KVM - pxeboot doesn't work after hardening

Depending on your compliance strategy, hardening can go very deep with setting kernel tunables using sysctl. I've recently borked my pxeboot using these variables on my kvm-hypervisors:

 net.ipv4.tcp_sack=0  
 net.ipv4.tcp_dsack=0  
 net.ipv4.tcp_fack=0

So, resetting these values was required using the 'sysctl' command:

 [root@hyv02 ~]# sed -i 's/net.ipv4.tcp_sack=0/net.ipv4.tcp_sack=1/g' /etc/sysctl.d/hardening.conf  
 [root@hyv02 ~]# sed -i 's/net.ipv4.tcp_dsack=0/net.ipv4.tcp_dsack=1/g' /etc/sysctl.d/hardening.conf  
 [root@hyv02 ~]# sed -i 's/net.ipv4.tcp_fack=0/net.ipv4.tcp_fack=1/g' /etc/sysctl.d/hardening.conf  
 [root@hyv02 ~]# sudo sysctl -p hardening.conf

Now, the lines can be removed from the file in /etc/sysctl.d:

 [root@hyv02 ~]# sed -i '/net.ipv4.tcp_dsack=1/d' /etc/sysctl.d/hardening.conf  
 [root@hyv02 ~]# sed -i '/net.ipv4.tcp_sack=1/d' /etc/sysctl.d/hardening.conf  
 [root@hyv02 ~]# sed -i '/net.ipv4.tcp_fack=1/d' /etc/sysctl.d/hardening.conf

After setting the kernel tunables, pxeboot should be working again.

Feel free to comment and / or suggest a topic.

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