1
00:00:02,431 --> 00:00:06,598
(light music with digital sounds)

2
00:00:09,177 --> 00:00:11,667
- In the last video, I
introduced you to the

3
00:00:11,667 --> 00:00:13,584
concept of VLAN Trunks.

4
00:00:14,456 --> 00:00:18,175
Which is really just on
a switch, a formal way of

5
00:00:18,175 --> 00:00:21,292
identifying different
broadcast domains that that one

6
00:00:21,292 --> 00:00:23,897
switch is keeping track
of, and keeping isolated

7
00:00:23,897 --> 00:00:24,875
from each other.

8
00:00:24,875 --> 00:00:28,430
In the context of VLANs,
we also learned that

9
00:00:28,430 --> 00:00:31,135
all the devices that are
in one VLAN are also at

10
00:00:31,135 --> 00:00:34,076
layer three in the same IP subnet.

11
00:00:34,076 --> 00:00:35,754
Now the switch is not aware of that.

12
00:00:35,754 --> 00:00:37,921
If we're talking about just
a regular layer two switch,

13
00:00:37,921 --> 00:00:39,552
the switch does not really know anything

14
00:00:39,552 --> 00:00:40,811
about IP and subnetting.

15
00:00:40,811 --> 00:00:43,878
All it knows is that
this group of ports here

16
00:00:43,878 --> 00:00:46,362
is contained in one broadcast domain.

17
00:00:46,362 --> 00:00:48,913
This group of ports is in a
different broadcast domain.

18
00:00:48,913 --> 00:00:51,448
And the two are not allowed to talk.

19
00:00:51,448 --> 00:00:55,764
Now that being the case,
what if you have a situation

20
00:00:55,764 --> 00:01:00,170
like this, and I have
worked this up here in GNS3

21
00:01:00,170 --> 00:01:03,230
so you could replicate this if you want.

22
00:01:03,230 --> 00:01:05,147
Where I have two VLANs.

23
00:01:06,448 --> 00:01:10,615
So in this particular case,
I have VLAN 1 here and here,

24
00:01:13,277 --> 00:01:16,411
and it's separated between
two different switches.

25
00:01:16,411 --> 00:01:21,104
So if all I had was VLAN 1,
then this connection between

26
00:01:21,104 --> 00:01:24,515
the switches could also
be placed in VLAN 1,

27
00:01:24,515 --> 00:01:27,438
and these guys would
be able to communicate.

28
00:01:27,438 --> 00:01:30,447
And in order to make this
more of a real-world scenario,

29
00:01:30,447 --> 00:01:33,652
I've also incorporated DHCP
server, which in this case

30
00:01:33,652 --> 00:01:35,130
is my router.

31
00:01:35,130 --> 00:01:37,424
Later on in some of the later
videos when we talk a little

32
00:01:37,424 --> 00:01:39,436
bit more extensively about
DHCP, you'll actually learn

33
00:01:39,436 --> 00:01:43,754
how to configure a router or
a switch as a DHCP server.

34
00:01:43,754 --> 00:01:46,507
The configuration's pretty
easy and it's the same whether

35
00:01:46,507 --> 00:01:49,699
you do it on a router or on a switch.

36
00:01:49,699 --> 00:01:52,830
Usually in real life, you
would have in a regular network

37
00:01:52,830 --> 00:01:56,377
a real server like a Windows
server or a Linux server,

38
00:01:56,377 --> 00:01:59,384
or something like that,
acting as your DHCP server.

39
00:01:59,384 --> 00:02:02,464
But in some smaller networks,
you can get away with just

40
00:02:02,464 --> 00:02:05,975
having your router or your
switch double up as a DHCP server

41
00:02:05,975 --> 00:02:08,908
so that's what I'm doing
here to make this simple.

42
00:02:08,908 --> 00:02:12,752
So these two PCs here are
going to have to get their

43
00:02:12,752 --> 00:02:14,709
IP information from the DHCP server.

44
00:02:14,709 --> 00:02:18,681
You can see that they are going
to be in the 1.1.1.x network

45
00:02:18,681 --> 00:02:22,514
and the server itself,
the router, is 1.1.1.1.

