7705 SAR Interfaces
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Interface Configuration Guide
3HE 11011 AAAC TQZZA Edition: 01
If the LAG has one member link on a first- or second-generation (Gen-1 or Gen-2)
Ethernet adapter card, and the other link on a third-generation (Gen-3) Ethernet
adapter card or platform, a mix-and-match scenario exists for traffic management on
the LAG SAP. In this case, all QoS parameters for the LAG SAP are configured but
only those parameters applicable to the active member link are used. See LAG
Support on Mixed-Generation Hardware for more information.
Configuring a multiservice site (MSS) aggregate rate can restrict the use of LAG
SAPs. For more information, refer to the “MSS and LAG Interaction on the
7705 SAR-8 and 7705 SAR-18” section in the 7705 SAR Quality of Service Guide.
3.2.13.2 LACP and Active/Standby Operation
On access, network, and hybrid ports, where multiple links in a LAG can be active at
the same time, normal operation is that all non-failing links are active and traffic is
load-balanced across all the active links. In some cases, however, it is desirable to
have only some of the links active and the other links kept in standby mode. The Link
Aggregation Control Protocol (LACP) is used to make the selection of the active links
in a LAG predictable and compatible with any vendor equipment. The mechanism is
based on the IEEE 802.1ax standard so that interoperability is ensured.
LACP is disabled by default and therefore must be enabled on the LAG if required.
LACP can be used in either active mode or passive mode. The mode must match
with connected CE devices for proper operation. For example, if the LAG on the
7705 SAR end is configured to be active, the CE end must be passive.
Figure 9 shows the interconnection between a DSLAM and a LAG aggregation node.
In this configuration, LAG is used to protect against hardware failure. If the active link
goes down, the link on standby takes over (see Figure 10). The links are distributed
across two different adapter cards to eliminate a single point of failure.
Note: LACP cannot be configured for static LAG. For more information on static LAG, see
Static LAG (Active/Standby LAG Operation without LACP).
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