how to debug/troubleshoot one-way traffic IPSec tunnel

Answered Question
Dec 3rd, 2009

I am setting up a corporate IPSec network that consists of a UC520 at the head end (corporate office) and several Linksys WRV routers as remotes nodes/networks.  I can see that ISAKMP and IPSec SA come up on both ends and I can ping the internal IP of the UC520 from remote networks.  However I cannot ping any other private IP on the corporate network.

I see from "show cry ips sa" that packets are being decapsulated (remote to corporate) but none are encapsulated (corporate to remote).  I also can see (from a traceroute) how packets from corporate to remote are sent out the UC520's default gateway to the Internet instead of being placed in the tunnel.  This jives with what I see with "sho cry ips sa".

I made sure to create an ACL for NAT so that corporate to remote subnets are not NATed but other than that I don't know what else to check.  I tried to do a "debug IP packet detail xxx" using an ACL to match corporate to remote traffic but the debug and ACL get no hits.

Any other ideas?

Thanks,
Diego

I have this problem too.
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Correct Answer by Herbert Baerten about 7 years 1 week ago

Well, it sounds like your Nat exemption is not working. Checking "show ip nat trans" while sending traffic will confirm this.

Can you perhaps post your (entire) NAT config?

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Correct Answer
Herbert Baerten Fri, 12/04/2009 - 04:51

Well, it sounds like your Nat exemption is not working. Checking "show ip nat trans" while sending traffic will confirm this.

Can you perhaps post your (entire) NAT config?

DIEGO ALONSO Sun, 12/06/2009 - 10:21

You are absoultely correct.  After doing more testing I realized the problem was only with private IPs (at the corporate site) that had a static NAT assigned to them.  The IPs using PAT are working OK.  I guess this is because the PAT  IPs have an ACL that denys the NAT when its private to private traffic.  The question now becomes how to do static NAT yet somehow use an ACL to deny private to private NAT like the PAT does.

Any ideas?

Thanks,

Diego

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