icnd 2 trunking and vtp 2010
TRANSCRIPT
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ICND2
Trunking & VTP
Rudy Drew
rudydrew@ rmit.edu.au
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Slide 2
A trunk carries traffic from multiple LANs.
Trunks connect switches to switches ORswitches to routers.
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Slide 3
1 A frame enters an access port that belongs to VLAN 200.
A port in access mode belongs to one VLAN and connects
to a PC or server. These frames are ordinary ethernetframes. The frames VLAN is known because of the VLAN
number that has been assigned to the port
(e.g. switchport access vlan 200)
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Slide 4
2 The frames on trunk links carry VLAN ID information
using dot1q encapsulation i.e. there are extra fieldsinserted into the layer 2 header.
VLAN traffic is given a VLAN ID (i.e tagged) only on
trunk links not on access port
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Slide 5
For switch ports that connect to other switches or to a
router, usually you need to set the port in in trunk mode.
VLAN traffic is tagged using dot1q or the Cisco ISL.
The standards based dot1q is used everywhere these
days.
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Slide 6
dot1q inserts a 4 byte field into the existing layer 2 header. The
VLAN ID field is 12 bits which allows for VLAN numbers up to 4094.The switch itself may only support a much smaller number of VLANse.g. 64 VLANs or 255 VLANs.
One special VLAN is called a Native VLAN. Frames belonging to thisVLAN are sent across a trunk without being tagged. The default Native
VLAN is VLAN 1 but for security this is usually changed to a different
VLAN.
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Slide 7
dot1q inserts a 4 byte field to make the frame slightly larger (a baby giant). One
of the dot1q fields (the priority field) is used forquality of service
Traffic like voice or video only works because it is given a high priority
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Slide 8
In CCNP you learn how to configure a special VLAN for
voice traffic. The tagged frames coming into the switch
belong to the voice vlan.
The untagged frames come from the PC and belong to
whatever the native VLAN is for that port.
e.g. switchport voice vlan 200
switchport access vlan 3 pmakes VLAN 3 the native
VLAN for that port.
More about this in CCNP BCMSN and ONT
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Vlan Trunking Protocol
(VTP)Create VLANs on one vtp server
switch (Sw1). Soon all of the vtp
client switches (Sw2, Sw3) in thesame VTP domain have learnt
the VLANs
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Slide 10
VLAN Trunking Protocol (VTP)
Purpose: maintain VLAN configuration
consistency across the entire domain.
Dont need to worry about typing errors when
adding vlans to other switches
e.g. -vlan)# name building_51_ITS_voice
A messaging protocol that uses Layer 2 trunk
frames to manage the addition, deletion, and
renaming of VLANs from a centralized switch that
is in the VTP server mode
Note: only VLAN information is advertised. You
still need to allocate switch ports to VLANs
manually.
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Slide 11
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Slide 13
VTP conditions:
- switch belong only to one domain.
-Cisco proprietary
-VTP frames only sent on trunk links to otherswitches in the same domain.
- 3 modes : server, client, transparent.
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Slide 14
Modes: server, client or transparent
A client switch in the same domain will change its VLAN
information to agree with the VTP advertisement sent by the VTPserver.
But a transparent mode switch willignore VTP messages butpass them to server or clients. VLANs created on transparent
switches are local only.
To turn off VTP
Sw2(config)# vtp mode transparent
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Slide 15
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Slide 17
Careful when adding a switch
The new switch should have its VLAN
information erased before being added to
the network. If not, the replacement switch
might have a revision number that makes it
seem to have newer information. Thisswitches trunking information then
replaces the existing information that is on
the switches.(The new switches existing revision
number would be what it had previously
wherever it waslocated)
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Slide 18
The newly added switch (SwitchB) has a
higher revision number. Its 7 VLANs
overwrites the existing 5 VLANs!NOTE: It doesnt matter whether the newly
introduced switch is a server or a client