CS6250 Computer Networks Exam 1 |
Questions and Verified Answers |
Rated A+ | Latest 2025/2026 Guide
1: The internet topology has been evolving from a ___ structure into a
___ structure.
Select one:
A. Hierarchical, flat
B. Flat, hierarchical
- Correct Answer - A
Rationale:
Originally the internet is made up of a hierarchy due to Tier-3 (Access
ISPs), Tier-2 (Regional ISPs), Tier-1 (Global ISPs).
Where each lower ISP connect to the higher tier-ed ISPs for connectivity.
In modern times, IXPs, CDNs (and other ways to connect) have been
very successful and have allowed lower-tier ISPs to directly connect at
IXPs bringing the hierarchy into a more flat shape.
2: An Autonomous System is a group of routers that operate under ___
administrative ___.
Select one:
A. Multiple, authorities
B. The same, authority
- Correct Answer - B
,3: Autonomous Systems implement their own set of policies, make their
own traffic engineering decisions and interconnection strategies, and
determine how traffic leaves and enters the network.
True or false?
- Correct Answer – True
4: The BGP protocol is used within an AS and focuses on optimizing a
path metric within the network. Examples of BGP protocols are Open
Shortest Paths First (OSPF) and Routing Information Protocol (RIP).
True or false?
- Correct Answer - False
Rationale:
BGP is used to export/import routes to/from external ASes.
They use two different types of sessions:
a) eBGP session (Gateway i.e. Border routers use this to communicate
with other Gateway Routers of other ASes for importing/exporting rules
externally)
b) iBGP session (Gateway Routers and Internal Routers of an AS use
these to share the imported/exported rules)
OSPF and RIP on the other hand, are the two main Interior Gateway
Protocols (Used to generate the routing lowest-cost paths within an AS)
1: In a peering relationship, the traffic exchanged between the two peers
must be highly asymmetric so that there is enough incentive for both
parties to peer with each other.
True or false?
- Correct Answer - False
Rationale:
In a peering relationship, both ASes (called Participant ASes) must be of
,similar size otherwise it won't be fair to one of the ASes. Peering is
sharing routing tables with each other for "free" to route traffic between
themselves
2: A customer-provider relationship between ASes is based on a
financial settlement, which determines how much the customer will pay
the provider. The provider takes care of connecting the customer
network with destinations found in the provider's routing table. The
customer pays regardless of the direction of the traffic.
True or false?
- Correct Answer - True
3: There is no incentive for smaller ISPs to peer with each other.
True or false?
- Correct Answer - False
Rationale:
Peering is free, therefore it makes sense for two smaller ISPs to peer
with each other (share their routing tables) and share their traffic to avoid
having to pay provider ISPs to send the traffic otherwise.
(Makes the most sense if the smaller ISPs' traffics tend to go to each
other)
4: Provider ASes have a financial incentive to forward as much of their
customers' traffic as possible.
True or false?
- Correct Answer - True
Rationale:
, Customer ASes are the ones who pay the Provider ASes, therefore it is
common sense that Provider ASes want to find the most avenues to
create more traffic opportunities going to and from the customer ASes
AND flowing through itself (the current Provider AS).
5: Select the correct order for an AS to import its routes based on their
incentive.
(Best = left, worst = right)
Select one:
A. Routes learned from customers --> providers --> peers
B. Routes learned from customers --> peers--> providers
C. Routes learned from peers --> customers --> providers
D. Routes learned from peers --> providers --> customers
E. Routes learned from providers --> customers --> peers
F. Routes learned from providers --> peers --> customers
- Correct Answer - B
Rationale:
We want to prioritize the Customer AS routes to import (routes to reach
the customer) as most important.
The second "best" is Peer ASes' routes. We don't lose anything from
importing them (since they're free), but it can promote money eventually
from exporting them to Customer ASes to go to them.
