syncookies load testing

syncookies load testing

[Alex Flex]

Hello Netfilter,

As some of you may know iam doing some work with syn cookies in my LAN.. 
Id like to understand the process better which is why i have a few 
questions:

Assume the system has conntrack off.

a.) I noticed that while creating a synflood with syn cookies enabled 
VRS syn cookies disabled the output of netstat remains exactly the same 
(even on different hardware architecture) ... :

[root@cl-t055-211cl ~]# netstat -nat | awk '{print $6}' | sort | uniq -c 
| sort -n
[...]
     256 SYN_RECV

Could anybody explain to me why this is so?

b.) From my understanding the syn back log is the memory of half open 
connections, could anybody tell me what effect this has on syn cookies? 
and if there is anyway to monitor its usage?

Thanks
Alex

Re: syncookies load testing

[Alex Flex]

Oh and one other thing i was wondering,

In regards to the sysctl variable: net.ipv4.tcp_synack_retries... Would 
anybody know if tweaking this have any effect over the behaviour when 
syncookies are being sent? Are there syn ack replies as well?

Thanks
Alex