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Is SIP Trunking Safe & Reliable in the DDoS World?

Since last Thursday when VoIP.ms suffered (and continues to suffer) one of the worst Distributed Denial of Service (DDOS) attacks in the VoIP era, we’ve been asked a thousand times whether any SIP trunking provider can provide a safe and reliable platform under circumstances similar to the VoIP.ms outage. We obviously cannot vouch for every trunking provider but, based upon our discussions with two of the major carriers that support Incredible PBX, we are confident that either of them could withstand a similar attack and your phones would still ring. Keep in mind that one of the hidden beauties of VoIP is the ability to configure your PBX to use multiple carriers for failover in making outbound calls, something we have always recommended. Unfortunately, inbound calls are tied to registration of each DID with one and only one carrier. Thus, if that carrier goes off line, incoming calls to DIDs registered with that carrier will fail.

To restate the obvious, no provider is going to publicly document their DDOS remediation methodology thereby providing attackers with a blueprint to their network design and remediation strategy. However, under non-disclosure agreements, we have spoken at length with the owners of our two major Incredible PBX providers: Skyetel and Clearly IP. Based upon our NDA discussions over the past few days, we are satisfied that the SIP trunking offerings of our two primary carriers are sufficiently robust to withstand a VoIP.ms-like DDOS attack. Having said that, we are optimistic that the VoIP.ms outage has placed a renewed spotlight on the seriousness of these DDOS attacks with the FBI and the U.S. Department of Homeland Security.

So what’s missing from the VoIP.ms design that has made their infrastructure so vulnerable? Lots. For openers, VoIP.ms apparently does not rely upon SIP proxies or firewalls using industry-standard network management procedures. In fact, until several days ago, VoIP.ms reportedly was hosting its own DNS servers exclusively. While that has been addressed by moving to Cloudflare, other design vulnerabilities have been more difficult to ameliorate. For example, SIP trunking with VoIP.ms by design requires registration to one of several dozen POPs on both your PBX and on their public-facing portal. An inability to access their public portal means an administrator cannot redirect traffic to another POP in case of an outage. And, if an individual POP is overwhelmed with a DDOS attack, that POP can no longer redirect its incoming calls to a failover location. And apparently it is the only server from which this redirection can be initiated. As the current five-day outage makes clear, reengineering this design would be a Herculean task. So an important lesson learned should be that FORWARDING DIDS TO ANOTHER NUMBER OR SIP ADDRESS SHOULD BE COMPLETELY INDEPENDENT OF YOUR PUBLIC-FACING ARCHITECTURE.

What can you do at this juncture to lessen your vulnerability to a future DDOS attack? First, don’t put all of your eggs in one carrier’s basket. This is especially true with your main phone numbers (DIDs). Second, if you are a major organization, move your most important DIDs to one of our preferred providers, Skyetel or ClearlyIP. And, if money is no object, consider an AT&T, Verizon, T-Mobile, or Google Voice trunk. With multi-path forwarding, simultaneous incoming calls can be redirected to other DIDs hosted with SIP trunking providers. These paths can easily be adjusted in the event of a DDOS attack. Many of these providers offer heavily discounted rates for forwarding calls to other SIP destinations which need not be publicly disclosed.

Latest VoIP.ms Update:

Originally published: Monday, September 20, 2021

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