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VLANs with IP Routing

Aaron Kovacich
Occasional Contributor

VLANs with IP Routing

I am working with a setup where VLANs are being extended over their WAN (fiber) link. Site A (core) has VLAN 20 setup, an IP set, and the port to site B tagged for VLAN20. Is this setup, Site B also has VLAN20 setup, IP set, and it's port to site A tagged for vlan 20. IP routing is enable at site B and has a an static route to Site A's VLAN20 IP. All works fine but my question is, does that traffic going from B to A stay tagged with VLAN20 since it is actually being routed? I hope this question makes sense. I am still very new to this enviroment and trying to understand how things are setup.
2 REPLIES
P Muralidhar Kini
Honored Contributor

Re: VLANs with IP Routing

Hi Aaron,

Check the following link -
http://h40060.www4.hp.com/procurve/uk/en/pdfs/5300xl_portbase.pdf
->IP Routing Between VLANs

Hope this helps.

Regards,
Murali
Let There Be Rock - AC/DC
Pieter 't Hart
Honored Contributor

Re: VLANs with IP Routing

Hi there Aaron,

Yes the packet will be sent tagged between the two sites.
What you do here is to create one (or more) logical link (vlan) over a physical link.

In a simple scenario (single link) tagging the vlan is not really neccessary, it could also be interface with only a single untagged vlan.

But in more complex networks where you want more routed links you between sites will need tagging.

Normally data that originates at site-A (lets say vlan10) sent to site-B (lets say vlan30) will be routed twice!
site-A routes to vlan20 as interconnect to site-B , there it's routed again to vlan30 where the destination resides.

NB!
Packets are only routed when sent from one subnet to another.
So if vlan20 not only contains the ports between the routers (vlan 20 spans across sites) all ports in vlan20 can communicatie with eachother directly, also from site-a to site-b without routing!