Currently I am working on designing a network. The problem is that at a certain point I got confronted with a weird request. The client has made some thoughts of her/his own. Now I am troubled because my knowledge in this matter is not deep enough. I cannot pin point whether there are inherent problems with the request on its own and if there are how to convey them to the client. The request applies to two servers in particular and is as follows:
Physical Network(simplified):
router.eth0 <--> switch.eth0 | switch.eth1 <--> server1.eth0 | server1.eth1 <--> server2.eth0
Logical Network:
+----------+ +----------+ +----------+ +----------+
| router | | switch | | server1 | | server2 |
| untagged | <--> | untagged | | | | |
+----------+ | vlan 10 | <----+----------+----> | vlan 10 |
| | | untagged | <--> | untagged |
+----------+ +----------+ +----------+
So every request from the router is first tagged to vlan 10 and send to server1. server1 then forwards those packets onward to server2 while server1 is not reacting to vlan 10 packets. After that server2 untags the packets from vlan 10 and depending on the packet's content forwards some of them back to server1 or process them itself. Finaly server1 can respond to those packets as they are now untagged.
To preempt some suggestions: I know that it would be easier to just connect server2 directly to the router and server1 to server2 but the client insists on going that way if there are no security problems with this approach. The client also sets it as a requirement that all packets directed at server1 have to be processed by server2.
My problem now is whether an attacker could compromise this setup. So that if he gains control other the router. Can the attacker use the flow of packets through server1 to his advantage (exluding denial of service)? Could the attacker for example forge packets which could be directly addressed to server1 and to not flow through server2?
