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Layer 2 Circuits and Layer 2 VPNs on MX Series, M Series, and T Series Routers Frequently Asked Questions
This section presents frequently asked questions and answers related to Layer 2 circuits and Layer 2 VPNs on Juniper MX Series, M Series, and T Series routers.
What is the solution for interprovider Option B connection between LDP-based Layer 2 circuits and BGP-based Layer 2 VPNs?
As of Junos OS version 9.3 and later, Layer 2 circuits with interworking iw0 interfaces can be manually stitched. If dynamic signaling is needed, the only option is to use FEC 129 multisegment pseudowires if you are not using BGP-based Layer 2 VPNs. FEC 129 is not currently supported in Junos OS. Dynamic pseudowires can be signaled using different interprovider options.
What are the supported Layer 2 interworking stitching configurations?
These are the stitching options in Junos OS 9.3 and later:
- Layer 2 circuit into Layer 2 VPN.
Note: In Junos OS 9.4 and later, you can use an iw interface instead of an lt interface for this purpose.
- Layer 2 circuit into Layer 2 circuit.
- Layer 2 VPN into Layer 2 VPN.
Can a Layer 2 circuit be terminated into VPLS?
Yes, Junos OS 9.2 and later uses mesh groups to terminate pseudowire emulation (pseudowireE) into VPLS. You can terminate one pseudowireE per mesh group within the VPLS. A maximum of 16 mesh groups is supported per VPLS instance.
What is the behavior of a virtual tunnel interface in different services routing instances?
If you configure a virtual tunnel (vt) interface on the egress PE router and that router is also a transit router for the point-to-multipoint LSP, the penultimate hop router sends just one copy of each packet over the link to the egress PE router. A vt interface can perform two lookups on an incoming packet, one for the multicast MPLS lookup and one for the IP lookup. This applies to Layer 3 VPNs and VPLS point-to-multipoint LSPs.
This is the behavior of vt-interface in different services:
- NG-MVPN: The MPLS lookup is performed first, with MPLS packet copying. One of the copies has a null label and is sent to vt-ifl. The null label in this case is a label pop operation. When the packet is received from vt-ifl, IP lookup and copying is performed in VRF.
- VPLS: Initial behavior is the same as in NG-MVPN: The MPLS lookup is performed first, with MPLS packet copying. One of the copies has a null label and is sent to vt-ifl. The null label in this case is a label pop operation. However, in VPLS, when a packet is received from vt-ifl, Ethernet MAC lookup and copying is performed in the VPLS edge (VE) or the virtual switch interface (VSI).
- CCC: Initial behavior is the same as in NG-MVPN and VPLS: The MPLS lookup is performed first, with MPLS packet copying. One of the copies has a null label, however, this label is sent to _egress CCC interface. A second lookup is not needed.
What is an example configuration to map a bridge domain into a Layer 2 circuit?
The following example shows a configuration to map a bridge domain into a Layer 2 circuit.
| Note: This configuration requires that the other end of the circuit is sending packets tagged with VLAN-ID 100. |
