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Cisco LAN-to-LAN IPsec Tunnel Between Two Routers with a NAT device in the middle


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Cisco 881 (Outside on the Internet) wanting to create a number of tunnels to Cisco 881's inside a MPLS network. The MPLS provider has provided a Gateway with a Public IP address and they  have created a different IKE and IPSEC port for each inside host that we want to create a tunnel too.

I.e IKE 4510 / IPSEC 45010 redirect inside to inside Host IKE 500 / IPSEC 4500

Can I on my Cisco 881 on the Internet specify the destination ports that happen in Phase 1 and Phase 2?

Running a very basic L2L Config atm between hosts within the MPLS as per Cisco - http://www.cisco.com/c/en/us/support/docs/routers/1700-series-modular-access-routers/71462-rtr-l2l-ipsec-split.html

 Kind Regards

Internet Protocol SecurityVPNRoutersCiscoNetwork Architecture

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Matt V

8/22/2022 - Mon
Matt V

I'm not sure why you want to use different ports for the tunnels.  You can have multiple tunnels connected over the same ports.

Different EP's behind the traversal device in the middle

Traversal device isn't terminating the tunnels
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Matt V

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I thought as much, the tunnels are created from the public internet through to the internal EP so they will need a dedicated public IP per private EP. One would assume.
Matt V

That would be my understanding as well.  No way you could combine those end points into one larger one and route the tunnels out from there?

I am afraid not, I wish. I pushed to have a connection into the site that was on the MPLS but some bright spark thought it best to put it behind a NAT traversal box.

I didn't think there was an option to specify the ports on a Cisco config but they insisted you can.
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Matt V

Looks like you can use encapsulation on an ASA, but if you are using IOS devices you are out of luck.