Paradyne BitStorm 2400, Руководство пользователя

Страница: 24 / 90

1. BitStorm 2400 Overview
1-14
December 2002 2400-A2-GB20-10
Multicast Implementation
The BitStorm 2400 supports the efficient forwarding, traffic shaping and
accounting for multicast flows.
The BitStorm 2400 listens for IGMP V1 or IGMP V2 messages. Upon hearing a
solicited or unsolicited report message for group, the BitStorm 2400 must build or
update a group-to-interface table entry to record the IGMP Group for which the
report message was generated, the IGMP Version of the reporting host, the IP
DSLAM port on which the report was heard, and reset a timer value to indicate the
last report relative time.
Due to the Report Suppression techniques implemented by IGMP hosts, the
BitStorm 2400 will typically only see one or two report messages for a specific
group from each port regardless of the number of interested hosts there may be.
The BitStorm 2400 may attempt to map the IGMP Report originators MAC address
to a shared MAC address table to map the Report message to a port. The tables
must be updated such that they reflect a single row for each multicast group on
each interface. The table must also note if any IGMP V1 format reports have been
received from hosts in that group.
If the IGMP Report message was forwarded in a tagged Ethernet frame, the VLID
information for that report should be noted in the table. The BitStorm 2400 must
keep a table entry for each multicast group learned on each tagged VLAN for each
port. VLANs in this mode of operation will be used to sub-address one or more
ports on a specific chassis.
IGMP Report Messages
On receipt of IP multicast packets at the BitStorm 2400, the group address is
extracted from the IP header information and compared to the values in the group-
to-interface forwarding table. The multicast packets are scheduled and forwarded
only to those interfaces that have at least one interested host.
Multicast packets may need to be replicated and forwarded to multiple interfaces
from the BitStorm 2400. One multicast packet must be sent to each
BitStorm 2400: VLAN logical interface with at least one reporting host interested in
that group.
For each VLAN tagged interface, a copy of the packet must be created with a
VLAN tag inserted and the packet CRC recalculated. The tagged packet may then
be scheduled for forwarding. Reserved Class D addresses, for example, all-hosts
(224.0.0.1), all-routers (224.0.0.2), should be forwarded on all interfaces
regardless of the IGMP table entries.