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Juniper SSG to Cisco ASA VPN with overlapping subnets

I needed to configure a site-to-site VPN connection between a Juniper SSG firewall and a Cisco ASA firewall. The configuration of a VPN connection is very straightforward, but this time the networks behind the firewalls are overlapping.

I have configured the Cisco ASA multiple times in such scenario, but the configuration of the Juniper SSG was new for me. I found a good article in the Juniper Knowledge Base. The article helped me to configure the VPN connection on the Juniper SSG firewall. The “tricky” part is the configuration of the MIP’s on the tunnel interface and the policy from the VPN network to the Trust network.

The only difference in my configuration is the definition of proxy ID’s within the VPN profile configuration. My scenario involves multiple subnets behind the Juniper SSG firewall en behind the Cisco ASA firewall. For every combination of subnets (Security Association) you have to configure a separate tunnel interface and VPN profile.