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Port Trunking
Distributed Trunking
Maximum DT Trunks and Links Supported
Table 12-1 shows the maximum number of DT trunks and DT links that are
supported.
Table 12-1. Maximum DT Trunks and Links
Description Max Number
Maximum number of groups (DT trunks) in a DT switch (that is, 60
maximum number of servers supported)
Maximum number of switches that can be aggregated 2
Maximum number of physical links that can be aggregated in a
single switch from a server (that is, maximum number of ports
that can be in a trunk connected to a single switch)
4
From the server perspective, this means that there could be a maximum total
of 60 servers connected to two DT switches. Each server can have up to four
physical links aggregated in a single switch, meaning that a single server could
have a maximum of eight links (that is, four on each DT switch) in a DT trunk.
Forwarding Traffic with Distributed Trunking and
Spanning Tree
Refer to figure 12-17 for the following discussion about forwarding traffic
when spanning tree is enabled. In this example, it is assumed that traffic is
sent through switch B from a host to a server and from the server back to the
host. STP can block any one of the upstream links; in this example STP has
blocked all the links except the I1 link connected to DT1.
Forwarding Unicast Traffic Upstream
The server uses load balancing when it sends traffic to a DT switch. The load
balancing is usually based on a SA/DA (source address/destination address)
combination. See “Outbound Traffic Distribution Across Trunked Links” on
page 12-37 for more information.
If unicast traffic is received on switch DT1, and the switch knows the desti-
nation MAC address of any of the devices on the upstream links, such as on
link I1, it forwards the unicast frames upstream using link I1. If switch DT2
receives the unicast traffic from the server, the destination MAC address was
already learned on the DT1 link, so the traffic is forwarded to the DT1 switch,
which then forwards the traffic upstream on link I1.
12-32