Alcatel-Lucent 7750 SR Manual page 750

Virtual Private LAN Services
The egress-multicast-group object is designed to allow the identification of SAPs with similar egress
characteristics. When a SAP is successfully provisioned into an egress-multicast-group, the system is
ensured that it may be batched together with other SAPs in the same group at the egress forwarding
plane for efficient multicast replication. A SAP that does not meet the common requirements is not
allowed into the egress-multicast-group.
At the forwarding plane level, a VPLS flooding list is categorized into chainable and non-chainable
destinations. Currently, the only chainable destinations are SAPs within an egress-multicast-group.
The chainable destinations are further separated by egress-multicast-group association. Chains are
then created following the rules below:
Further subcategories are created for an IGMP (s,g) flooding list. A Layer 2 (s,g) record is created in
a specific VPLS instance (the instance the (s,g) flow ingresses). SAPs within that VPLS context that
join the (s,g) record are considered native SAPs within the flooding list. SAPs that join the (s,g)
flooding list through the multicast VPLS registration process (MVR) from another VPLS context
using the from-vpls command are considered alien SAPs. The distinction between native and alien in
the list is maintained to allow the forwarding plane to enforce or suspend split-horizon-group (SHG)
squelching. When the source of the (s,g) matching packet is in the same SHG as a native SAP, the
packet must not be replicated to that SAP. For a SAP in another VPLS context, the source SHG of the
packet has no meaning and the forwarding plane must disregard SHG matching between the native
source of the packet and the alien destination. Because the SHG squelch decision is done for the
whole chain based on the first SAP in the chain, all SAPs in the chain must be all native or all alien
SAPs. Chains for IGMP (s,g) flooding lists are created using the following rules:
When a packet associated with a flooding list is received by the egress forwarding plane, it processes
the packet by evaluating each destination on the list sequentially in a replication context. If the current
entry being processed in the list is a non-chained destination, the forwarding plane processes the
packet for that destination and then moves on to process other packets currently in the forwarding
plane before returning to process the next destination in the list. If the current entry being processed is
a chained destination, the forwarding plane remains in the replication context until it has forwarded to
each entry in that chain. Once the replication context finishes with the last entry in the chain, it moves
on to process other packets waiting for egress processing before returning to the replication context.
Processing continues in this manner until the packet has been forwarded to all destinations in the list.
Batch chain processing of a chain of SAPs improves replication efficiency by bypassing the functions
that perform egress mirroring decisions on SAPs within the chain and making a single ACL filtering
decision for the whole chain. Each destination in the chain may have a unique egress QoS policy and
per destination queuing is still performed for each destination in the chain. Also, while each SAP in
the chain must be on access ports with the same encap-type, if the encap-type is dot1q, each SAP may
have a unique dot1q tag.
One caveat to each SAP having a unique egress QoS policy in the chain is that only the Dot1P
marking decisions for the first SAP in the list is enforced. If the first SAP's QoS policy forwarding
class action states that the packet should not be remarked, none of the replicated packets in the chain
will have the dot1P bits remarked. If the first SAP's QoS policy forwarding class action states that the
Page 750
• A replication batch chain may only contain SAPs from the same egress-multicast-group
• A replication batch chain length may not exceed the dest-chain-limit of the egress-multicast-
group to which the SAPs are members
1. A replication batch chain may only contain SAPs from the same egress-multicast-group.
2. A replication batch chain may only contain all alien or all native SAPs.
3. A replication batch chain length may not exceed the dest-chain-limit of the egress-multicast-
group to which the SAPs are members
7750 SR OS Services Guide