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  1. #1

    How to stop DDOS/DOS attacks?

    Hey WHT,

    I've been lurking on WHT for a while, and recently I joined up as a systems administrator on a Minecraft server (full administrator, as in I set up everything and keep it running smoothly, I fully manage it myself), and while I got everything working perfectly fine on our Limestone Networks dedi (C2Q 9400 2.66ghz, 8GB RAM, 500GB HDD, 100mbps port), I've been having some troubles with DDOS/DOS attacks recently.

    Yes, a 3 week old server having troubles with attacks. (The most recent ones I've been having are from a very disgruntled banned player).

    Now I can handle CentOS and the like fine for most tasks, but I've never learned much about what to do about DDOS/DOS attacks, especially with the scale of these attacks (75-100 mbps usually, which often maxes out our line). Limestone has great support, and they automatically stop most attacks within a few minutes, but I'm wondering if there's a way to detect/stop/log these attack instead of waiting for Limestone to get rid of them? We're also thinking of switching hosts due to cost issues, and I would especially need a method to stop attacks on hosts with stricter bandwidth and QOS policies.

    I caught the attacker's IPs once (they were using Amazon EC2), but Amazon denied that the IPs ever touched us.

    Basically, how and with what tools would I be able to stop/log DOS and DDOS attacks on CentOS 5.5, with that hardware/network.

    I would love any and all advice on this matter.

  2. #2
    Quote Originally Posted by battlekid View Post
    Hey WHT,

    I've been lurking on WHT for a while, and recently I joined up as a systems administrator on a Minecraft server (full administrator, as in I set up everything and keep it running smoothly, I fully manage it myself), and while I got everything working perfectly fine on our Limestone Networks dedi (C2Q 9400 2.66ghz, 8GB RAM, 500GB HDD, 100mbps port), I've been having some troubles with DDOS/DOS attacks recently.

    Yes, a 3 week old server having troubles with attacks. (The most recent ones I've been having are from a very disgruntled banned player).

    Now I can handle CentOS and the like fine for most tasks, but I've never learned much about what to do about DDOS/DOS attacks, especially with the scale of these attacks (75-100 mbps usually, which often maxes out our line). Limestone has great support, and they automatically stop most attacks within a few minutes, but I'm wondering if there's a way to detect/stop/log these attack instead of waiting for Limestone to get rid of them? We're also thinking of switching hosts due to cost issues, and I would especially need a method to stop attacks on hosts with stricter bandwidth and QOS policies.

    I caught the attacker's IPs once (they were using Amazon EC2), but Amazon denied that the IPs ever touched us.

    Basically, how and with what tools would I be able to stop/log DOS and DDOS attacks on CentOS 5.5, with that hardware/network.

    I would love any and all advice on this matter.

    You would need something that is sitting outside of the server to stop the attacks from reaching your server. Once they have reached your server it starts to affect the performance and bandwidth availability of the server. There are small time scripts to stop user's from getting a response from certain services running on your server but none of them keep the attack from reaching your physical server which is the key in stopping them.

    I would recommend looking for a host that specializes in DDOS mitigation that does not just null route IPs when attacks occur. Some can add the IPs to their ACLs so they do not reach your physical server which will help mitigate the DOS and DDOS attacks.

  3. #3
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    Ask your provider to place a hardware firewall (this can even be a server configured as a firewall) between the switch and your server.
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  4. #4
    Join Date
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    DDoS Attacks have always been a major problem on all game servers.

    I would try this script: http://deflate.medialayer.com/

    Also, if you can prove that the attacks are coming from Amazon EC2 (Get Limestone to write a statement for proof, too, with the IP address in logs), and Amazon EC2 is denying the attack (Even after you send the log), then hire a lawyer and see what can be done. DDoS attacks are a major problem, and when a host does not comply with reports then there can be trouble.

  5. #5
    Upgrade to gigabit port. problem solved.

  6. #6
    Quote Originally Posted by misspink View Post
    Upgrade to gigabit port. problem solved.
    Yup. If the attacker can only manage to send about 100 megabit to your server, a gig port is the easiest way to deal with this. If you can find a host who doesn't meter incoming bandwidth, then this should be fine, unless the particular user can find a way to throw 10x as much bandwidth into the attack.
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  7. #7
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    Quote Originally Posted by funkywizard View Post
    Yup. If the attacker can only manage to send about 100 megabit to your server, a gig port is the easiest way to deal with this. If you can find a host who doesn't meter incoming bandwidth, then this should be fine, unless the particular user can find a way to throw 10x as much bandwidth into the attack.
    you would also find a host that doesnt nullroute your ip on 1gbps port based on network spikes like softlayer does

  8. #8
    Quote Originally Posted by Maikon View Post
    you would also find a host that doesnt nullroute your ip on 1gbps port based on network spikes like softlayer does
    That's true, but it's not really a fair comparison because softlayer will null you even if there isn't a spike, just quite a bit of use. I've had this issue a number of times, and so wouldn't use them for anything requiring much reliability. For what it's worth, I've only heard of softlayer doing this for 100tb clients, it seems they treat direct clients better.
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  9. #9
    Quote Originally Posted by TheHeartSmasher View Post
    You would need something that is sitting outside of the server to stop the attacks from reaching your server. Once they have reached your server it starts to affect the performance and bandwidth availability of the server. There are small time scripts to stop user's from getting a response from certain services running on your server but none of them keep the attack from reaching your physical server which is the key in stopping them.

