Virtual Private LAN Services
7750 SR OS Services Guide Page 447
In the case where subscriber SLA management is enabled on the SAP and the SAP queues are not
available, the queues created by the non-sub-addr-traffic SLA-profile instance are used.
One caveat is that egress Dot1P markings for dot1q SAPs in the replication chain are only
evaluated for the first SAP in the chain. If the first SAP defines an egress Dot1P override for the
packet, all encapsulations in the chain will share the same value. If the first SAP in the chain does
not override the egress Dot1P value, either the existing Dot1P value (relative to ingress) will be
preserved or the value 0 (zero) will be used for all SAPs in the replication chain. The egress QoS
policy Dot1P remark definitions on the other SAPs in the chain are ignored by the system.
Efficient Multicast Egress SAP Chaining
The egress IOM (Input Output Module) automatically creates the SAP chains on each egress
forwarding plane (typically all ports on an MDA are part of a single forwarding plane except in the
case of the 10 Gigabit IOM which has two MDAs on a single forwarding plane). The size of each
chain is based on the dest-chain-limit command defined on the egress multicast group to which the
SAPs in the chain belong.
A set of chains is created by the IOM for each egress flooding list managed by the IOM. While
SAPs from multiple VPLS contexts are allowed into a single egress multicast group, an egress
flooding list is typically based on a subset of these SAPs. For instance, the broadcast/multicast/
unknown flooding list for a VPLS context is limited to the SAPs in that VPLS context. With
IGMP snooping on a single VPLS context, the flooding list is per Layer 2 IGMP (s,g) record and
is basically limited to the destinations where IGMP joins for the multicast stream have been
intercepted. When MVR (Multicast VPLS Registration) is enabled, the (s,g) flooding list may
include SAPs from various VPLS contexts based on MVR configuration.
The system maintains a unique flooding list for each forwarding plane VPLS context (see section
VPLS Broadcast/Multicast/Unknown Flooding List on page 449). This list will contain all SAPs
(except for residential SAPs), spoke SDP and mesh SDP bindings on the forwarding plane that
belong to that VPLS context. Each list may contain a maximum of 127 SAPs. In the case where
the IOM is able to create an egress multicast chain, the SAPs within the chain are represented in
the flooding list by a single SAP entry (the first SAP in the chain).
The system also maintains a unique flooding list for each Layer 2 IP multicast (s,g) record created
through IGMP snooping (see sections VPLS IGMP Snooping (s,g) Flooding List on page 450 and
MVR IGMP Snooping (s,g) Flooding List on page 450). A flooding list created by IGMP
snooping is limited to 127 SAPs, although it may contain other entries representing spoke and
mesh SDP bindings. Unlike a VPLS flooding list, a residential SAP may be included in a Layer 2
IP multicast flooding list.
While the system may allow 30 SAPs in a chain, the uninterrupted replication to 30 destinations
may have a negative effect on other packets waiting to be processed by the egress forwarding
plane. Most notably, massive jitter may be seen on real time VoIP or other time-sensitive
applications. The dest-chain-limit parameter should be tuned to allow the proper balance between
To Next Page
Loading...
