One of the most powerful iptables match is the u32 module.
Using the u32 match you are able to write a firewall rule matching against a single bit of a network packet.

If you wanna play with u32 module you have to be prepared to deal with a syntax very ...

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I up against this problem on a server hosted by Hetzner.My server is a virtual hypervisor containing several virtual machines.The Hetzner's politics is to statically associate a public IP to a single mac address, is therefore impossible to have multiple IP address on a single ethernet device ...

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