Eigrp configuration between two core switches

[john smith]

i have a LAN setup already configured and working in a branch office network but now i have another building that is very near to that branch office

i have two routers 3900 and 3750 12S switch as a core will be used there in new building but in the existing building i have 6500 series core switches

what i want to do is

i want to configure a Layer 3 link between the new building (routers 3900) and the existing office (6500 switch) i seguested to use eigrp routhing protocol

but i want the new building's lan network will be separatefrom the old existing office's network (just i want to use L3 link between them) but the DHCP server for the new building will be configured in new 3750 12S core switch in new building

what about DNS server can i use DNS from the old existing office for my new building???

how i can configure that the router and core switches in both buildings(old office and new building)

your reply will be highly appreciated

thanks

[Jon Marshall]

Just connect the routers to the 6500 switches with L3 P2P links and then run EIGRP between these devices eg.

router 6500

=========

int gi0/1 <-- connects to 3900

no switchport 

ip address 192.168.5.1 255.255.255.252

router eigrp

no auto-summary

network 192.168.5.0 0.0.0.3

+ other networks

3900

====

int gi0/1  <-- connects to 6500

ip address 192.168.5.2 255.255.255.252

router eigrp

no auto-summary

network 192.168.5.0 0.0.0.3

+ other networks

For DHCP any vlans you have that need to get a DHCP address add this to the vlan interface -

int vlan 10

ip helper-address x.x.x.x  <--- where x.x.x.x is the DHCP server

Yes you can use the same DNS server for both buiildings.

Jon