ROS 3.30 on RB1000 work as IPSec/PPTP server.
I start achieve a strange problem after a long time using ROS 
I enable proxy-arp on ether4-lan (for assign IP-address to VPN-PPTP clients from same subnet).
Problem:
When i try to add secondary IP-address(really any address from any subnet) to PC(WinXP) as alias, it say “ip conflict detected”.
In system log i find MAC-address of conflicting machine, it is address of ROS ether4-lan interface.
In ROS arp-table i see the same thing, “secondary IP” - “MAC of ROS ether4-lan interface”.
If i disable proxy-arp, problem disappears.
Ideas?
Additional information:
If disable/enable PC interface(or add second IP on disabled if, and then enable it) - no conflict appears.
Win7 - get ip normally, WinXP - got a error
Same effect if just enable “proxy-arp” on interface, instead “enabled”.
I test on RB493 ROS3.30 - same result.
Hi, It’s been a while since your problem. but now I’am having the same issue.
I have RB750 acting as nat router + pptp server and in LAN PC who have 2 ip address in the same interface I have that problem
how did you figure it out?
Add a static ARP entry on the router that maps the secondary IP to the MAC address of the host.
The router does what it’s supposed to do when proxy ARP is enabled: if it doesn’t know the ARP mapping for a host and is asked an ARP question it replies with its own record. When you assign the secondary IP the host first asks the network if that IP is already in use by trying to resolve it via ARP. The router responds just like you told it to, and the host takes that to mean that it detected a duplicate address.
Generally the preferred solution would be to use routed subnets for VPN and not use the ugly hack that is proxy ARP at all.