• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 1186
  • Last Modified:

DDOS Protection

I offer psybncs and shell access and all that, and my server recently was hit by DDOS. I have recently blocked any ICMP packets, and blocked any incoming UDP packets except port 53 (for DNS). I tried to ddos myself, and succeeded in preventing any PING ddos but when i UDP'ed myself my server was still hit. Where have I gone wrong? I also want to prevent TCP syn packet DDOSing, and i read somewhere that by filtering incoming TCP syn requests to drop any packets after a certain number of packet/sec is possible, but I am fairly new to this and I need some help in configuring my firewall. Can anyone give some examples on how to prevent DDOS attacks, or at least minimize them?
  • 3
  • 2
  • 2
1 Solution
Rich RumbleSecurity SamuraiCommented:
What is your firewall? If it's a cisco pix, or router, they are able to "deflect" ddos to a certain degree. If other please specify. Also, what server are you running, windows IIS windows apache, linux apache... other?
Here are some things to understand, and possibly minimize dos attacks.: http://www.cisco.com/warp/public/707/newsflash.html
I also recommend DJBDNS (aka tinydns) over BIND,  2Billion times better than bind... http://cr.yp.to/djbdns.html
Right, you should address firewall individually, RTFM, and use appropriate TA for better response:

> but when i UDP'ed myself my server was still hit. Where have I gone wrong?

Check here:


xns-time         52/tcp     XNS Time Protocol
xns-time         52/udp    XNS Time Protocol
#                                   Susie Armstrong <Armstrong.wbst128@XEROX>
domain           53/tcp     Domain Name Server
domain           53/udp    Domain Name Server
#                                    Paul Mockapetris <PVM@ISI.EDU>
xns-ch             54/tcp     XNS Clearinghouse
xns-ch             54/udp    XNS Clearinghouse

TCP and UDP are different protocols, so you must default block all ports for both of them. Also, where you do not block, you may choose to condifer blocking only one way, probably inbound traffic.
<ugh> condifer = consider
WEBINAR: GDPR Implemented - Tips & Lessons Learned

Join the WatchGuard team on Thursday, March 29th as we recount some valuable lessons learned in weighing the needs of a business against the new regulatory environment, look ahead at the two months left before implementation, and help you understand the steps you can take today!

rudyzainalAuthor Commented:
richrumble: I am using Linux IPCHAINS.

sunbow: I cant block any inbound TCP due to the nature and the purpose of the server. My current firewall has been configured to accept all inbound TCP packets, drop all ICMP, and drop all UDP packets EXCEPT UDP 53 for DNS. I am still losing my server and having to reboot after my test DDOS with a mere 30 DSL drone UDP attack
Rich RumbleSecurity SamuraiCommented:
Try to change your rules to DENY instead of REJECT, if your rules are set this way.
Are you using 30 dsl host's to dos a single host... yourself? That's not "mere" that quite a bit, even if upstream isn't so good, you may be dos'ing your router more than your own box. It's pretty tough to dos a 10/100mb nic. I would think you'd dos the router (cable modem, dsl router) way before your server would be dos'd- espically with 30 host's to throw at it.
Are your able to upgrade to iptables? Iptables is the newer more supported firewall for linux.

DDoS info
SANS, Help Defeat Denial of Service Attacks: Step-by-Step: http://www.sans.org/dosstep/index.htm
SANS, ICMP Attacks Illustrated: http://rr.sans.org/threats/ICMP_attacks.php
CERT, Denial of Service Attacks: http://www.cert.org/tech_tips/denial_of_service.html
NWC, Fireproofing Against DoS Attacks (forms of): http://www.nwc.com/1225/1225f38.html
SANS, Consensus Roadmap for Defeating Distributed Denial of Service Attacks: http://www.sans.org/ddos_roadmap.htm
SANS, Spoofed IP Address Distributed Denial of Service Attacks: Defense-in-Depth: http://rr.sans.org/threats/spoofed.php
SANS, Understanding DDOS Attack, Tools and Free Anti-tools with Recommendation: http://rr.sans.org/threats/understa...anding_ddos.php
Juniper.net, Minimizing the Effects of DoS Attacks: http://arachne3.juniper.net/techcen...ote/350001.html
CISCO, Strategies to Protect Against Distributed Denial of Service (DDoS) Attacks: http://www.cisco.com/warp/public/707/newsflash.html
Dave Dittrich's references: http://staff.washington.edu/dittrich/misc/ddos/
Xinetd Sensors: ~http://www.gate.net/~ddata/xinetd-sensors.html
Xinetd FAQ: http://synack.net/xinetd/faq.html

rudyzainalAuthor Commented:
its already set to drop, not reject. and my box is not behind any router. its situated on a datacenter. And yes i'd say about 30 DSL host to DDOS my own box for testing purpose, more or less.

But my original question was, is restricting incoming packets by filtering incoming TCP syn requests to drop any packets after a certain number of packet/sec possible, and if so will it help much, and the way to go about doing it. I have read up a bit on some burst rate limits and such, but the book I read wasnt meant for a novice like me, i guess.

I've upped the points for this question cause I was hit yet again and its getting quite irritating to have to go down to the datacenter to reboot my box twice in a fortnight.
rudyzainalAuthor Commented:
thanks rich the links are useful. but so far it doesnt actually stop the ddos to my current box, but it does give certain insights as to what is needed and the lot.
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Train for your Pen Testing Engineer Certification

Enroll today in this bundle of courses to gain experience in the logistics of pen testing, Linux fundamentals, vulnerability assessments, detecting live systems, and more! This series, valued at $3,000, is free for Premium members, Team Accounts, and Qualified Experts.

  • 3
  • 2
  • 2
Tackle projects and never again get stuck behind a technical roadblock.
Join Now