1
00:00:00,590 --> 00:00:07,520
So we now need to fix this link between 2951 and 2952.

2
00:00:07,970 --> 00:00:10,580
Both switches are showing.

3
00:00:11,550 --> 00:00:13,920
Messages that there's a duplex problem.

4
00:00:15,050 --> 00:00:17,330
So CDP does a nice job here.

5
00:00:18,720 --> 00:00:20,520
Of showing us that there's a problem.

6
00:00:21,580 --> 00:00:24,470
Rather show run interface.

7
00:00:24,490 --> 00:00:26,080
f0/4.

8
00:00:26,560 --> 00:00:29,290
We can see the speed and duplex are hardcoded.

9
00:00:29,740 --> 00:00:31,630
Show run interface if zero.

10
00:00:31,630 --> 00:00:32,680
Slash four.

11
00:00:33,720 --> 00:00:34,350
On this side.

12
00:00:34,350 --> 00:00:36,010
It's one half duplex.

13
00:00:36,030 --> 00:00:38,820
On this side, it's 100 full duplex.

14
00:00:42,460 --> 00:00:45,730
So that's a simple fix of setting the duplex to full.

15
00:00:47,230 --> 00:00:50,950
The interface has gone down and comes up again.

16
00:00:53,250 --> 00:00:55,710
And hopefully that's resolved the problem.

17
00:00:55,920 --> 00:00:59,310
We could clear the counters as an example.

18
00:00:59,460 --> 00:01:03,720
On if 0/4 and do the same here.

19
00:01:05,220 --> 00:01:07,800
Clear counters if 0/4.

20
00:01:09,310 --> 00:01:15,910
And then we could, after a while, look at those counters and see if we find any problems.

21
00:01:17,020 --> 00:01:20,890
But that should have solved the problem of a duplex mismatch.

22
00:01:22,620 --> 00:01:23,540
To confirm it.

23
00:01:23,550 --> 00:01:25,830
Show Interface f04.

24
00:01:27,040 --> 00:01:28,330
Right at the top here.

25
00:01:28,330 --> 00:01:29,560
We can see.

26
00:01:30,740 --> 00:01:32,330
So here's the command.

27
00:01:32,360 --> 00:01:35,450
Here's the speed and duplex of the interface.

28
00:01:35,820 --> 00:01:38,300
Interface is up, up, and it's connected.

29
00:01:38,480 --> 00:01:42,020
Show interface if 0/4 on switch to.

30
00:01:43,760 --> 00:01:45,500
He has the command once again.

31
00:01:47,060 --> 00:01:50,900
Duplex and speed are shown here as well.

32
00:01:51,260 --> 00:01:53,690
Interfaces up, up and it's connected.

33
00:01:54,050 --> 00:02:04,460
We're not seeing any errors on the interface and on this one we are also not seeing any errors.

34
00:02:04,730 --> 00:02:11,300
So that hopefully has resolved the problem on this link and this link.

35
00:02:11,510 --> 00:02:13,610
So be careful.

36
00:02:13,640 --> 00:02:22,130
Hard coding, speed and duplex auto negotiation may negotiate correctly, but it may not generally today

37
00:02:22,130 --> 00:02:24,000
with gigabit and foster links.

38
00:02:24,020 --> 00:02:27,290
Your problems are not as bad as they used to be.

39
00:02:27,500 --> 00:02:29,060
On ten 100 links.

40
00:02:29,570 --> 00:02:35,720
Let's see what happens if we configure speed and duplex on one side and leave the other side for auto

41
00:02:35,720 --> 00:02:36,740
negotiation.

42
00:02:37,370 --> 00:02:42,140
So on 2951, we will configure this interface.

43
00:02:44,670 --> 00:02:46,320
With a speed of 100.

44
00:02:46,350 --> 00:02:50,460
Duplex of full interface has gone down.

45
00:02:51,610 --> 00:02:54,670
Interface will hopefully come up and there you go.

46
00:02:58,570 --> 00:02:59,980
Here is the.

47
00:03:01,200 --> 00:03:02,370
3750.

48
00:03:03,330 --> 00:03:07,130
And we can see that it's complaining about a duplex mismatch.

49
00:03:07,140 --> 00:03:10,020
So sho run interface f zero.

50
00:03:12,010 --> 00:03:23,380
If 103 no duplex or speed has been configured on this interface show interface f103 the site is using

51
00:03:23,380 --> 00:03:26,530
100 meg Hoff duplex whereas this site.

52
00:03:29,640 --> 00:03:33,300
Is using 100 meg full duplex.

53
00:03:34,990 --> 00:03:40,990
So if you have one side configured for auto negotiation and the other side is hardcoded.

54
00:03:42,450 --> 00:03:48,090
You may have a problem because the site is not negotiating with the other side and the side may take

55
00:03:48,090 --> 00:03:49,530
a fallback position.

56
00:03:49,890 --> 00:03:56,520
Sometimes it's able, especially on gigabit and later interfaces, to still work out what the other

57
00:03:56,520 --> 00:04:01,110
side is using and set its duplex and speed accordingly.

58
00:04:01,110 --> 00:04:06,540
But here it wasn't able to do that because the 2950s are older switches.

59
00:04:07,050 --> 00:04:14,400
So to resolve this, let's configure the 2954 auto negotiation.

60
00:04:16,519 --> 00:04:21,110
So if 0/1 this interface speed.

