01-07-2013 09:09 AM - edited 03-07-2019 10:57 AM
I was wondering if someone could help me understand what's happening with VLAN tagging on my network setup. I included a picture for reference.
This configuration has the intention to offer redundancy. The server (has 4 nics) is actually connected to another switch in the same manner, so if one switch went down it could still communicate with both networks. We don't need to share the Vlans over a trunk link since Vlan 1 stays on Network 1 and Vlan 2 stays on Network 2. I wonder if this is a proper configuration of switches because I'm not sure how S1 Vlan 2 communicates with S3 if the frames are tagged with vlan 2. Would S3 still accept this data and remove the Vlan 2 tagging information and forward to Network 2? VLAN config is all manual no VTP is being used.
Currently S1 is only displaying a Vlan mismatch for the port going to S2. I thought I would also see an error for the port going to S3?
Thank you in advance for helping me understand how information is traveling in this configuration!
01-07-2013 09:18 AM
I think I might have answered my own question. I really didn't know what I was asking until I wrote out this post. I guess I am wondering why tagged traffic functions to another switch that isn't configured for a VLAN. I read in another discussion about vlan mismatch that vlan tags are only applicable when using trunks, I'm not using trunks. Does this mean the S1 switch is basically seperated in half for both networks in my scenario? When frames leave S1 are they tagged and then removed at S3/S2 or to they leave S1 untagged since the other end isn't configured?
In my scenario is there a better way to split the switch in half for use on 2 networks?
01-07-2013 09:52 AM
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If ports are not VLAN trunks, i.e. they pass frames untagged. It's certainly possible to interconnect switches (or a switch) whose ports are assigned to different VLANs. (Normally you very much want to avoid doing this.)
From you topology diagram, and you description, I'm guessing your server is bridging the two VLANs. If Cisco CDP is active, is will "notice" the port VLANs don't agree and throw the warning about the VLAN mismatch.
PS:
As how network redundancy might be provided to your server hosts, there's various ways to deal with that. How "best" depends much on the capabilities of the edge host and also what your network devices support.
01-07-2013 10:01 AM
The servers are just connected to access ports that are in Vlan 1 or 2, they're not doing any bridging.
"If ports are not VLAN trunks, i.e. they pass frames untagged. It's certainly possible to interconnect switches (or a switch) whose ports are assigned to different VLANs. (Normally you very much want to avoid doing this.)"
No trunk ports are configured, although it seems that vlan tagging is still occuring since there is a vlan mismatch error being displayed.
01-07-2013 09:24 AM
Does the native VLAN match on each trunked unlink with another switch - i.e. are you using the same native VLAN on the trunked interface between S1 and S2? Same for the uplink between S1 and S3.
01-07-2013 09:28 AM
No trunk ports are being used. The links on S1 are are on vlans that don't match S2 or S3.
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