On mlists.linux.kernel, on comp.os.linux.development.sys, I keep hearing from
people who say T/TCP is fundamentally broken because it has various serious
1. T/TCP guesses an unreasonable window size (4k) for its peer and sends SYN
with data accordingly.
It can be easily changed into 2*MSS, which is used in standard TCP
2. T/TCP has great potential for DoS attacks.
Because T/TCP sends data along with first SYN, ttcp is more vulnerable to DoS
attacks. But, if ttcp queues the data only TAO succeeds and discards it if TAO
fails, this problem can be greatly lessened. Adding some host validation
methods may fully solve this problem.
3. T/TCP has great potential for r-* services attacks.
TCP also has it! It's always recommended that r-* be turned off. And r-* is
being replaced by SSH etc. Besides, ttcp sends packets with PUSH flag. r-*
refuses any packet with PUSH flag. So, there should be no problem.
FreeBSD integrates ttcp in its kernel. This can be a strong evidence about
T/TCP is considered flawed mainly because RFC 1644 doesn't consider security
problems. It definitely needs improvements. A new RFC is necessary at the end.
What I'm going to do is to implement a "basic" ttcp patch based on RFC 1644.
Then, when people download the patch and test it, I'll collect every posted
problems along with it and modify the patch accordingly. During the same
process, I'll find out what improvements are needed for RFC 1644 and draft a
So, I hope people don't simply discard TTCP. Anyway, there will be more
benefits for all of us if TTCP is fixed instead of being thrown away. I can't
do that alone without your support and help.