Ethernet speed and duplex configuration

   September 21, 2009  Leave a comment

Speed mismatching issues may result in no connectivity. However, issues withauto-negotiation of duplex generally do not result in link establishment issues. Instead, auto-negotiation issues mainly result in performance-related issues. The most common problems when investigating NIC(Network Interface Card) issues deal with speed and duplex configuration. The table below summarizes all possible settings of speed and duplex for FastEthernet NICs and switch ports.

 

NIC
(Speed
/Duplex)		 Switch
(Speed
/Duplex)		 Result on
NIC		 Result on
Switch		 Comments
AUTO AUTO 1000 Mbps,
Full-duplex		 1000 Mbps,
Full-duplex		 Gigabit port support only Fullduplex
1000 Mbps
/Full-duplex		 AUTO 1000 Mbps
/Full-duplex		 1000 Mbps
/Full-duplex		 Link is established, but the switch does not see any autonegotiation information from NIC.
Since Switch supports only full-duplex operation with 1000 Mbps, they default to full-duplex, and this happens only when operating at 1000 Mbps.
1000 Mbps
/Full-duplex		 1000 Mbps
/Full-duplex		 1000 Mbps
/Full-duplex		 1000 Mbps
/Full-duplex		 Manually Configured
100 Mbps
/Full-duplex		 1000 Mbps
/Full-duplex		 No Link No Link Speed mismatch
100 Mbps
/Full-duplex		 AUTO 100 Mbps
/Full-duplex		 100 Mbps
/Half-duplex		 Duplex Mismatch
AUTO 100 Mbps
/Full-duplex		 100 Mbps
/Half-duplex		 100 Mbps
/Full-duplex		 Duplex Mismatch
100 Mbps
/Full-duplex		 100 Mbps
/Full-duplex		 100 Mbps
/Full-duplex		 100 Mbps
/Full-duplex		 Manually Configured
100 Mbps
/Half-duplex		 AUTO 100 Mbps
/Half-duplex		 100 Mbps
/Half-duplex		 Switch does not see any autonegotiation information from NIC and defaults to halfduplex when operating at 10/100 Mbps.
10 Mbps /Halfduplex AUTO 10 Mbps /Halfduplex 10 Mbps /Halfduplex switch does not see Fast Link Pulse (FLP) and defaults to 10 Mbps half-duplex.
10 Mbps /Halfduplex 100 Mbps
/Half-duplex		 No Link No Link Speed mismatch.
AUTO 100 Mbps
/Half-duplex		 100 Mbps
/Half-duplex		 100 Mbps
/Half-duplex		 NIC does not see any autonegotiation information and
defaults to 100 Mbps, half-duplex.
AUTO 10 Mbps /Halfduplex 10 Mbps /Halfduplex 10 Mbps /Halfduplex NIC does not see Fast Link Pulse(FLP) and defaults to 10 Mbps, half-duplex.

** Any questions, email us or check Cisco.com site.

Reference: http://www.cisco.com/warp/public/473/46.html

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