Brocade Communications Systems Upgrade Pef IPMC5000PEF IPMC5000PEF Manual De Usuario

Forwarding mechanism in hardware

IP-based forwarding implementation on FCX and ICX devices

The following information about *,G or S,G fdb-based implementation is specific to FCX, ICX 6610, ICX
6430, ICX 6450, and ICX 6650 devices.

On both switch and router software images, MLD snooping is either *,G based or S,G based. The
hardware can either match the group address only (* G), or both the source and group (S, G) of the
data stream. The hardware can match only the lowest 32 bits of a 128 bit IPv6 address. This is 32-bit IP
address matching, not 32-bit multicast MAC address 33-33-xx-xx-xx-xx matching.

If MLDv2 is configured in any port of a VLAN, the VLAN uses an (S, G) match, otherwise it uses (* G).
Because the hardware can match only the lowest 32 bits of a 128 bit IPv6 address, the output interfaces
(OIF) of a hardware resource are the superset of the OIF of all data streams sharing the same lowest
32 bits. For example, if groups ff10::1234:5678:abcd and ff20::5678:abcd share the same hardware
resource, then the OIF of the hardware matching (* 5678:abcd) is the superset of these two groups.

MAC-based forwarding implementation on FastIron X Series and ICX 7750 devices

Multicast Listening Discovery (MLD) snooping on Brocade devices is based on MAC address entries.
When an IPv6 multicast data packet is received, the packet destination MAC is matched with the MAC
address entries in the IPv6 multicast table. If a match is found, packets are sent to the ports associated
with the MAC address. If a match is not found, packets are flooded to the VLAN and copied to the CPU.

For IPv6 multicast, the destination MAC address is in the format 33-33-xx-yy-zz-kk, where xx-yy-zz-kk
are the 32 lowest bits of the IPv6 multicast group address. For example, the IPv6 group address
0xFF3E:40:2001:660:3007:123:0034:5678 maps to the IPv6 MAC address 33-33-00-34-56-78.

For two multicast traffic streams, Source_1 and Group1 (S1,G1) and Source_2 and Group2 (S2,G2),
with the same or different source addresses, if the lowest 32 bits of the 128-bit IPv6 group address are
the same, they would map to the same destination MAC. Because FSX devices support MAC-based
forwarding for MLD snooping, the final multicast MAC address entry would be a superset of all the IPv6
groups mapped to it. For example, consider the following three IPv6 multicast streams sent from port 5
of a Brocade device:

•

(S1,G1) = (2060::5, ff1e::12), client port 1, port 2

•

(S2,G2) = (2060::6, ff1e:13::12), client port 2, port 3

•

(S3,G1) = (2060::7, ff1e::12), client port 4

Because the lowest 32 bits of the group address for G1 and G2 are the same, all three streams would
use 33-33-00-00-00-12 as the destination MAC address. MLD snooping would build a MAC entry with
the MAC address 33-33-00-00-00-12 on egress ports 1, 2, 3, and 4. As a result, all three streams would
be sent to ports 1, 2, 3, and 4. Note that the above example assumes the following:

•

The Brocade device is running MLD snooping on VLAN 10 and all three streams are in VLAN 10

•

There are clients on port 1 and port 2 for (S1,G1)

•

There are clients on port 2 and port 3 for (S2,G2)

•

There are clients on port 4 for (S3,G1)

Hardware resources for MLD and PIMv6 SM snooping

Brocade devices allocate/program fdb/mac entries and application VLAN (vidx) to achieve multicast
snooping in hardware. If a data packet does not match any of these resources, it might be sent to the
CPU, which increases the CPU burden. This can happen if the device runs out of hardware resource, or

Forwarding mechanism in hardware