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Understanding of VLAN - VLAN Switch

Latest reply: Jun 14, 2021 13:48:38 206 20 20 0 0

OBJECTIVE


The purpose of this post is to present an introduction to VLAN Switch.


VLAN Switch


VLAN switch is a forwarding technology based on VLAN tags. VLAN switch requires a pre-configured static forwarding path along the switching nodes on the network. After receiving VLAN-tagged frames that meet forwarding requirements, a switching node directly forwards the frames to corresponding interfaces by searching the VLAN switch table rather than the MAC address table. This improves forwarding efficiency and network security, and prevents MAC address attacks and broadcast storms.


VLAN switch functions are as follows:


  • Adding an outer VLAN tag (the VLAN switch stack-vlan function)


  • Switching the outer VLAN tags between interfaces (the VLAN switch switch-vlan function)


VLAN Switch stack-vlan


Similar to VLAN stacking, VLAN switch stack-vlan is a Layer 2 technology used to encapsulate the outer VLAN tag to frames according to user VLANs. Table 1 lists the comparison between VLAN stacking and VLAN switch stack-vlan.


i_f42.gifFor VLAN stacking functions, see VLAN Stacking.


Function SimilarityDifferenceAdvantage/Disadvantage 
VLAN switch stack-vlan
  • You can add another VLAN tag to a received frame with an outer tag.


  • Frames are processed as follows:


  • An interface can be configured with multiple VLANs and add different outer VLAN tags to frames from different VLANs.


  • When receiving a frame, the interface adds a VLAN tag to the frame; when sending a frame, the interface removes the outmost VLAN tag.

VLAN switch requires a pre-configured static forwarding path along the switching nodes on the network. After receiving VLAN-tagged frames that meet forwarding requirements, the switching node directly forwards the frames by searching the VLAN switch table rather than the MAC address table.


The VLAN IDs specified in the vlan-switch command should not conflict with the global VLAN. If a specified VLAN ID has been applied in VLAN switch, the VLAN cannot be configured as the global VLAN.

  • Advantage:


Switching nodes can forward frames without searching the MAC address table, which improves forwarding efficiency and network security, and prevents MAC address attacks and broadcast storms.


  • Disadvantage:


If a large number of users access a switching node, you need to configure each user device in advance to establish a static forwarding path. This increases the workload of the network administrator and is inconvenient for network management.

VLAN stackingAfter VLAN stacking is configured, frames are forwarded according to the MAC address table.
  • Advantage:


It is convenient for user access without any pre-configuration. Frames are forwarded according to the MAC address table.


  • Disadvantage:


Frame forwarding efficiency is low, which easily results in broadcast storms or MAC address attacks.

Table 1 - Comparison between VLAN stacking and VLAN switch


VLAN Switch switch-vlan


Similar to VLAN mapping, VLAN switch switch-vlan implements communications between VLANs. Table 2 lists comparison between VLAN mapping and VLAN switch.


i_f42.gifFor VLAN mapping functions, see VLAN Mapping.


Function SimilarityDifferenceAdvantage/Disadvantage
VLAN switch switch-vlan
  • After receiving VLAN-tagged frames, an interface replaces the outer VLAN tag.


  • After an interface is configured with either VLAN mapping or VLAN switch, it replaces the local VLAN tag with the external VLAN tag when sending local frames to an external VLAN.


  • The interface replaces the VLAN tag of the frames with the local VLAN tag when receiving frames from an external VLAN.

VLAN switch requires a pre-configured static forwarding path along the switching nodes on the network. After receiving VLAN-tagged frames that meet forwarding requirements, the switching node directly forwards the frames by searching the VLAN switch table rather than the MAC address table.


The VLAN IDs specified in the vlan-switch command should not conflict with the global VLAN. If a specified VLAN ID has been applied in VLAN switch, the VLAN cannot be created in the global VLAN.

  • Advantage:


Switching nodes can forward frames without searching the MAC address table, which improves forwarding efficiency and network security, and prevents MAC address attacks and broadcast storms.


  • Disadvantage:


If a large number of users access a switching node, you need to configure each user device in advance to establish a static forwarding path. This increases the workload of the network administrator and is inconvenient for network management.

VLAN mapping

After VLAN Mapping is configured, frames are forwarded according to the MAC address table.


When using VLAN Mapping to implement inter-VLAN communications, you need to ensure that the IP addresses of devices in both VLANs are in the same network segment.

  • Advantage:


It is convenient for user access without any pre-configuration. Frames are forwarded according to the MAC address table.


  • Disadvantage:


Frame forwarding efficiency is low, which easily results in broadcast storms or MAC address attacks.

Table 2 - Comparison between VLAN mapping and VLAN switch




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Saqib123
Created Jun 13, 2021 16:11:55

Thanks for sharing
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EL.BODO
EL.BODO Created Jun 13, 2021 17:20:51 (0) (0)
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Faridrami
Created Jun 13, 2021 16:39:01

good dear friend and Thanks for sharing
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EL.BODO
EL.BODO Created Jun 13, 2021 17:21:12 (1) (0)
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Faridrami
Faridrami Reply EL.BODO  Created Jun 15, 2021 08:32:01 (0) (0)
 
Faridrami
Faridrami Reply EL.BODO  Created Jun 15, 2021 08:32:12 (0) (0)
 
LilStylz237
Created Jun 13, 2021 16:44:46

Very good explanation
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LilStylz237
Created Jun 13, 2021 16:44:58

Thanks
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EL.BODO
Created Jun 13, 2021 17:21:37

Well done
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EL.BODO
Created Jun 13, 2021 17:21:54

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Herediano
Created Jun 13, 2021 17:41:01

Great thank you
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wissal
MVE Created Jun 13, 2021 17:47:10

Interesting to know
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Vlada85
MVE Author Created Jun 13, 2021 18:02:15

Very good article. Thank you
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