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Restricting Layer 2 Flooding
Restricting Layer 2 Flooding is supported only on platform: e
t
When Layer 2 multicast traffic must be forwarded on a VLAN that has multiple ports with different speeds
on the same port-pipe, forwarding is limited to the speed of the slowest port. Restricted Layer 2 Flooding
prevents slower ports from lowering the throughput of multicast traffic on faster ports by restricting
flooding to ports with a speed equal to or above a link speed you specify.
For example, if a VLAN that has an (auto-negotiated) 100M port and a 1G port on the same port-pipe, and
you enable Restricted Layer 2 Flooding with a minimum speed of 1G, multicast traffic is only flooded on
the 1G port.
Enable Restricted Layer 2 Flooding using the command
restrict-flooding from INTERFACE VLAN mode.
In combination with
restrict-flooding, you can use the command mac-flood-list from CONFIGURATION
mode, without the
min-speed option, to allow some specific multicast traffic (identified using a MAC
address range you specify) to be flooded on all ports regardless of the
restrict-flooding configuration.
Conversely, if you want all multicast traffic to be flooded on all ports, but some specific traffic to be
restricted, use
mac-flood-list with the min-speed option, but without restrict-flooding configured. This
configuration restricts flooding only for traffic with destination multicast MAC addresses within the
multicast MAC address range you specify.
In Figure 25-9, flooding of unknown multicast traffic is restricted to 1G ports on VLAN100 using the
command
restrict-flooding. However, the command mac-flood-list allows traffic with MAC addresses
01:01:e8:00:00:00 to 01:01:e8:ff:ff:ff to be flooded on all ports regardless of link speed.
Figure 25-9. Restricting Layer 2 Multicast Flooding over Low Speed Ports
FTOS(conf)#$1:01:e8:00:00:00 ff:ff:ff:00:00:00 vlan 100-200,300
FTOS#show run | find mac-flood-list
mac-flood-list 01:01:e8:00:00:00 ff:ff:ff:00:00:00 vlan 100-200,300
[output omitted]
FTOS(conf)#interface vlan 100
FTOS(conf-if-vl-100)#restrict-flooding multicast min-speed 1000
FTOS(conf-if-vl-100)#show config
!
interface Vlan 100
restrict-flooding multicast min-speed 1000
no shutdown
FTOS(conf-if-vl-100)#