[Asterisk-Users] TFTP - Good or Bad?

Rich Adamson radamson at routers.com
Fri Aug 5 06:02:04 MST 2005


> > I don't post here often but I read with interest all the postings. - I've
> > been on a lot of mailing lists, but this one is by far the most interesting.
> > 
> > I've been doing a lot of work with 'tftp' loading Cisco 79xx phones with
> > firmware, configs. for asterisk, etc.
> > 
> > And I see where a lot of folks have trouble with 'tftp', use alternate port
> > numbers (probably to get around firewall issues), etc. - And I've even seen
> > where some folks complain that 'tftp' is one of the 'worst' protocols on the
> > Internet.
> > 
> > At the end of this posting, I've included a little tid-bit on
> > 'primary/alternate' 'tftp' servers for the Cisco 79xx phone setup.
> > 
> > This next part is mainly for 'newbies' who are new to asterisk & haven't got
> > a clue as to what 'tftp' is. - Advanced users, geeks, etc., please disregard
> > the next part if you want.
> > 
> > Apologize in advance if this is boring.
> > 
> > Going back to 'Networking 101', just exactly what is 'tftp'? - Is there any
> > reason WHY it came into being in the first place?
> > 
> > 'tftp' stands for 'Trivial File Transfer Protocol'. - Unlike the more
> > popular 'ftp' protocol, 'tftp' is considered 'non-secure'. - Meaning that no
> > login name/password challenge is require. - The 'device' (computer, phone,
> > whatever) sends a request to the 'tftp' server for the file & the server
> > sends it. - Plain and simple.
> > 
> > 'tftp' also uses the 'UDP' (User Datagram Protocol). - The main difference
> > between 'UDP' and 'TCP' is that 'UDP' uses NO ERROR CORRECTION. - No 'acks'
> > & 'naks' to make sure all the packets arrive okay at the receiving end. -
> > It's up the receiving end to make sure everything was received okay.
> 
> It also makes it relatively simpler for someone on the same LAN (mostly)
> to fake being a tftp server for that client (or vice versa). A UDP
> packet is generally more predictable, so if I wanted to send the phone
> bogus firmware or bogus config, it would generally be easier for me than
> if the server has read the files using, e.g. HTTP.
> 
> HTTP is simple, well-supported and supports all the "file transfers" 
> operations TFTP supports.

And, FWIW, there are a large number of tftp implementations (mostly in
the non-linux pc arena) that have issues dealing with the last packet 
in a tftp transfer causing failures. (Based on about 15 years of using
various tftp products as a mechanism to upgrade cisco ios's.)





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