7. protocols

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7. protocols

  1. 1. 7 – Protocols7 – ProtocolsMarian MarinovMarian MarinovCEO of 1H Ltd.CEO of 1H Ltd.mm@1h.commm@1h.comBorislav VaradinovBorislav VaradinovSystem AdministratorSystem Administratorbobi [ at ] itp.bgbobi [ at ] itp.bg
  2. 2. ● ARP/RARP● ICMP● UDP● TCP● TCP Congestion● SCTP● DCCP● DNS
  3. 3. Type of requests - Unicast
  4. 4. Type of requests - Broadcast
  5. 5. Type of requests - Multicast
  6. 6. Address Resolution Protocol● Address resolution– Forward– Reverse● ARP– Probe– Proxy– Mediation– Stuffing
  7. 7. Address Resolution Protocol● Address resolution– Forward (what is the MAC of this machine)08:11:96:03:B2:2808:11:96:03:B2:28FF:FF:FF:FF:FF:FFFF:FF:FF:FF:FF:FF192.168.2.254192.168.2.254192.168.2.58192.168.2.58Request0x08000x08001 - req1 - req 2 - reply2 - reply
  8. 8. Address Resolution Protocol● Address resolution– Forward (what is the MAC of this machine)40:b3:95:80:c5:aa40:b3:95:80:c5:aa08:11:96:03:b2:2808:11:96:03:b2:28192.168.2.58192.168.2.58192.168.2.254192.168.2.254Reply
  9. 9. Address Resolution Protocol● Address resolution– Reverse (what is the IP of this machine)08:11:96:03:B2:2808:11:96:03:B2:2840:b3:95:80:c5:aa40:b3:95:80:c5:aa192.168.2.254192.168.2.2540.0.0.00.0.0.0Request
  10. 10. Address Resolution Protocol● Address resolution– Reverse (what is the IP of this machine)40:b3:95:80:c5:aa40:b3:95:80:c5:aa08:11:96:03:B2:2808:11:96:03:B2:28192.168.2.58192.168.2.58192.168.2.254192.168.2.254Reply
  11. 11. Address Resolution Protocol● How it actually looks15:12:43.772954 ARP, Ethernet (len 6), IPv4 (len 4),Request who-has 192.168.2.58 tell 192.168.2.254, length 2815:12:43.962834 ARP, Ethernet (len 6), IPv4 (len 4),Reply 192.168.2.58 is-at 40:b3:95:80:c5:aa, length 46● ARP probe● ARP proxy● ARP mediation● ARP stuffing
  12. 12. Internet Control Message Protocol - ICMP
  13. 13. Internet Control Message Protocol - ICMP● ICMP types– 0 – Echo replay– 1,2 – Reserved– 3 – Destination unreachable– 8 – Echo request– 9 –TTL Exceeded– 30 –Traceroute
  14. 14. Internet Control Message Protocol - ICMP● Type codes3 – Destination unreachable0 – network unreachable1 – host unreachable2 – protocol unreachable3 – port unreachable6 – network unknown7 – host unknown9 – network prohibited10 – host prohibited11 – Time to live exceeded0 – in transit1 – in reassembly
  15. 15. Protocol EncapsolationLayer 2Layer 3Layer 2Layer 4/5Ethernet payloadEthernet HeaderIP Header IP PayloadTCP Header IP Payload
  16. 16. Machine YMachine YUser Datagram Protocol - UDP12341234Machine XMachine XUDP (RFC768 Jon Postel 1980)
  17. 17. User Datagram Protocol - UDP
  18. 18. 12341234Machine YMachine YTransmission Datagram Protocol -TCP12341234Machine XMachine XUDPTCPTCP (RFC793 Jon Postel 1981)
  19. 19. Transmission Datagram Protocol -TCP
  20. 20. Transmission Datagram Protocol -TCP● TCP (RFC793 Jon Postel 1981)– Session establishment and tear-down– Window procedure– Slow start and congestion avoidance (VanJacobson 1988)– Fast open– Syn cookies
  21. 21. Transmission Datagram Protocol -TCPTCPProcessTCPProcessMachine XMachine Y
  22. 22. Transmission Datagram Protocol -TCPFlags: ACKFlags: SYN, ACKSeq: Y, Ack: X+1Flags: SYN, ACKFlags: SYN Seq: XSeq: X + 1, Ack: Y+1Client ServerThree way handshakeSYN RCVDServerEstablishedSYN SENTEstablished
  23. 23. Transmission Datagram Protocol -TCPTCP Fast open
  24. 24. Transmission Datagram Protocol -TCPTCP Fast open
  25. 25. Transmission Datagram Protocol -TCPFlags: ACKFlags: FIN, ACKSeq: Y, Ack: X+1Flags: FIN Seq: XSeq: X + 1, Ack: Y+1Client ServerConnection CloseFIN WAIT 1CLOSE WAITFIN WAIT 2 LAST ACKTIME WAITCLOSE
  26. 26. TCP Congestionhttp://en.wikipedia.org/wiki/TCP_congestion_avoidance_algorithmhttp://en.wikipedia.org/wiki/TCP_congestion_avoidance_algorithm
  27. 27. TCP Congestion➢ Slow start➢ Congestion avoidance➢ Fast retransmit➢ Fast Recovery
  28. 28. TCP Congestion – Slow start➢ The initial window size is initialized to one MSS➢ Each time a packet is ACKed the congestion window iincreased➢ When the ssthresh is reached, the next phase startshttp://en.wikipedia.org/wiki/Slow-starthttp://en.wikipedia.org/wiki/Slow-start
