TCP_SYNCOOKIES - Negative impact(s) when enabled?

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Hi all,

it seems to be clear that "tcp_syncookie" (beside others) might help to better prevent/survive syn flood attacks. So why is this option not enabled by default?

When searching the web for negative impact of enabeling syn_cookies, i found lots of posts, saying "it's a fallback facility" and "must not be used on highly loaded servers". That it "violates TCP protocol" and "does not allow to use TCP extensions".

On the other hand i found, that are all rumors of the "SYN cookie monster" stated by D.J. Bernstein on "http://cr.yp.to/syncookies.html";.

So my question is, is it ok to enable "tcp_syncookies" on higly loaded servers by default without any negative impact(s) or if it would be better to change kernel configuration to make use of this feature only in certain situations.

Could you please shed some light on this.

Best regards - philipp


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