3Com OfficeConnect WX1200 Release Note page 14

14 W LAN S
IRELESS WITCH AND
Distributed MAP Best Practice When Using STP
A Distributed MAP is a leaf device. You do not need
to enable STP on the port that is directly connected to
the MAP.
If Spanning Tree Protocol (STP) is enabled on the port
that is directly connected to a Distributed MAP, you
might need to change the STP configuration on the
port, to allow the MAP to boot.
STP on a port directly connected to a Distributed MAP
can prevent the MAP from booting.
As part of the boot process, a MAP disables and reen-
ables the link on the port over which the MAP is
attempting to boot. If STP is enabled on the device
that is directly connected to the port, the link state
change can cause the port on the other device to
leave the forwarding state and stop forwarding traf-
fic. The port remains unable to forward traffic for the
duration of the STP forwarding delay.
A MAP waits 30 seconds to receive a reply to its
DHCP Discover message, then tries to boot using the
other MAP port. If the boot attempt fails on the other
port also, the MAP then reattempts to boot on the
first port. The process continues until a boot attempt
is successful. If STP prevents the other device's port
from forwarding traffic during each boot attempt, the
MAP repeatedly disables and reenables the link, caus-
ing STP to repeatedly stop the other device's port
from forwarding traffic. As a result, the boot attempt
is never successful.
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To allow a MAP to boot over a link that has STP
enabled, do one of the following on the other device:
Disable STP on the other device's port.
Enable the port fast convergence feature, if sup-
ported, on the other device's port. (On some ven-
dors' devices, this feature is called PortFast.)
Use IGMP Snooping Effectively
Using IGMP (11909, 12863, 12866)
MSS supports the Internet Engineering Task Force
(IETF) draft draft-ietf-magma-snoop for controlling
the forwarding of IP multicast traffic by a Layer 2
switch. The draft mandates the use of a 0.0.0.0
source IP address if no IP address is available on the
switch for the subnet. However, some multicast rout-
ers and even other Layer 2 switches report errors in
the presence of the 0.0.0.0 source IP address.
Apply the following methods to use IGMP snooping
effectively:
Set IP addresses on all VLAN interfaces. This
straightforward workaround prevents most known
issues. If querier functionality might be needed,
ensure that the IP address of the WX switch VLAN
is higher than the address of any multicast router
servicing the same subnet.
Consider disabling IGMP proxy reporting. The
IGMP proxy reporting function is enabled by
default, but some multicast routers do not accept
reports using a 0.0.0.0 source IP address. In this
case, either assign an IP address to the VLAN inter-