NTP traffic from WAN to some W/LAN clients delayed/lost

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LizardMan
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Joined: 30 May 2007
Posts: 1

PostPosted: Wed May 30, 2007 2:16    Post subject: NTP traffic from WAN to some W/LAN clients delayed/lost Reply with quote
I have several clients accessing the Net through a WRT-54GS v1.0 running V23sp2 in NAT mode. Each of these systems' NTP client uses the same set of external NTP servers. Some sync with all of the external servers while others either fail to sync with some servers, or suffer extreme jitter. The WRT-54GS uses one of these same external NTP servers, but appears to query it very infrequently.

A packet sniffer on the clients shows that when clients fail to sync with an external NTP server it is because they NEVER receives any response packets from that server. I know the external NTP server and my network are working, because other clients work correclty.

The clients that have problems syncing or high jitter change as the various clients are rebooted or shutdown for a period of time. It looks like the firewall connection tracking code in the WRT-54GS only supports a couple W/LAN NTP clients per external server before becoming confused. NTP responses to packets sent by W/LAN clients beyond the first X number of clients are dropped, or at best delayed by 100 - 400 ms leading to high jitter values.

Another LAN routed over the same link to the Net through a non-WRT box has multiple clients accessing the same NTP servers without any problems. I know the external NTP servers are working correctly and my connection to the Net isn't the problem.

Everything points to the firewall code in DD-WRT. Any ideas on correcting this problem?
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