PlayStationNetwork blocking of CGNAT public addresses

Tom Smyth tom.smyth at
Sun Sep 18 12:30:52 UTC 2016

Hi Simon,

as other responders have said it is an inherent issue with NAT in general,
on workaround is to limit the ratio of  actual users to an external IPv4
address, the other thing we have seen from our Abuse contact emails from
PSN, is that malicious activity towards the PSN is often accompanied by
other malicious activities such as SSH brute force outbound and spaming...

I would suggest that

1) limit the ratio of users to an external ipv4 address as much as possible
(which would reduce the impact of one compromised customer bringing down
play time for other clients behind the same nat

2)do some "canary in the mine" monitoring for obviously malicious traffic
(loads of SMTP traffic outbound) and lots of connection requests to SSH
servers ...   if you see that traffic from behind your CGNAT device .. just
temporarily block the internal ip of the user until they clean up their

this is the pain with NAT you have to do extra work in order prevent
infected users interrupting internet connectivity for other innocent
I think you can use simple firewall rules  on your edge router to identify
multiple connections to SMTP and SSH in a short period of time..

If you do the minimum to detect that abuse  then you cant be accused of
invading peoples privacy...  (bear in mind obvious false positives)
(Monitoring systems etc) ...

Hope this helps,

On Fri, Sep 16, 2016 at 2:12 PM, Simon Lockhart <simon at> wrote:

> All,
> We operate an access network with several hundred thousand users.
> Increasingly
> we're putting the users behind CGNAT in order to continue to give them an
> IPv4
> service (we're all dual-stack, so they all get public IPv6 too). Due to the
> demographic of our users, many of them are gamers.
> We're hitting a problem with PlayStationNetwork 'randomly' blocking some
> of our
> CGNAT outside addresses, because they claim to have received anomalous, or
> 'attack' traffic from that IP. This obviously causes problems for the other
> legitimate users who end up behind the same public IPv4 address.
> Despite numerous attempts to engage with PSN, they are unwilling to give us
> any additional information which would allow us to identify the 'rogue'
> users
> on our network, or to identify the 'unwanted' traffic so that we could
> either
> block it, or use it to identify the rogue users ourselves.
> Has anyone else come up against the problem, and/or have any suggestions on
> how best to resolve it?
> Many thanks in advance,
> Simon

Kindest regards,
Tom Smyth

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