Ecmp Flow-Based Forwarding On Acx Series Routers - Juniper ACX1000 Configuration Manual

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ECMP Flow-Based Forwarding on ACX Series Routers

Copyright © 2017, Juniper Networks, Inc.
Junos OS VPNs Library for Routing Devices
An equal-cost multipath (ECMP) set is formed when the routing table contains multiple
next-hop addresses for the same destination with equal cost. (Routes of equal cost have
the same preference and metric values.) If there is an ECMP set for the active route, the
Junos OS software uses a hash algorithm to choose one of the next-hop addresses in
the ECMP set to install in the forwarding table.
You can configure the Junos OS so that multiple next-hop entries in an ECMP set are
installed in the forwarding table. On ACX Series routers, per-flow load balancing can be
performed to spread traffic across multiple paths between routing devices. ECMP
flow-based forwarding is supported for IPv4, IPv6, and MPLS packets on aggregated
Ethernet (ae) interfaces.
Load balancing is used to evenly distribute traffic when there are multiple equal-cost
next hops over different interfaces or a single next hop over an aggregated interface. By
default, when load balancing is used to help distribute traffic, Junos OS employs a hash
algorithm to select a next-hop address to install into the forwarding table.
If a next-hop address is no longer part of the ECMP set or if it is removed from the routing
table because of a route change, a flow that uses the next hop is rerouted and the session
is not affected. Rerouting of the flow also occurs if there is a configuration change that
takes away the next-hop address or if an administrator takes down the next-hop interface
without deleting it. If a next-hop address is removed from the routing table because the
interface is deleted or the session is intentionally cleared, the session is killed without
being rerouted.
To select which packet header data to use for per-flow load balancing, include the
hash-key statement at the
IPv4 traffic by using the port data into the hash key, include the
the
[edit forwarding-options hash-key]
Layer 3 IP port data, or the Layer 4 TCP or UDP port data into the hash key. To
load-balance based on the MPLS label information, configure the
at the
[edit forwarding-options hash-key]
Forwarding of MPLS traffic by using penultimate-hop popping (PHP) and label-switched
routing (LSR) is not supported on ACX Series routers. For ECMP flow-based forwarding
over pseudowires, MPLS flows are assigned to one of the ECMP routes by using the
hashing algorithm based on user-to-network interface (UNI) index.
To configure ECMP flow-based forwarding on ACX Series routers, first define a
load-balancing routing policy by including one or more
statements at the [ edit policy-options
. Then apply the routing policy to routes exported from the routing table to
per-packet
the forwarding table. To do this, include the
statements at the [ edit routing-options
Chapter 25: Configuring Layer 2 and Layer 3 Services
[edit forwarding-options] hierarchy level. To load-balance
hierarchy level. You can incorporate either the
hierarchy level.
] hierarchy level, with the action
forwarding-table
] hierarchy level.
statement at
family-inet
family mpls statement
configuration
policy-statement
load-balance
and configuration
export
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