Chapter 5
Configuring the Switch
42
48-Port 10/100 + 4-Port Gigabit Switch with WebView and Power over Ethernet
Spanning Tree > MSTP Interface Settings > MSTP Port Setting Detail
Designated Cost The cost for a packet to travel from this
port to the root in the current Spanning Tree configuration.
The slower the media, the higher the cost.
Designated Port The port priority and number of the
port on the designated bridging device through which the
Switch must communicate with the root of the Spanning
Tree.
Designated Bridge The bridge priority and MAC address
of the device through which this port must communicate
to reach the root of the Spanning Tree.
Path Cost This parameter is used by the STP to determine
the best path between devices. Therefore, lower values
should be assigned to ports attached to faster media, and
higher values assigned to ports with slower media. (Path
cost takes precedence over port priority.) Note that when
the Path Cost Method is set to “short,” the maximum path
cost is 65,535.
Range –
Ethernet: 200,000-20,000,000
Fast Ethernet: 20,000-2,000,000
Gigabit Ethernet: 2,000-200,000
Default –
Ethernet – Half duplex: 2,000,000; full duplex: 1,000,000;
LAG: 500,000
Fast Ethernet – Half duplex: 200,000; full duplex: 100,000;
LAG: 50,000
Gigabit Ethernet – Full duplex: 10,000; LAG: 5,000
Interface Priority Defines the priority used for this port
in the Spanning Tree Protocol. If the path cost for all ports
on a switch are the same, the port with the highest priority
(i.e., lowest value) will be configured as an active link in
the Spanning Tree. This makes a port with higher priority
less likely to be blocked if the Spanning Tree Protocol is
detecting network loops. Where more than one port is
assigned the highest priority, the port with lowest numeric
identifier will be enabled.
Default: 128
Range: 0-240, in steps of 16
Multicast
The Internet Group Management Protocol (IGMP) runs
between hosts and their immediately adjacent multicast
router/switch. IGMP is a multicast host registration
protocol that allows any host to inform its local router that
it wants to receive transmissions addressed to a specific
multicast group.
A router, or multicast-enabled switch, can periodically ask
their hosts if they want to receive multicast traffic. If there
is more than one router/switch on the LAN performing IP
multicasting, one of these devices is elected “querier” and
assumes the role of querying the LAN for group members.
It then propagates the service requests on to any adjacent
multicast switch/router to ensure that it will continue to
receive the multicast service.
Based on the group membership information learned
from IGMP, a router/switch can determine which (if any)
multicast traffic needs to be forwarded to each of its ports.
At Layer 3, multicast routers use this information, along
with a multicast routing protocol such as DVMRP or PIM,
to support IP multicasting across the Internet.
NOTE: IGMP neither alters nor routes IP
multicast packets. A multicast routing protocol
must be used to deliver IP multicast packets
across different subnetworks.
