GRE Tunnel as Preferred Path
Preferred tunnel path feature allows you to map pseudowires to specific GRE tunnels. Attachment circuits
are cross-connected to GRE tunnel interfaces instead of remote PE router IP addresses (reachable using IGP
or LDP). Using preferred tunnel path, it is always assumed that the GRE tunnel that transports the L2 traffic
runs between the two PE routers (that is, its head starts at the imposition PE router and terminates on the
disposition PE router).
Multipoint Layer 2 Services Label Switched Multicast
Multipoint Layer 2 Services Label Switched Multicast (LSM) is a Layer 2 based solution that sends multicast
traffic over a multiprotocol label switching (MPLS) network. In Multipoint Layer 2 Services, point-to-point
(P2P) pseudowires (PWs) are setup at PE routers participating in a Multipoint Layer 2 Services domain, to
provide Ethernet LAN emulation. Broadcast, multicast and unknown unicast traffic can be sent through ingress
replicaton or label switched multicast in the Multipoint Layer 2 Services domain.
Ingress Replication and its Limitations
In ingress replication, broadcast, multicast and unknown unicast traffic are replicated at the ingress PE router.
Individual copies of the same packets are sent to remote PE routers that participate in the same VPLS domain.
However, ingress replication has these limitations:
• Results in significant waste of link bandwidth when there is heavy broadcast and multicast VPLS traffic
• Is resource intensive because the ingress PE router is most impacted by the replication
VPLS LSM as a Solution
VPLS Label Switched Multicast (LSM) is an effective multicast solution for overcoming the limitations of
ingress replication. This solution employs point-to-multipoint (P2MP) label switched path (LSP) in the MPLS
network to transport multicast traffic over a VPLS domain.
Only broadcast, multicast or unknown unicast traffic is sent over P2MP LSPs
Note
The VPLS LSM solution supports BGP based P2MP PW signaling. As a result, remote PEs participating in
the VPLS domain are discovered automatically using the BGP autodiscovery mechanism. Creating a P2MP
PW for each VPLS domain allows emulating VPLS P2MP service for PWs in the VPLS domain.
Multicast trees used for VPLS can be of two types:
• Inclusive trees
• Selective trees
Inclusive trees—This option supports the use of a single multicast distribution tree in the SP network to carry
all the multicast traffic from a specified set of VPLS sites connected to a given PE. A particular multicast tree
can be set up to carry the traffic originated by sites belonging to a single VPLS instance, or belonging to
different VPLS instances. The ability to carry the traffic of more than one VPLS instance on the same tree is
called Aggregate Inclusive. The tree needs to include every PE that is a member of any of the VPLS instances
that are using the tree. A PE may receive multicast traffic for a multicast stream even if it doesn't have any
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
227
Implementing Multipoint Layer 2 Services
GRE Tunnel as Preferred Path
To Next Page
Loading...
Need help?
General
