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local-bias (ae load-balance)

 

Syntax

Hierarchy Level

Release Information

Statement introduced in Junos OS Release 19.2R1.

Description

Next hop addresses may be local or remote, and traffic can be expected to be more-or-less evenly distributed among the available next-hop addresses whether they are local or remote. You can skew distribution to favor local addresses, however, by setting a value for local bias (local relative to the packet forwarding engine (PFE) performing the packet look up).

For example, a value of 100 would exclude remote next-hop addresses from the traffic distribution by forcing 100% of next-hop traffic flows to use local addresses. A value of 50, on the other hand, would skew 50% of the flows that would otherwise use remote links so they use local links instead. That is, for a value set to 50, given four next-hop links, two of which are local and two of which are remote, each of the remote links could be expected to get one eighth of the flows (25% / 2) = 12.5%. Likewise, each of the local links could also be expected to receive about a third of the flows (25% + 12.5%) = 37.5%.

In contrast, with no value set for local bias, each of the four links would be expected to receive 25% of the total flows.

You can use local-bias with adaptive load balancing, which uses a feedback mechanism to automatically correct load imbalance by adjusting the bandwidth and packet streams traversing links within an AE bundle. In this case, local-bias also employes a combination of link-saturation prediction, and random restart delay, to govern link utilization in a way that prevents oscillation of the load and load balancing schemes in effect.

Note

MPC5 and MPC6 line cards include XM and XL-based packet forwarding engines, or PFEs, and locality is decided on the basis of the XL chip, not the XM chip. Therefor, when an AE bundle has child links hosted on two different XMs that are connected (in the chip architecture) to a single XL, they are considered local to the XL PFE. In practice, what this means is that if a single AE interface includes member links that happen to be spread over two XMs but are actually served by the same XL, local-bias may not work as expected because links considered local to the XL PFE.

Required Privilege Level

interface - To view statement in the configuration.

interface-control - To add this statement to the configuration.