffic destined for Router A?
Solution:
All of Router D’s traffic destined for Router A will go through Router C instead of Router B.
More importantly, why would Router D’s traffic go through Router C instead?
Solution
Router C manipulated the network by falsifying the information about the distance between it
and Router A.
Practice Problem 16.2
What primary pillar of information assurance is violated in each thing Router C can do once it is in the middle
of Router D and Router A?
(a) The ability to observe traffic violates:
Solution: Confidentiality
(b) The ability to change traffic violates:
Solution:
Integrity
(c) The ability to stop traffic violates:
Solution:
Availability
Practice Problem 16.3
Construct the routing table for Router A.
3
Solution:
192.168.65.0
Practice Problem 16.4
What is the first and last IP address of the 4.4.5.0/24 network where the webserver is located?
Solution: 4.4.5.1 (not counting the network address)
Looking at Router A’s table, what network ID and mask should the evil instructor choose? Other options? Yes!
Target’s
Network
Target’s
Attacker’s
Lie
4
.
4
.
5
.
0
0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0
4
.
4
.
5
.
155
0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 1 0 0 1 1 0 1 1
4
.
4
.
5
.
144
0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 1 0 0 1 0 0 0 0
What is the first and last address of the false network the evil instructor will advertise?
Solution: 4.4.5.145
Solution: 4.4.5.158
Does the IP address of the webserver fall within the IP address block that the evil instructor will advertise?
Solution: Yes
4
Practice Problem 16.5
What will Router A’s routing table look like, once it hears the lie about the fake network from Router B?
192.168.65.0
Thus, whenever a student sends a packet destined for the webserver at 4.4.5.155, where will Router A
forward their packet? Will the EC310 students ever be able to reach the course web page?
No, all traffic will be forwarded to Router B because it is advertising a more specific network prefix.
5
Practice Problem 16.6
Briefly describe two technical solutions to protect against false route injection and identify who is responsible
for implementing them.
Solution #1: Plaintext-password. Added to all LSPs so each route can authenticate the information they send.
The Network Administrator would be responsible for implementing this.
Solution #2: Passive interfaces. Once an interface is set as passive, the router will ignore all routing
information sent over that interface. The Network Administrator would be responsible for implementing this.
6
```