How to connect two networks using Cisco?

Question

Cisco

All the best.
There are two locales that need to be linked together.
One locale 10.1.112.0/24 is computers and 10.1.113.0/24 telephony. Locale is simple, flat. At the end is 2960 in which two VLANs are registered. 2 - computers, 4 - phones.
Now it works like this. Everything comes to 2960 and through the crypto-gateway (10.1.112.100) goes to Rostelecom in the departmental network.
The second locale 10.1.120.0/24 - computers and 10.1.121.0/24 telephony.
It costs 3750. Lokalka through the crypto-gateway (10.1.120.3) goes to the departmental network through Rostelecom, there is a separate computer - proxy 10.1.120.1 through which the Internet is accessed.
Previously, these were different sites, now the equipment has been brought into one. And the question arose - how to connect 112 and 120 grids together, bypassing Rostelecom?
There is access to both tsiska, knowledge in this matter is initial. It is advisable to make minimal changes to the settings. It is not possible to drive everyone into one network for a number of reasons.
Final goal. Users from grid 112 see resources 120 and can access the Internet through a proxy. Users from the 120 network see the resources 112 of the network. Thanks in advance for your kind help

Answer 1

Connect ciscos and prescribe static routes or configure OSPF (3750 seems to be able to do OSPF for sure).
BUT! Considering that these are networks that go to departmental networks through crypto-gateways, then there is a question of security and permission for such an association from the security guards.

Answer 2

can you attach the diagram? Ip base ios must support OSPF and basic routing functionality.