[CentOS] how to enable Flow Control on CentOS?

[Giles Coochey]

On 10/07/2011 10:22, Charles Polisher wrote:
> Gigabit is different.
> My reading of the spec is that when a port is configured for 1GbE
> over 1000BASE-T (copper), "disabling" auto-negotiation disables the
> advertising of the auto-negotiation for 10BASE-T and 100BASE-T, but
> auto-negotiation is still advertised and operational for 1GbE.
> Auto-negotiation cannot be disabled for 1000BASE-X (optical fiber).
>
> Deviation from the spec would mean such kit is Ethernet-like.
> An ability to "set" auto-negotiation one way in the user interface
> while leaving the hardware in a different - standards conforming -
> state is possible.
>
Fiber is not a CSMA/CD medium, it's a Point to Point medium - Duplex is 
meaningless.

I've been referring to the Spec of 10/100 ports. For Gigabit ports 
1000Base-T, auto-negotiation is mandatory.

Quoting from Wikipedia [http://en.wikipedia.org/wiki/Autonegotiation]


    Interoperability problems

The first version of the autonegotiation specification, IEEE 802.3u, was 
open to different interpretations. Although most manufacturers 
implemented this standard in one way, some others, including network 
giant Cisco, implemented it in a different way. Autonegotiation between 
devices that implemented it differently failed. This led many network 
administrators to not depend on autonegotiation and instead manually set 
the speed and duplex mode of each network interface card. Even Cisco 
recommended its customers not to use autonegotiation. However, the use 
of manually set configuration often led to duplex mismatches, in 
particular when two connected devices are:

  * One manually set to half duplex and one manually set to full duplex
  * One set to autonegotiation and one manually set to full duplex
  * Both sides manually set to full duplex where one side still expects
    an autonegotiating link partner and the other side has
    autonegotiation completely disabled (the side that expects an
    autonegotiating link partner will fall back to half duplex because
    it does not detect a partner capable of full duplex)^[/citation
    needed/]

Duplex mismatch problems are difficult to diagnose because the network 
is apparently working, and simple programs used for network tests such 
as ping report a valid connection; however, the network is much slower 
than expected.

The debatable portions of the autonegotiation specifications were 
eliminated by the 1998 release of 802.3. This was later followed by the 
release of IEEE 802.3ab in 1999. The new standard specified that gigabit 
Ethernet over copper wiring requires autonegotiation. Currently, all 
network equipment manufacturers—including Cisco^[3] —recommend to use 
autonegotiation on all access ports. Cisco also recommends that you 
check back with them yearly for any potential changes in their 
recommendation as this has caused much confusion over the years. ^[4]

In some large installations that have had to deal with negotiation 
issues, network staff may believe that "autonegotiation doesn't work", 
and consider turning it off a best-practice. This should be avoided - 
once autonegotiation is turned off, it will not work by definition, 
creating a self-enforcing problem.



-- 
Best Regards,

Giles Coochey
NetSecSpec Ltd
NL T-Systems Mobile: +31 681 265 086
NL Mobile: +31 626 508 131
GIB Mobile: +350 5401 6693
Business Email: giles.coochey at netsecspec.co.uk
Email/MSN/Live Messenger: giles at coochey.net
Skype: gilescoochey


-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 4320 bytes
Desc: S/MIME Cryptographic Signature
URL: <http://lists.centos.org/pipermail/centos/attachments/20110710/fdf867ec/attachment.p7s>