[ntp:hackers] i think it's time to review ntp's default acl's

Paul Vixie paul at vix.com
Thu Mar 23 22:58:58 UTC 2006

# DNS and NTP are just the tip of the iceberg, and I think it's a huge one.


# Could somebody give me a lesson in the big picture?  (URL would be great.)

<http://www.ietf.org/rfc/rfc2827.txt> or the PHB summary of same, writ by me:

# Are we going to have to give up on UDP because it's easily abused by bad
# guys?

that depends on who you mean by "we" and what you mean by "bad".  there will
always be udp, and people using udp.  their service will suffer, and their
suffering will create market pressure in unexpected places/kinds/directions.

the "bad" guys in this case are ISP's who choose not to deploy BCP38 based on
the lack of economic incentive, thus creating unexpected and less desireable
outcomes like my plan to create a BGP blackhole list for open recursive DNS

it's possible that T/TCP or SCTP should be used instead of UDP for transaction
based services like DNS.  but the timing characteristics of either are so much
sloppier than UDP, that i don't imagine either being usable by NTP.  so, no.

# Is it possible to get routers to drop packets with forged source addresses?  

yes.  every modern router has this functionality.

# I assume there are both technical and social/political issues.  I don't know 
# if it's reasonable to solve either.

it costs money to train staff for, write policies for, debug, and handle
customer complaints about, BCP38.  the ISP who does this will save no money
(since the pain caused by not doing it is felt by others, not by them), and
will make no money (since customers will not pay extra for a change like this
that adds no performance or features to their service.)  so, it's economics,
not social/political issues, that leaves us where we now are (which to say,
"a deer in the headlights".)

# For NTP, it seems possible to allow access only by previous arrangements.  
# The administrative overhead would probably eliminate public servers as they 
# are currently used.  That would encourage/require ISPs to setup NTP servers 
# for their customers.

the way you say that doesn't make it sound bad.  is it actually bad and you're
just really good at the kind of spin control that i find attractive, or is it
really as good as you imply?

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