1. Dave Roberts

2.  Dynamic Host Configuration Protocol  DHCP  Simple Mail Transport Protocol  SMTP 2

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4.  Address of default router  Network mask  Addresses of mail server, DNS server  MTU of local network  TTL value to use for IP datagrams  IP address of host 4

5.  People make mistakes  There aren’t enough people  Hosts may be dumb and unable to remember settings So—we use IP to get the IP addresses that we need. The “limited broadcast” IP address is used to broadcast even before the client knows its own IP address. 5

6.  Responsibility for reliable communication on the client  Requires that UDP checksum be on  Requires that do not fragment bit be on  Client sets timeout, retransmits when timeout expires  Delay has a random number added  After failure, delay is doubled, up to 60 seconds 6

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8.  Manual allocation: Each IP address is allocated to a single device. DHCP communicates that address  Automatic allocation: DHCP automatically assigns an IP address permanently to a device, selecting from a pool  Dynamic allocation: DHCP assigns an IP address from a pool for a time chosen by the server or until the client gives it up (most used, by far) 8

9.  DHCP administrator must pick lease length for IP addresses  Short lease lengths make most effective use of IP addresses  Long lease lengths produce more network stability  Lease lengths might be from one hour to months 9

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11.  DHCPv4 is run by hosts at startup  It configures the host for network operation What about v6? 11

12.  Designers wanted startup without DHCP  Designed stateless autoconfiguration  But ISPs and network managers wanted more control, so DHCPv6 was also developed 12

13.  Server for each network; host contacts server  Host generates link-local address, uses link- local multicast to reach server  DHCPv6 allows for authentication  RFC for DHCPv6 is twice the size as RFC for DHCPv4 13

14.  Uses IPv6 Neighbor Discovery Protocol (NDP)  Host generates an IPv6 address and checks its uniqueness on its network  Link-local address generated with prefix in leftmost bits and MAC address in rightmost bits. Any in between are set to zero.  Host uses Duplicate Address Detection (DAD) to test whether the link-local address s unique on the subnet 14

15.  Host sends neighbor solicitation message asking for address it wants to use  If other host is using it, it responds and requesting host stops autoconfiguration  This rarely happens because MAC addresses are intended to be unique  Next, host sends router solicitation message to all-routers multicast address  Response from router tells host whether to use DHCP, whether to create global address 15

16.  Router Discovery  Next-hop routes  Neighbor discovery  Neighbor unreachability detection  Address prefix discovery  Configuration parameter discovery  Stateless autoconfiguration  Duplicate address detection  Address resolution  DNS server discovery  Redirect 16

17.  Router Solicitation  Router Advertisement  Neighbor Solicitation  Neighbor Advertisement  Redirect 17

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23.  For IPv6, configurations can be managed by DHCP or automatically  Either method can provide all the parameters needed on startup  DHCP allows for more complete control of which hosts can connect to a network 23

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25. Email allows users to send memos across the Internet.  Notes can be short or quite large  Notes can have multiple attachments  Must work when remote machine is unreachable 25

26.  Post Office  SMTP servers move email between each other  SMTP servers store email for delivery to end users  Users  POP clients pick up email from SMTP servers  POP clients hand outgoing mail to SMTP servers 26

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28. 28 Sender and receiver do not need to be connected to the server at the same time

29.  MAIL command: establishes return address and bounce address  RCPT command: establishes recipient of this message  DATA signals beginning of the message text 29

30.  What protocol do SMTP servers use to deliver messages?  How does SMTP differ between v4 and v6? 30

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32.  S: 220 smtp.example.com ESMTP Postfix  C: HELO relay.example.org  S: 250 Hello relay.example.org, I am glad to meet you  C: MAIL FROM:  S: 250 Ok  C: RCPT TO:  S: 250 Ok  C: RCPT TO:  S: 250 Ok  C: DATA  S: 354 End data with.  C: From: "Bob Example"  C: To: "Alice Example"  C: Cc: theboss@example.com  C: Date: Tue, 15 January 2008 16:02:43 -0500  C: Subject: Test message  C:  C: Hello Alice.  C: This is a test message with 5 header fields and 4 lines in the message body.  C: Your friend,  C: Bob C:.  S: 250 Ok: queued as 12345  C: QUIT  S: 221 Bye  {The server closes the connection} 32

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34.  TCP/IP internet makes universal delivery service possible  Mail systems built on TCP/IP are inherently reliable because of end-to-end delivery  Alternatively, mail gateways are used  Allow mail transfer between different systems  When gateway has a message, sender discards it 34 Question: Is email through a gateway better or worse than a direct SMTP transfer?

35.  Format and computer interaction are specified separately  Format: header, blank line, body  Body unspecified  Header is key word, colon, value  Some keywords required, others optional  Header is readable 35

36. local-part @ domain-name  domain-name: name of mail destination  local-part: address of a mailbox at destination Note: when gateways are employed, mail addresses are site-dependent 36

37.  Simple Mail Transport Protocol  Focuses on how mail delivery system passes messages from one machine to a server on another machine  Does not specify anything about user interface  Does not specify how mail is stored 37

38.  SMTP server forms TCP/IP connection with receiving server  Once receiving server has put message into safe store, then it acknowledges and sender discards message  If SMTP can’t transfer message on the first try, it keeps trying  After several days of failure, SMTP reports failure to deliver. 38

39.  All communications is readable ASCII text  Transcript of interactions is readable  Each message is acknowledged separately  Addresses of the form local-part@domain- name 39

40.  POP3—Post Office Protocol  POP3 client creates TCP connection to POP3 server on mailbox computer  Mailbox computer runs two servers:  SMTP to place mail into user mailboxes  POP3 server to allow user to extract messages from user mailbox  POP3 retrieves messages, deletes from user mailbox  Two servers must coordinate use of the user mailbox 40

41.  POP stores messages offline; not compatible with the use of multiple computers  IMAP allows message access, manipulation from multiple computers  Platform-independent access to mail 41 Question: How does server resource usage of IMAP compare with POP?

42. MIME—Multipurpose Internet Mail Extensions  Defined to allow transmission of non-ASCII data through mail  MIME allows arbitrary data to be encoded in ASCII, transmitted as standard email message  MIME message tells recipient type of data, type of encoding used  Data type and subtype is specified  MIME information is in 822 mail header 42

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44. From: bill@acollege.edubill@acollege.edu To: john@example.comjohn@example.com MIME-Version: 1/0 Content-Type: image/gif Content-Transfer Encoding: base64 ….data for the image…. 44

45.  Post Office Protocol—client login with userid/password  Client can then retrieve, delete messages  Server computer must run two servers: POP and SMTP  POP and SMTP must coordinate use of mailbox 45

46.  Email is a very important Internet service  Separate standards are used for message format and transfer  SMTP—how a mail system on one machine transfers to a server on another  POP3—how a user can retrieve contents of a mailbox  IMAP—user protocol for use from multiple computers  MIME allows arbitrary data to be exchanged using SMTP 46