Showing results for 
Search instead for 
Did you mean: 

Routing to 3rd Party Network from L3 Switch


Hi Folks,

I need to access a subnet belonging to a large 3rd party Network which is in a remote building connected via WAN.

The customer doesn't want to reconfigure this network with a return route as they already have a subnet using the same range as our subnet has been configured to use.

Basically I have a Layer 3 switch (not part of the customers network) with 2 VLANS 10 & 20.

A PC on VLAN 20  needs to see 3 devices on the customers Network.

The customer has provided a connection to a 2960 edge switch which when connected to laptop receives DHCP address from their DC and provides access to the three devices we need to connect to.

Question: How do I link the customers switch to my switch allowing VLAN 20 to access the 3 devices without the customer adding additional config?


paul driver
VIP Expert VIP Expert
VIP Expert


not much you can do without this 3rd party assistance - And then for security reasons you would require maybe a IPSec VPN between the two sites to gain the connectivity you require.



Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards

Thanks Paul,

Given my limited knowledge of routing, would you have any recommendations for the correct configuration required on the third party network? Could NAT be used here?

At this point I would not be concerned about Security. Just proof off concept.



Are there any IP overlaps? Any option for you to change your IP scheme?

Rising star
Rising star

This might seem a little basic but could you not stick a Router between your L3 switch and their 2960?

Configure the Routers WAN port to pickup a DHCP address and plug this into the cable accessing their network.

Make sure the router does NAT so the only address they see is the one assigned to you via DHCP.

The LAN port of the router would need to be on Vlan 20 or could be on any Vlan as long as it had a static route.

Bash a static route on your L3 switch (for their IP network) to point to the LAN address of the router. Then another static on the router for the destination subnet, the next hop being the default gateway of the WAN interface.

Not a brilliant solution but should work.


Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: