TFTP over anycast

Thu Feb 22 19:32:26 UTC 2024

On Thu, Feb 22, 2024 at 10:47 AM Javier Gutierrez
<GutierrezJ at westmancom.com> wrote:
>  I was wondering if someone had some experience with using anycast for TFTP or DHCP services?

Hi Javier,

Anycast for TFTP is more or less the same as anycast for TCP-based
protocols: it has corner cases which fail and fail hard, but otherwise
it works. Outside the corner cases, the failure mode for tftp clients
should be the same as the failure mode when the tftp server goes down
in the middle of a transfer and comes back up some time later.

The corner cases are variations on the theme that your routing causes
packets from a particular source to oscillate between the tftp
servers. In the corner cases, the tftp client can't communicate with
the -same- tftp server long enough to complete a transfer.

Experiments with anycast TCP suggest that the corner cases happen for
less than 1% of client sources, but when they do happen tend to be
persistent, affecting all communication between that client and the
anycast IP address for an extended duration, sometimes weeks or
months.

Regards,
Bill Herrin

-- 
William Herrin
bill at herrin.us
https://bill.herrin.us/