Limitation In Multi-Auth Per User Vlan Assignment - Cisco Catalyst 2960-X Security Configuration Manual

802.1x Multiple Authentication Mode
The number of hosts per multi-auth port is 8, however there can be more hosts.
The Multi-auth Per User VLAN assignment feature is not supported for Voice domain. All clients in Voice
Note
domain on a port must use the same VLAN.
The following scenarios are associated with the multi-auth Per User VLAN assignments:
Scenario one
When a hub is connected to an access port, and the port is configured with an access VLAN (V0).
The host (H1) is assigned to VLAN (V1) through the hub. The operational VLAN of the port is changed to
V1. This behaviour is similar on a single-host or multi-domain-auth port.
When a second host (H2) is connected and gets assigned to VLAN ( V2), the port will have two operational
VLANs (V1 and V2). If H1 and H2 sends untagged ingress traffic, H1 traffic is mapped to VLAN (V1) and
H2 traffic to VLAN (V2), all egress traffic going out of the port on VLAN (V1) and VLAN (V2) are untagged.
If both the hosts, H1 and H2 are logged out or the sessions are removed due to some reason then VLAN (V1)
and VLAN (V2) are removed from the port, and the configured VLAN (V0) is restored on the port.
Scenario two
When a hub is connected to an access port, and the port is configured with an access VLAN (V0). The host
(H1) is assigned to VLAN (V1) through the hub. The operational VLAN of the port is changed to V1.
When a second host (H2) is connected and gets authorized without explicit vlan policy, H2 is expected to use
the configured VLAN (V0) that is restored on the port. A ll egress traffic going out of two operational VLANs,
VLAN (V0) and VLAN (V1) are untagged.
If host (H2 ) is logged out or the session is removed due to some reason then the configured VLAN (V0) is
removed from the port, and VLAN (V1) becomes the only operational VLAN on the port.
Scenario three
When a hub is connected to an access port in open mode, and the port is configured with an access VLAN
(V0) .
The host (H1) is assigned to VLAN (V1) through the hub. The operational VLAN of the port is changed to
V1. When a second host (H2) is connected and remains unauthorized, it still has access to operational VLAN
(V1) due to open mode.
If host H1 is logged out or the session is removed due to some reason, VLAN (V1) is removed from the port
and host (H2) gets assigned to VLAN (V0).
The combination of Open mode and VLAN assignment has an adverse affect on host (H2) because it has
Note
an IP address in the subnet that corresponds to VLAN (V1).

Limitation in Multi-auth Per User VLAN assignment

In the Multi-auth Per User VLAN assignment feature, egress traffic from multiple vlans are untagged on a
port where the hosts receive traffic that is not meant for them. This can be a problem with broadcast and
multicast traffic.
Catalyst 2960-X Switch Security Configuration Guide, Cisco IOS Release 15.0(2)EX
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Configuring IEEE 802.1x Port-Based Authentication
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