Two network same subnet question

[leadtheway]

Have a weird situation I've mentioned before.. Basically we have a existing network that will be completely replaced with meraki.  The goal is to try to move things in chunks instead of a hard cut.  Problem is, the main vlan that has all the directorys services/dns etc are on the same subnet on both the old and meraki subnet.  The old service provider provides no access so we can't connect the two. Theres a 3rd party vendor that has an interface on that network. What we've been doing is removing that subnet from the MX, the 3rd party vendor sets an access mode port on the vlan in question, then I create an access port on on of the MS switches to allow that vlan, then we can put machines in that vlan and they can talk across to the equipment still on the other side. Problem is all the other vlans that egress the MX can't talk to that vlan.  Is there something I can do that could get everything talking the way it should.  I thought about taking that uplink from the 3rd party and run to mx and assign it an IP in that main vlan, change the subnet on the mx to something else, then create a route for that vlan on the mx to point to the 3rd party router.  Any thoughts

[PhilipDAth · Accepted solution]

If the existing network has multiple subnets and you don't have the cooperation of the existing service provider then I don't think this is going to work, as you need a degree of routing changes.

If you only need to reach into this remote network, and the remote network does not need to initiate connections back in, you could consider plugging the remote network into a WAN port on the MX.  Then all access to this remote networked will be NATed.

[Nick]

Did you get a solution working? 

[leadtheway]

did not get it to work