VLANs - Revision history

Pio2pio: /* Native VLAN */

2015-04-10T20:43:13Z

Native VLAN

← Older revision		Revision as of 22:43, 10 April 2015
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	= Native VLAN =		= Native VLAN =
	;Tagged Frames on the Native VLAN		;Tagged Frames on the Native VLAN - are discarded
	Some devices that support trunking, add a VLAN tag to native VLAN traffic. Control traffic sent on the native VLAN should not be tagged. If an 802.1Q trunk port receives a tagged frame with the VLAN ID the same as the native VLAN, it drops the frame. Consequently, when configuring a switch port on a Cisco switch, configure devices so that they do not send tagged frames on the native VLAN. Devices from other vendors that support tagged frames on the native VLAN include IP phones, servers, routers, and non-Cisco switches.		Some devices that support trunking, add a VLAN tag to native VLAN traffic. Control traffic sent on the native VLAN should not be tagged. If an 802.1Q trunk port receives a tagged frame with the VLAN ID the same as the native VLAN, it drops the frame. Consequently, when configuring a switch port on a Cisco switch, configure devices so that they do not send tagged frames on the native VLAN. Devices from other vendors that support tagged frames on the native VLAN include IP phones, servers, routers, and non-Cisco switches.

	;Untagged Frames on the Native VLAN		;Untagged Frames on the Native VLAN
	When a Cisco switch trunk port receives untagged frames (which are unusual in a well-designed network), it forwards those frames to the native VLAN. If there are no devices associated with the native VLAN (which is not unusual) and there are no other trunk ports (which is not unusual), then the frame is dropped. The default native VLAN is VLAN 1. When configuring an 802.1Q trunk port, a default Port VLAN ID (PVID) is assigned the value of the native VLAN ID. All untagged traffic coming in or out of the 802.1Q port is forwarded based on the PVID value. For example, if VLAN 99 is configured as the native VLAN, the PVID is 99 and all untagged traffic is forwarded to VLAN 99. If the native VLAN has not been reconfigured, the PVID value is set to VLAN 1.		When a Cisco switch trunk port receives untagged frames (which are unusual in a well-designed network), it forwards those frames to the native VLAN. If there are no devices associated with the native VLAN (which is not unusual) and there are no other trunk ports (which is not unusual), then the frame is dropped. The default native VLAN is VLAN 1. When configuring an 802.1Q trunk port, a default Port VLAN ID (PVID) is assigned the value of the native VLAN ID. All untagged traffic coming in or out of the 802.1Q port is forwarded based on the PVID value. For example, if VLAN 99 is configured as the native VLAN, the PVID is 99 and all untagged traffic is forwarded to VLAN 99. If the native VLAN has not been reconfigured, the PVID value is set to VLAN 1.

	= Troubleshooting =		= Troubleshooting =

Pio2pio: /* Troubleshooting */

2015-04-10T20:38:16Z

Troubleshooting

← Older revision		Revision as of 22:38, 10 April 2015
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	; Lack of connectivity - missing VLAN		; Lack of connectivity - missing VLAN
	# Make sure your devices have correct ip addresses in correct subnets		# Make sure your devices have correct ip addresses in correct subnets
	# Check whether ports are a members of the correct VLAN~~<br>~~<code>show vlan</code~~><br~~>		# Check whether ports are a members of the correct VLAN <code>'''show vlan'''</code>
	# Issue <code>show interfaces switchport</code> and search for ''Inactive'' means that the VLAN has been deleted from <tt>vlan.dat</tt> file and needs recreating. This is because each port in a switch belongs to a VLAN.		# Issue <code>'''show interfaces switchport'''</code> and search for ''Inactive'' means that the VLAN has been deleted from <tt>vlan.dat</tt> file and needs recreating. This is because each port in a switch belongs to a VLAN.

	; Trunk link troubleshooting		; Trunk link troubleshooting

Pio2pio: /* Troubleshooting */

2015-01-06T16:35:40Z

Troubleshooting

← Older revision		Revision as of 18:35, 6 January 2015
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	# '''Trunk status''' - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.		# '''Trunk status''' - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.
	# '''Allowed VLANs on trunk''' - use <code>show interfaces trunk</code> to see allowed VLANs on the trunk link. There can be missing or not allowed VLAN causing the problem.		# '''Allowed VLANs on trunk''' - use <code>show interfaces trunk</code> to see allowed VLANs on the trunk link. There can be missing or not allowed VLAN causing the problem.

			= Security - control traffic =
			All control traffic is sent on '''VLAN 1'''. Therefore, when the native VLAN is changed to something other than VLAN 1, all control traffic is tagged on IEEE 802.1Q VLAN trunks (tagged with VLAN ID 1). A recommended security practice is to change the native VLAN to a different VLAN than VLAN 1.

