LAN9311 Datasheet, PDF (74/461 Pages) SMSC Corporation – Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Datasheet
6.4.7
Broadcast Storm Control
In addition to ingress rate limiting, the LAN9311/LAN9311i supports hardware broadcast storm control
on a per port basis. This feature is enabled via the Switch Engine Broadcast Throttling Register
(SWE_BCST_THROT). The allowed rate per port is specified as the number of bytes multiplied by 64
allowed to be received every 1.72 mS interval. Packets that exceed this limit are dropped. Typical
values are listed in Table 6.4. When a port is receiving at 10Mbps, any setting above 34 has the effect
of not limiting the rate.
Table 6.4 Typical Broadcast Rate Settings
Broadcast Throttle Level
252
168
134
67
34
17
8
4
3
2
1
Bandwidth
75 Mbps
50 Mbps
40 Mbps
20 Mbps
10 Mbps
5 Mbps
2.4 Mbps
1.2 Mbps
900 Kbps
600 Kbps
300 Kbps
6.4.8
In addition to the rate limit, the Buffer Manager Broadcast Buffer Level Register (BM_BCST_LVL)
specifies the maximum number of buffers that can be used by broadcasts, multicasts, and unknown
unicasts.
IPv4 IGMP Support
The LAN9311/LAN9311i provides Internet Group Management Protocol (IGMP) hardware support
using two mechanisms: IGMP monitoring and Multicast Pruning.
On ingress, if IGMP packet monitoring is enabled in the Switch Engine Global Ingress Configuration
Register (SWE_GLOBAL_INGRSS_CFG), IGMP multicast packets are trapped and redirected to the
IGMP monitoring port (typically set to the port to which the host CPU is connected). IGMP packets are
identified as IPv4 packets with a protocol of 2. Both Ethernet and IEEE 802.3 frame formats are
supported as are VLAN tagged packets.
Once the IGMP packets are received by the host CPU, the host software can decide which port or
ports need to be members of the multicast group. This group is then added to the ALR table as detailed
in Section 6.4.1.3, "Multicast Pruning," on page 64. The host software should also forward the original
IGMP packet if necessary.
Normally, packets are never transmitted back to the receiving port. For IGMP monitoring, this may
optionally be enabled via the Switch Engine Global Ingress Configuration Register
(SWE_GLOBAL_INGRSS_CFG). This function would be used if the monitoring port wished to
participate in the IGMP group without the need to perform special handling in the transmit portion of
the driver software.
Revision 2.0 (02-14-13)
74
DATASHEET
SMSC LAN9311/LAN9311i