46
00:02:24,294 --> 00:02:26,421
Now to make things a little
bit more interesting,

47
00:02:26,421 --> 00:02:27,973
I also incorporated a second VLAN.

48
00:02:27,973 --> 00:02:31,039
VLAN 2, as you can see
right here, and that's also

49
00:02:31,039 --> 00:02:32,759
split across the switches.

50
00:02:32,759 --> 00:02:35,596
Now that poses an interesting dilemma.

51
00:02:35,596 --> 00:02:39,153
Because I only have a
single connection here

52
00:02:39,153 --> 00:02:41,188
between these switches.

53
00:02:41,188 --> 00:02:44,271
If I put that connection
into a VLAN 1, and I put this

54
00:02:44,271 --> 00:02:46,827
connection here between
the switch and the router

55
00:02:46,827 --> 00:02:50,086
and VLAN 1, then these
two PCs will be happy.

56
00:02:50,086 --> 00:02:52,633
We'll have one big broadcast
domain that will, they'll

57
00:02:52,633 --> 00:02:55,891
be able to communicate
with each other via ARP.

58
00:02:55,891 --> 00:02:58,769
Their DHCP broadcast will be
able to go down here to the

59
00:02:58,769 --> 00:03:01,121
router and they'll get
their DHCP information.

60
00:03:01,121 --> 00:03:04,941
Well that'll leave the people
in VLAN 2 out in the cold.

61
00:03:04,941 --> 00:03:09,276
So for VLAN 2, one option I
could do is I could connect

62
00:03:09,276 --> 00:03:12,470
another connection between these switches,

63
00:03:12,470 --> 00:03:13,855
put that in VLAN 2.

64
00:03:13,855 --> 00:03:16,763
Connect another connection
from the switch to the router.

65
00:03:16,763 --> 00:03:18,908
Put that also in the 2 subnet.

66
00:03:18,908 --> 00:03:21,850
And then our VLAN 2 people would be happy.

67
00:03:21,850 --> 00:03:23,880
They could communicte
across the second link.

68
00:03:23,880 --> 00:03:26,847
They could get to their DHCP
server across this link.

69
00:03:26,847 --> 00:03:31,145
Now that might be okay if we're
only talking about two VLANs

70
00:03:31,145 --> 00:03:34,025
but in a real network, most
likely you're going to have

71
00:03:34,025 --> 00:03:37,615
dozens, if not hundreds of
VLANs, depending on how large

72
00:03:37,615 --> 00:03:38,925
your network is.

73
00:03:38,925 --> 00:03:42,756
And you're not going to have
enough scalability to just

74
00:03:42,756 --> 00:03:46,749
assign individual ports
for something like this.

75
00:03:46,749 --> 00:03:50,190
So in this particular case,
it's a more scalable solution.

76
00:03:50,190 --> 00:03:52,396
If you haven't heard that
term scalable before,

77
00:03:52,396 --> 00:03:55,832
what I'm talking about is
designing your network in such

78
00:03:55,832 --> 00:03:59,080
a way that it has room for future growth.

79
00:03:59,080 --> 00:04:01,946
It has room to add more
subnets in the future, or room

80
00:04:01,946 --> 00:04:04,209
to add more VLANs in the future.

81
00:04:04,209 --> 00:04:07,203
So you're thinking about, what
features can I use, how can I

82
00:04:07,203 --> 00:04:09,033
configure things that
will allow me to grow in

83
00:04:09,033 --> 00:04:11,639
the future more easily.

84
00:04:11,639 --> 00:04:14,273
That's what we mean by scalability.

85
00:04:14,273 --> 00:04:16,571
So in this particular case,
adding some extra links

86
00:04:16,571 --> 00:04:18,614
isn't really an option for me.

87
00:04:18,614 --> 00:04:21,651
So, what we need to do is we
need to figure out some way

88
00:04:21,651 --> 00:04:24,971
that this one link here
between the two switches

89
00:04:24,971 --> 00:04:28,396
is actually capable of being in more than

90
00:04:28,396 --> 00:04:30,146
one broadcast domain.

