101 · Question #710
An administrator configures a custom MAC masquerade address on a redundant BIG-IP system. What will be the result?
The correct answer is C. The MAC masquerade address will only be used by the active unit. The standby unit in use the. In a BIG-IP redundant (HA) pair, the MAC masquerade address is only held by the active unit at any given time, enabling seamless failover without requiring gratuitous ARP updates across the network.
Question
An administrator configures a custom MAC masquerade address on a redundant BIG-IP system. What will be the result?
Options
- AThe administrator will be prompted during configuration to define which until will use the MAC
- BThe MAC masquerade address will be concurrently used by both active and standby unit
- CThe MAC masquerade address will only be used by the active unit. The standby unit in use the
- DThe MAC masquerade address will only be used by the un.t with higher unit ID. The other unit
How the community answered
(46 responses)- A7% (3)
- B15% (7)
- C76% (35)
- D2% (1)
Why each option
In a BIG-IP redundant (HA) pair, the MAC masquerade address is only held by the active unit at any given time, enabling seamless failover without requiring gratuitous ARP updates across the network.
BIG-IP does not prompt the administrator to choose which unit uses the MAC masquerade address during configuration - the active/standby state automatically determines ownership.
Both units cannot concurrently use the same MAC masquerade address; doing so would cause a MAC address conflict on the network and disrupt traffic.
A MAC masquerade address is a virtual MAC assigned to a traffic group on a BIG-IP HA pair so that failover does not require downstream devices to update their ARP caches. Only the currently active unit uses and responds with the MAC masquerade address; the standby unit retains its factory-assigned burned-in MAC and only assumes the masquerade MAC if it transitions to the active role.
MAC masquerade ownership is determined by active/standby unit state, not by unit ID; the unit with the higher unit ID is not guaranteed to be the active unit.
Concept tested: BIG-IP HA MAC masquerade address failover behavior
Source: https://techdocs.f5.com/en-us/bigip-17-1-0/big-ip-device-service-clustering-administration/using-mac-masquerade.html
Topics
Community Discussion
5
Brenda K.Nov 27, 2025C is your answer, and it is a quick win you should bank in under 30 seconds. In a redundant BIG-IP pair, the MAC masquerade address floats with the active unit so that upstream devices never have to relearn a MAC after a failover, and the standby unit simply holds that address in reserve until it takes over.
Luis F.Dec 16, 2025Yeah C is right, the MAC masquerade address floats with the active unit so when a failover happens the standby takes over that MAC and downstream devices never have to update their ARP tables. That is the whole point of MAC masquerade in a redundant pair, keeping traffic flowing without ARP flapping after a state change.
Hiroshi T.Dec 14, 2025The MAC masquerade address floats with the active unit so that downstream devices do not have to update their ARP tables after a failover, which is the whole point of the feature. Does anyone know off the top of their head whether the standby unit retains the MAC masquerade in its config but simply does not advertise it, or if it is fully suppressed until that unit becomes active?
Yusuf A.Nov 30, 2025D for sure, higher unit ID takes the masquerade, other one stays passive.
Luis F.Nov 30, 2025Hey Yusuf, actually it is C on this one, the router with the lower Bridge ID wins the election and becomes the root bridge, so higher does not take priority here.