	[[Category:cisco]]		[[Category:cisco]]

Pio2pio: /* Troubleshooting */

2015-01-06T14:28:58Z

Troubleshooting

← Older revision		Revision as of 16:28, 6 January 2015
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	# '''Native VLAN check''' - use <code>show interfaces trunk</code> at both ends to check whether a native VLAN matches on both sites. If not VLAN leaking occurs meaning that port can accept frames form a different VLAN that is assigned to. If CDP is enabled it will display <tt>%CDP-4-NATIVE_VLAN_MISMATCH</tt> message.<br>In a native VLAN mismatch scenario connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.		# '''Native VLAN check''' - use <code>show interfaces trunk</code> at both ends to check whether a native VLAN matches on both sites. If not VLAN leaking occurs meaning that port can accept frames form a different VLAN that is assigned to. If CDP is enabled it will display <tt>%CDP-4-NATIVE_VLAN_MISMATCH</tt> message.<br>In a native VLAN mismatch scenario connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.
	# '''Trunk status''' - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.		# '''Trunk status''' - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.
	# '''Allowed VLANs on trunk''' - use <code>show interfaces trunk</code> to see allowed VLANs on the trunk link.		# '''Allowed VLANs on trunk''' - use <code>show interfaces trunk</code> to see allowed VLANs on the trunk link. There can be missing or not allowed VLAN causing the problem.

	[[Category:cisco]]		[[Category:cisco]]

Pio2pio: /* Troubleshooting */

2015-01-06T14:27:29Z

Troubleshooting

← Older revision		Revision as of 16:27, 6 January 2015
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	# '''Native VLAN check''' - use <code>show interfaces trunk</code> at both ends to check whether a native VLAN matches on both sites. If not VLAN leaking occurs meaning that port can accept frames form a different VLAN that is assigned to. If CDP is enabled it will display <tt>%CDP-4-NATIVE_VLAN_MISMATCH</tt> message.<br>In a native VLAN mismatch scenario connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.		# '''Native VLAN check''' - use <code>show interfaces trunk</code> at both ends to check whether a native VLAN matches on both sites. If not VLAN leaking occurs meaning that port can accept frames form a different VLAN that is assigned to. If CDP is enabled it will display <tt>%CDP-4-NATIVE_VLAN_MISMATCH</tt> message.<br>In a native VLAN mismatch scenario connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.
	# '''Trunk status''' - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.		# '''Trunk status''' - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.
	# '''Allowed VLANs on trunk - use <code>show interfaces trunk</code> to see allowed VLANs on the trunk link.		# '''Allowed VLANs on trunk''' - use <code>show interfaces trunk</code> to see allowed VLANs on the trunk link.

	[[Category:cisco]]		[[Category:cisco]]

Pio2pio: /* Troubleshooting */

2015-01-06T14:27:18Z

Troubleshooting

← Older revision		Revision as of 16:27, 6 January 2015
Line 138:		Line 138:
	; Trunk link troubleshooting		; Trunk link troubleshooting
	# '''Native VLAN check''' - use <code>show interfaces trunk</code> at both ends to check whether a native VLAN matches on both sites. If not VLAN leaking occurs meaning that port can accept frames form a different VLAN that is assigned to. If CDP is enabled it will display <tt>%CDP-4-NATIVE_VLAN_MISMATCH</tt> message.<br>In a native VLAN mismatch scenario connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.		# '''Native VLAN check''' - use <code>show interfaces trunk</code> at both ends to check whether a native VLAN matches on both sites. If not VLAN leaking occurs meaning that port can accept frames form a different VLAN that is assigned to. If CDP is enabled it will display <tt>%CDP-4-NATIVE_VLAN_MISMATCH</tt> message.<br>In a native VLAN mismatch scenario connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.
	# '''Trunk status''' - - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.		# '''Trunk status''' - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.
			# '''Allowed VLANs on trunk - use <code>show interfaces trunk</code> to see allowed VLANs on the trunk link.

	[[Category:cisco]]		[[Category:cisco]]

Pio2pio: /* Troubleshooting */

2015-01-06T14:24:02Z

Troubleshooting

← Older revision		Revision as of 16:24, 6 January 2015
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	= Troubleshooting =		= Troubleshooting =
			; Lack of connectivity - missing VLAN
	# Make sure your devices have correct ip addresses in correct subnets		# Make sure your devices have correct ip addresses in correct subnets
	# Check whether ports are a members of the correct VLAN<br><code>show vlan</code><br>		# Check whether ports are a members of the correct VLAN<br><code>show vlan</code><br>

Pio2pio: /* Troubleshooting */

2015-01-06T14:23:19Z

Troubleshooting

← Older revision		Revision as of 16:23, 6 January 2015
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	# Check whether ports are a members of the correct VLAN<br><code>show vlan</code><br>		# Check whether ports are a members of the correct VLAN<br><code>show vlan</code><br>
	# Issue <code>show interfaces switchport</code> and search for ''Inactive'' means that the VLAN has been deleted from <tt>vlan.dat</tt> file and needs recreating. This is because each port in a switch belongs to a VLAN.		# Issue <code>show interfaces switchport</code> and search for ''Inactive'' means that the VLAN has been deleted from <tt>vlan.dat</tt> file and needs recreating. This is because each port in a switch belongs to a VLAN.

