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The reason why we see OP traffic rather than ICMP traffic is on Ethernet before two devices can communicate.

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They need to use OP to discover one another's MAC addresses so before ICMP traffic can even be sent

3
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rather to acting as PC two needs to send an OP to discover Router Four's Mac address, but it never

4
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discovers it because the traffic never reaches router four, so it never receives an OP reply and therefore

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cannot send ICMP traffic.

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So in switch to.

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Interface.

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Range gigabit.

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Zero two.

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Two three.

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Switch port.

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Trunk encapsulation port one key switch port mode trunk switch port.

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No.

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Negotiate at the moment.

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Interface gigabit zero two.

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On switch to is shut down.

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I'll just do the same here.

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To prove the point, we are forcing the traffic basically to go via the hub so that we can do a Wireshark

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capture and see traffic on the network.

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So now let's start another Wireshark capture.

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Ken wrote a to paying writer for now.

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Notice the ping succeeds.

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If we look at our traffic.

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We can see the OP.

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I'll stop this Wireshark capture for the moment.

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There's the broadcast asking for Mac address associated with IP address ten.

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One, two, four.

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As you can see, it's a broadcast sent from router two.

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It's an ADA two, two, one, q frame.

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So in the eight two, two, two, one Q portion, once again we can see that the VLAN is two.

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There is the OP request looking for the MAC address associated with IP address ten 124.

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He has the reply.

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What you'll also notice is the VLAN ID is two, so it's coming back as a tagged frame from ten one to

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4 to 10 1 to 2.

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So there's the OP reply.

36
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It's not a broadcast because it knows the MAC address of router two already, so it goes directly to

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the MAC address of router two.

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And then if we scroll down a bit further, we can see the ICMP echo messages.

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So here's an echo from ten one to 2 to 10 1 to 4.

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Once again, notice the VLAN ID is two.

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Here's the reply from ten 1 to 4.

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So it's an echo reply to ten.

43
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One, two, two.

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VLAN id is two.

45
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So those frames are being tagged between the two devices.

46
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Let's stop that capture and started again in genius three.

47
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Now what about traffic from rather one, two, rather three.

48
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That's using vlan one which is the untagged VLAN.

49
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So rather one pinging router three ping succeeds.

50
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Router two pinging.

51
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Router four ping succeeds.

52
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I'll just filter for ICMP.

53
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So there's the ICMP message from router one to router three.

54
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Notice it's a standard ethernet frame.

55
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The ISA type is IP version four.

56
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There is no ED one q tagging on the echo or the echo reply.

57
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It's standard ethernet frames because that's the native VLAN.

58
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Scrolling down, however, he has router two, pinging router four and notice once again there is the

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tag.

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So let's put router one and router three into VLAN ten and see how that affects the tagging of traffic.

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So on switch one.

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VLAN ten interface gigabit zero zero.

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Switch port access vlan ten.

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Do something similar on switch to VLAN ten.

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Interface gigabit zero zero switch port access.

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VLAN ten.

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So now when router one.

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Ping's router three.

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What happens now?

70
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It might take a while because spanning tree needs to converge.

71
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So back on switch one show spanning tree.

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For VLAN.

73
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Ten ports are now forwarding.

74
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So let's do the ping again.

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Notice the ping now succeeds and in our Wireshark capture.

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If we scroll right down.

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What we should see now is the.

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VLAN number as an example is VLAN ten.

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So ID is ten can see the hexadecimal.

80
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There's the decimal.

81
00:05:06,950 --> 00:05:13,340
So at layer two in the Ethernet frame, notice the type is a 2 to 1 Q in edit 2 to 1.

82
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Q The type is IP version four indicating that IP version four is used at layer three.

83
00:05:19,460 --> 00:05:22,550
There's the ping, here's the reply.

84
00:05:22,700 --> 00:05:26,810
But notice once again the VLAN number is VLAN ten.

85
00:05:27,320 --> 00:05:30,830
If I changed this VLAN to VLAN 11 as an example.

86
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With the ping succeed.

87
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So vlan 11 rather interface gigabit zero zero switch port access.

88
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VLAN 11.

89
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I made the mistake of putting interface vlan 11.

90
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I should have said simply VLAN 11 to create the VLAN, but in this case the switch did create the VLAN

91
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for me.

92
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You need to be careful with that because some switches won't do that for you.

93
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But you can see VLAN 11 has been created.

94
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Gigabit zero zero is in VLAN 11.

95
00:06:02,650 --> 00:06:09,940
So this is in VLAN 11, the support is in VLAN ten can router one, ping router three and you can see

96
00:06:09,940 --> 00:06:11,410
at the moment it can't.

97
00:06:11,800 --> 00:06:20,140
In our Wireshark capture rather wan still has a cached mac address for router three, so it's sending

98
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ICMP traffic, but notice it's tagged with VLAN 11 and no reply is received back because the traffic

99
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never gets to router three.

100
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The support is in VLAN ten, the support is in VLAN 11, so the traffic never reaches this port.

101
00:06:38,950 --> 00:06:42,160
We can see that once again by doing a capture.

102
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Helping rather three from rather one.

103
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And what you'll notice in the output here is there is no OP and no ICMP traffic received on this port

104
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at all.

105
00:06:56,850 --> 00:07:00,210
Even though we're out of one is pinging rather three.

106
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On the captur between the switches we can see the ICMP traffic with VLAN 11, but the switch when it

107
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receives traffic on VLAN 11 is not going to forward it out of this port or this port.

108
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So essentially goes nowhere.

109
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It's going to be dropped by the switch because there are no access ports in VLAN 11.

110
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So the traffic never hits rather three but on switch two.

111
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If we created VLAN 11 and then went onto the port and put it into VLAN 11, what we would see now is

112
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that the pings do succeed.

113
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Now once again, it may take a while for spending tree to converge.

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You can see the pings arriving.

115
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Notice, 913 is the sequence number.

116
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Pings are arriving at switch to.

117
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But we may need to just wait a while for spending tree to converge.

118
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And there you go.

119
00:08:04,270 --> 00:08:14,410
Just converged so we can see the ping from router one to router three using VLAN 11 and there's a reply

120
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on VLAN 11.

121
00:08:16,520 --> 00:08:18,710
So physically this topology looks.

122
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As follows Just ignore the hub for the moment.

123
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So pretend that the hub is not there.

124
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Physically.

125
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We've got two PCs connected to switch one and two pieces connected to switch two, but logically rather

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one acting as PC one and router three acting as PC three are connected to each other and two and four

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are connected to each other.

128
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They are totally separated from each other and won't be able to ping each other unless we enable interval

129
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and routing on one of the switches and configure default gateways on the PCs to talk to each other via

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their default gateway.