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How To Configure a l2-GRE tunnel That Bridges a VLAN

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TitleHow To Configure a l2-GRE tunnel That Bridges a VLAN
Egress a VLAN across a GRE Tunnel
  • S-Series
  • K-Series
1. Configure a loopback address that will be used to peer with the other router
interface loop.0.1
ip address primary
no shutdown

2. Configure the tunnel interface with the following parameters
  • Loopback as tunnel source
  • Other router loopback as tunnel destination
  • L2-GRE Tunnel bridge port
interface tun.0.1
tunnel destination
tunnel mode gre l2 tbp.0.1
tunnel source
no shutdown

3. Egress vlan(s) on the tunnel bridge port
set vlan egress 10 tbp.0.1 tagged
4. Disable spanning tree on the tunnel bridge port and the port between the two routers so the tunnel bridge port does not block
set spantree portadmin tbp.0.1 disable
set spantree portadmin ge.1.24 disable
Additional notes
  • NOTE: In some scenario's, you may need to enable jumbo frames on the links GRE traffic is traversing ( set port jumbo enable <PORT_STRING> )
  • You must advertise the loopback via static routes or a dynamic routing protocol
    • Peering to the loopback provides redundancy  for the tunnel by allowing the tunnel  destination to be reached through a backup path if an interface fails but a physical interface IP can be used without disadvantage in topologies with only one path between the routers
  • The switch Cannot  add  an MPLS  tag and GRE header to the same packet so you need to use multiple routers if switching MPLS through a layer two GRE Tunnel.  Use two routers for the GRE and use the other two for MPLS
  • Spanning tree is disabled  because the two routers are directly connected and the tunnel  bridge port and directly connected  vlan would cause spanning tree to block the tunnel port



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