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06.29.2008 at 08:58PM PDT, ID: 23525860
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8.2

Cisco Site to Site VPN with inbound ACL on each side

Asked by Jebutter in IPSec Security Protocol, Network Routers

I have a site to site vpn from a Cisco IOS router to Cisco IOS router.  Both routers have an inbound ACL applied to the same interface as the crypto map.  The ACL allows the IPSEC protocols in from the respective peers.  Without the ACLs the tunnel gets established and I can ping from remote subnet to remote subnet.  With the ACLs applied, the tunnel gets established but I cannot ping from remote subnet to remote subnet UNLESS I add statements to the ACL that allow traffic from remote subnet inbound to the internal subnet (i have to do this on both sides).  So it appears the packet gets encrypted and tunnelled over to the other router, unencrypted and then the ACL is applied to the packet.  I confirmed this by applying a set of ACLS on a 3rd router that sits in between the two site to site routers.  The 3rd router essentially blocks all traffic from Router A's internal subnet to Router B's internal subnet and vice versa.  So if the packets aren't tunnelled, they get blocked.   So I confirmed that the packets are tunnelled via IPSEC otherwise the 3rd router blocks them, which I confirmed by removing the crypto maps and doing a test ping, and the 3rd router blocks them.

To recap it looks like the packets coming in from an IPSEC peer are unecrypted and then the ACL is applied, which doesn't make sense.  The ACL is applied as the IPSEC packet comes in, otherwise it would even make it that far, so it seems like it is applied twice, once before unecryption, and once after?  Is this normal behavior?Start Free Trial
[+][-]06.30.2008 at 09:31AM PDT, ID: 21900630

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[+][-]06.30.2008 at 12:05PM PDT, ID: 21902029

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[+][-]06.30.2008 at 04:49PM PDT, ID: 21903932

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[+][-]07.15.2008 at 09:43AM PDT, ID: 22008582

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About this solution

Zones: IPSec Security Protocol, Network Routers
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Solution Provided By: Jebutter
Participating Experts: 1
Solution Grade: A
 
 
 
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