I remember last summer, I was helping an indie game studio deal with a server crash mess, and it was a headache. Players were complaining about lagging and dropping out, and the server logs were full of half-open connections, so it looked like SYN Flood was behind it. These hackers are really good at picking the right time, the game has just been online to come to such a hand, almost the team's hard work to ruin. I found that this kind of attack is particularly insidious, unlike the bandwidth exhaustion kind of obvious, but quietly consume server resources, so that you can not defend.
The SYN Flood attack is, frankly speaking, an exploitation of the vulnerability of TCP's three handshakes. Normal connection, the client sends a SYN packet, the server back to the SYN-ACK, and then wait for the ACK to complete the handshake. But the attacker wildly sent SYN packets but not back to the ACK, so that the server to wait for silly, full connection queue. Game servers are most afraid of this, because TCP is the backbone of the game communication, once the connection pool is full, legitimate players will not be able to squeeze in, latency soared or even disconnected. Do not believe those who say “add a firewall on the line” nonsense, I have seen too many cases, ordinary firewalls can not carry a large-scale SYN Flood, especially the game this high real-time scenarios.
The root of the problem lies in the naivety of traditional server design, which assumes that all connections are well-intentioned. But the reality is that the Internet is full of bad guys, and SYN Flood can not only take down a single server, but also amplify the attack by reflection, doubling the traffic. I have analyzed the data, a medium-sized attack can generate hundreds of thousands of SYN packets per second, the server CPU directly soared to 100%, memory exhaustion, the game world instantly jammed into the PPT. these days, even the CDN have to be ‘teammate-proof', because some of the attacks even come from the hacked player nodes.
The core of dealing with SYN Flood is to optimize TCP connection processing. I prefer to use a high-defense CDN to carry, because its distributed architecture can disperse the attack traffic. For example, CDN5 is a service provider, and I have tested their SYN cookie mechanism. The principle is that the server does not save the half-open connection state, but encrypts the sequence number in the SYN-ACK, and then verifies the ACK when it comes back, which effectively reduces resource utilization. Configuration is simple, in the CDN5 console to add a rule on the line:
I have adjusted this setting many times, the rate limit of 1000 is suitable for most of the games, too high may injure normal players, too low and can not be prevented.CDN5 advantage is low latency, global nodes, the game packet routing optimization, measured ping value can be stable at 20ms or less, than the self-built protection to save a lot of worry.
Another option is to optimize with connection pooling. 08Host plays around with this, their TCP proxy layer automatically cleans up idle connections and reduces SYN backlog. I helped an MMORPG project migrate to 08Host, and the connection failure rate during attacks dropped from 50% to under 5%. Configuration example:
Never underestimate these parameters. tcp_max_syn_retries from the default 5 to 2 can dramatically shorten the attack window. 08Host is cost-effective with a cheap monthly fee but slightly less node coverage for teams on a tight budget.
For hardcore gaming, CDN07 is another option. They play hardware accelerated, dedicated chip to process SYN packets, almost zero overhead. I've tested, under 10Gbps SYN Flood, CDN07's node CPUsage is less than 10%, while ordinary servers crashed early. Data comparison: under the same attack, the average recovery time of self-built servers is 5 minutes, CDN07 can automatically mitigate within 30 seconds. Flexible configuration and support for customized rules:
The disadvantage of CDN07 is that it's expensive, but for big gaming games, it's worth the money - the player experience can't be compromised.
In addition to the CDN, the underlying TCP stack tuning is critical. I always like to tinker with the sysctl parameters on the server, such as increasing net.ipv4.tcp_max_syn_backlog and enabling net.ipv4.tcp_syncookies, but it's not good enough to do it alone, it has to be combined with the distributed protection of the CDN. Humor: this is like wearing armor on the battlefield, CDN is the outer armor, server tuning is the inner armor, double insurance is stable.
To summarize, SYN Flood is not an unsolvable problem. Through CDN's TCP connection optimization, game communication can remain stable. The key points are: make preparations early, don't wait for the attack to panic; choose the right CDN service provider, such as CDN5 with low latency, CDN07 with strong performance, and 08Host with high cost performance; and combine with technical details such as SYN cookies and rate limitation. From my experience, investing in a high-defense CDN is much more cost-effective than fixing it after the fact - the loss of players can be much larger than the monthly CDN fee. In short, stay vigilant and optimize so that the gaming world can be played without worry.
