This is why A2S_INFO requires a challenge :| Thanks, - Saul.
2009/9/5 Matt Stanton <[email protected]> > If these attacks are coming from ips that are outside of the range of > your standard users' network range, then it's possible you could filter > out requests from unallocated ip blocks and ip blocks from areas of the > internet that are gnerally too far away to have decent latency on your > server. Unfortunately, this would mean building a database of ip blocks > that are allocated to networks that are within a reasonable distance of > your server's network and checking every A2S_INFO packet that comes in > against this database, which would likely eat a decent amount of CPU. > > Nephyrin Zey wrote: > > The bandwidth involved in this attack is tiny. The issue is srcds chokes > > on large numbers of A2S_INFO packets, its not the traffic that's doing > > machines in. I'd reckon a single residential connection could take down > > a server this way. Once you fix the srcds issue, the problem stops. I > > have a daemon that intercepts server queries and handles them itself. > > It's currently handling this attacker hammering on two servers without > > breaking 1% CPU or making a single-pixel dent in my bandwidth graphs, > > and my tf2 servers continue to run just fine. > > > > And if you actually examine the attack, it's very obviously a single > > source with spoofed IPs. I rather doubt someone has a million-strong > > botnet containing nearly 30% unallocated IP ranges, that all happen to > > have the same exact path length. > > > > - Neph > > > > On 09/05/2009 12:50 PM, [email protected] wrote: > > > >> This... actually isn't a bad idea. It's a pain to implement, though, > for a > >> couple of reasons. > >> > >> First, the assumption by most on this thread is that it's a single guy > >> operating from a single (or just a handful) of computers. They further > >> assume that he's forging the source IP addresses so the requests look > like > >> they're coming from many many different machines. If this is true, > there's > >> no way to trace or block him based upon the information included in the > >> packets he's creating. I think this assumption is wrong, as I'll > explain > >> below. > >> > >> Second, if this assumption is incorrect you need to find a way to > identify > >> each and every source and block them one at a time. Netblocks are at > best a > >> crude measure which risks blocking many legitimate clients. Such a > process > >> needs to be automated as much as possible or it's not effective. > >> > >> Now, why do I think that this is probably not coming from just a handful > of > >> sources? Simple. DDoS stands for Distributed Denial of Service, after > >> all. Botnets are reaching incredible proportions. It's easy to rent as > >> many as a quarter million compromised machines if you want to and you > have > >> the cash. > >> > >> Too cheap or too poor to rent someone else's network of infected PCs? > No > >> problem. Tools exist to build new malware and they're easy to come by > if > >> you're willing to start looking in the right places. All you have to do > is > >> build your bot code and figure out a way to get it loaded on 5,000, > 10,000, > >> or more PCs. After that, DDoS to your heart's content. Script kiddies > do > >> this _all_ _the_ _time_. > >> > >> So, when under attack your choices are: > >> > >> * Wait it out. > >> > >> * Work with your vendor to figure out a way block the attack in the > first > >> place. (Valve, obviously, in this case.) > >> > >> * Automate the process of identifying sources and filtering them out. > >> > >> * Cry a lot. > >> > >> Generally, I settle for a combination of the first and second options. > If > >> an attack gets bad enough, I work with my local ISP to implement the > third. > >> (My server is co-located in their datacenter and they're really good > guys to > >> work with.) Generally, some combination of tcpwrapper, netfilter, and > >> iptables will do the job on my Linux server. Sometimes we find it > easier to > >> just block it at one of their routers so they don't have to deal with > the > >> traffic on their network. > >> > >> Every now and again, I find myself following the fourth option until I > >> figure out what's going on and fall back on some combination of the > first > >> three options. :-) > >> > >> HTH. > >> > >> =JpS=SgtRock > >> > >> > > > > _______________________________________________ > > To unsubscribe, edit your list preferences, or view the list archives, > please visit: > > http://list.valvesoftware.com/mailman/listinfo/hlds > > > > > > > _______________________________________________ > To unsubscribe, edit your list preferences, or view the list archives, > please visit: > http://list.valvesoftware.com/mailman/listinfo/hlds > _______________________________________________ To unsubscribe, edit your list preferences, or view the list archives, please visit: http://list.valvesoftware.com/mailman/listinfo/hlds
