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Duplex.. full, half, auto?

Posted on 2005-03-23
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Last Modified: 2012-06-27
We seem to be having issues with our LAN. As you can see in the logs below we are getting errors and dropped packets.
Here are the logs from the trusted interface of our router and also the logs from our traffic monitor which is showing the duplex changing from half to full frequently for device IP 192.168.1.11.
Pease have a look and let me know what you think could resolve this.
Thanks for the help.
JC

eth1 Link encap:Ethernet HWaddr 00:90:7F:2E:D5:C7
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:2
RX packets:257412 errors:207 dropped:0 overruns:207 frame:0
TX packets:329778 errors:0 dropped:2112 overruns:0 carrier:0
Collisions:0
Interrupt:5 Base address:0xc000



02/19/05 19:59 kernel: eth1: Setting half-duplex based on MII #32 link partner ability of 0000.
02/20/05 04:15 kernel: eth1: Setting full-duplex based on MII #32 link partner ability of c5e1.
02/20/05 04:15 dhcpd[130]: DHCPACK on 192.168.1.11 to 00:0f:1f:d0:e4:10 via eth1
02/20/05 04:45 dhcpd[130]: saved DHCP lease database
02/20/05 05:22 kernel: eth1: Setting half-duplex based on MII #32 link partner ability of 0000.
02/20/05 20:10 dhcpd[130]: DHCPACK on 192.168.1.11 to 00:0f:1f:d0:e4:10 via eth1
02/20/05 20:10 kernel: eth1: Setting full-duplex based on MII #32 link partner ability of c5e1.
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Question by:PCLANTECHS
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13 Comments
 
LVL 24

Expert Comment

by:SunBow
ID: 13617702
I like full, but in ethernet most seem to prefer half.

Know that you cannot do both.  Pick one and stick with it religiously.

That means, never let a PC get a NIC installed to autodetect, autoconfigure anything like that.  Always manually configure (in script, but use a good interfacing tool on monitor).

Do not look only at PCs but at every device on the network, the NICs in the wiring closet, routing devices, perhaps even printers.  Every device must talk same language (including protocol, linespeed, duplex etc) or it will bog down to real slow if anything gets through at all
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LVL 24

Expert Comment

by:SunBow
ID: 13617717
I am unaware of this relating to dhcp btw, it is NIC relevant for MAC 00:0f:1f:d0:e4:10 via eth1
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LVL 24

Expert Comment

by:SunBow
ID: 13617784
PCLANTECHS > our traffic monitor which is showing the duplex changing from half to full frequently for device I our traffic monitor which is showing the duplex changing from half to full frequently for device IP 192.168.1.11.

No. Device is not IP 192.168.1.11. IP is logical address, dhcp can hand it to anyone. Physical Device is 00:0f:1f:d0:e4:10 via eth1, the NIC, Network Interface Card.

PCLANTECHS > Duplex.. full, half, auto?
PCLANTECHS > our traffic monitor which is showing the duplex changing from half to full frequently

The problem looks like configuring too much "auto" and it getting unstable in trying to figure that out well, possibly one or two others configured differently. Make a rule, set all to exactly the same. Try it, all the same fixed (not auto) duplex and you'll see improvement.  I seem to recall a test done in a prior thread here that you may be able to get up to 80 % bandwidth with half duplex, but do not quote me on that.
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LVL 23

Expert Comment

by:sciwriter
ID: 13617830
Dropped packets are not abnormal in any network.  How do you know (other than the logs) that you have a serious problem?  WHat is happening, physically?  What are the symptoms of low-duplex output.  Realize, any 10 base and many 10.100s will not consistently full duplex.  You cannot use half as a necesary indication of a problem
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Author Comment

by:PCLANTECHS
ID: 13618468
Ok its agreed that device is not the physical address of 192.168.1.11 but the MAC.
I was simply stating that so you would see in the log that the routing device seems to have dificulty auto negotiating weather full or half duplex; hence the problem. There is only one device that is connecting to the trusted interface. This device is getting several errors and dropped packets. The external interface is not getting any errors nor dropped packets.
The reason I bring this issue up is we are having issues with latency. Our connection is well above 2mbps and we are only able to get 900k. I have bypassed the routing device and get the 2mbps.
Any help is appreciated.
Thanks
JC
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LVL 27

Accepted Solution

by:
pseudocyber earned 1000 total points
ID: 13618558
If you do a search in here for "autonegotiate problems" or "duplex settings" I'm sure you'd come across many of my posts on this topic - it seems to be pretty misunderstood.

When an autonegotiate device is connected to a full duplex device on the other end, the Auto side will say to itself (by design I may add) - the other side doesn't want to negotiate, since it's not responding to my negotiate pulses - it must not be able to operate at full duplex, so I'd better set myself to half duplex.

Autonegotiate ---- Autonegotiate = 100 Full Duplex (most of the time, but it depends - watch for problems)
100 Full ----- Autonegotiate = Duplex mismatch 100 Full and 100 Half.  One side will see CRC and Alignment errors.  Other side sees collisions and giants.
Autonegotiate ---- 100 Full = Duplex mismatch.
100 Full ----- 100 Full = no problems related to duplex negotiation or line speed matching.

If you have servers and mangeable equipment I like to set all servers at 100 Full.  if you have PC's which don't move, I like them to be 100 Full.  If you have laptops which go home and plug into SOHO gear at home, such as a Linksys router, make them Autonegotiate.

If you ONLY have unmanaged network equipment, and you can't set ports to 100 Full Duplex for optimal networking at that speed, you MUST set everything to Autonegotiate.

Hope this helps.
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LVL 23

Expert Comment

by:sciwriter
ID: 13618717
<<  Our connection is well above 2mbps and we are only able to get 900k. I have bypassed the routing device and get the 2mbps. >>

Autonegotiation aside, if you can bypass the router and get full speed, it is time for a newer one that exceeds the capabilities of the speeds and bandwidths you are throughputting.  A modern one should run 85-95% of top speed, not less than 50%.
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LVL 24

Assisted Solution

by:SunBow
SunBow earned 1000 total points
ID: 13623178
pseudocyber > equipment I like to set all servers at 100 Full.  ...  you MUST set everything to ...

:-))   As I tried to indicate, manage it be setting all identically.  Do not place full faith in auto trust

PCLANTECHS > This device is getting several errors and dropped packets. The external interface is not getting any errors nor dropped packets.

It used to be that improper filtering near a large network could cause a congestion problem. However, the art has changed since RAM is cheaper, the tables and storage are larger, and you are not claiming to have major traffic. So, why not swap out the NIC?   Routers are not infallible, equipment goes bad, and NICs are among the top failures and easiest items to replace, even to test temporarily with replacements.  Is it a router or a smart hub? Either way, if it is now the designated failure, deal specifcally with it, even if you must replace it or do without it. Warranty?
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Expert Comment

by:rmcferren
ID: 13626752
Speeds and Duplexes

10:  Usually only likes half, but will work with full
100:  Designed for full, can run half
1G:  Best on Full, Half not recommended
10G: Full only, standard does not allow for half
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LVL 27

Expert Comment

by:pseudocyber
ID: 14237123
Interested.
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