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April 8th, 2025 23:04
Clarification needed on how to trunk two Dell S4048T-ON switches
Switch 1 (ethernet 1/1/48)
vlan 20
ip address 10.20.30.1/23
no shutdown
ethernet 1/1/48
mtu 9198
switchport mode trunk
switchport trunk allowed vlan 20
Switch 2 (ethernet 1/1/48)
vlan 20
ip address 10.20.30.2/23
no shutdown
ethernet 1/1/48
mtu 9198
switchport mode trunk
switchport trunk allowed vlan 20
*My question: my expectation is I should be able to ping 10.20.30.2 from switch 1.
From switch 2, I should be able to ping 10.20.30.1.
This does not work and states destination unreachable.
This continues to fail unless I remove with switchport trunk allowed vlan 20 from both interfaces on both switches and replace it with switchport access vlan 20. Then I can ping as much as I want.
Both interfaces and vlans are up and line protocol up.
My thought is that setting switchport access vlan 20 locks the port to only vlan 20. It shouldn't work as a trunk allowing all specified vlans. Can someone please clarify if I understand this right?
But my main question, is why do the pings not work with the config I outlined above?
Thanks!
DELL-Joey C
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3.9K Posts
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April 9th, 2025 07:54
Hi,
I'm assuming you're running OS10 on the -ON switch, as this switch by default runs on OS9.
Can you try these commands, adding switchport access vlan 1 and mtu 9216 instead 9198
interface ethernet1/1/48
description Vlan_configuration_for_trunkport
switchport mode trunk
switchport access vlan 1
switchport trunk allowed vlan 20
mtu 9216
flowcontrol receive on
flowcontrol transmit off
no shutdown
bweddell
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31 Posts
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April 8th, 2025 23:06
Note that the interfaces 1/1/48 are also set to no shutdown.
bweddell
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April 9th, 2025 22:12
@DELL-Joey C thank you, that worked!
The config makes sense, mostly.
Why is there a requirement to allow access vlan 1 on a trunk port?
It seems it wouldn't be needed but I never could ping anything without it.
DELL-Joey C
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3.9K Posts
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April 10th, 2025 06:34
Hi,
Yes, your configuration seems to be correct, but adding switchport access vlan 1; the switch will allow untagged vlan. But I think there is an issue with the configuration, which it should not need to add switchport access vlan 1. Have you already reconfigured MTU to 9216?
Perhaps if you can, reconfigure the switch after you have deleted the startup config. Try not to use MTU yet. Then:
Switch 1 (ethernet 1/1/48)
vlan 20
ip address 10.20.30.1/24
no shutdown
(Check if you are able to ping 10.20.30.1 within switch1; it should reply)
ethernet 1/1/48
switchport mode trunk
switchport trunk allowed vlan 20
no shut
Switch 2 (ethernet 1/1/48)
vlan 20
ip address 10.20.30.2/24
no shutdown
(Check if you are able to ping 10.20.30.2 within switch2; it should reply)
ethernet 1/1/48
switchport mode trunk
switchport trunk allowed vlan 20
no shut
Now Switch2 ping Switch1 10.20.30.1, it should work. If it doesn't, the switches are having issues. You might need to collect the logs to share.