[VoiceOps] Mitigating or stopping TDOS attacks - any advice?

Carlos Perez cperez at sansay.com
Mon May 15 12:56:57 EDT 2017

(with the context being unwanted calls) An alternative that should be
considered since it will add the intelligence to identify abnormal patterns
and not complicating your signaling path (introducing an additional
possible point of failure and or post dial delay) is using a machine data
analyzer solution such as Splunk or ELK.

This approach is based on near-realtime processing of CDRs therefore it can
manage one or many brands. It is highly scalable (since the data processing
is done off-board) and highly customizable to tailor any needs. The idea is
that upon detecting an abnormal pattern the data analyzer interacts with
the switch in the form of a hook/API instruction to have the logic on the
switch to block the offending traffic pattern (instead of throttling or
blocking an entire source IP or trunk which may not be wanted in this case
as it will block wanted traffic).

Carlos Perez
Sansay, Inc.

On Mon, May 15, 2017 at 8:05 AM, Victor Chukalovskiy <
victor.chukalovskiy at gmail.com> wrote:

> Hi,
> You are talking PSTN --> customer call flow scenario in CLEC setting.
> Usually  a class 4/5 switch is set to "transparently" pass all incoming
> calls from PSTN side to whatever customers trunk or line the DID or range
> is pointed to. And then either that resource gets full due to call volume
> or your switch starts failing or lagging due to CPS.
> You have two options however:
> If you were to pass all your traffic through a SIP proxy, like Kamallio or
> OpenSIPS like Alex suggested, that  proxy can be programmed to do any kind
> of fancy call admissions control, dynamic filtering, number pattern etc.‎
> This however means you put an extra box in the call path between your PSTN
> switch and a customer.
> Alternatively, you may try to see if all your PSTN switches can do some
> kind of external dip or routing query on incoming calls (radius, SIP refer
> etc). If they can, you can set a server or a cluster that would answer all
> those dips and decide on per-call basis wether the call should be admitted
> or not. So think external "brain" for your switches. This way call
> admission controll decision is made externally, but enforced right at your
> PSTN switch, and you don't have extra box in the call path. Making it
> somewhat more elegant.
> This is pretty high-level, but if I understood your topology right, these
> are basically your two options.
> -Victor
> Sent from my BlackBerry 10 smartphone.
> *From: *Matthew Yaklin
> *Sent: *Monday, May 15, 2017 10:44
> *To: *voiceops at voiceops.org
> *Subject: *[VoiceOps] Mitigating or stopping TDOS attacks - any advice?
> Hello all,
> I am curious what others have in place or actions they take when a
> customer is the target of a TDOS attack?
> TDOS being Telephony Denial of Service. An attack where the perp uses
> whatever means to flood a customer's telephone service with unwanted calls.
> Say you are a multi state CLEC. You have multiple brands of switches
> (Meta, Taqua, DMS, Genband, etc...) as well as ACME and Perimeta SBCs in
> use. You have legacy TDM as well as SIP trunks. Your customers are served
> via legacy and modern methods. You have hosted PBX as well (Broadsoft).
> Many customers are on your LAN but many are on the internet. So that is our
> situation. Or you can be bigger or smaller. No matter the size I would
> welcome how you handle it.
> We have asked our manufacturers for advice but they have only provided
> the basic number blocking available by default on the switch. Meta and
> Genband have provided little other than pointing to existing features. If
> you have any thoughts on whether there is something we can provide based
> upon SIP messaging or other creative solutions that would be awesome!
> So I welcome a discussion on this and any advice other operators can give.
> Thank you very much,
> Matt
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