Networking

1

TCN-6430 Fall 2017 Midterm Exam

Take Home Exam

• You have FOUR days to finish the exam. The FIRM deadline is midnight EDT on

Thursday October 26, 2017 • This exam has 7 pages, including this cover page. Do all your work on these exam sheets

and WITHIN the designated boxes. Either print and fill boxes or use Acrobat or your favorite PDF view/comment software to write directly on the exam PDF. DO NOT USE DIFFERENT FORMAT OR DIFFERENT LAYOUT OF THE EXAM.

• NO EXTRA PAGES, ANSWER BOXES MUST REMAIN IN THE EXACT POSITIONS! • Exam must be submitted to https://gradescope.com/ by the deadline. • Cross out all the scratch work that you do not want to be counted as part of your answer

before you submit the exam. • Be specific, clear, concise in your answers, and explain your answers. • When the answer to a problem is not immediately clear, do not simply dump everything,

relevant or irrelevant, on the paper. Irrelevant answers may lead to point-deduction as they show the lack of understanding of the problem.

Your name: Student ID:

2

Problem 1 (20 points) 1.1 Circle zero or several application-layer protocols that use only TCP as their transport layer protocols?

(a) HTTP 1.1/2 (b) QUIC

(c) SMTP (d) IMAP/POP3

(e) BitTorrent (f) DNS

(g) MPEG/DASH (h) Skype/VoIP

1.2 Circle zero or several application-layer protocols that are stateful?

(a) HTTP 1.1/2 (b) QUIC

(c) SMTP (d) IMAP/POP3

(e) BitTorrent (f) DNS

(g) MPEG/DASH (h) Skype/VoIP

1.3 List network management challenges 1.4 List at least three elements that network protocols (and protocols in general) define 1.5 DNS protocol is a highly available database because DNS zone information (resource records) can be

____________________________________ and ____________________________________. 1.6 HTTP protocol can scale because WEB data can be

____________________________________ and ____________________________________. 1.7 The common function (at least one) between TCP and UDP transport-layer protocol is

_____________________________________________________. 1.8 In addition to this function, TCP also provides

______________________________, ______________________________ and ________________________________.

3

Problem 2 (20 points) Consider the following environment with a local DNS caching resolver and a set of authoritative DNS name servers. Assume that initially,

• the caching resolver cache is empty, • TTL values for all records is 1 hour, • RTT between stub resolvers (hosts A, B, and C) and the caching

resolver is 20 ms, • RTT between the caching resolver and any of the authoritative name servers is 150 ms • There are no packet losses • All processing delays are 0 ms

2.1 At T=0 min, Host-A sends a query for “A record for amazon.com”, and after receiving the answer sends a query for “A record for www.amazon.com”. How long did it take to receive all the answers? 2.2 At T=40 min, Host-B sends a query for “MX record for google.com” that returns

google.com. 3600 IN MX 10 primary.google.com. google.com. 3600 IN MX 30 backup.google.com. primary.google.com. 3600 IN A 74.125.28.27 backup.google.com. 3600 IN A 173.194.211.27

(Similar to NS records, the DNS server may return “glue” A/AAAA records in addition to the requested MX records.) How long did it take to get the answer? 2.3 At T=70 min, Host-C sends a query for “AAAA (IPv6) record for mail.google.com”, following at T=75 mins with a query for “AAAA (IPv6) record for hangout.google.com”. How long did it take for Host-C to receive each of the answers (i.e., relative to T=70min for the first, and relative to T=75 mins for the second)? 2.4 List DNS records that the caching resolver has at T=90 minutes 2.5 At T=110 minutes, all the authoritative servers for .com go offline. Circle the domain names that can be resolved by Host-A?

(a) www.google.com (b) hangout.google.com (c) doc.google.com (d) www.amazon.com (e) video.amazon.com (f) aws.amazon.com

root domain

edu. com.

google.com. amazon.com.

caching resolver

A B C

4

Problem 3 (20 points) 3.1 List at least three benefits of using VLANs 3.2 Below is an illustration of two VLAN configurations between two switches. Briefly describe what potential network errors these configurations may cause?

3.3 For one of the configurations above, show commands how to configure the above policy on Cisco or Juniper switches.

5

Problem 4 (20 points) 4.1 Describe traditional switch/router architecture (data structures and how they are programmed) 4.2 How SDN changes the switch architecture, what are the benefits and drawbacks 4.3 Is there any relationship between SDN (OpenFlow) and MPLS? Briefly explain your answer

6

Problem 5 (20 points) Please describe how the flow table entries on a SDN switch can represent. For each case, you need to describe how the “pattern” and “action” fields of the flow table rules should be set. 5.1 Layer-2 forwarding table entries 5.2 Layer-3 routing table entries 5.3 Standard access list rules 5.4 Provide a step-by-step description of how switching is performed in SDN, using the example topology below. Assume host A sends a flow (i.e., a stream of packets) to host B, and later B replies to A. Assume that the layer-2 forwarding tables on the controller are all empty at the beginning. For each step in your description, be sure to include the following information: how the controller builds the layer-2 forwarding tables; The flow table entries that the controller installs on the switches.

7

Problem 6 (20 points) 6.1 Describe problems that NETCONF protocol addresses 6.2 Describe relation between NETCONF, RESTCONF, and YANG 6.3 Describe problems that MPLS switches can cause when end hosts exchange jumbo frames / large IPv4/IPv6 datagrams? Hint: https://youtu.be/edEDJKGzcEU