Is Tor network resistant to TCP SYN flood DoS attacks from outside of Tor?

[ImproveTor]

@Vort

Recent Tor slowdown and SYN flood should not be related.

Why has the Tor relay operator reported about DoS attack against his relay then? Read this:

Is there currently a major DDOS affecting the network's availability?

I’ve been experiencing overload on both my relays, which is not the usual. Running 2 relays on 4 cores and 8GB of RAM. RAM is not an issue but CPU load is usually at 60%. These last days it’s been over 80-85%, getting warnings from time to time about my computer not being able to hold that many circuits for long. Over a span of 20 days uptime: 06:08:12 [NOTICE] Heartbeat: DoS mitigation since startup: 1.078 circuits killed with too many cells, 60.081.539 circuits rejected, 751 marked addresse…

Isn’t it a DoS attack?

@sunshinecowboy

But because Tor only transports correctly formed TCP streams, not all IP packets, you cannot send UDP packets over Tor.

My thread is about “Is Tor network resistant to TCP SYN flood DoS attacks from outside of Tor?” I know that Tor relay operator can block all incoming ICMP and UDP traffic. But how can it help against TCP SYN flood attacks?

@sunshinecowboy

Since the goal is to overpower the bandwidth of the victim, they typically send UDP packets since those don’t require handshakes or coordination.

An attacker can send millions of raw TCP SYN packets which don’t require handshakes too. Have you heard about TCP SYN flood attack?

SYN flood

The question is: how does Tor network fight against TCP SYN flood attacks?