How to check TTL for multicast on Centos 7 ?

bsparks · 12-07-2023, 08:30 PM

Hi,
I have Centos 7 VM. Network guys are saying that TTL for multicast of this VM is set to 25, hence firewall assumes it is DDOS and drops the packets. On OS level, is there a way to know, what is TTL ?
I want to set it to 10. I found one this URL , and it gives me two options to set :

Code:

# iptables -t mangle -A OUTPUT -d <multicast_ip_addr> -j TTL --ttl-set 64

Code:

# firewall-cmd --direct --add-rule ipv4 mangle OUTPUT 0 -d <multicast_ip_addr> -j TTL --ttl-set 64

But I do not have firewall and iptables enabled on my servers. Is there any different way to set it to 10 ?
Please suggest.
Thanks

Ser Olmy · 12-15-2023, 09:47 PM

iptables doesn't have to be enabled, it's part of the Linux kernel.

Try the iptables command (sudo will probably be required), it should work. How to add it to the CentOS startup scripts to ensure it sticks across reboots is another matter.

tuxthegreat · 12-20-2023, 07:35 AM

To save a iptables firewall configuration that is saved and is there after a reboot you can try

Code:

netfilter-persistent save

It works on my Ubuntu install.