Alcatel-Lucent 7710 SR OS, Interface Configuration Manual

Page: 75 / 436

Interface Configuration
7710 SR OS Interface Configuration Guide Page 75
• VPLS multicast, broadcast and unknown unicast traffic transmitted on SAPs is not
sprayed on a per-frame basis, but instead the SAP ID is used to pick ECMP and LAG
paths statically.
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VPLS multicast, broadcast and unknown unicast traffic transmitted on SDPs is and
hashed on a per packet basis in the same way as VPLS unicast traffic. However, per
packet hashing is applicable only to the distribution of traffic over LAG ports, as the
ECMP path is still chosen statically based on the service ID.
Data is hashed twice to get the ECMP path. If LAG and ECMP are performed on the
same frame, the data will be hashed again to get the LAG port (three hashes for LAG).
However, if only LAG is performed, then hashing will only be performed twice to get
the LAG port.
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VPLS multicast traffic transmitted on SAPs with IGMP snooping enabled is load-
balanced based on the internal multicast ID which is unique for every (s,g) record.
This way, multicast traffic pertaining to different streams is distributed across
different LAG member ports.
• VLL traffic from a service access point is not sprayed on a per-packet basis, but as for
VPLS flooded traffic, the service ID is used to pick one of the ECMP/LAG paths. The
exception to this is when shared-queuing is configured on an Etherpipe SAP or Frame
Relay pipe SAP. In this case, traffic spraying is the same for VPLS known unicast traffic.
• IP multicast is sprayed over LAG based on the unique multicast ID.
• IP multicast Layer 4 UDP traffic will not be hashed.
For all cases that involve per-packet hashing, the NPA produces a 20-bit result based on hashing
the relevant packet data. This result is input to a modulo like calculation (divide by the number of
routes in the ECMP and use the remainder) to determine the ECMP index.
If the ECMP index results in the selection of a LAG as the next hop, then the hash result is hashed
again and the result of the second hash is input to the modulo-like operation (divide by the number
of ports in the LAG and use the remainder) to determine the LAG port selection.
Note that when the ECMP hash results in an ECMP index corresponding to an IP interface
configured on a spoke SDP, such as an IES/VPRN spoke interface, the unicast IP packets of the
IES/VPRN service will not be sprayed over multiple RSVP LSPs or multiple LDP FEC next-hops
when available. A single RSVP LSP or LDP FEC next-hop will be selected based on a modulo
operation of the service ID in this case. The second round of the hash is exclusively used for LAG
link selection. If multiple IES/VPRN services have spoke interfaces bound to the same SDP,
packets from individual services will be distributed across RSVP LSPs or LDP FEC next-hops in
the same SDP based on the modulo operation of the service ID.