			; Trunk link troubleshooting
			# '''Native VLAN check''' - use <code>show interfaces trunk</code> at both ends to check whether a native VLAN matches on both sites. If not VLAN leaking occurs meaning that port can accept frames form a different VLAN that is assigned to. If CDP is enabled it will display <tt>%CDP-4-NATIVE_VLAN_MISMATCH</tt> message.<br>In a native VLAN mismatch scenario connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.
			# '''Trunk status''' - - use <code>show interfaces trunk</code> at both ends. If possible configure interfaces to ''trunk'' mode. Cisco Catalyst switch ports use DTP by default and attempt to negotiate a trunk link.

	[[Category:cisco]]		[[Category:cisco]]

Pio2pio: /* Trouble shooting */

2015-01-06T14:12:45Z

Trouble shooting

← Older revision		Revision as of 16:12, 6 January 2015
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	When a Cisco switch trunk port receives untagged frames (which are unusual in a well-designed network), it forwards those frames to the native VLAN. If there are no devices associated with the native VLAN (which is not unusual) and there are no other trunk ports (which is not unusual), then the frame is dropped. The default native VLAN is VLAN 1. When configuring an 802.1Q trunk port, a default Port VLAN ID (PVID) is assigned the value of the native VLAN ID. All untagged traffic coming in or out of the 802.1Q port is forwarded based on the PVID value. For example, if VLAN 99 is configured as the native VLAN, the PVID is 99 and all untagged traffic is forwarded to VLAN 99. If the native VLAN has not been reconfigured, the PVID value is set to VLAN 1.		When a Cisco switch trunk port receives untagged frames (which are unusual in a well-designed network), it forwards those frames to the native VLAN. If there are no devices associated with the native VLAN (which is not unusual) and there are no other trunk ports (which is not unusual), then the frame is dropped. The default native VLAN is VLAN 1. When configuring an 802.1Q trunk port, a default Port VLAN ID (PVID) is assigned the value of the native VLAN ID. All untagged traffic coming in or out of the 802.1Q port is forwarded based on the PVID value. For example, if VLAN 99 is configured as the native VLAN, the PVID is 99 and all untagged traffic is forwarded to VLAN 99. If the native VLAN has not been reconfigured, the PVID value is set to VLAN 1.

	= ~~Trouble shooting~~ =		= Troubleshooting =

	# Make sure your devices have correct ip addresses in correct subnets		# Make sure your devices have correct ip addresses in correct subnets

Pio2pio: /* Native VLAN */

2015-01-06T14:12:11Z

Native VLAN

← Older revision		Revision as of 16:12, 6 January 2015
Line 129:		Line 129:
	;Untagged Frames on the Native VLAN		;Untagged Frames on the Native VLAN
	When a Cisco switch trunk port receives untagged frames (which are unusual in a well-designed network), it forwards those frames to the native VLAN. If there are no devices associated with the native VLAN (which is not unusual) and there are no other trunk ports (which is not unusual), then the frame is dropped. The default native VLAN is VLAN 1. When configuring an 802.1Q trunk port, a default Port VLAN ID (PVID) is assigned the value of the native VLAN ID. All untagged traffic coming in or out of the 802.1Q port is forwarded based on the PVID value. For example, if VLAN 99 is configured as the native VLAN, the PVID is 99 and all untagged traffic is forwarded to VLAN 99. If the native VLAN has not been reconfigured, the PVID value is set to VLAN 1.		When a Cisco switch trunk port receives untagged frames (which are unusual in a well-designed network), it forwards those frames to the native VLAN. If there are no devices associated with the native VLAN (which is not unusual) and there are no other trunk ports (which is not unusual), then the frame is dropped. The default native VLAN is VLAN 1. When configuring an 802.1Q trunk port, a default Port VLAN ID (PVID) is assigned the value of the native VLAN ID. All untagged traffic coming in or out of the 802.1Q port is forwarded based on the PVID value. For example, if VLAN 99 is configured as the native VLAN, the PVID is 99 and all untagged traffic is forwarded to VLAN 99. If the native VLAN has not been reconfigured, the PVID value is set to VLAN 1.

			= Trouble shooting =

			# Make sure your devices have correct ip addresses in correct subnets
			# Check whether ports are a members of the correct VLAN<br><code>show vlan</code><br>
			# Issue <code>show interfaces switchport</code> and search for ''Inactive'' means that the VLAN has been deleted from <tt>vlan.dat</tt> file and needs recreating. This is because each port in a switch belongs to a VLAN.

	[[Category:cisco]]		[[Category:cisco]]