Hello Reza,
>> Which IP address should I add to the Core switch for routing?
if you want to implement a L3 routed core every link betweeen core device and a distribution device is a L3 link with its own IP subnet.
For example if you have 16 distribution pairs and two core switches:
10.10.10.0/30 dis11 to core1
10.10.10.4/30 di12 to core2
10.10.10.8/30 dis21 to core1
10.10.10.12/30 di22 to core2
...
10.10.10.128/30 disF1 to core1
10.10.10.132/30 disF2 to core2
this under the idea to have not a full mesh between core routers and distribution devices
then you need also a L3 link between the two cores (at least one)
Each L3 device should also have a loopback interface to be used as OSPF router-id and for management purposes (telnet and so on)
you can use /32 loopbacks taken from same block for example
10.255.254.1/32 core1
10.255.254.2/32 core2
10.255.254.3/32 dis11
10.255.254.4/32 dis12
to make the routing function the core switches have to talk OSPF on all links to distribution nodes
router ospf 10
router-id 10.255.254.1
network 10.10.10.0 0.0.0.255 area 0
network 10.255.254.1 0.0.0.0 area 0
network area commands work like ACL statements and first statement starts OSPF on each interface whose ip address belongs to 10.10.10/24 space
Second command is used to advertise its own loopback.
router-id command allows to define the OSPF router-id.
Distribution nodes have to advertise client Vlans and to take part in OSPF communication on point to point link.
if you use a L2 access layer design client vlans are served by distribution nodes.
if you use a L3 access layer design the access layer switches take part in OSPF and have to advertise their own client vlans.
Hope to help
Giuseppe
