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Pix rule

Posted on 2004-09-02
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Last Modified: 2013-11-16
How can I only allow SSH acess to a specific netblock of external IPs? Say, 192 is an external in this case ...

This is the basic config at the moment allowing all access ...
access-list 101 permit tcp any host 10.0.0.10 eq ssh

access-list 101 permit tcp 192.168.1.0 255.255.255.220 10.0.0.10 eq ssh??? would that allow 192.168.1.0 - 192.168.1.35

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Question by:af500
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3 Comments
 
LVL 11

Expert Comment

by:PennGwyn
ID: 11968321
Almost.  Access lists don't use a *subnet* mask, they use a *wildcard* mask, sometimes thought of as a complemented subnet mask.  The mask specifies the bits that are allowed to vary.

So "192.168.1.0 0.0.0.31" specifies 192.168.1.0-192.168.1.31, and "192.168.1.32 0.0.0.3" specifies 192.168.1.32-192.168.1.35.  So two rules will get you the range you've specified.

I'm fairly certain, though, that access lists also list the *source* first, and then the destination.  So the final rules look like:

access-list 101 permit tcp host 10.0.0.10 192.168.1.0 0.0.0.31 eq ssh
access-list 101 permit tcp host 10.0.0.10 192.168.1.32 0.0.0.3 eq ssh

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lrmoore earned 50 total points
ID: 11968682
Actually, the PIX does use a netmask and not a wildcard mask, so it's a little more difficult..
Sorry, PennGwyn...

access-list permit tcp host 10.0.0.10 192.168.1.0 255.255.255.224  eq ssh     (.1 - .30)
access-list permit tcp host 10.0.0.10 host 192.168.1.31 eq ssh
access-list permit tcp host 10.0.0.10 host 192.168.1.32 eq ssh
access-list permit tcp host 10.0.0.10 host 192.168.1.33 eq ssh
access-list permit tcp host 10.0.0.10 host 192.168.1.34 eq ssh
access-list permit tcp host 10.0.0.10 host 192.168.1.35 eq ssh

Or, you could create a host group, and assign the group to the acl:

object-group network SSH
        network-object 192.168.1.0 255.255.255.0
        network-object 192.168.1.31 255.255.255.255
        network-object 192.168.1.32 255.255.255.255
        network-object 192.168.1.33 255.255.255.255
        network-object 192.168.1.34 255.255.255.255
        network-object 192.168.1.35 255.255.255.255

access-list permit tcp host 10.0.0.10 object-group SSH eq ssh

This gives you the flexibility to selectively add/remove one or more IP addresses instead of using a whole range..




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Expert Comment

by:billwharton
ID: 11980439
af500

If you are looking to allow SSH to remotely administer the PIX firewall, you can use:

ssh <network> <subnet mask> <interface>

Examples:
1) If you want inside network 192.168.1.0 to be able to SSH into the PIX, use
ssh 192.168.1.0 255.255.255.0 inside

2) If you want only IP address 192.168.1.22 to be able to SSH into the pix, use
ssh 192.168.1.22 255.255.255.255 inside
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