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DM9006 Datasheet(PDF) 63 Page - Davicom Semiconductor, Inc.

Part No. DM9006
Description  10/100 Mbps 2-port Ethernet Switch Controller with General Processor Interface
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Maker  DAVICOM [Davicom Semiconductor, Inc.]
Homepage  http://www.davicom.com.tw
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DM9006 Datasheet(HTML) 63 Page - Davicom Semiconductor, Inc.

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DM9006
2-port Switch with Processor Interface
Preliminary datasheet
63
DM9006-13-DS-P01
September 1, 2009
9.2.17 IGMP Snooping
IGMP introduction
The Internet Group Management Protocol (IGMP) is
a communications protocol used to manage the
membership of Internet Protocol multicast groups.
IGMP is used by IP hosts and adjacent multicast
routers to establish multicast group memberships.
There are three versions of IGMP, as defined by
"Request for Comments" (RFC) documents of the
Internet Engineering Task Force (IETF). IGMP v1 is
defined by RFC 1112, IGMP v2 is defined by RFC
2236 and IGMP v3 is defined by RFC 3376.
IGMP snooping is a feature that allows the switch to
"listen in" on the IGMP protocol conversation
between hosts and routers.
The IGMP snooping switch hears an IGMP report
from a host with a given multicast group address. It
adds the host's port number to the multicast list for
that group, and when the switch hears an IGMP
Leave, it removes the host's port from the table entry.
Finally, switch will only forward multicast traffic to the
hosts interested in that traffic. Therefore, this function
can effectively reduce multicast traffic.
Hardware-based IGMP Snooping
The DM9016 supports IGMP v1/v2 snooping and the
maximal group is 16 without any software effort.
The DM9016 automatically manipulates and updates
IGMP
membership
table
and
Multicast
table
according to IGMP control packets, such as
membership report and leave.
If IGMP membership table is full, the later incoming
IGMP Membership Report (Join) packet will be
ignored and the group address won’t be registered
into
multicast
address
table.
After
that,
the
unregistered IP multicast packets (the destination
MAC address can not be found in the multicast
address table) will be treated as normal multicast
packets by default. The additional forwarding control
method can see the register Reg78H.[6:5].
The DM9016 supports router ports auto-detect and
auto-aging mechanism. The port which receives
IGMP Query packets will be treated as router port by
default. The router port also can be define as static
one by user (see Reg78H.4) and the port map of the
router port can be programmed at Reg79H.[2:0].
Keep in mind that the uP port (port 3) is never treated
as router port. The DM9016 leaves the router port if
the time (Router Present Timeout, 400sec by default)
is expired that the port never receives IGMP Query
during this period.
If receiving V1REPORT or V2REPORT (group join),
DM9016 creates new or updates the entry. If
receiving LEAVE, DM9016 deletes the entry directly
when Fast Leave is enabled, or waiting until timeout.
DM9016 removes the entry that was never updated
after the timer of host timeout (Group Membership
Interval) is expired. This timer is programmable in
DM9016 and defined by RFC 2236 as ((the
Robustness Variable) times (the Query Interval)) plus
(one Query Response Interval). The setting of the
Robustness Variable and the Query Interval can see
Reg7AH and Reg7BH.
9.2.18 Port Security
DM9016 supports three types of port security function
on each port, see the Port Security & STP Register
(Reg6CH.[1:0]).
(1). First Lock:
The DM9016 locks the source MAC address of first
received packet on the port and the disables the
learning function in this mode.
After that, on detecting incoming packet, the DM916
compares source MAC address of incoming with the
locked one. The DM9016 forwards the packet if
match, or drops by default.
If port’s link status is changed, the first received
packet would be locked again after link on. It’s
noticeable that the previous one was kept in address
table until aging out or removed by user.
(2). First Link Lock:
The lock scheme is same as first lock except that
don’t lock again when link status is changed.
(3). Assign Lock:
The DM9016 allows user to assign the locked entries
by programming instead of dynamic learning. The
port’s learning function is disabled in this mode.
9.2.19 IPv6 MLD Snooping
The DM9016 forwards the IPv6 Multicast Listener Discovery
(MLD) packets to the processor port when MLD Snooping is
enabled and the MLD packets meet following scenario:


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