91
00:04:31,001 --> 00:04:34,109
You see, these access
ports going to the hosts,

92
00:04:34,109 --> 00:04:37,460
well an access port by
definition is only in

93
00:04:37,460 --> 00:04:39,226
one broadcast domain.

94
00:04:39,226 --> 00:04:41,496
This access port right here
is in the broadcast domain

95
00:04:41,496 --> 00:04:42,957
known as VLAN 2.

96
00:04:42,957 --> 00:04:45,966
And this access port up here
is in the broadcast domain

97
00:04:45,966 --> 00:04:47,896
known as VLAN 1.

98
00:04:47,896 --> 00:04:50,570
But in the middle here,
between the switches and from

99
00:04:50,570 --> 00:04:53,458
the switch to the router, I
have a need to actually put

100
00:04:53,458 --> 00:04:56,476
those links into multiple VLANs.

101
00:04:56,476 --> 00:04:59,732
And this is where the
concept of VLAN Trunks

102
00:04:59,732 --> 00:05:01,065
comes into play.

103
00:05:01,975 --> 00:05:06,142
So a VLAN Trunk Port has
two or more VLANs across it.

104
00:05:09,118 --> 00:05:12,062
So look at the last bullet point here.

105
00:05:12,062 --> 00:05:16,610
By default all VLAN traffic
is allowed from a trunk port.

106
00:05:16,610 --> 00:05:18,496
Now, we know that on the
switch, let me ask you

107
00:05:18,496 --> 00:05:19,957
a review question:

108
00:05:19,957 --> 00:05:22,028
What was the default VLAN?

109
00:05:22,028 --> 00:05:25,278
VLAN number "what" is the default VLAN?

110
00:05:26,129 --> 00:05:28,718
Hopefully you said VLAN 1, that's right.

111
00:05:28,718 --> 00:05:31,745
Now, what is the highest
numbered VLAN that

112
00:05:31,745 --> 00:05:33,162
you could create?

113
00:05:34,803 --> 00:05:36,386
That was VLAN 4094.

114
00:05:37,682 --> 00:05:41,338
So you had from VLAN 1 to VLAN 4094.

115
00:05:41,338 --> 00:05:46,142
Now, all those VLANs don't
exist by default on a switch.

116
00:05:46,142 --> 00:05:48,908
The only ones that exist by
default are VLAN 1, and then

117
00:05:48,908 --> 00:05:53,058
those sort of VLANs in the
middle, like 1002 - 1005,

118
00:05:53,058 --> 00:05:54,474
and that's it.

119
00:05:54,474 --> 00:05:59,271
So, what Trunk Ports do, is,
as you create a new VLAN,

120
00:05:59,271 --> 00:06:03,080
let's say you create VLAN 17, or VLAN 333,

121
00:06:03,080 --> 00:06:06,619
before you even apply
it to any access ports,

122
00:06:06,619 --> 00:06:10,810
because remember using a
VLAN is a two-step process.

123
00:06:10,810 --> 00:06:15,034
You create the VLAN globally,
config T, and then VLAN 25,

124
00:06:15,034 --> 00:06:16,708
and VLAN 17.

125
00:06:16,708 --> 00:06:18,884
Then, if you actually have
any ports on the switch

126
00:06:18,884 --> 00:06:21,946
connecting to hosts, you have
to go to that port and say

127
00:06:21,946 --> 00:06:26,113
switch port access VLAN 25, or
switch port access VLAN 333.

128
00:06:29,500 --> 00:06:33,343
But, even before you apply
a VLAN to an access port,

129
00:06:33,343 --> 00:06:37,263
the moment you type in VLAN 5
or VLAN 99, and that becomes

130
00:06:37,263 --> 00:06:39,549
a VLAN in the switch,

131
00:06:39,549 --> 00:06:42,762
if that switch has any functional
VLAN Trunks, so now we're

132
00:06:42,762 --> 00:06:44,931
talking about a different mode now.

133
00:06:44,931 --> 00:06:47,781
Previously we talked about
switchport mode access,

134
00:06:47,781 --> 00:06:50,029
now we're talking about a different mode:

135
00:06:50,029 --> 00:06:51,960
switchport mode trunk.

