Multiple ipv6 addresses on an interface

To prevent being tracked on the intertubes, ipv6 has security extensions that, (if they are enabled via sysctl net.ipv6.conf.all somewhere), from time to time creates random a address, and expire the old ones for outgoing traffic. To see the addresses do

ip -6 addr

and look for temporary.  The expired addresses (that still work) have the word "deprecated".  If you get sick of seeing them, delete an address from an interface with

ip -6 addr del dev eth0

or delete all deprecated addresses like this

ip -6 addr | awk '/deprecated/ {print "ip -6 addr del " $2 " dev eth0"}' | sudo bash -s