02-11-2019 11:09 PM - edited 03-08-2019 05:18 PM
Hi,
I have below two topologies for Access port and trunk port
Let me know your thought whether it will work or not
As per my view it should not work.
PC1(access)vlan10-------vlan10 SW1(access)-------(access)vlan20 SW2----------(access)vlan 20 PC2
PC1(access)vlan10-------vlan10 SW1(trunk)-------(trunk)vlan20 SW2----------(access)vlan 20 PC2
Solved! Go to Solution.
02-12-2019 03:23 AM
Assuming at either end of the trunk link, both switchports are configured with:
! switchport mode trunk switchport trunk allowed vlan all !
...the tagged frames will transit the link fine, however the two PCs will remain in separate VLANs so will be unable to communicate. You need a Layer3 interface to make this topology work.
If your switches are configured like:
! SW1 ! switchport mode trunk switchport trunk vlan 10 ! !SW2 ! switchport mode trunk switchport trunk vlan 20 !
...broadcast frames will transit the link however they will be silently dropped by the receiving switch as they are received on a switchport which has not been configured to receive that VLAN ID.
cheers,
Seb.
02-11-2019 11:33 PM
02-12-2019 01:52 AM
Hi there,
If I am reading you diagram correctly in scenario 1, the link between the switches, SW1 interface is mode access on VLAN 10 connected to SW2 on a switchport with mode access on VLAN20. If so, the frame would travel across the link untagged and when it reaches the other switch would then be tagged with the 'other' VLAN ID.
So in effect PC1 and PC2 are in the same broadcast domain. They would only be able to communicate if they were in the same IP subnet.
With the second scenario PC1 and PC2 would remain in separate broadcast domains.
cheers,
Seb.
02-12-2019 02:58 AM
So do you mean when packet from PC1 is received on SW, packet will be tagged with vlan10 and while egressing out on switch port2 it will be untagged?
02-12-2019 03:02 AM
Yes if it is leaving via a mode access port, then there will be no VLAN ID on the frame, therefore SW2 can receive it on its own access port and it will end up in VLAN20.
02-12-2019 03:06 AM
02-12-2019 03:17 AM
02-12-2019 07:25 AM
02-12-2019 03:07 AM
Can you please provide your opinion on case2 when there is trunk?
02-12-2019 03:23 AM
Assuming at either end of the trunk link, both switchports are configured with:
! switchport mode trunk switchport trunk allowed vlan all !
...the tagged frames will transit the link fine, however the two PCs will remain in separate VLANs so will be unable to communicate. You need a Layer3 interface to make this topology work.
If your switches are configured like:
! SW1 ! switchport mode trunk switchport trunk vlan 10 ! !SW2 ! switchport mode trunk switchport trunk vlan 20 !
...broadcast frames will transit the link however they will be silently dropped by the receiving switch as they are received on a switchport which has not been configured to receive that VLAN ID.
cheers,
Seb.
02-12-2019 10:10 AM
Thank you all for bearing my questions. It was very informative.
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