The third worst option is importing Providers' routes. This is because we
don't want to route through them (because this current AS will be
Questions and Verified Answers |
Rated A+ | Latest 2025/2026 Guide
1: The internet topology has been evolving from a ___ structure into a
___ structure.
Select one:
A. Hierarchical, flat
B. Flat, hierarchical
- Correct Answer - A
Rationale:
Originally the internet is made up of a hierarchy due to Tier-3 (Access
ISPs), Tier-2 (Regional ISPs), Tier-1 (Global ISPs).
Where each lower ISP connect to the higher tier-ed ISPs for connectivity.
In modern times, IXPs, CDNs (and other ways to connect) have been
very successful and have allowed lower-tier ISPs to directly connect at
IXPs bringing the hierarchy into a more flat shape.
2: An Autonomous System is a group of routers that operate under ___
administrative ___.
Select one:
A. Multiple, authorities
B. The same, authority
- Correct Answer - B
,3: Autonomous Systems implement their own set of policies, make their
own traffic engineering decisions and interconnection strategies, and
determine how traffic leaves and enters the network.
True or false?
- Correct Answer – True
4: The BGP protocol is used within an AS and focuses on optimizing a
path metric within the network. Examples of BGP protocols are Open
Shortest Paths First (OSPF) and Routing Information Protocol (RIP).
True or false?
- Correct Answer - False
Rationale:
BGP is used to export/import routes to/from external ASes.
They use two different types of sessions:
a) eBGP session (Gateway i.e. Border routers use this to communicate
with other Gateway Routers of other ASes for importing/exporting rules
externally)
b) iBGP session (Gateway Routers and Internal Routers of an AS use
these to share the imported/exported rules)
OSPF and RIP on the other hand, are the two main Interior Gateway
Protocols (Used to generate the routing lowest-cost paths within an AS)
1: In a peering relationship, the traffic exchanged between the two peers
must be highly asymmetric so that there is enough incentive for both
parties to peer with each other.
True or false?
- Correct Answer - False
Rationale:
In a peering relationship, both ASes (called Participant ASes) must be of
,similar size otherwise it won't be fair to one of the ASes. Peering is
sharing routing tables with each other for "free" to route traffic between
themselves
2: A customer-provider relationship between ASes is based on a
financial settlement, which determines how much the customer will pay
the provider. The provider takes care of connecting the customer
network with destinations found in the provider's routing table. The
customer pays regardless of the direction of the traffic.
True or false?
- Correct Answer - True
3: There is no incentive for smaller ISPs to peer with each other.
True or false?
- Correct Answer - False
Rationale:
Peering is free, therefore it makes sense for two smaller ISPs to peer
with each other (share their routing tables) and share their traffic to avoid
having to pay provider ISPs to send the traffic otherwise.
(Makes the most sense if the smaller ISPs' traffics tend to go to each
other)
4: Provider ASes have a financial incentive to forward as much of their
customers' traffic as possible.
True or false?
- Correct Answer - True
Rationale:
, Customer ASes are the ones who pay the Provider ASes, therefore it is
common sense that Provider ASes want to find the most avenues to
create more traffic opportunities going to and from the customer ASes
AND flowing through itself (the current Provider AS).
5: Select the correct order for an AS to import its routes based on their
incentive.
(Best = left, worst = right)
Select one:
A. Routes learned from customers --> providers --> peers
B. Routes learned from customers --> peers--> providers
C. Routes learned from peers --> customers --> providers
D. Routes learned from peers --> providers --> customers
E. Routes learned from providers --> customers --> peers
F. Routes learned from providers --> peers --> customers
- Correct Answer - B
Rationale:
We want to prioritize the Customer AS routes to import (routes to reach
the customer) as most important.
The second "best" is Peer ASes' routes. We don't lose anything from
importing them (since they're free), but it can promote money eventually
from exporting them to Customer ASes to go to them.
The third worst option is importing Providers' routes. This is because we
don't want to route through them (because this current AS will be
