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Dropping unsollicited connections

Posted on 2012-04-04
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Last Modified: 2012-04-05
Hi!

I have a cisco 1760 router which has port forwarding for ports 25, 80 and 443 for my web services. So if, let's say, I want to open a connection on port 21 of the router, it should not be allowed. The router sends a "connection refused" packet.

What I want to do, is reproduce the DROP behavior of iptables. If I open a connection on port 21, the router should not respond at all and drop the packet.

How can I achieve that?

interface FastEthernet0/0
ip address x.x.x.89 255.255.255.0
no ip unreachables
ip nat outside
ip virtual-reassembly
speed auto
full-duplex
!
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Question by:alex3948
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4 Comments
 
LVL 15

Expert Comment

by:Nayyar HH (CCIE RS)
ID: 37808614
That is part of the TCP/IP mode of operation - If the requested service in unavailable a TCP RESET will be sent to the source in response to the SYN

Try using local-policy routing to send this type of traffic to null0: (drop packet)
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Author Comment

by:alex3948
ID: 37809021
I did the command:

# ip local policy route-map null0

Still same result
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LVL 35

Accepted Solution

by:
Ernie Beek earned 500 total points
ID: 37810166
I see you have no access list on your outside interface?

Try adding this:
access-list 100 permit tcp any host x.x.x.89 eq 25
access-list 100 permit tcp any host x.x.x.89 eq 80
access-list 100 permit tcp any host x.x.x.89 eq 443
access-list 100 deny ip any any

interface FastEthernet0/0
ip access-group 100 in


I also took the liberty of hiding your public ip.
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Author Comment

by:alex3948
ID: 37814311
Works like a charm, thanks !
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