136
00:06:51,960 --> 00:06:54,441
And when an interface is
considered as a trunk,

137
00:06:54,441 --> 00:06:57,398
whatever VLANs are on that
switch are automatically

138
00:06:57,398 --> 00:06:59,693
allowed to go across that trunk.

139
00:06:59,693 --> 00:07:02,943
So if I've got five broadcast
domains, VLANs one, two,

140
00:07:02,943 --> 00:07:05,931
three, four, and five, all
five of them will automatically

141
00:07:05,931 --> 00:07:07,961
be carried by that trunk.

142
00:07:07,961 --> 00:07:10,376
Now that raises and interesting
question if we go back

143
00:07:10,376 --> 00:07:12,543
to our diagram right here.

144
00:07:13,930 --> 00:07:15,263
If this PC, PC 1

145
00:07:19,205 --> 00:07:20,705
generates a frame,

146
00:07:22,063 --> 00:07:24,249
actually let's forget
about PC 1 for a second.

147
00:07:24,249 --> 00:07:26,408
Let's take a look at PC 2.

148
00:07:26,408 --> 00:07:31,343
If PC 2 generates a frame that
needs to go across this trunk

149
00:07:31,343 --> 00:07:35,888
and then go down here to PC
4, let's say it's a broadcast,

150
00:07:35,888 --> 00:07:38,397
maybe he is sending
and ARP request saying,

151
00:07:38,397 --> 00:07:41,653
"Hey PC 4, I need to
know what your MAC is."

152
00:07:41,653 --> 00:07:45,820
Once that ethernet frame arrives
here on fast ethernet 0/15

153
00:07:46,659 --> 00:07:49,618
of ether switch 2, and let me
go ahead and zoom in on that

154
00:07:49,618 --> 00:07:50,701
a little bit.

155
00:07:52,433 --> 00:07:55,332
Right there, okay, let's
move this guy out of the way.

156
00:07:55,332 --> 00:07:58,940
Once it comes in right
here, switch 2 has to have

157
00:07:58,940 --> 00:08:02,294
some way of knowing, okay this
a broadcast that just came in

158
00:08:02,294 --> 00:08:06,188
and I have actually two broadcast
domains that I'm aware of,

159
00:08:06,188 --> 00:08:08,105
VLAN 1 and VLAN 2. Hmm.

160
00:08:08,939 --> 00:08:11,441
Which broadcast domain am I allowed to put

161
00:08:11,441 --> 00:08:13,560
this broadcast into?

162
00:08:13,560 --> 00:08:15,204
Because when the broadcast
comes across here,

163
00:08:15,204 --> 00:08:19,316
this ARP request, we don't want
him to flood it into VLAN 1

164
00:08:19,316 --> 00:08:22,752
because it originated over
here in VLAN 2, so it has to be

165
00:08:22,752 --> 00:08:24,419
flooded into VLAN 2.

166
00:08:25,313 --> 00:08:27,819
So that means that as frames
go back and forth across

167
00:08:27,819 --> 00:08:31,512
this trunk, there has to
be some way of identifying

168
00:08:31,512 --> 00:08:34,679
which broadcast domain they belong to.

169
00:08:36,040 --> 00:08:40,123
And 802.1Q has a very
creative way of doing this.

170
00:08:41,913 --> 00:08:46,080
802.1Q applies an extra field
to the layer to header called

171
00:08:48,799 --> 00:08:49,966
an 802.1Q tag.

172
00:08:52,147 --> 00:08:55,186
Sometimes they just
shorten it as a .1Q tag.

173
00:08:55,186 --> 00:08:57,758
So if were actually to look
at what this looks like,

174
00:08:57,758 --> 00:09:00,258
if this was my IP packet here,

175
00:09:03,298 --> 00:09:07,366
so from the perspective of
ethernet that's just the data.

176
00:09:07,366 --> 00:09:11,533
And we know that ethernet as
a trailer, we call it an FCS

177
00:09:15,070 --> 00:09:16,874
to the end of it.

178
00:09:16,874 --> 00:09:21,041
And then here is my ethernet
header at the front end.

