Re: block connections in IPS

[Geoff <gpoer () arizona edu>]

I don't think you are correct on what an IPS is. A normal IDS can preform flex-response (in snort land) which send s resets. Active response features 
like ICMP error codes and shunning (applying dynamic acl's to routered interfaces or firewalls) are also enployed by different IDS vendors. IPS's work 
in a different fashion.

They sit inline with your connection (or they are just an IDS).

                |---------------|
|---------|     |               |     |-----------|
| Border  |<--->| IPS     |<--->|  Internal |
| Router  |     |               |     |  Router   |
|_________|     |_______________|     |___________|
                

Their is nothing that says on IDS can not sit inline as well however an IPS can ONLY sit in line and IDS can do both and still function. The 
difference is how far the packet goes after detection.

An IPS will drop the packet BEFORE it ever leaves the opposite interface from where it came in on.
(X = Bad Packet)

                
                |----------------|
|---------|  X  |       X        |     |-----------|
| Border  |<--->| IPS      |<--->|  Internal |
| Router  |     |(Packet Dropped)|     |  Router   |
|_________|     |________________|     |___________|


Some vendors will also write and ACL on the IN and OUT interfaces of the IPS for the source/destination IP and PORT pairs and block all traffic for a 
certain time (90 sec).

And IDS will send a reset of apply an acl but that is well after the packet has reached it destination.

As far as false positives... that is a whole other email :)

Geoff

Ravi Kumar wrote:
> Hi All,
> IPS uses TCP Reset or ICMP to block connections. The drawback with this 
> approach could be unsuccessful ness in resetting the connection. Do IPS 
> have any other mechanism to block connections.
> Snort_inline uses TCP reset and ICMP error messages.
> The other approach currently followed by some products is to configure 
> policies automagically in the firewall to block particular connections. 
> This may lead to many false positives.
>
> Is there any mechanism to reduce false positives and effectively block 
> connections.
> Regards,
> Ravi
>
>
>
>
>
>
>
> The Views Presented in this mail are completely mine. The company is not 
> responsible for what so ever.
>
> ----------
> Ravi Kumar CH
> Rendezvous On Chip (I) Pvt Ltd
> Hyderabad, INDIA
>
> ROC HOME PAGE:
> http://www.roc.co.in
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