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vlan best practice?

Hello

I have two 3560's that I have to monitor but wont physically be on my network. I vlan'd these switches so that one port would be seperated strictly so I could uplink them with my physical network for SMTP and monitoring.

My question is what port settings are best for this one port that goes back to my network? I would assume that technically being a trunk the port should be switchport mode trunk? and not access.

Funny thing is that when I set it as trunk and plug it in i see a topo change propogate out. Whereas when its set for switchport mode access I do not. STP is running in PVST

port stats are as follows

switchport access vlan 2

switchport trunk encapsulation dot1q

switchport mode trunk

spanning-tree portfast

i'm confused as to why this mode would cause the topo changes.

thanks

Eric

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Accepted Solutions
Blue

Re: vlan best practice?

you will see a topo change when you set this port to a trunk as STP must assure a loopfree topology.

(a trunk acts like an extension of the bridge, ie: topo change when changing trunk operational status)

if the port is simply set to access w/portFast you will not see STP topo change.

also note, that this link only needs to be a trunk if it needs to support multiple VLANs. if there is only one VLAN on your LAN/switches, then a trunk is unecessesary.

it sounds like you could/want to set this up as only a routed interface uplink to the network, not necessarily a switched uplink to the network.

2 REPLIES
Blue

Re: vlan best practice?

you will see a topo change when you set this port to a trunk as STP must assure a loopfree topology.

(a trunk acts like an extension of the bridge, ie: topo change when changing trunk operational status)

if the port is simply set to access w/portFast you will not see STP topo change.

also note, that this link only needs to be a trunk if it needs to support multiple VLANs. if there is only one VLAN on your LAN/switches, then a trunk is unecessesary.

it sounds like you could/want to set this up as only a routed interface uplink to the network, not necessarily a switched uplink to the network.

Re: vlan best practice?

Hi,

you have configured a port to access vlan2. Also the same port as trunk port.

Note:Trunk ports are supposed to carry all VLans but not a single vlan.

If you using only a single vlan means trunk port can be used to connect between a switch & a router. In that case you can use switch's uplink port as the trunk port.

eg: int faeth 0/24

switchport trunk encapsulation dot1q

switchport mode trunk

spanning-tree portfast

Also in router the same:

#encapsulation dot1q

Portfast: If a port with portfast enabled means you should connect a device into it eg:switch/router/bridge but not a system becoz port with portfast enabled will make the port to comeup immediately even if goesdown ie., it skips the initial/listen state during the process and directly comes to forwarding state.

If a system is connected to a port with portfast enabled means STP loop may form and network congestion may occur.

Hope this will help you a lot!!!!

Plz rate if this help you!!!!

Regards,

Guru Prasad.R

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