Troubleshooting guidelines for switching and VLANs
After configuring your switch with Vlans you notice that something is wrong.
I will give you a simple guide to troubleshoot Vlans and make things work again.
- First check for Layer 1 and Layer 2 issues
- Is the cable plugged into the correct port?
- Is the link light on, and if so, what color is it? (If the led has a green color, it means that the switch port is in the forwarding state, if the port led has a yellow color the port is in the blocking state and if the port has a yellow blinking led, it is in the error state.
- We can use the Switch# show interface command to confirm link state
- Check the duplex mode
- Check the speed of the port
- Avoid autonegotiation
- Check Vlan 1 for IP address
- Check if default gateway is set on the switch
- Verify the trunking configuration
- Check the trunking protocol (802.1Q or ISL)
- If you have more than one vlans that you want to communicate one with the other you must configure intervlan routing.
- Verify that you have add the Vlans to your switch and that you have assigned the correct ports to the correct vlan
- Use the command Switch# Show vlan
- Check the spanning-tree configuration
- Use the command Switch# show spanning-tree
- Check the VTP settings (VTP domain name, mode, password and revision number)
That are the most common mistakes when we try to setup a vlan and i hope i covered most of them. Seems troubleshooting articles are a good source of information that can help a lot of people so, expect some more in the near future.
Dear Mr. jim,
your articles are very nice and simple to understand.
can you please write an articles about loop & loop avaidance and finding root bridge/port, designated,blocked etc.
Regards
Hazem.
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Dear Sir,
This is an off topic question.
I am connected with other computers in a network at my workplace.
We are connected through the internet through a default gateway.
Since I run the place, not all the computers are granted access to the internet.
The question is, how do I check which computers are connected to the ip address that allows them to connect to the internet?
I am suspecting that one of my employees is connected to the net without my consent.
The computer I am using is not the server.
Please help me with this problem.
Thank you and I’ll wait for your email.
Hello,
I found you site and I must say it is very simple to follow you steps, and for someone that is new to Cisco doing CCENT I just love how simple everything is explained. I downloaded the the Use passwords to Secure Your Cisco Network, at the bottom it says stay tuned…
I can’t find the next post, can you send me the link and any other links that yo have about config a Cisco router, I just got a 871 router to do labs and love to get to it as soon as possible.
Thanks for all of your help.
С Новым Годом! Больше читателей в новом году!
кто бы мог подумать=) так держать!
действительно, довольно интересно…
откуда у вас такие сведения?
Легче нести ахинею, чем бревно.
Эх, взять бы автомат, да разрядить обстановку!!!!=)
Аксиома с тоской вспоминала то время, когда она была еще теоремой…
Разговор начистоту обычно заканчивается взаимным обливанием грязью.
Наивность - это редкий дар смотреть на мир невооруженным взглядом…
Последнее время читаю между строк. Стал меньше уставать.
Хорошая статья. Краткость явно сестра автора
Молодец! Поддерживаю!