User guide

6
The advantage of arranging switches as a line cascade is that the communication
links between them effectively form a simple bus structure that avoids the IGMP
traps encountered by the pyramid arrangement.
Layer 2 Switch
Layer 2 Switch
20GB link
10GB link
1GB links
ALIF TX
ALIF RX
ALIF RX
ALIF RX
ALIF RX
ALIF RX
ALIF RX
ALIF TXALIF RX
ALIF RXALIF RX
ALIF TX
Layer 3
Switch
(Querier)
A signicant requirement in line cascades is the need for sizeable bandwidth
between the switches in order to provide redundancy and in so doing prevent
data bottlenecks. When linking 48 port switches, generally a 20GB link bandwidth
is required between the Layer 3 switch and the rst switch. A 10GB link
bandwidth is then required between the rst and second switches. The reason for
this become clearer when data paths are added to the diagram.
The streaming output from any transmitting device must travel up to the Querier,
even if a recipient is located on the same switch as the transmitter. Given that the
top layer 2 switch must also pass up and down all data from the lower switch, this
is the reason for its double bandwidth link with the L3 switch.
The links between switches could either be multiple Gigabit Ethernet connections
or, more favourably, bre channel connections. Due to the interlink bandwidths
required to prevent bottlenecks, it is recommended that there are no more than
two cascade levels in any single line cascade arrangement.
ALIF TXALIF RX
ALIF RXALIF RX
Layer 2 Switch
Layer 2 Switch
ALIF TX
ALIF RX
ALIF RX
ALIF RX
ALIF RX
ALIF RX
ALIF RX
ALIF TX
Layer 3
Switch
(Querier)