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Firewall fails to block an established UDP connection...

GreatByte
Hello Guys,

I am have a weird situation here. I have a PC communicating with a server, both connected to my Sophos Firewall (Firmware: 9.100-16 - not an appliance).

I have a Rule that allows this connection, and it works. Without that Rule, the connection cannot be established. So far so good.
Once established, however, the communication continues even if I disable that rule, or add a rule above it to block that connection. [:S]
It just keeps on working and there doesnt seem to be a way to block it if I wanted to...

I tried it using a PC connected via the Internet and I can even disable the DNat Rule and the connection still continues. Only new connections are being blocked. Is this an expected behavior? Doesnt seem right to me.

Greatbyte


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  • 0
    Later in that same thread, da_merlin comments: 
    you also have to enable "Use strict TCP session handling" under Network Security >> Firewall >> Advanced (nf_conntrack_tcp_be_liberal).
     Otherwise the connection is picked up and allowed again after client sends another data packet.

    Note that the applicable timeout has a default of 180 seconds.

    Cheers - Bob
     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
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  • 0
    Later in that same thread, da_merlin comments: 
    you also have to enable "Use strict TCP session handling" under Network Security >> Firewall >> Advanced (nf_conntrack_tcp_be_liberal).
     Otherwise the connection is picked up and allowed again after client sends another data packet.

    Note that the applicable timeout has a default of 180 seconds.

    Cheers - Bob
     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
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