179
00:09:24,624 --> 00:09:28,828
Review question: very first
field of an ethernet header,

180
00:09:28,828 --> 00:09:31,360
what do we call that field?

181
00:09:31,360 --> 00:09:32,884
That is the preamble.

182
00:09:32,884 --> 00:09:36,299
I'll just put PRE. That's the preamble.

183
00:09:36,299 --> 00:09:38,863
What follows the preamble?

184
00:09:38,863 --> 00:09:41,821
That is the destination MAC.

185
00:09:41,821 --> 00:09:44,878
What follows the destination MAC?

186
00:09:44,878 --> 00:09:47,210
That is the source MAC.

187
00:09:47,210 --> 00:09:50,907
Now, in a regular ethernet
frame, what typically follows

188
00:09:50,907 --> 00:09:52,157
the source MAC?

189
00:09:53,291 --> 00:09:56,958
That would be the type
code, the type field.

190
00:09:58,142 --> 00:10:00,356
So there would be a number
that we would put in here

191
00:10:00,356 --> 00:10:02,431
if this is IP version 4.

192
00:10:02,431 --> 00:10:04,861
There would be a number, a
different number we would put

193
00:10:04,861 --> 00:10:06,566
here if it's IP version 6.

194
00:10:06,566 --> 00:10:10,405
well, if this ethernet frame
is going across a VLAN Trunk,

195
00:10:10,405 --> 00:10:12,531
and it has to be
identified as belonging to

196
00:10:12,531 --> 00:10:14,008
a particular VLAN,

197
00:10:14,008 --> 00:10:16,925
we actually put our tag right here.

198
00:10:19,623 --> 00:10:22,331
So the type field
actually contains the tag.

199
00:10:22,331 --> 00:10:26,498
So now here we have a
special number, a type number

200
00:10:28,291 --> 00:10:30,458
that says "This is 802.1Q"

201
00:10:32,478 --> 00:10:35,886
So instead of the type field
saying "Oh I'm carrying IPv4,

202
00:10:35,886 --> 00:10:39,717
or I'm carrying IPv6," there's
actually another number,

203
00:10:39,717 --> 00:10:43,183
a reserve number that
says "This is a .1Q tag."

204
00:10:43,183 --> 00:10:44,996
Then there's a couple of
other fields in here that we

205
00:10:44,996 --> 00:10:49,300
don't really care about all
that much, and then here

206
00:10:49,300 --> 00:10:51,448
is where we put the VLAN.

207
00:10:51,448 --> 00:10:55,118
So if this frame belongs
to VLAN 55, you would see

208
00:10:55,118 --> 00:10:57,350
the number 55 in here.

209
00:10:57,350 --> 00:11:02,228
If it belongs to VLAN 6, you
would see the number 6 in here.

210
00:11:02,228 --> 00:11:05,199
If I just left it that
way, I would be doing you

211
00:11:05,199 --> 00:11:07,643
a disservice because I'd
be letting you think,

212
00:11:07,643 --> 00:11:10,981
"Okay, every frame that goes
across the VLAN trunk has

213
00:11:10,981 --> 00:11:14,237
a special tag that actually
indicates the number

214
00:11:14,237 --> 00:11:15,229
of the VLAN."

215
00:11:15,229 --> 00:11:18,460
And that is true 99% of the time.

216
00:11:18,460 --> 00:11:20,693
But take a look at the second bullet here.

217
00:11:20,693 --> 00:11:23,505
It says all traffic except
the native VLAN is inserted

218
00:11:23,505 --> 00:11:25,088
with an 802.1Q tag.

219
00:11:26,476 --> 00:11:29,643
By default, the native VLAN is VLAN 1.

220
00:11:30,995 --> 00:11:34,597
Which means, that when, if
I'm a switch, and let's say

221
00:11:34,597 --> 00:11:37,614
I just got a frame on VLAN
1 and I say okay I need

222
00:11:37,614 --> 00:11:40,696
to send it to you, you're
another switch, and we have

223
00:11:40,696 --> 00:11:42,613
a 802.1Q tag between us

224
00:11:43,764 --> 00:11:48,071
I'm sorry, we have an 802.1Q
VLAN trunk between us,

225
00:11:48,071 --> 00:11:51,400
well if I'm going to put a
VLAN 1 frame on here, I'm not

226
00:11:51,400 --> 00:11:52,884
going to tag it.

