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Chapter 3: Getting Started
50
Instead of disabling the link between the fabrics, the ISL could also be segregated into a VLAN
that is not used for the CPC5565s.
If the network architecture segregates the ports into VLANs to prevent loops, but there is a path
from one VLAN to the other, then an additional measure must be taken. While separation into
VLANs does prevent broadcast storms, having a path for packets between VLANs may cause
MAC address learning problems. This is illustrated in
Figure 3-12 .
The blue line illustrates a broadcast packet (eg. ARP) that is sent by the CPU's eth0 port. This
packet is sent through VLAN 1 on the embedded switch and forwarded to Host-A via the two
fabric switches. The packet is also sent back to the CPC5565 into VLAN 2 from Fabric-B. The
embedded switch sees the Source MAC address of eth0 and learns that MAC on the Fabric-B
port. If Host-A sends a packet (eg. ARP Reply) to that MAC address (red line), the fabric
switches deliver it to the CPC5565 on the correct port, but the embedded switch discards the
packet. This is because the target is a MAC that was learned in VLAN 2, but the ingress port is
in VLAN 1. This problem can be avoided by disabling MAC address learning. Refer to
“MAC
Address Handling Configuration,” on page 47 .
Figure 3-12: ISL Segregation and MAC Address Learning
Spanning Tree Redundancy
If you do not wish to include a high-availability protocol like:
• SCTP
• Linux Bonding
• Solaris Multipathing
Front Panel
Midplane
CPC5565
BCM5389
CPU
VLAN 1 VLAN 2
J8
ISL
eth0 eth1
J9
CPC5565
ISL
ane Midpla
Fabric-A Fabric-B
Host-A
eth0 eth1