This might be a pedestrian question but what is the difference between a "Floating IP" address and a "Virtual IP" address? Are they synonyms?
To me, the terms mean different things.
A floating IP address is used to support failover in a high-availability cluster. The cluster is configured such that only the active member of the cluster "owns" or responds to that IP address at any given time. Should the active member fail, then "ownership" of the floating IP address would be transferred to a standby member to promote it as the new active member. Specifically, the member to be promoted issues a gratuitous ARP, announcing the new MAC address–to–IP address association.
A virtual IP address refers to the IP address of a virtual server, and is a more nebulous term. With F5 load balancers, for example, the virtual servers are the services (websites, etc.) you want to host.
More concretely, suppose you have a pair of load balancers in an active-standby cluster. For each interface or VLAN, the load balancers would each have a self IP address, as well as a floating IP address that is shared between both members. When the load balancer relays incoming requests to the back-end nodes, it uses the floating IP address as the source address, so if the load balancer dies, its partner will be able to take over and receive the response. Each website or other service being hosted on the load balancers would have its own IP address, which you could call a "virtual" IP address. (You could say that these virtual IPs "float" as well, since control of them would transfer to the standby node in the event of a failover.)
No, both are very similar but are usually used in different contexts.
Virtual IP (or
VIP) normally is used as a term to express the fact, that an IP does not belong to one specific physical interface. In that sense the
VIP is independent of a physical interface (in Physics particles which lack a physical representation are called
virtual. Looks like IPs without a physical interface are terefor called
virtual, too). Hence, a non-virtual IP is meant to go up and down with it's interface and belong only one single interface, while a
VIP can break out of this in several ways (it even is possible to exist on more than one interface at the same time, very like virtual particles can exist inside and outside of a black hole at the same time - see https://en.wikipedia.org/wiki/Hawking_radiation).
Floating IP (or
FIP) seems to be the term coined by some failover/virtual hosting solutions to name the public reachable outside IP address (some even reserve the term
FIP to IPs from the public IP area).
So following is true:
FIPnormally is a
VIP, too, but there are exceptions
VIPcan be a
FIPwhen used in certain setups
FIPusually means much more than just a special form of
It probably is not wise to use the terms interchangeably or to think, they are the same.
If you use the term
FIPfor an IP on a virtual interface, you probably will confuse many people and should stick to callig it
There may be more than one
VIPs which refer to the same
FIP, for example the external
VIP(which comes from the public IP area) and the internal "natted"
VIP(which usually comes from the private IP area) of this
FIP. So if you use the term
VIPhere, this will create a grave misunderstanding.
To add to the confusion, let's have a look into Wikipedia:
bezeichnet die dynamische IP-Adresse eines Aktiv/Passiv-Clusters, unter der das momentan aktive Primärsystem adressiert ist
Hence, according to German Wikipedia,
VIP ⊂ FIP.
A virtual IP address (VIP or VIPA) is an IP address that doesn't correspond to an actual physical network interface (port). Uses for VIPs include Network Address Translation (especially, One-to-many NAT), fault-tolerance, and mobility.
Hence the English Wikipedia tells a completely different story, namely
FIP ⊂ VIP
And as both articles are contradicting, please do not fall into the trap to think
FIP ≡ VIP
To sum it up:
Virtual IPis a well known technical common term, used for IPs which are not bound strictly to one single interface
Floating IPusually is more or less marketing speak to denote a specially used IP which most often, but not always, is a
A FIP which is access-able publicly can point to a VIP which is shared by multiple backends. So when one backend is down the request can fail over to another backend without changing the FIP
Practical example of using VIP and FIP in OpenStack