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Author Topic: Why Packets can Flow through different vlans  (Read 785 times)

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Offline HTHSeven

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Why Packets can Flow through different vlans
« on: January 14, 2017, 02:18:53 AM »
As attached from my network diagram, may I know that why my PC under vlan 100 can retrieve ip from dhcp server and communicate to internet even though the packet going through gateway is under vlan1?

Whereas for my wireless access point, the client can't access internet under vlan 100 and everything has to be set back to vlan 1 then only client manages to retrieve ip from dhcp to access the internet.

The 2 switches that I'm using is Avaya PoE switch. For the ports with vlan 100, the default vlan1 has been removed. untag ports.

Can someone advice what's happening here?


Offline Michael McNamara

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Re: Why Packets can Flow through different vlans
« Reply #1 on: January 14, 2017, 09:13:20 AM »
Welcome to the forums....

There are a few things that could be wrong.. have you check the PVID on each port? Is the AP in question tagging frames with an 802.1q header (VLAN tag)? Somewhere along the lines you are likely using VLAN 1 even though you think you are using VLAN 100. Look at the MAC/FDB table and see what VLAN the MAC address of the client is landing in, that's probably the easiest way to start off... then check your PVID settings on every port again.

Good Luck!
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Offline HTHSeven

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Re: Why Packets can Flow through different vlans
« Reply #2 on: January 17, 2017, 09:59:58 PM »
Hi,

Much appreciated for your reply. I'm sorry for the late reply.

Before that, may I know that is it necessary for the Gateway to be configured with Vlan100. Because the gateway is coming from office network and I think it should be fall to Vlan1.

So packets starting from gateway is Vlan1, when it enters the Avaya switch port which is access Vlan 100 and pvid 100, will it allowed to access?

According to my understanding, it shouldn't, and to me it is reasonable that that AP unable to retrieve DHCP. However, when the PC which is connected to port with vlan100, pvid100, untag, it is allowed to access, hence this made me confused.

Any comment for this issue? Thank you!

Offline HTHSeven

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Re: Why Packets can Flow through different vlans
« Reply #3 on: January 19, 2017, 11:02:09 PM »
Welcome to the forums....

There are a few things that could be wrong.. have you check the PVID on each port? Is the AP in question tagging frames with an 802.1q header (VLAN tag)? Somewhere along the lines you are likely using VLAN 1 even though you think you are using VLAN 100. Look at the MAC/FDB table and see what VLAN the MAC address of the client is landing in, that's probably the easiest way to start off... then check your PVID settings on every port again.

Good Luck!

Dear Michael,

I would like to update my findings here with. First of all, the Access Point that I'm using is Aruba IAP225. As from the attachment, I need to configure the client vlan assignment to be default vlan which is vlan1 only client would receive the dhcp and connects to internet.

Before that, I configured it to be on Vlan100 but things didn't work. As attached as your reference.

Hence, from above scenario, why does client on vlan100 unable to connect to internet but yes when client is on vlan1? Thank you in advanced for your further explanation and assist!