How do I troubleshoot a VLAN problem?
How do I troubleshoot a VLAN problem?
How to Troubleshoot a VLAN Configuration
- The first thing you need to do is to make sure that your cable and switch port are good.
- Next, check your switche’s interface configuration.
- If two hosts cannot communicate then check whether they are in the same VLAN.
What are VLAN troubleshooting commands?
VLAN Troubleshooting Commands
- show vlan. When devices are not communicating with each other while supposedly configured on the same VLAN, the first command you should run on the switch is show vlan.
- show interfaces vlan (#)
- show interfaces trunk.
Why VTP is not working?
If VTP is not updating the VLANs correctly, check to make sure the MD5 digest on all VTP domain switches is the same. The MD5 digest is calculated using the revision number, domain name, and password to make sure the information in the VTP update can be trusted.
How do you resolve a problem with spanning tree?
One solution to the problem is to simply disable spanning tree on the switch. This is the wrong solution. The right solution is to configure a feature called PortFast on Cisco switches. (Most switch vendors have a similar feature.)
What are the common issues in VLAN?
Table 3-9 Common Problems with Trunks
| Problem | Result |
|---|---|
| Native VLAN mismatch | Poses a security risk and creates unintended results |
| Trunk mode mismatch | Causes loss of network connectivity |
| Allowed VLANs on trunks | Causes unexpected traffic or no traffic to be sent over the trunk |
How do I test a VLAN?
You can generate bidirectional traffic across the routers to test the VLAN performance by hanging one PC off each router to be the destination for SmartBits-generated traffic and connecting the two SmartBits ports to the opposite routers and driving traffic both ways through the configuration.
How do you troubleshoot a switch problem?
List of steps
- Define the problem.
- Find device(s) having issues.
- Check VLANs configuration.
- Verify trunk ports configuration.
- Check access ports configuration.
- Troubleshoot client issues.
What are the common issues of VTP?
– VTP domain and password must match. – Configuration has been overwritten by another VTP device. – Consider making VTP domain smaller.
How do I know if VTP is working?
The command to verify VTP operation is show vtp status, which is shown in Example 3.1 on SwitchA. It looks like SwitchA is in the default (unmodified) VTP configuration. The key (highlighted) configuration items follow: VTP Version/VTP V2 Mode: By default, Cisco switches run VTP version 1.
What causes spanning tree loops?
What Action Causes a Loop? The spanning-tree protocol family is responsible for breaking loops in a network of bridges with redundant links. However, hardware failures can create forwarding loops (STP loops) and cause major network outages. Spanning-tree protocols break loops by blocking ports (interfaces).
What is spanning tree VLAN?
Per VLAN Spanning Tree (PVST) is a Cisco proprietary protocol that allows a Cisco device to have multiple spanning trees. The Cisco device can interoperate with spanning trees on other PVST devices but cannot interoperate with IEEE 802.1Q devices. An IEEE 802.1Q device has all its ports running a single spanning tree.
What is VLAN leakage?
Sometimes a switch port may behave like a trunk port even if it is not configured as a trunk port. For example, an access port might accept frames from VLANs different from the VLAN to which it is assigned. This is called VLAN leaking, which is caused by a mismatched native VLAN or misconfigured trunk.
How do I know if my VLAN tag is working?
So, your quickest and best bet to determine if tagging is working is either to mirror a port (not all switches will mirror trunk ports) or simply do basic connectivity tests.
What is the range of normal VLANs?
VLAN Ranges
| VLANs | Range | Usage |
|---|---|---|
| 1 | Normal | Cisco default. You can use this VLAN but you cannot delete it. |
| 2-1001 | Normal | For Ethernet VLANs; you can create, use, and delete these VLANs. |
| 1002-1005 | Normal | Cisco defaults for FDDI and Token Ring. You cannot delete VLANs 1002-1005. |
| 1006-4094 | Extended | For Ethernet VLANs only. |
What is VTP domain mismatch?
Core issue. The DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port [chars] because of VTP domain mismatch error message indicates that the two ports in the trunk negotiation belong to different VTP domains. Trunking can be configured only when the ports belong to the same VTP domain.
How do I check VTP mode?
What is the difference between VLAN and VTP?
VLAN configuration is done on one switch (i.e. switch in VTP server mode). The VTP protocol automatically propagates VLAN information to all the switches in the domain i.e. switches with VTP client modes.
Can you have two VTP servers?
NOTE Multiple VTP servers can coexist in a domain. This usually is recommended for redundancy. The servers do not elect a primary or secondary server; they all simply function as servers. If one server is configured with a new VLAN or VTP parameter, it advertises the changes to the rest of the domain.
