Two DHCP servers in separate buildings

[swips88]

What is best way to increase speed and separate two building's networks.

Building A has firewall/router which is gateway to internet. DHCP currently DISABLED on this box.
about 75 hosts ip addresses in building not all in use at one time.
20 port switch in same building with 5 WIFI access points also.

500' COAXIAL connection to Building B using DSL converter boxes

Building B has Cisco switch and two smaller switches for printers and a few shop computers.
Windows Server in this building is configured as DHCP Server providing both buildings with IP range 192.168.1.x

Another 50-75 or so ip host addresses in this building.

Most network traffic stays in building B other than internet access. Most network traffic in Building A stays in building A occasionally accessing another application server and a file server in building B.

Having the Windows DHCP server giving out IP addresses to building A is not very efficient considering the coaxial link between buildings.

I am thinking there should be two DHCP servers with a subnet in building B keeping existing Windows server for all DHCP addresses in Building B

Configure Router to be DHCP server for building A with different ip range 192.168.2.x
Does router LAN port get new address for gateway in new subnet ip range and Windows DHCP Server points Router and gateway to this address?

thanks in advance for any suggestions.

[mcr-ksh]

I literally have the EXACT same problem! I have the same networks across two building both connected via COAX and would love to separate the buildings' default GW for those clients in buildingA and buildingB. The clients need to be in the same VLAN but should use the local switch (buildingA-CBS350) and (buildingB-C3650). This is due to some extra latency introduced by the COAX. So far the DHCP server in the Datacenter (buildingB) is providing the default GW, which will result in a useless overhead back-and-forth when routing between VLANs.

1. Separating the IP space is not an option as I need to have the clients in the same VLAN + IP space. 

2. I thought of PBR but I cant rewrite the route on CBS350 to use the local switch VLAN IP. "Unreachable" is provided in the status.

3. I thought of using a DHCP relay but that doesn't make much sense as they are in the same network segment and DHCP server from the other building is providing the IP space and thus default GW. Not sure if Small Business line would even support that.

4. The only option that comes to my mind is to statically assign the IPs via DHCP on all the clients in the other building, but what would be the benefit of a DHCP Server then?

Any other thoughts on how to takle the problem here?

[Joseph W. Doherty]

"4. The only option that comes to my mind is to statically assign the IPs via DHCP on all the clients in the other building, but what would be the benefit of a DHCP Server then?"

It allows you to manage those clients, effectively static IPs, from your DHCP server rather than having to touch/configurate now (and in possible future) each individual host.

Anyway, so what you want to do, is jump between the same subnets/VLANs, that span two buildings, using a local gateway router for the local jump between VLANs, correct?  This also assumes, that the destination would also be physically in the same building although you cannot tell that by the subnet, correct?

BTW, why must the same VLAN be used across buildings?

I have not reread all my prior postings in this tread, but if you had a DHCP server (like on the local building router), its DHCP offer would likely be received by a same building host before getting the DHCP offer from the other building's DHCP server.

[mcr-ksh]

Hi Joseph,

yes sure. I get that with the DHCP management, but it's still manual effort to manage the entries.

> Anyway, so what you want to do, is jump between the same subnets/VLANs, that span two buildings, using a local gateway router for the local jump between VLANs, correct?  

CORRECT. I want to evade that traffic leaves the building if it is destined for the same building but would simply require to touch a different VLAN (in the same building).

> BTW, why must the same VLAN be used across buildings?

Ah well, the clients or servers belong to the same group. Having more subnets would simply increase the complexity and firewall rules. The biggest sh*tshow would be mdns and the additional network management. The clients heavily rely on that and all the cisco dns-sd gateway etc. implementation is crap. simply put, the devices belong to the same network segment.

> I have not reread all my prior postings in this thread, but if you had a DHCP server (like on the local building router), its DHCP offer would likely be received by a same building host before getting the DHCP offer from the other building's DHCP server.

Yes, that's right. Like the ARP requests from the closer switch. They both use proxy arp. Then I need to connect both DHCP servers so there wont be any overlapping IPs and Small Business line is not quite there where IOS is. Don't want to mess with yet another requirement.