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White Paper Issue: October 2006 Integration of BX600 SB9 Switches in Cisco Networks Page 4 / 47
2 Switch Connectivity
2.1 Auto Negotiation
2.1.1 Introduction
The SB9 is equipped with at least six Gigabit Ethernet ports which are implemented as specified in the 1000BaseT standard.
(Since ten Gigabit Ethernet is not usual in datacenters’ server access layer, the 10GBaseCX4 and XFP interfaces that are also
available are not covered here.)
These ports can be run with different data rates and different duplex settings comparable to Cisco Switches. Table 1 shows the
possible combinations of a Cisco Switch and an SB9. Only the combinations marked green are viable: the combinations marked
red are risky because they will lead to a duplex failure.
SB9
Fix Half Duplex 10
Fix Half Duplex 100
Fix Full Duplex 10
Fix Full Duplex 100
Auto
Fix Half Duplex 10 Ok N/A BAD
N/A Ok
Fix Half Duplex 100 N/A
Ok N/A BAD
Ok
Fix Full Duplex 10 N/A
N/A Ok N/A BAD
Fix Full Duplex 100 N/A
BAD
N/A Ok BAD
Fix Full Duplex 1000 N/A
N/A N/A N/A Ok
Cisco Switch
Auto Ok Ok BAD
BAD
Ok
Table 1 : Speed and Duplex Settings
During the ports’ autonegotiation phase the flow control mechanism can also be negotiated. Switches are not the best location
for buffering packets during congestion; this mechanism should therefore not be activated on links between switches but
preferably between servers and switches. In this case the server would be able to buffer the packets if the switch were to detect
congestion on the uplink. Since flow control depends very much on the server hardware and software, this issue is not covered
in this paper.
2.1.2 Recommended Solution
We recommend setting the ports on both sides to auto negotiation. In this setting the switches will negotiate their capabilities
and will find the best possible setting. When connected to the usual 1000BaseT port of a Cisco switch using a crossover or
straight thru 8 wire Cat5E, or (better) a patch cable, the SB9 will negotiate 1000 Mbit with full duplex.
Flow control should be disabled between switches.
2.1.3 Configuration
You set a port of the SB9 (e.g. 0/12) to auto negotiation and no flow control by entering the following commands in configuration
mode:
interface 0/12
negotiate
no storm-control flowcontrol
exit
Here is the corresponding Cisco configuration:
interface GigabitEthernet0/2
speed auto
duplex auto
flowcontrol receive off
end