    I would recommend looking for a host that specializes in DDOS mitigation that does not just null route IPs when attacks occur. Some can add the IPs to their ACLs so they do not reach your physical server which will help mitigate the DOS and DDOS attacks.
    We use Limestone Networks, so they _do_ mitigate DDOS/DOS attacks for us instead of null routing our IPs, but they are a little too expensive for us to continue using, and it takes between 5min-3hours to mitigate the attacks on their side, and because we run a gaming community ANY downtime becomes a major problem, even in the Minecraft gameplay environment.

    Quote Originally Posted by xema View Post
    Ask your provider to place a hardware firewall (this can even be a server configured as a firewall) between the switch and your server.
    As I mentioned above, they get rid of attacks for us after shortish delays, but they do not sell hardware firewalls and the cost of renting a second server just for that is very prohibitive.

    Quote Originally Posted by Appdeveloper View Post
    DDoS Attacks have always been a major problem on all game servers.

    I would try this script: http://deflate.medialayer.com

    Also, if you can prove that the attacks are coming from Amazon EC2 (Get Limestone to write a statement for proof, too, with the IP address in logs), and Amazon EC2 is denying the attack (Even after you send the log), then hire a lawyer and see what can be done. DDoS attacks are a major problem, and when a host does not comply with reports then there can be trouble.
    Yeah, we've been having a LOT of problems..

    http://img813.imageshack.us/img813/3...10716at101.png

    When you try running a gaming community, it sucks when your users can't access the server due to network attacks...

    I'll take a look at the script, thanks!

    I contacted Limestone, they said that "They log all attacks and automatically send reports to the authorities". That wasn't enough for me, so I went and managed to capture a attacker's IP (3 IPs, registered to Amazon EC2), but when I sent a report in they claimed to have no record of such a attack... I ran whois lookups on all IPs I found connected the one time I was on the SSH when we were being hammered, and those 3 were the only ones that tripped any flags, plus they quickly disconnected and the attack stopped...

    We're a (very) small gaming community, we barely cover operating costs, so we simply have no money for lawyers.

    Quote Originally Posted by funkywizard View Post
    Yup. If the attacker can only manage to send about 100 megabit to your server, a gig port is the easiest way to deal with this. If you can find a host who doesn't meter incoming bandwidth, then this should be fine, unless the particular user can find a way to throw 10x as much bandwidth into the attack.
    A 1gbps port from Limestone is $45/month extra, a little too much when we can barely afford the bills as-is, and we're thinking of moving to Hetzner to save money and get more power (and possibly a 1gbps port, although we're not sure if we even want to switch providers, especially so when we found out that Hetzner has a policy to null route your server if a attack is detected).

    Limestone doesn't meter incoming BW, but again, the amount pushed in isn't the problem here, it's our line being saturated. I might be a little whiny, seeing as the attacks are usually stopped by Limestone with no interaction on our part in a relatively timely manner, but downtime for the type of services we are trying to offer can be catastrophic.

    ======

    The software firewall is up, but the attackers just target random ports and overwhelm the line with brute force... Would there be a firewall rule that I could set up to LOG any suspicious connections on any port at any time? I'm still playing around with setup, trying to get a compromise between a massive log file and detailed log info.
    Last edited by battlekid; 07-16-2011 at 11:51 PM. Reason: Spelling errors

  10. #10
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    Quote Originally Posted by battlekid View Post
    we're thinking of moving to Hetzner to save money and get more power (and possibly a 1gbps port, although we're not sure if we even want to switch providers, especially so when we found out that Hetzner has a policy to null route your server if a attack is detected).
    Correct, Soon as Hetzner notices your under attack they null route you within minutes...

    I suggest you contact BurstNET they might beable to help you
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  11. #11
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    Quote Originally Posted by funkywizard View Post
    Yup. If the attacker can only manage to send about 100 megabit to your server, a gig port is the easiest way to deal with this. If you can find a host who doesn't meter incoming bandwidth, then this should be fine, unless the particular user can find a way to throw 10x as much bandwidth into the attack.
    100 Mbps could still be enough to exhaust the resources of the server in other ways, causing the server to go down regardless of the port size.

  12. #12
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    Quote Originally Posted by Appdeveloper View Post

    I would try this script: http://deflate.medialayer.com/

    Does it work?

  13. #13
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    Quote Originally Posted by chhit View Post
    Does it work?
    It doesnt for me when i got ddoes.

  14. #14
    Quote Originally Posted by IRCCo Jeff View Post
    100 Mbps could still be enough to exhaust the resources of the server in other ways, causing the server to go down regardless of the port size.
    Yes, that's certainly the case, depending on the kind of attack. For a script kiddie / udp flood, I've seen 1gbps attacks before that just slowed down the server a bit. Clearly if the attacker knows what they're doing, that can be a different story altogether.
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  15. #15
    Alright, just found out that we're being targeted by some idiot hacker group (quantumbooter.info), this is not going well...

    We basically told them to piss off and went and patched several major security holes they had been exploiting, so now they've decided to hammer us with a ~50mbps attack... Again.....

    I must say, although Limestone is very expensive, they are very good about attacks!

    Anyways, I guess the best idea right now is for us to just keep cleaning up security and rely on Limestone to mitigate the attacks as they appear.

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