227
00:11:52,884 --> 00:11:55,246
So when you receive it,
it's just going to look like

228
00:11:55,246 --> 00:11:56,993
any other ethernet frame.

229
00:11:56,993 --> 00:11:59,292
It'll have some type code
in there that says IPv4,

230
00:11:59,292 --> 00:12:02,550
or maybe a type code that
says IPv6, but it'll just look

231
00:12:02,550 --> 00:12:05,841
like a normal ethernet frame to you.

232
00:12:05,841 --> 00:12:10,089
Now if I receive a frame
on VLAN 7, as an example,

233
00:12:10,089 --> 00:12:13,535
then before I put on this
wire, I'm going to modify

234
00:12:13,535 --> 00:12:17,848
the type code to say this
is 802.1Q and this frame

235
00:12:17,848 --> 00:12:19,348
belongs to VLAN 7.

236
00:12:20,234 --> 00:12:22,904
So when you get it, you'll
actually see that tag,

237
00:12:22,904 --> 00:12:25,430
and you'll explicitly
know it belongs to VLAN 7.

238
00:12:25,430 --> 00:12:29,796
So every frame I put in this
VLAN trunk will have a tag

239
00:12:29,796 --> 00:12:33,963
unless it belongs to the
broadcast domain known as VLAN 1.

240
00:12:34,892 --> 00:12:37,562
Those frames are untouched,
they go across the trunk

241
00:12:37,562 --> 00:12:39,551
in their native format.

242
00:12:39,551 --> 00:12:40,719
They are untouched.

243
00:12:40,719 --> 00:12:43,277
That's why we call it the native VLAN.

244
00:12:43,277 --> 00:12:45,915
Now as with pretty much
everything else, if you have

245
00:12:45,915 --> 00:12:48,467
a desire to do so you can
change the native VLAN

246
00:12:48,467 --> 00:12:50,356
to something else.

247
00:12:50,356 --> 00:12:52,570
But the main thing is that
if we change it, you and I

248
00:12:52,570 --> 00:12:54,452
both have to agree.

249
00:12:54,452 --> 00:12:56,891
If I decide that okay the
frames I put on this trunk are

250
00:12:56,891 --> 00:12:59,766
going to be untagged, just
regular frames that belong

251
00:12:59,766 --> 00:13:03,667
to VLAN 99, you need to know
that, you need to have that

252
00:13:03,667 --> 00:13:07,123
configured, because,
how else would you know?

253
00:13:07,123 --> 00:13:09,559
Like, let's say that I
kept that as a secret.

254
00:13:09,559 --> 00:13:12,913
Let's say that on my switch
I decide, okay, I'm not going

255
00:13:12,913 --> 00:13:15,290
to use VLAN 1 as the native
VLAN, I'm going to use

256
00:13:15,290 --> 00:13:17,516
VLAN 99 as a native VLAN.

257
00:13:17,516 --> 00:13:20,231
So whenever I get a frame here
from VLAN 99, when I put on

258
00:13:20,231 --> 00:13:23,593
this trunk, I'm going to leave
it alone, I'm not going to

259
00:13:23,593 --> 00:13:25,171
tag it at all.

260
00:13:25,171 --> 00:13:28,097
Well if you didn't know that,
and you still thought that

261
00:13:28,097 --> 00:13:30,908
VLAN 1 was the native VLAN,
once you receive that plain

262
00:13:30,908 --> 00:13:35,075
old ethernet frame without
a tag, what broadcast domain

263
00:13:36,179 --> 00:13:40,124
do you think you would
assume it belongs to?

264
00:13:40,124 --> 00:13:43,289
You would assume it belongs
to VLAN 1 because you didn't

265
00:13:43,289 --> 00:13:46,122
know what I was thinking, you
didn't know what I configured.

