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Re: [FW-1] anti-spoofing clarification



:: Thanks for the input so far.  I probably should have specified a bit more
:: clearly that there are networks other than my own who need access to the DNS
:: server, so I do not think I can use THIS NET for the DMZ interface... unless
:: I am still not understanding this correctly..

The anti-spoofing rules, if setup the way I outlined, shouldn't prevent
legit users from using the services on any of those networks.  That's what
the rulebase is for.  Anti-spoofing/valid addresses merely dictate what
IP's are valid for packets that are trying to traverse that interface.

For example,

          Internet
              |
              |
              |
            Int#1
            FW-1 Int#2----- DMZ (1.2.3.0/24)
              |
              |
              |
            Int#3
          Intranet
        (10.0.0.0/8)

In this setup, installing anti-spoofing rules as I mentioned in my earlier
message would prevent any packets in the 10.0.0.0/8 address space from
originating anywhere except off of #3 interface.  So, if someone from the
Internet was trying to perform a spoofing attack on your webserver, for
example, claiming to come from 10.2.3.44/32, your FW would reject them
because 10/8 addresses are only valid when coming from Int#3.

Is this a bit more clear?

Cheers - Erick

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