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Using ACL to block access to other internal networks

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pointless_l
Beginner
Beginner

‎10-26-2010 09:20 AM - edited ‎03-06-2019 01:44 PM

I have a Cisco 1900 router configured with 3 subinterfaces. I want one subinterface to only access the internet and not the other 2 interfaces. When I use access-group 130 in on the interface my users don't even get a DHCP lease, when I use access-group 130 out my clients can't reach any network. Any ideas on when I'm overlooking?

interface GigabitEthernet0/0.3

encapsulation dot1Q 240

ip address 192.168.240.1 255.255.255.0

ip access-group 130 in

ip nat inside

ip virtual-reassembly

ip tcp adjust-mss 1452

no cdp enable

!

access-list 130 deny   ip any 192.168.20.0 0.0.0.255

access-list 130 deny   ip any 192.168.33.0 0.0.0.255

access-list 130 permit ip 192.168.240.0 0.0.0.255 any

Any help is much appreciated.

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gatlin007
Enthusiast
Enthusiast

‎10-26-2010 10:49 AM

Apply this inbound as you have in the example.  Add the following to account for a DHCP request.  Remember the client doesn't have an IP address when it sends a DHCP request, so it won't match the 192.168.240.0/24 permit any line.

access-list 130 permit udp any any eq 67

If your DHCP server is in 192.168.20.0/24 or 192.168.33.0/24 then this line must occur at the beginning of the ACL.


Chris

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