google search threshold

Philip Lavine source_route at
Mon Feb 29 15:53:54 UTC 2016

I have about 2000 users behind a single NAT. I have been looking at netflow, URL filter logs, IDS logs, etc. The traffic seems to be legit. 

I am going to move more users to IPv6 and divide some of the subnets into different NATS and see if that alleviates the traffic load.
Thanks for the advice.

      From: Damian Menscher <damian at>
 To: Philip Lavine <source_route at> 
Cc: "nanog at" <nanog at>
 Sent: Friday, February 26, 2016 6:05 PM
 Subject: Re: google search threshold
On Fri, Feb 26, 2016 at 3:01 PM, Philip Lavine via NANOG <nanog at> wrote:

Does anybody know what the threshold for google searches is before you get the captcha?I  am trying to decide if I need to break up the overload NAT to a pool.

There isn't a threshold -- if you send automated searches from an IP, then it gets blocked (for a while).

So... this comes down to how much you trust your machines/users.  If you're a company with managed systems, then you can have thousands of users share the same IP without problems.  But if you're an ISP, you'll likely run into problems much earlier (since users like their malware).
Some tips:   - if you do NAT: try to partition users into pools so one abusive user can't get all your external IPs blocked  - if you have a proxy: make sure it inserts the X-Forwarded-For header, and is restricted to your own users  - if you're an ISP: IPv6 will allow each user to have their own /64, which avoids shared-fate from abusive ones
Damian (responsible for DDoS defense)-- Damian Menscher :: Security Reliability Engineer :: Google :: AS15169


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