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ARP Issue with Multiple Subnets

We have a 4500-X as our core at our head office, connected to a Nexus 5K where our MS NLB Exchange cluster is (Virtualized).

On the 4500-X there is a static MAC and static ARP entry for the NLB VIP.

The servers are in VLAN 100 and the desktops are in VLAN 200

No desktop can ping or access Exchange via the NLB virtual IP from VLAN 200 (or any other non-server VLAN) but can access each server individually.

If I put a desktop in VLAN 100 I can access the VIP without a problem.

All devices at sites across our MPLS-connected WAN can access Exchange without problem using the NLB VIP, as well as clients connecting via VPN.

I can't figure out why remote sites, on different subnets can hit Exchange, but locally it doesn't work.

As a note: We have another network at our head office that sits behind a firewall. Clients were not able to access the VIP until a static ARP entry was put on the firewall.

Config is pretty straight forward.


4500-X Config:


VLAN 100

     name SERVER

VLAN 200

     name DESKTOP


interface VLAN100

     ip address

     no ip redirects


interface VLAN200

     ip address

     no ip redirects


mac address-table static 1111.1111.1111 vlan 100 interface Po1

arp 1111.1111.1111 ARPA







Hello.Could you draw a


Could you draw a diagram of interconnections between 4500, MPLS and Exchange?

Are you sure about MAC and port? Can you ping VIP address from 4500?

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