61
00:04:22,950 --> 00:04:23,700
Auto.

62
00:04:25,400 --> 00:04:26,390
Duplex.

63
00:04:27,130 --> 00:04:27,820
Order.

64
00:04:29,340 --> 00:04:31,770
Interface has gone down.

65
00:04:32,070 --> 00:04:33,450
Hopefully it'll come up.

66
00:04:35,240 --> 00:04:38,420
And hopefully they'll be able to negotiate successfully.

67
00:04:38,660 --> 00:04:40,940
So 3750 is showing up.

68
00:04:41,420 --> 00:04:43,010
2950 showing up.

69
00:04:43,610 --> 00:04:46,820
Show interface f103.

70
00:04:48,590 --> 00:04:50,480
Full duplex 100 meg.

71
00:04:50,810 --> 00:04:52,910
So that site is 100 meg.

72
00:04:52,910 --> 00:04:57,860
Full duplex to show interface f01.

73
00:04:59,340 --> 00:05:02,450
On this side, full duplex 100 meg.

74
00:05:02,460 --> 00:05:04,470
So they've negotiated successfully.

75
00:05:04,680 --> 00:05:10,620
So moral of the story is either configure both sides for auto negotiation or hard code.

76
00:05:10,620 --> 00:05:11,550
Both sides.

77
00:05:12,710 --> 00:05:17,270
Generally today, you're going to allow both sides to want to negotiate.

78
00:05:17,720 --> 00:05:22,460
So run interface f101.

79
00:05:24,420 --> 00:05:28,140
Show run interface f101.

80
00:05:28,920 --> 00:05:35,700
Now this is the link between the two 3750s f101.

81
00:05:36,550 --> 00:05:38,680
This interface is and currently connected.

82
00:05:38,680 --> 00:05:44,200
So we've got one interface f101 between the two 3750s.

83
00:05:44,710 --> 00:05:49,660
One side is not set for speed and duplex, it's set for auto.

84
00:05:49,690 --> 00:05:52,360
The other side is using 100 half.

85
00:05:52,990 --> 00:05:54,220
But in this case.

86
00:05:58,050 --> 00:06:02,880
The site set for auto negotiation has reverted to 100 Meg Hoff duplex.

87
00:06:03,510 --> 00:06:06,210
So that's worked out okay in this example.

88
00:06:06,240 --> 00:06:16,170
However, if I change this to have a duplex or full, the negotiation will probably fail and we'll have

89
00:06:16,170 --> 00:06:17,400
a duplex mismatch.

90
00:06:18,880 --> 00:06:20,230
Interfaces have come up.

91
00:06:23,130 --> 00:06:24,420
Let's see what it's done.

92
00:06:26,760 --> 00:06:35,130
In this example it's negotiated correctly full duplex 100 meg the side DU Show Interface F1 zero one.

93
00:06:39,290 --> 00:06:40,970
Full duplex a100 meg.

94
00:06:40,970 --> 00:06:48,890
So we manually configured the side with speed and duplex this side.

95
00:06:51,340 --> 00:06:56,860
Has been able to work out what the speed and duplex should be.

96
00:06:57,550 --> 00:07:04,390
So let's set the speed here to ten and the duplex to half.

97
00:07:07,930 --> 00:07:11,080
And let's see if the switches can successfully negotiate that.

98
00:07:11,620 --> 00:07:12,910
So interfaces come up.

99
00:07:13,660 --> 00:07:16,360
Show interface f101.

100
00:07:16,510 --> 00:07:22,000
And I'll simply include the duplex so we don't see all the output.

101
00:07:22,270 --> 00:07:24,670
Notice here it's negotiated properly.

102
00:07:26,090 --> 00:07:28,010
So on this switch.

103
00:07:30,260 --> 00:07:36,770
It's been manually configured for half duplex ten meg and this switch has successfully negotiated that.

104
00:07:37,160 --> 00:07:45,350
If I change the duplex here to full, let's see what happens now when the interface comes up.

105
00:07:45,740 --> 00:07:48,230
So here it's ten meg full duplex.

106
00:07:48,260 --> 00:07:51,260
On this side it's also ten meg full duplex.

107
00:07:51,590 --> 00:07:57,710
So the 3750s are negotiating correctly without any problems.

108
00:07:58,070 --> 00:08:05,390
But that wasn't happening between a 3750 and a 2950.

109
00:08:05,690 --> 00:08:07,730
So let's set the speed to 100.

110
00:08:11,300 --> 00:08:16,430
So show interface and look at the duplex that's been set.

111
00:08:17,420 --> 00:08:18,470
Try that again.

112
00:08:18,800 --> 00:08:22,430
100 full duplex on the side.

113
00:08:22,430 --> 00:08:23,930
100 full duplex.

114
00:08:24,530 --> 00:08:30,800
So in this case, when I set the one side, it's successfully negotiating with the other side.

115
00:08:31,130 --> 00:08:35,710
But we had problems with negotiation between the 3750 and 2950.

116
00:08:35,720 --> 00:08:42,990
So generally the moral of the story is or to negotiation on both sides or hard code on both sides.

117
00:08:43,010 --> 00:08:46,130
Mixing and matching can cause problems.

118
00:08:46,460 --> 00:08:53,540
Today the general recommendation is use auto everywhere except perhaps between core links where you

119
00:08:53,540 --> 00:08:58,790
want a hard code, both sides to increase the speed of that interface coming up.