266
00:13:46,122 --> 00:13:49,660
That's why if you change
the native VLAN on one side

267
00:13:49,660 --> 00:13:52,179
of the trunk, you have to
make sure it matches on

268
00:13:52,179 --> 00:13:53,342
the other side of the trunk.

269
00:13:53,342 --> 00:13:56,958
If it doesn't, like in that
example where I think VLAN 99

270
00:13:56,958 --> 00:14:00,525
is the native VLAN; you think
VLAN 1 is the native VLAN,

271
00:14:00,525 --> 00:14:01,711
guess what's going to happen?

272
00:14:01,711 --> 00:14:04,961
Here comes in the broadcast on VLAN 99.

273
00:14:05,943 --> 00:14:10,704
I put on that trunk untagged,
regular ethernet frame,

274
00:14:10,704 --> 00:14:13,732
and guess what, when it
comes to you, you dump that

275
00:14:13,732 --> 00:14:15,565
broadcast into VLAN 1.

276
00:14:16,793 --> 00:14:18,758
Because you didn't know
it came from VLAN 99.

277
00:14:18,758 --> 00:14:21,951
So here's a broadcast that
started in VLAN 99, and on your

278
00:14:21,951 --> 00:14:24,820
side is now being dumped into VLAN 1.

279
00:14:24,820 --> 00:14:26,935
That is a bad situation.

280
00:14:26,935 --> 00:14:30,176
So that is why the
native VLAN has to match.

281
00:14:30,176 --> 00:14:32,750
And in just a second, one
of the reasons why I created

282
00:14:32,750 --> 00:14:35,569
this whole thing in GNS3, is
because like I said in some of

283
00:14:35,569 --> 00:14:39,061
the earlier videos, GNS3
has Wireshark built into it,

284
00:14:39,061 --> 00:14:41,801
so we'll actually do a packet
capture of some packets going

285
00:14:41,801 --> 00:14:44,030
across the trunk so I can
show you what that tag

286
00:14:44,030 --> 00:14:46,176
actually looks like.

287
00:14:46,176 --> 00:14:49,309
So 802.1Q as you can see just
by the fact it was created

288
00:14:49,309 --> 00:14:52,766
by the IEEE is a standard VLAN trunking.

289
00:14:52,766 --> 00:14:55,344
This is not a CISCO-proprietary method.

290
00:14:55,344 --> 00:14:59,511
So any switch should be able
to suport 802.1Q trunking.

291
00:15:02,530 --> 00:15:05,656
And we've talked about all this.

292
00:15:05,656 --> 00:15:07,817
If you want to change
the native VLAN, it is

293
00:15:07,817 --> 00:15:09,295
an interface command.

294
00:15:09,295 --> 00:15:11,326
So you would go into the
interface that's your trunk,

295
00:15:11,326 --> 00:15:14,903
whatever interface fast
ethernet 0/7 or whatever it is,

296
00:15:14,903 --> 00:15:19,070
and then you'd say switchport
trunk navtive VLAN 99,

297
00:15:19,953 --> 00:15:21,172
like in my example.

298
00:15:21,172 --> 00:15:23,730
And both of us would have
that in these interfaces that

299
00:15:23,730 --> 00:15:26,147
were connected to each other.

300
00:15:27,151 --> 00:15:32,043
Okay, so the simplest way
to configure trunking is to

301
00:15:32,043 --> 00:15:33,978
go into the interface.

302
00:15:33,978 --> 00:15:38,829
And then say switchport
trunk encapsulation dot1q.

303
00:15:38,829 --> 00:15:42,323
Now you might be wondering,
"Well, why do I need that?"

304
00:15:42,323 --> 00:15:46,321
If 802.1Q is the way of
adding tags, why do I

305
00:15:46,321 --> 00:15:48,071
have to specify that?

306
00:15:48,908 --> 00:15:53,809
The reason for that is CISCO
a while ago, many many years

307
00:15:53,809 --> 00:15:57,234
ago actually came up with
this idea of trunking before

308
00:15:57,234 --> 00:15:58,988
the IEEE did.

309
00:15:58,988 --> 00:16:01,027
And they had their own proprietary way of

310
00:16:01,027 --> 00:16:02,776
doing trunking called ISL.

