Re: Ambiguities in TCP/IP - firewall bypassing

From: Luis Bruno (lbrunoat_private)
Date: Fri Oct 18 2002 - 23:04:27 PDT

  • Next message: David Wagner: "Re: Ambiguities in TCP/IP - firewall bypassing"

    Alan DeKok wrote:
    > Benjamin Krueger <benjaminat_private> wrote:
    > > > [snip RFC 1025 (TCP and IP bake-off)]
    > > 
    > >   Identify what the packet should be, and treat it as such? If that is
    > > the correct way to handle these packets, then these stacks are correct.
    > 
    >   So... what should the packet be?  As I said, the spec is ambiguous.
    > If you don't know what the packet is, you obviously don't know how to
    > treat it.
    
    Think of ECN; should older stacks simply reject a packet with Syn+0x42
    because they don't know what 0x42 is?
    
    If I've understood correctly, you were suggesting to drop "bad" packets.
    I agree; only let established traffic through your firewall, and only
    let packets with Syn or Syn+Ack set and with Fin and Rst unset establish
    state in the firewall. Ignore the rest of the flags.
    
    Of course, if anyone finds this un-interoperable, please chime in!
    



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