What is the effect of native VLAN mismatch?
What is the effect of native VLAN mismatch?
Recall that the native VLAN is the VLAN associated with untagged traffic. Mismatched native VLANs on opposite sides of a trunk can inadvertently create “VLAN hopping.” This is often a method of intentional attack used to sneak into a network and is an open security risk.
How do I disable native VLAN mismatch?
How to disable CDP-4-NATIVE_VLAN_MISMATCH (native vlan mismatch)
- Configure at least one of the two switches to be in transparent mode. You may not want that, but if you don’t know what this means then just do it:
- Change the VTP domain of that switch: Switch(config)# vtp domain a_unique_name.
Does STP prevent native VLAN mismatches?
STP is running an instance per vlan. As vlan 1 is native (and assuming we have not configured the software to explicitly tag native vlan), it sends and expects untagged frames to be on vlan 1. STP doesn’t like this, so it block as being inconsistent. Same for the other mismatched vlan.
Should I change the native VLAN?
Changing the native VLAN is mostly related to preventing VLAN hopping attacks. If this is of a concern you should use a different native VLAN on trunk ports between switches. For safety, this should be a VLAN not in use in the network. You want every valid VLAN to be tagged between switches.
What is the difference between native VLAN and default VLAN?
The default VLAN is always VLAN 1, and it can’t be changed. By default, Native VLAN is VLAN 1, but it can be changed to any VLAN. Traffic will be sent when both Default and Native VLAN are the same.
Is native VLAN tagged or untagged?
In Cisco LAN switch environments the native VLAN is typically untagged on 802.1Q trunk ports. This can lead to a security vulnerability in your network environment. It is a best practice to explicitly tag the native VLAN in order to prevent against crafted 802.1Q double-tagged packets from traversing VLANs.
Why am I getting a native VLAN mismatch?
A VLAN mismatch occurs when two connected switchports have different VLAN configurations. For example, switch 1 port 1 is configured for native VLAN: 1, allowed VLANs: all. This port connects to switch 2 port 48 which is configured for native VLAN: 1, allowed VLANs: 1 and 2 only.
When you have a native VLAN mismatch on a configured trunk which protocol will alert you to the issue?
Cisco Discovery Protocol (CDP)
* The native VLAN mismatch is discovered though the exchange of Cisco Discovery Protocol (CDP) or Link Layer Disccovery Protocol (LLDP) messages, not through examination of the trunk itself.
What is native VLAN tagging?
Native VLAN Tagging is used when you want 802.1q to act a bit more like ISL in one way, namely you want it to tag the frames destined for the native VLAN. Normally, 802.1q does not tag frames. All VLANs are allowed. Any frame sent or received for VLAN 1 will be untagged and the rest of the VLANs will be tagged.
Why is it bad to use VLAN 1?
Even though normal network traffic crossing a trunk link is going to require a VLAN tag in the headers, the switch-to-switch control-plane communication is sent with no header present. If we leave the default native VLAN as 1, then a malicious developer could exploit this to gain access to another segment.
Which VLAN should be native?
VLAN 1
As VLAN 1 is the default native VLAN, it is used for untagged traffic. If you need to pass frames tagged VLAN 1, you will not be able to, by default. The solution is to change the default VLAN to another value. Once this is done, VLAN 1 can be passed across the trunk just the same as any other VLAN.
Is VLAN 1 Native VLAN?
Default VLAN is VLAN 1 which cannot be shut down in any case and also it carries controlling traffic. In the case of Cisco (and most vendors), the Default Native VLAN is VLAN 1.
