[VoiceOps] DDOS Attacks and ITSP's
ryandelgrosso at gmail.com
Fri Mar 18 20:07:56 EDT 2016
With the current mega-thread about VI I figured I would get an
educational discussion going about DDOS. Search the archives, Ive
probably started this discussion a few times in the past but each time
the context is different.
I have given talks at several different venues (anyone here a CFCA
member, or been to a Metaswitch forum event?) about DDOS and what the
current arsenal of internet attacks means to voice. Unfortunately many
network operators treat DDOS like a shameful thing and don't share
information about it. This makes it that much harder for network
operators to do the right thing and take meaningful and decisive action
and ultimately makes the jobs of the attackers that much easier.
Keep in mind sharing these kinds of tactics isn't "helping the
attackers". They know this stuff. Its OK to tell them what they know.
Who doesn't know this stuff are other operators that haven't been hit yet.
Have you been hit by DDOS? Have you built out solutions to cope with DDOS?
Ill start things off:
1. How do you know its a DDOS and something isn't just broken?
2. SBC retransmissions (this will often be your first warning)
3. Significant deviation from normal traffic volumes
2. As a VoIP carrier, my network looks like a DDOS attack all the time
(oodles of UDP traffic). this makes most commercial solutions a
square peg / round hole problem.
3. DDOS survivability must be designed into the network not bolted on.
1. Place Access SBC's, Peering SBC's, Webservers, etc on different
networks and on different BGP adertisements.
2. Have multiple access SBC's on different networks / routers / BGP
3. Use DNS to home ALL clients. When your Access SBC succumbs to a
reflection attack you can flip your customers using SRV records
to the surviving SBC's. Customers using straight IP will remain
4. Use CDN networks like Cloudflare / Cloudfront or just put
webservers in EC2. Keep web away from voice. Webservers are
5. Build defense in depth. Your network is a medieval castle, have
moats and walls and soldiers.
4. Be a good netizen. If you are an ISP, implement BCP38. No open DNS
recursors, no open NTP or SNMP services that are reflection targets.
Leave no loaded weapons for others in your network.
5. Traffic scrubbing services typically don't mix well with VoIP
carriers. This is basically the TSA of the network. (there are
exceptions, the price tags have commas).
6. How do you go about testing your protections? Don't just sit smugly
in your house made of straw.
7. Most upstream carrier DDOS protection strategies include "blackhole
the destination to protect the network". This saves them but
accomplishes your attackers goal.
8. Do you know how big of a DDOS it actually takes to hurt you? Ill bet
its less than you think.
So lets hear it. Who has experience on this front? What would you like
to share? Comments on the above?
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