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Ubuntu and MacBook private network not connecting

I have a MacBook private address 172.20.20.20 and an ubuntu 10.0.0.172 and after searching the web it does not seem they can ssh to each other.

The MacBook did have an address of 10.0.0.29 and there were no problems ssh between them. But the macbook’s private address suddenly changed without me doing anything.

Since the MacBook arbitrarily changed its private IP, now neither laptop can access the other, although both can access www without any problems.

Anything on the internet posted on this?