A one-armed router is a router that routes traffic between
virtual local area networks (VLANs). A one-armed router operates
on the 80/20 rule, which states that 80% of traffic in a network
remains within a virtual local area network and doesn't need
routing service. The other 20% of network traffic is between
VLANs and goes through the one-armed router. Because the one-
armed router takes care of the more intensive traffic between
VLANs, it frees the primary data path in a network for inter-
VLAN traffic. In order for a one-armed router to be beneficial,
the VLAN must be configured to the 80/20 rule. One disadvantage
of using the one-armed router structure is that it represents a
single point of failure in a network. Another disadvantage is it
can develop into a bottleneck if there are large amounts of
traffic between VLANs.