  29. 29. TCP Congestion –Congestion avoidance➢ In this phase window size is increased linearly untiltimeout occurs or duplicate ACK is received
  30. 30. TCP Congestion – Fast retransmit➢ If more then 3 ACKs are received for the same segmenthe sender has to send that particular segment even beits timer has expiredhttp://en.wikipedia.org/wiki/Fast_retransmithttp://en.wikipedia.org/wiki/Fast_retransmit
  31. 31. TCP Congestion – Fast Recovery➢ In this phase window size is decreased to ssthresh ratthen the smaller initial value and increase its size linehttp://histrory.visualland.net/tcp_fast_recovery.htmlhttp://histrory.visualland.net/tcp_fast_recovery.html
  32. 32. TCP Congestion Avoidance - Problems➢ Slow-start assumes that unacknowledged segments adue to network congestion, which is usually NOT the cin wireless networks, where dropped packets are mainbecause of poor data link quality.➢ The slow-start protocol performs badly for short-livedconnections, because it actually slows down thetransmission of data.➢ It is possible to trick the congestion avoidance algoritto think that the pipe is full and slow down all connectoriginating from that machine.
  33. 33. TCP Keepalive➢ The keepalive packets are packets which contain no dsent at regular interval to confirm that this connectionalive➢ Keepalive time is the duration between two keepalivetransmissions in idle condition. TCP keepalive periodrequired to be configurable and by default is set to nothan 2 hours.➢ Keepalive interval is the duration between two succekeepalive retransmissions, if acknowledgement to theprevious keepalive transmission is not received. Usualaround 75 seconds.➢ Keepalive retry is the number of retransmissions to bsent out before declaring that remote end is not availa
  34. 34. Datagram Congestion Control Protocol➢ Basically DCCP is UDP with congestion control mechanIt features➢ Unreliable flows of datagrams➢ Reliable handshakes for connection setup and teardow➢ Negotiation of a suitable congestion control mechanism➢ Acknowledgment mechanisms communicating packet lo➢ Path Maximum Transmission Unit (PMTU) discovery➢ RFC4340
  35. 35. DCCP header (x = 1)0 1 2 30 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Source Port | Dest Port || Source Port | Dest Port |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Data Offset | CCVal | CsCov | Checksum || Data Offset | CCVal | CsCov | Checksum |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| | |X| | .| | |X| | .| Res | Type |=| Reserved | Sequence Number (high bits) .| Res | Type |=| Reserved | Sequence Number (high bits) .| | |1| | .| | |1| | .+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+. Sequence Number (low bits) |. Sequence Number (low bits) |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+If X is 1 the Sequence Number field is 48 bits longIf X is 1 the Sequence Number field is 48 bits long
  36. 36. DCCP header (x = 0)0 1 2 30 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Source Port | Dest Port || Source Port | Dest Port |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Data Offset | CCVal | CsCov | Checksum || Data Offset | CCVal | CsCov | Checksum |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| | |X| || | |X| || Res | Type |=| Sequence Number (low bits) || Res | Type |=| Sequence Number (low bits) || | |0| || | |0| |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+If X is 0 the Sequence Number field is 24 bits longIf X is 0 the Sequence Number field is 24 bits longData Offset - the offset from the start of the packets DCCP header to thData Offset - the offset from the start of the packets DCCP header to thstart of its application data areastart of its application data areaCCVal - Defines the congestion control algorithm usedCCVal - Defines the congestion control algorithm usedCCVal = 2 - TCP like congestion avoidanceCCVal = 2 - TCP like congestion avoidanceCCVal = 3 - TCP friendly congestion avoidanceCCVal = 3 - TCP friendly congestion avoidanceCsCov - Checksum Coverage determines the parts of the packet that areCsCov - Checksum Coverage determines the parts of the packet that arecovered by the Checksum field.covered by the Checksum field.Checksum – DCCP header checksumChecksum – DCCP header checksumType – DCCP packet typeType – DCCP packet typeX - Extended Sequence Numbers (may be 0 or 1)X - Extended Sequence Numbers (may be 0 or 1)
