Hello Ohal,
the new location should use a different IP subnet.
the design should be reviewed because it is insane.
otherwise you should use NAT or some L2 transport tecnique like L2TPv3 but:
these have requirements on device types:
NAT can be done only on SW based routers or C6500 with sup720.
L2TPv3 can only be done on sw based routers.
But all this has complexity and performance penalties.
if this is a new site it is better to use a different IP subnet.
for L2TPv3 see
http://www.cisco.com/en/US/docs/ios/12_3t/12_3t2/feature/guide/gtl2tpv3.html
vlan based L2TPv3
for NAT: you need to assign two IP subnets to represent the common subnet in the different sites
siteC should see net 192.168.5.0/24 as equivalent to 192.168.10.0/24.
first site should use something like 192.168.7.0/24 when attempting to access other site's ip address.
Each router should nat its own block
ip nat pool mypool 192.168.5.2 19.168.5.254 netmask 255.255.255.0
access-list 10 permit 192.168.10.0 0.0.0.255
int loop5
ip address 192.168.5.1 255.255.255.0
int lan 0
ip nat inside
int wan0
ip nat outside
ip nat inside source list 10 pool mypool
router ospf xx
network 192.168.5.0 0.0.0.255 area YY
something similar should be done in other site
hope to help
Giuseppe
