Unique IP address for the daughter board

Question

Computer networks

Colleagues, tell me.

There is a device (let's call it "A") that works on the intranet, receives its IP via DHCP.

The next version of this device will contain an additional module (let's call it "B") - a daughter board, with its own OS. Communication between "A" and "B" will take place via TPC / IP, through an additional network interface. Device "B" does not need any connection with the LAN, it is desirable that they do not see each other at all.

Question - how to correctly assign an IP address for device "B"? Statically? But where is the guarantee that this address will never intersect with the address in the LAN? Dynamically? How exactly?

Answer 1

After reading the answers and comments on them, I would venture to offer more options:
1. When an interface configured via DHCP does not receive responses, it assigns an address like 169.254.XY, where XY is calculated by some algorithm from the MAC address.
2. IPv6
3. Well, as a brainstorming session: try assigning the address 127.0.0 to it. 2 . And set up routes, suddenly take off.

Answer 2

The addresses will not overlap if the two interfaces connected to A have different subnets. Accordingly, the interface connected to the Internet receives information about the subnet automatically. You need to look at them and assign a different subnet for another interface. If you write what OS, I think there will be specific instructions.

Answer 3

Or you can assign a reservation to the MAC address in DHCP or add it to the range of non-issued addresses.

Answer 4

And indeed, if the pool from which addresses are given from DHCP is known, bypass it when issuing address "B".

Answer 5

On startup, generate a random /30 subnet in the global address space. If the device will work on the intranet, then 100% will not cross anything. If the device is transferred to the Internet, then the probability of a jamb in routing is slightly more than 1:1000000000, and even if a jamb occurs, it can be easily solved by restarting the device.

Answer 6

The only correct solution for IPv4 that guarantees no conflicts is to register a PI network for this case via RIPE and allocate /30 from this network.
www.ripe.net/ripe/docs/ripe-524#8
Among the disadvantages is the annual fee.

Answer 7

And what is the option with IPv6 not suitable for? link-local addresses will depend on the poppy and are unlikely to intersect.