  37. 37. DCCP headerAll currently defined packet types except DCCP-Request and DCCP-DataAll currently defined packet types except DCCP-Request and DCCP-Datacarry an Acknowledgment Number Subheadercarry an Acknowledgment Number SubheaderWhen X=1, its format is:When X=1, its format is:+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Reserved | Acknowledgment Number .| Reserved | Acknowledgment Number .| | (high bits) .| | (high bits) .+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+. Acknowledgment Number (low bits) |. Acknowledgment Number (low bits) |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+When X=0, only the low 24 bits of the Acknowledgment Number areWhen X=0, only the low 24 bits of the Acknowledgment Number aretransmitted, giving the Acknowledgment Number Subheader this format:transmitted, giving the Acknowledgment Number Subheader this format:+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Reserved | Acknowledgment Number (low bits) || Reserved | Acknowledgment Number (low bits) |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  38. 38. DCCP packet typesType MeaningType Meaning---- ----------- -------0 DCCP-Request0 DCCP-Request1 DCCP-Response1 DCCP-Response2 DCCP-Data2 DCCP-Data3 DCCP-Ack3 DCCP-Ack4 DCCP-DataAck4 DCCP-DataAck5 DCCP-CloseReq5 DCCP-CloseReq6 DCCP-Close6 DCCP-Close7 DCCP-Reset7 DCCP-Reset8 DCCP-Sync8 DCCP-Sync9 DCCP-SyncAck9 DCCP-SyncAck10-15 Reserved10-15 Reserved
  39. 39. MultihomingISP xISP xISP yISP yISP mISP mISP jISP jISP sISP sThe InternetThe Internet
  40. 40. Stream ControlTransmission Protocol➢ Multihoming support in which one or both endpoints of aMultihoming support in which one or both endpoints of aconnection can consist of more than one IP address,connection can consist of more than one IP address,enabling transparent fail-over between redundant networkenabling transparent fail-over between redundant networkpaths.paths.➢ Delivery of chunks within independent streams eliminateDelivery of chunks within independent streams eliminateunnecessary head-of-line blockingunnecessary head-of-line blocking➢ Path selection and monitoringPath selection and monitoring➢ Validation and acknowledgment mechanisms protectValidation and acknowledgment mechanisms protectagainst flooding attacks and provide notification ofagainst flooding attacks and provide notification ofduplicated or missing data chunks.duplicated or missing data chunks.➢ Improved error detection suitable for Ethernet jumboImproved error detection suitable for Ethernet jumboframes.frames.
  41. 41. Stream ControlTransmission Protocol0 1 2 30 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Common Header || Common Header |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Chunk #1 || Chunk #1 |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| ... || ... |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Chunk #n || Chunk #n |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+RFC4960RFC4960
  42. 42. Stream ControlTransmission ProtocolCommon HeaderCommon Header0 1 2 30 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Source Port Number | Destination Port Number || Source Port Number | Destination Port Number |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Verification Tag || Verification Tag |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Checksum || Checksum |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+RFC4960RFC4960
  43. 43. IP & Domain allocation➢ IANA – www.iana.org➢ Number resources➢ IP Addresses➢ Autonomous System (AS)➢ Protocol number assignments➢ Domain assignments➢ Root zone management➢ gTLD database➢ .int and .arpa domains➢ IP registrars➢ ARIN, LACNIC, Africa, APNIC, RIPE
  44. 44. IP & Domain allocation➢ Regional Internet Registrar(RIR)➢ Local Internet Registrar(LIR)➢ There are two types of IP addresses that can be reques➢ Provider dependent➢ These you get from your ISP➢ Provider independent➢ You get them from the local LIR or the regional RIR➢ These allocations can not be smaller then /24 networ➢ Autonomous System (AS)➢ Used for the BGP routing protocol➢ Aggregated IP route announcements are made from ato them➢ The corner stone of the Internet routing➢ Look at http://www.youtube.com/watch?v=oK-lgjJhC4
