I'm reading strom-comtrol feature but I'm confusing about DLF (destination lookup failure) What kind of DLF packet? I'm thinking it's non-unicast packet, right?



1 Answer 1


A destination lookup failure happens when the switch hasn't learned the port association for a frame's unicast destination address and needs to flood the frame, mimicking a repeater hub or a shared medium.

DLFs don't really happen in practice but a switch must be equipped to handle them. Effectively, a DLF frame is forwarded the same way as a broadcast or a multicast frame (without snooping/filtering), thus causing the same problems with a bridge loop.

Note that simply limiting a broadcast storm removes the most imminent effect of a bridge loop, but it doesn't entirely solve the problem. Bluntly limiting the rate of broad/multicast frames (=dropping any frame that exceeds the limit) impacts the reliability of broad/multicast-based communication (primarily ARP and NDP). It does enable continued unicast traffic instead of drowning it out, but the network is not entirely operational.

In contrast, a proper loop-free forwarding structure created by a spanning tree protocol (like MSTP, RSTP or RPVST+) or e.g. shortest path bridging guarantees a fully operational network with redundant links.

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