a question about tftp

[ilyas001]

hi guys i study networking and while listening to a video tutorial the guys said that tcp is reliable and why and tcp is no and there is why . ok normal i got that i seems simple then here  in the picture i sent with the question he sais that udp and ip aren't reliable anymore i don't really get what was he talking about  i got lost hope that this picture in enough to give you an idea of the deal 

[Mark77]

Well basically IP packets are routed through and between networks on a best-efforts basis.  If a link is overloaded, some IP packets get dropped.

 

If you open up, say, a telnet or ssh session, you don't want your information to be lost.  So the telnet or ssh protocol uses a protocol layer called "TCP" to ensure reliable delivery and ordering of packets that are ultimately transmitted over an IP network.  Re-sending packets, and acknowledging receipt of packets, as necessary, to facilitate a reliable data link.

 

UDP and TCP are accessed and dealt with differently if you are an applications programmer for obvious reasons.

 

 

 

[Lurick]

By default, without going into things like QoS (Quality of Service) IP packets are, as @Mark77 said, best effort. The IP Protocol provides for things like QoS to be layered into the packet but doesn't by itself provide any guarantee of a packets getting from point A to B. QoS goes in the ToS (Type of Service) or DiffServ field and tells a router or switch to treat it based on the defined Quality of Service on that router or switch.

 

[ilyas001]

Just now, Mark77 said:

Well basically IP packets are routed through and between networks on a best-efforts basis.  If a link is overloaded, some IP packets get dropped.

 

If you open up, say, a telnet or ssh session, you don't want your information to be lost.  So the telnet or ssh protocol uses a protocol layer called "TCP" to ensure reliable delivery and ordering of packets that are ultimately transmitted over an IP network.  Re-sending packets, and acknowledging receipt of packets, as necessary, to facilitate a reliable data link.

 

UDP and TCP are accessed and dealt with differently if you are an applications programmer for obvious reasons.

 

 

 

you didn't understood my question i know all this and i know that udp is reliable and even when packets gets lost they can sent them again i understand all this mly question is when he talked about tftp this reliability is gone why ? if you look donw left he says tftp provides reliability and ip udp don't why ? that's my question 

[ilyas001]

Just now, Lurick said:

By default, without going into things like QoS (Quality of Service) IP packets are, as @Mark77 said, best effort. The IP Protocol provides for things like QoS to be layered into the packet but doesn't by itself provide any guarantee of a packets getting from point A to B. QoS goes in the ToS (Type of Service) or DiffServ field and tells a router or switch to treat it based on the defined Quality of Service on that router or switch.

 

pls read my answer to mark77 to understand my problem 

[Lurick]

5 minutes ago, ilyas001 said:

pls read my answer to mark77 to understand my problem 

TFTP is a reliable protocol because each packet must be acknowledged even though it's being transported via UDP which is connectionless/unreliable. TFTP uses UDP for the transfer, which is a connectionless protocol. FTP, SCP, HTTP or other methods of transfer typically use TCP. UDP requires less overhead and is generally faster than TCP. There is no TCP acknowledgements nor the TCP window to account for during the transfer. There are generally other methods to verify the data once it has arrived, typically by comparing a calculated hash to a known value.

[Mark77]

tftp is a TCP protocol file transfer protocol which dispenses with the authentication aspects of the traditional ftp protocol.  Its easier to implement with less code in embedded and lightweight systems.  That is why it is used, although not very much anymore. 

 

Think of scp or rsync as being, say, a BMW.  You go to the dealer, and because you don't have money for a BMW, they take you to their used car lot, and find you a very basic Honda or Hyundai that doesn't even have power windows or air conditioning.  This is like tftp.  Very basic, but still does the job. 

[ilyas001]

Just now, Lurick said:

TFTP is a reliable protocol because each packet must be acknowledged even though it's being transported via UDP which is connectionless/unreliable.

i don't understand still i thought that udp is reliable and it knowledge the packets so why now it decided to no be reliable any more what's the difference 

[Lurick]

Just now, ilyas001 said:

i don't understand still i thought that udp is reliable and it knowledge the packets so why now it decided to no be reliable any more what's the difference 

So by default UDP doesn't have any acknowledgement packet sent, that's TCP. UDP relies on the above layers to do the verification and request a packet be re-transmitted if needed.

[ilyas001]

Just now, Mark77 said:

tftp is a TCP protocol file transfer protocol which dispenses with the authentication aspects of the traditional ftp protocol.  Its easier to implement with less code in embedded and lightweight systems.  That is why it is used, although not very much anymore. 

 

Think of scp or rsync as being, say, a BMW.  You go to the dealer, and because you don't have money for a BMW, they take you to their used car lot, and find you a very basic Honda or Hyundai that doesn't even have power windows or air conditioning.  This is like tftp.  Very basic, but still does the job. 

still don't get it from you perspective tftp is at the base a type of tcp ok then why from the video in the picture the tcp is not reliable when the tftp is ? just look at the picture tftp reliable and ip at layer 3 and  udp at layer 4 don't provides reliability if the tftp is a an old version of udp so it should be like when udp can't afford reliability tftp shouldn't too that's what i don't get 

[Mark77]

3 minutes ago, ilyas001 said:

still don't get it from you perspective tftp is at the base a type of tcp ok then why from the video in the picture the tcp is not reliable when the tftp is ? just look at the picture tftp reliable and ip at layer 3 and  udp at layer 4 don't provides reliability if the tftp is a an old version of udp so it should be like when udp can't afford reliability tftp shouldn't too that's what i don't get 

tftp is an application.

 

UDP is a protocol. 

 

tftp, running over UDP port 69, has to provide for its own "reliability".  ie: it does not rely upon TCP's inherent reliability.

 

Hence, in the protocol implementation of tftp (as defined in the RFCs), there are provisions for ensuring reliability. 

 

https://en.wikipedia.org/wiki/Trivial_File_Transfer_Protocol  <-- is a pretty good read.