Cisco ASA 5500 – Deny a Single IP Address External Access

KB ID 0000743 


This got asked on Experts Exchange today, the poster specifically asked for an ASDM solution, so here goes. However I will also do the commands as well.


Block an IP via ASDM

1. Connect to the ASDM > Configuration > Firewall > Add ‘Network Object’.

Note: You could create a Network Object Group, then add a Network Object to that group. This is handy if there are liable to be more IP addresses you want to block in the future. In that case you would then simply add the new Network Objects to the existing group.

ASA Firewall Rules

2. Give the host a name, set its type to ‘Host’ > Enter the IP > The description is not mandatory.

Add Network Object

3. Locate the rules that are applied to the inside interface (incoming), select the first one.

Note: I refer to these as ‘Outbound’ rules, they apply to traffic flowing IN through the INSIDE interface.

ASA Firewall Rules Outbound

4. Add a new access rule > Set to Deny > Select the source as the host (or group) you have just created > OK.

Deny Outbound ASA

5. Make sure your new rule is at the TOP > Click Apply.


6. Warning: Below your ‘deny’ rule you need to ‘allow’ the traffic that should be allowed, or all other traffic will get blocked.

Allow IP any Any

7. Save the changes to memory > File > Save Running Configuration to Flash.

ASA Save To Flash


Block an IP via Command

Note: This assumes you do NOT have an outbound ACL (Issue a show acess-group command to find out), if you do it will say access-group {name} in interface inside, Simply replace the word outbound below for the name of yours and DONT issue the command that starts access-group.

User Access Verification

Password: Type help or ‘?’ for a list of available commands. PetesASA> enable Password: ******** PetesASA# configure terminal PetesASA# access-list line 1 outbound deny ip host any PetesASA# access-list line 2 outbound permit ip any any PetesASA# access-group outbound in interface inside PetesASA(config)# write mem Building configuration… Cryptochecksum: b984ffbc dd77cdbf f2cd8d86 0b8f3f96

3965 bytes copied in 1.490 secs (3965 bytes/sec) [OK]


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Author: Migrated

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