-------------------------------------------------------------------------- Mohamed G. Gouda CS 356 Spring 2018 Homework 1 -------------------------------------------------------------------------- 1. (2 points) Describe a scenario that involves two hosts, H1 and H2, and three routers, R1, R2, and R3. In this scenario, H1 generates and sends msg m1 followed by msg m2. The ultimate destination of both msgs is H2. Ensure that in this scenario, H1 sends m1 first then sends m2 second, and H2 receives m2 first then receives m1 second. Assume that in this scenario, no sent msg is lost and only links connecting computers can fail and can become up again. When a link connecting two computers fails, then no msg can be sent over the failed link. -------------------------------------------------------------------------- 2. (3 points) A client needs to get a web page whose URL is http://hname1/pname1 Assume that this page refers to three objects whose URLs are http://hname2/pname2 http://hname2/pname3 http://hname3/pname3 (a) What connections need to be established by the client. (b) What GET msgs need to be sent by the client. --------------------------------------------------------------------------- 3. (3 points) (a) Computing the IP addresses of what servers is needed to resolve the name (www.utexas.edu) of a web server into an IP address? (b) Computing the IP addresses of what servers is needed to resolve the name (www.cs.utexas.edu) of a web server into an IP address? (c) Computing the IP addresses of what servers is needed to resolve the name (www.lab.cs.utexas.edu) of a web server into an IP address? ---------------------------------------------------------------------------- 4. (2 points) Assum that a mail server is deployed in a company whose domain is x.com, and assume that the following three parameters have been chosen for this server alias name: x.com canonical name: mail.x.com IP address: 212.83.7.118 Describe how this mail server is registered in DNS. -------------------------------------------------------------------------- Solutions -------------------------------------------------------------------------- 1. The required scenario is as follows: 1. H1 sends m1 to R1 2. The link from R1 to R2 fails and so R1 forwards m1 to R3 3. H1 sends m2 to R1 4. The link from R1 to R2 becomes up again and so R1 forwards m2 to R2 5. R3 forwards m1 to R2 6. R2 forwards m2 to H2 7. R2 forwards m1 to H2 -------------------------------------------------------------------------- 2. (a) Client needs to establish the following connections: A connection from client to hname1 A connection from client to hname2 A connection from client to hname3 (b) Client needs to send the following GET messages: GET pname1 from hname1 GET pname2 from hname2 GET pname3 from hname2 GET pname3 from hname3 -------------------------------------------------------------------------- 3. (a) Computing the IP addresses of following servers is needed to resolve the name www.utexas.edu: edu, utexas.edu, www.utexas.edu (b) Computing the IP addresses of following servers is needed to resolve the name www.cs.utexas.edu: edu, utexas.edu, www.cs.utexas.edu (c) Computing the IP addresses of following servers is needed to resolve the name www.lab.cs.utexas.edu: edu, utexas.edu, www.lab.cs.utexas.edu -------------------------------------------------------------------------- 4. Store the following two RRs in the "A" DNS server of the domain x.com: (x.com, mail.x.com, MX, TTL) (mail.x.com, 212.83.7.118, A, TTL) --------------------------------------------------------------------------