311
00:16:02,776 --> 00:16:05,776
It stood for Inter-Switch Link, ISL.

312
00:16:06,669 --> 00:16:11,094
And the IEEE came up
with, later on, 802.1Q.

313
00:16:11,094 --> 00:16:14,014
So there's some CISCO
switches out there today,

314
00:16:14,014 --> 00:16:18,181
still quite a few of them, that
support either ISL or 802.1Q

315
00:16:19,625 --> 00:16:22,580
And so if you're on a switch
like that, you have to specify

316
00:16:22,580 --> 00:16:26,268
this command to let it know,
I want you to do the IEEE way

317
00:16:26,268 --> 00:16:28,119
of doing 802.1Q.

318
00:16:28,119 --> 00:16:30,906
Now if you're on a switch that
does not support that command

319
00:16:30,906 --> 00:16:32,358
let's say you're on a
switch and you type in

320
00:16:32,358 --> 00:16:36,525
switchport trunk encapsulation
? and it says "unrecognized,"

321
00:16:37,411 --> 00:16:38,844
well then you don't
have to worry about it.

322
00:16:38,844 --> 00:16:41,709
That is a switch that
is only doing 802.1Q.

323
00:16:41,709 --> 00:16:43,862
It doesn't even do ISL, so it's not even

324
00:16:43,862 --> 00:16:46,068
giving you that command.

325
00:16:46,068 --> 00:16:48,375
But it's just, sort of like
I've been saying, there's

326
00:16:48,375 --> 00:16:50,589
certain things you should do
in network, and it's just like

327
00:16:50,589 --> 00:16:52,128
a knee-jerk reaction, like write memory.

328
00:16:52,128 --> 00:16:55,180
Every time I make a change to
my configuration write memory,

329
00:16:55,180 --> 00:16:58,392
save it, just get in
the habit of doing that.

330
00:16:58,392 --> 00:17:00,851
Going on to an interface
and before you leave it,

331
00:17:00,851 --> 00:17:03,426
doing no shutdown, just
doing that by habit.

332
00:17:03,426 --> 00:17:06,439
You should do this also,
whenever configuring a trunk

333
00:17:06,439 --> 00:17:08,406
just by habit you should type in

334
00:17:08,406 --> 00:17:11,553
switchpot trunk encapsulation dot1q

335
00:17:11,553 --> 00:17:14,746
If it doesn't recognize
the command, nothing lost,

336
00:17:14,746 --> 00:17:18,665
no worries, it's just a
good habit to get into.

337
00:17:18,665 --> 00:17:20,212
But then we have to change the mode.

338
00:17:20,212 --> 00:17:23,487
Here we type switchport mode trunk.

339
00:17:23,487 --> 00:17:25,625
And now that makes sure
that this is operating

340
00:17:25,625 --> 00:17:26,958
as a VLAN trunk.

341
00:17:29,770 --> 00:17:32,593
Probably should do no shutdown,
that's not in the slide here

342
00:17:32,593 --> 00:17:36,293
but once again, just as a habit,
you should type no shutdown

343
00:17:36,293 --> 00:17:39,075
before you leave the interface.

344
00:17:39,075 --> 00:17:43,694
And there's a couple of ways
that we can verify trunking.

345
00:17:43,694 --> 00:17:47,033
Show VLAN actually doesn't
show you if an interface

346
00:17:47,033 --> 00:17:50,169
is a trunk, it just shows
you what VLANs you've got.

347
00:17:50,169 --> 00:17:51,853
We looked at that in the previous video.

348
00:17:51,853 --> 00:17:55,686
The command that I use the
most often to see, do I have

349
00:17:55,686 --> 00:17:57,981
any interfaces that are
trunking and what interfaces

350
00:17:57,981 --> 00:18:00,986
are they, is show interface trunk.

351
00:18:00,986 --> 00:18:02,272
That's a command I use a lot.

352
00:18:02,272 --> 00:18:04,480
You can also use show interface status

353
00:18:04,480 --> 00:18:06,779
or show interface switchport.

354
00:18:06,779 --> 00:18:09,862
(quick, light tones)