LAN9353 Datasheet, PDF (219/523 Pages) Microchip Technology – Interfaces at up to 200Mbps via Turbo MII

LAN9353
10.3.7 BROADCAST STORM CONTROL
In addition to ingress rate limiting, the device supports hardware broadcast storm control on a per port basis. This fea-
ture 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 10-3. When a port is receiving at 10 Mbps, any setting above 34
has the effect of not limiting the rate.
TABLE 10-3: TYPICAL BROADCAST RATE SETTINGS
Broadcast Throttle Level
Bandwidth
252
75 Mbps
168
50 Mbps
134
40 Mbps
67
20 Mbps
34
10 Mbps
17
5 Mbps
8
2.4 Mbps
4
1.2 Mbps
3
900 kbps
2
600 kbps
1
300 kbps
In addition to the rate limit, the Buffer Manager Broadcast Buffer Level Register (BM_BCST_LVL) specifies the maxi-
mum number of buffers that can be used by broadcasts, multicasts and unknown unicasts.
10.3.8 IPV4 IGMP / IPV6 MLD SUPPORT
The device provides Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) hardware
support using two mechanisms: IGMP/MLD monitoring and Multicast Pruning.
On ingress, if the Enable IGMP Monitoring field in the Switch Engine Global Ingress Configuration Register (SWE_-
GLOBAL_INGRSS_CFG) is set, IGMP multicast packets are trapped and redirected to the MLD/IGMP Monitor Port (typ-
ically 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.
On ingress, if the Enable MLD Monitoring field in the Switch Engine Global Ingress Configuration Register (SWE_-
GLOBAL_INGRSS_CFG) is set, MLD multicast packets are trapped and redirected to the MLD/IGMP Monitor Port (typ-
ically set to the port to which the host CPU is connected). MLD packets are identified as IPv6 packets with a Next Header
value or a Hop-by-Hop Next Header value of 58 decimal (ICMPv6). Optionally, via the Enable Other MLD Next Headers
field in the Switch Engine Global Ingress Configuration Register (SWE_GLOBAL_INGRSS_CFG), IPv6 Next Header
values or Hop-by-Hop Next Header values of 43 (Routing), 44 (Fragment), 50 (ESP), 51 (AH) and 60 (Destination
Options) can be enabled. Optionally, via the Enable Any MLD Hop-by-Hop Next Header field in the Switch Engine Global
Ingress Configuration Register (SWE_GLOBAL_INGRSS_CFG), all Hop-by-Hop Next Header values can be enabled.
Both Ethernet and IEEE 802.3 frame formats are supported as are VLAN tagged packets.
Note:
There is a limitation with packets using the IEEE 802.3 frame format. For single and double (such as in the
case of a CPU tag and VLAN tag) tagged packets, the Hop-by-Hop Next Header value can not be reached
within the 64 byte processing limit and therefore would not be detected.
Once the IGMP or MLD 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 10.3.1.3, "Mul-
ticast Pruning," on page 208. The host software should also forward the original IGMP or MLD packet if necessary.
 2015 Microchip Technology Inc.
DS00001925A-page 219