  45. 45. Domain Name System - DNSEverything was hosts:Everything was hosts:127.0.0.1127.0.0.1 localhostlocalhost192.168.0.174192.168.0.174 store1store1192.168.0.238192.168.0.238 store2store2192.168.0.244192.168.0.244 store3store3192.168.155.2192.168.155.2 operationsoperations192.168.155.149192.168.155.149 zimbra0.siteground.comzimbra0.siteground.com193.107.36.190193.107.36.190 sapport.bgsapport.bg www.sapport.bgwww.sapport.bg8.8.8.88.8.8.8 ns.google.comns.google.com89.25.120.3189.25.120.31 google.comgoogle.com89.25.120.2489.25.120.24 www.google.comwww.google.comLinux: /etc/hostsLinux: /etc/hostsWindows: C:WindowsSystem32driversetchostsWindows: C:WindowsSystem32driversetchosts
  46. 46. DNS➢ Internet Corporation For Assigned Names and Numbe➢ IANA is now part of it➢ Handles ccTLDs➢ Handles gTLDs➢ Handles the Root zone➢ Country level domains➢ .bg, .co.za, .co.uk, .edu.us➢ Top-level domains➢ .com, .net, .org, .edu, .gov, .mil➢ .biz, .name, .info➢ Instances of J and L root servers are hosted in Sofia
  47. 47. DNS
  48. 48. DNS➢ Internet Corporation For Assigned Names and Numbe➢ IANA is now part of it➢ Handles ccTLDs➢ Handles gTLDs➢ Handles the Root zone➢ Internationalized domain name (IDN)➢ Domain names are encoded using Punycode➢ .ru = .рф➢ We are expecting soon .bg = .бг➢ Country level domains➢ .bg, .co.za, .co.uk, .edu.us➢ Top-level domains➢ .com, .net, .org, .edu, .gov, .mil➢ .biz, .name, .info
  49. 49. DNS➢ Name servers➢ Authoritative only➢ Recursive➢ Authoritative + recursive➢ .in-addr.arpa➢ .ip6.arpa
  50. 50. DNS - ResolvingDefault service port TCP/UDP: 53
  51. 51. DNS - Resolving➢ Forward resolving➢ Host/FQDN to IP➢ Reverse resolving➢ IP to Host➢ Reverse resolver delegation➢ RIR -> LIR -> Local ISP -> YOU
  52. 52. DNS
  53. 53. DNS Resource recordsTYPE value and meaningA 1 a host addressNS 2 an authoritative name serverCNAME 5 the canonical name for an aliasSOA 6 start of a zone of authorityWKS 11 a well known service descriptionPTR 12 a domain name pointerHINFO 13 host informationMINFO 14 mailbox or mail list informationMX 15 mail exchangeTXT 16 text stringsAXFR 252 A request for a transfer of anentire zoneRFC1035
  54. 54. DNS Resource recordskar-do.cc. 86400 IN SOA ns1.ex1.com.mm.yuhu.biz. (2013013106 ;Serial Number86400 ;refresh7200 ;retry3600000 ;expire86400 ;minimum)kar-do.cc. IN NS ns1.ex1.com.kar-do.cc. IN NS ns2.ex1.com.kar-do.cc. IN A 134.154.23.12localhost IN A 127.0.0.1kar-do.cc. IN MX 0 mail.kar-do.cc.mail IN CNAME mail.yuhu.biz.www IN A 134.154.23.12www IN A 134.142.65.81kar-do.cc. IN TXT"v=spf1 +a +mx +ip4:134.154.23.12 ?all"
  55. 55. Send MailTransport Protocol - SMTPRFC5321
  56. 56. SendMailTransportProtocol-SMTPS: 220 smtp.example.com ESMTP PostfixC: HELO relay.example.orgS: 250 Hello relay.example.org, I am glad to meet youC: MAIL FROM:<bob@example.org>S: 250 OkC: RCPT TO:<alice@example.com>S: 250 OkC: RCPT TO:<theboss@example.com>S: 250 OkC: DATAS: 354 End data with <CR><LF>.<CR><LF>C: From: "Bob Example" <bob@example.org>C: To: "Alice Example" <alice@example.com>C: Cc: theboss@example.comC: Date: Tue, 15 January 2008 16:02:43 -0500C: Subject: Test messageC:C: Hello Alice.C: This is a test message with 5 header fields and 4 lines in the message body.C: Your friend,C: BobC: .S: 250 Ok: queued as 12345C: QUIT
  57. 57. HTTP➢ In this phase window size is increased linearly untiltimeout occurs or duplicate ACK is received
  58. 58. 7 - Protocols7 - Protocolshttp://academy.telerik.com/student-courses/software-technologies/os-windows-linux/http://academy.telerik.com/student-courses/software-technologies/os-windows-linux/
  59. 59. Beer timeBeer time
  60. 60. FreeTrainings @Telerik Academy Operating Systems @Telerik Academy http://telerikacademy.com/Courses/Courses/Details/35 Telerik Software Academy academy.telerik.com Telerik Academy @ Facebook facebook.com/TelerikAcademy Telerik Software Academy Forums forums.academy.telerik.com

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