[ntp:questions] Wireless Routers and NTP

Pierre Dubuc pldubuc at yahoo.ca
Fri Nov 30 17:57:48 UTC 2007

Replying to message <ufmdnVnis5LqCdDanZ2dnUVZ8qGdnZ2d at bt.com>

> Does anyone have recommendations for an ADSL Wireless Router that I can
> manually set the NTP Server address on? My Belkin unit comes pre-configured
> with external server addresses. I want to use my own one here (Meinberg
> LanTime), as doing some tests on NTP jitter over wireless, and want all PCs
> and Router to be taking time from same source.

I think I implemented something similar to what you want to accomplish.

I put the wireless router behind my gateway (a NetBSD box) and used IP 
redirection to override the router's hardcoded attempts to connect to an 
external NTP server.

It was rather straightforward. I set up some ipf rules to accept and log 
outgoing requests on UDP port 123, then used ipmon to capture the 
information and figure out the address the wireless router attempts to 
connect to. Then, I put the following line in /etc/ipnat.conf:

rdr re1 port 123 -> port 123 udp

With this configuration, my wireless router no longer connects to the 
outside world. My own gateway's NTP server provides the answers.

Pierre Dubuc
pldubuc at yahoo.ca

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