ASA 5520 inside interface used for Clients Default Gateway

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Dec 12th, 2008
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I'm having issues when I point my clients DHCP lease gatway to the inside addr of the ASA ( they can not connect to any internal network the ASA has routes too. I validated from the ASA inside addr can see these networks "ping" and he recieves replies... So, I'm thinking the ASA is trying to nat the internal source ADDR when the source conects to him " internal side of the Asa" for the route next hop.

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husycisco Fri, 12/12/2008 - 10:17
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Hello Scott,

Try this

access-list inside_nat0_outbound permit ip insidenetwork insidenetmask routednetworks routednetmask

nat (inside) 0 access-list inside_nat0_outbound

Also make sure your access-list applied to inside interface does not block traffic.


sct0321 Fri, 12/12/2008 - 10:34
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Thanks for the info.. One question.. with the NAT (inside) 0 on the inside interface I think it will blow away all my normal inside to outside traffic..?

husycisco Fri, 12/12/2008 - 10:59
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The commadn will effect only the traffic between networks specified in access list. For example, your inside network is, and you have an internal network routed via ASA If you type the following,

access-list inside_nat0_outbound permit ip

nat (inside) 0 access-list inside_nat0_outbound

Traffic between these networks wont be NATed bidirectionally, so hosts on these network will be able to connect each other on their actual IPs. But traffic from to any other destination, for example a host in internet, this traffic will be natted and connection will be successful.

Robert Ho Fri, 12/12/2008 - 12:47
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i'm not really sure how your internal routing is setup but keep id mind that it does not support asymmetrical routing.

so, if packet flow is as follows, pc1-asa-router-pc2, then return trip pc2-router-pc1 (because pc1 and router lan on same subnet), then it will fail. bi-directional traffic must flow through the asa.

Note: ASA/PIX does not support ICMP redirects, because it does not support asymmetric routing.


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