Configuring Per-Packet Load Balancing
In Junos OS, you enable per-flow load balancing by setting the load-balance per-packet action in the routing policy configuration. The naming may be counter-intuitive, because in Junos, per-packet load balancing is functionally equivalent to what other vendors may term per-flow load balancing.
To configure per-packet load balancing, include the load-balance per-packet statement either as an option of the route-filter statement at the [edit
policy-options policy-statement policy-name term term-name from] hierarchy level:
[edit policy-options policy-statement policy-name term term-name from]
route-filter destination-prefix match-type {
load-balance per-packet;
}
or at the [edit policy-options policy-statement policy-name term term-name then] hierarchy level:
[edit policy-options policy-statement policy-name term term-name then] load-balance per-packet;
To complete the configuration you must apply the routing policy to routes exported from
the routing table to the forwarding table, by including the policy name in the list specified
by the export statement:
export [ policy-names ];
You can include this statement at the following hierarchy levels:
[edit routing-options forwarding-table][edit logical-systems logical-system-name routing-options forwarding-table]
By default, Junos ignores port data when determining flows. To include port data in
the flow determination, include the family inet statement at the [edit forwarding-options
hash-key] hierarchy level:
[edit forwarding-options hash-key]
family inet {
layer-3;
layer-4;
}
If you include both the layer 3 and layer 4 statements, the device uses the following Layer 3 and Layer 4 information to load-balance:
Source IP address
Destination IP address
Protocol
Source port number
Destination port number
Incoming interface index
IP type of service
When all of the layer 3 and layer 4 parameters are identical, the device sends packets in the flow through the same interface, which in turn helps prevent out of order delivery for TCP and UDP flows..
Internet Control Message Protocol (ICMP) packets are handled differently because the field location offset is the checksum field, which makes each ping packet a separate “flow.” There are other protocols that can be encapsulated in IP that may have a varying value in the 32-bit offset. This may also be problematic because these protocols are seen as a separate flow.
With M Series (with the exception of the M120 router) and T Series routers, the first fragment is mapped to the same load-balanced destination as the unfragmented packets. The other fragments can be mapped to other load-balanced destinations.
For the M120 router only, all fragments are mapped to the same load-balanced destination. This destination is not necessarily the same as that for unfragmented packets.
By default, or if you include only the layer 3 statement, the router uses the incoming interface index as well as the following Layer 3 information in the packet header to load balance traffic:
Source IP address
Destination IP address
Protocol
By default, IP version 6 (IPv6) packets are automatically load-balanced based on the following Layer 3 and Layer 4 information:
Source IP address
Destination IP address
Protocol
Source port number
Destination port number
Incoming interface index
Traffic class
Per-Packet Load Balancing Examples
Perform per-packet load balancing for all routes:
[edit]
policy-options {
policy-statement load-balancing-policy {
then {
load-balance per-packet;
}
}
}
routing-options {
forwarding-table {
export load-balancing-policy;
}
}
Perform per-packet load balancing only for a limited set of routes:
[edit]
policy-options {
policy-statement load-balancing-policy {
from {
route-filter 192.168.10/24 orlonger;
route-filter 10.114/16 orlonger;
}
then {
load-balance per-packet;
}
}
}
routing-options {
forwarding-table {
export load-balancing-policy;
}
}
To configure per-packet random spray load balancing, include the load-balance random statement at the [edit policy-options policy-statement policy-name term term-name then] hierarchy level:
[edit policy-options policy-statement policy-name term term-name then] load-balance random;
To complete the configuration you must apply the routing policy to routes exported from
the routing table to the forwarding table, by including the policy name in the list specified
by the export statement at the [edit routing-options forwarding-table] hierarchy level
[edit routing-options forwarding-table] export [ policy-names ];