Week 6 Flashcards

1
Q

What is a user agent for mail?

A

allows users to send/read messages.

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2
Q

What are the 3 major components of the Internet Mail System?

A
  1. User Agent
  2. Mail Server
  3. Simple Mail Transfer Protocol (SMTP)
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3
Q

What is a mail server?

A

A server that stores a users “mailbox” .
there can be multiple mailboxes in a mail server

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4
Q

What is the SMTP?

A

Allows to transfer mail from one mail server to another. Has both a client and server side –> for receiving mail from users and other mail servers, and for sending them to other mail servers

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5
Q

What does SMTP use to transfer mail? And what port number?

A

TCP, Port 25. It uses persistent connections.

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6
Q

Does SMTP use intermediate mail servers for sending mail?

A

No. It uses Direct Transfer.

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7
Q

What are the 3 phases of a SMTP transfer?

A
  1. handshake
  2. send/receive message
  3. close
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8
Q

Some restrictions of SMTP format?

A
  • rrequires header and body to be in 7-bit ASCII
  • uses persistent connections
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9
Q

How is HTTP and SMTP different?

A

HTTP has client pull, SMTP has client push

HTTP has each object encapsulated, SMTP has multiple objects

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10
Q

What are some stuff a client sends into SMTP?

A
  1. HELO [client’s hostname]
  2. MAIL FROM:
  3. RCPT TO:
  4. DATA
  5. QUIT
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11
Q

How does the client SMTP indicate the end of the mail?

A

A single period. “.”

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12
Q

What are the 2 ways to retrieve mail from a mail server?

A
  1. HTTP for web-based
  2. IMAP for mail clients
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13
Q

What is the DNS?

A

The Domain Name System

  • a directory tha translates hostnames –> IP address
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14
Q

What are 2 ways to identify internet hosts?

A
  1. Host name
  2. IP address
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15
Q

What layer is the DNS implemented in?

A

App-Layer protocol.

hosts and servers communicate to resolve names.

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16
Q

What are 3 other jobs of DNS?

A
  1. host aliasing
  2. mail server aliasing
  3. load distrubution (many IP addresses correspond to 1 name)
17
Q

Cons of a centralized DNS

A
  1. single point of failure
  2. too much traffic
  3. cannot be close to all clients
  4. unscalable
18
Q

What are the 3 classes of DNS servers in a Distributed Databse?

A

Root DNS > Top-Level Domain > Authoritative DNS

19
Q

How does the client find an IP address? (Order)

A

Root -> Top-Level Domain -> Authoritative

20
Q

What is a Local DNS server?

A
  • when a host makes a DNS query it is sent to the local DNS server.
  • local DNS server returns a reply answering translations and requests (from its cache)
21
Q

What is iterated query for DNS name resolution?

A
  • contacted server replies with name of server to contact
  • “idk this name but ask this server”
22
Q

What is recursive query for DNS name resolution?

A

put the burden of name resolution on the contacted name server (pass the responsibility)

23
Q

What are resource records of a DNS?

A

DNS provides RRs (resource records) to provide mappings in response to a query.

24
Q

What is the RR format?

A

(Name, Value, Type, Ttl)

Name&Value: depends on type
TTL: time to live

25
Q

What are the 4 “Types” in RR format?

A
  1. A
  2. NS
  3. CNAME
  4. MX
26
Q

What is the value if Type=A

A

name = hostname
value = IP address

27
Q

What is the value if Type=NS

A

name = domain (foo.com)
value = hostname of DNS server of the domain

28
Q

What is the value if Type=CNAME

A

name = alias name
value = CANONICAL hostname

29
Q

What is the value if Type=MX

A

value = CANONICAL name of SMTP mail server associated with name

30
Q

Pull based vs Push based protocols?

A

Pull based: IMAP

Push based: SMTP

Either: HTTP