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Cannot block traffic destined to a Mapped IP address

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Article ID: KB6311 KB Last Updated: 20 Mar 2009Version: 3.0
Summary:
Cannot block traffic destined to a Mapped IP address
Symptoms:

Problem Environment:

  • The MIP is defined on the interface in the untrusted zone and mapped to a private IP on the trusted zone
  • The MIP policy permits all traffic to pass through the firewall
  • Policy has been defined from Untrust to Global for the MIP
  • The deny policy was configured on the top of the policy list from untrust to trust to deny PING

Solution:

When the packet enters the firewall, the process order by default on the firewall is as follows:

Screen filters
Session lookup
MIP/VIP
PBR
Route lookup (SIBR -> SBR -> DBR)
Policy lookup
NAT Dst
NAT Src
Create session

For more information refer to the 'Packet Flow Sequence' in the Concepts & Examples ScreenOS Reference Guide - Volume 2 - Fundamentals
  1. Go to the ScreenOS Documentation link
  2. Click your Release version
  3. Click the Concepts & Examples Reference Guide: Volume 2, Fundamentals
  4. Refer to 'Packet Flow Sequence' section in Chapter 1


The global nature of the MIP is based on the lookup sequence above. Because the MIP/VIP lookup always occurs before all other route lookups, it does not matter which zone it is configured in, it will always miss a policy to "any". The only way to drop the traffic is to invoke the specific MIP addresses in the deny policy with the same from and to zones as the permit policy.

Add the following policy to deny traffic destined to MIP addresses:

fw-> get policy from untrust to global
    ID From     To       Src-address  Dst-address  Service  Action State   STLCB
     9 Untrust  Global   Any          MIP(63.124.~ PING     Deny   enabled --X-X
     7 Untrust  Global   Any          MIP(63.124.~ ANY      Permit enabled --X-X
fw->

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