1
00:00:00,480 --> 00:00:07,530
Some points to remember with regards to speed and duplex negotiation and mismatches. Duplex and speed

2
00:00:07,530 --> 00:00:15,900
mismatches occur when auto-negotiation fails or when manual configurations are mismatched.

3
00:00:15,900 --> 00:00:21,600
So, for example, one side is configured to use full-duplex and the other side is configured to use half

4
00:00:21,600 --> 00:00:29,220
duplex auto-negotiation may fail because of physical problems in the network such as cabling problems

5
00:00:29,640 --> 00:00:36,400
or a hub somewhere in the network duplex mismatches do cause performance problems.

6
00:00:36,660 --> 00:00:46,230
Your pings may succeed but the movement of large files may be negatively affected and UDP may especially

7
00:00:46,500 --> 00:00:53,470
have problems with recovering from duplex mismatch issues so a quick bit of history.

8
00:00:53,590 --> 00:00:58,880
Originally ethernet was half duplex because devices were connected to hubs.

9
00:00:59,050 --> 00:01:06,370
So a decision was made that when you can't negotiate with the other side you would revert back to 10

10
00:01:06,370 --> 00:01:11,990
meg half-duplex older devices weren't designed to auto- negotiate.

11
00:01:12,070 --> 00:01:19,660
So the auto-negotiating device would revert back to half-duplex mode if it wasn't able to negotiate

12
00:01:19,660 --> 00:01:27,340
with the other side because it assumed that that device must only support half-duplex. Auto-negotiation

13
00:01:27,340 --> 00:01:33,130
of speed and duplex didn't work well in the old days and often caused problems with the speed and duplex

14
00:01:33,130 --> 00:01:34,240
mismatch.

15
00:01:34,690 --> 00:01:41,170
If one side is using half-duplex and the other side is using full-duplex, the full-duplex side thinks

16
00:01:41,260 --> 00:01:45,540
that it can transmit it any time even when it's receiving traffic.

17
00:01:45,580 --> 00:01:52,320
The half-duplex side however because it uses carrier sense multiple access collision detection or CSMA

18
00:01:52,360 --> 00:01:56,990
slash CD will want the line to be clear before transmitting.

19
00:01:57,220 --> 00:02:02,860
And when it does transmit and the packet is transmitted by the other side running at full-duplex a collision

20
00:02:02,860 --> 00:02:03,790
occurs.

21
00:02:04,090 --> 00:02:09,940
So the half duplex side will back off because of the collision and then try and transmit again when

22
00:02:09,940 --> 00:02:16,780
the line is clear and we'll have the constant issue of late collisions with the full-duplex side is

23
00:02:16,780 --> 00:02:20,680
transmitting data and can starve the half duplex side.

24
00:02:20,680 --> 00:02:25,930
In other words, it can use up all the bandwidth causing a lot of collisions and retransmissions on the

25
00:02:25,930 --> 00:02:31,900
half-duplex side this would cause the frames on the half-duplex side to que up and eventually be dropped.

26
00:02:32,590 --> 00:02:33,790
When looking for problems

27
00:02:33,790 --> 00:02:39,180
have a look at the areas which I'll demonstrate in a moment on the full-duplex side you will see errors

28
00:02:39,190 --> 00:02:46,620
such as CRC errors or runts, on the half-duplex side you typically see late collisions and perhaps

29
00:02:46,620 --> 00:02:52,750
buffer overloading, management systems from companies such as solar winds and others allow you to see

30
00:02:52,750 --> 00:02:58,480
where you've got Duplex problems on your network and help you resolve these issues more easily.