Which source IP is used by the kernel is determined primary by your
routing tables.This does not help, since if I want to use my secondary IP address
instead of my primary, I cannot delete the primary otherwise all of my
secondary IPs are lost as well (and since I can only have only one
primary IP address).
The requirements for an IP address to be allowed to be used in the
routing table is that the IP address does exists on any of your
interfaces, either as primary or secondary.
When you add/delete a primary address to a interface the kernel
automatically adds/deletes routes accordingly, including source IP
If the routing table does not have information about which source IP
address to use for this traffic then the kernel searches the interface
for a valid primary address.I update all the routing entries and eventually things start to work
again. The problem is that:
-If I use a secondary IP and try to invalidate the primary (i.e. by
removing its routing table entry), it takes about 500ms for the actual
change (data packets sent on the secondary IP instead of the primary) to
-If I try to update the primary address directly without creating any
secondary IP, then it still takes about 300ms for the change to take place.
I honestly do not understand what harm could do to have more than one
primary address, especially on different subnets.