Alcatel-Lucent 7750 Configuration Manual page 125

L4 load balancing can be enabled/disabled on system and interface levels. When enabled, the extra
L4 port inputs apply to per-flow hashing for unicast IP traffic and multicast traffic (if mc-enh-
load-balancing is enabled).
System IP Load Balancing
This enhancement adds an option to add the system IP address into the hash algorithm. This adds a
per system variable so that traffic being forward through multiple routers with similar ECMP
paths will have a lower chance of always using the same path to a given destination.
Currently, if multiple routers have the same set of ECMP next hops, traffic will use the same
nexthop at every router hop. This can contribute to the unbalanced utilization of links. The new
hash option avoids this issue.
This feature when enabled, enhances the default per-flow hashing algorithm described earlier. It
however does not apply to services which packets are hashed based on service-id or when per
service consistent hashing is enabled. This hash algorithm is only supported on IOM3-XPs/IMMs
or later generations of hardware.The System IP load balancing can be enabled per-system only.
TEID Hash for GTP-Encapsulated Traffic
This options enables TEID hashing on L3 interfaces. The hash algorithm identifies GTP-C or
GTP-U by looking at the UDP destination port (2123 or 2152) of an IP packet to be hashed. If the
value of the port matches, the packet is assumed to be GTP-U/C. For GTPv1 packets TEID value
from the expected header location is then included in hash. For GTPv2 packets the TEID flag
value in the expected header is additionally checked to verify whether TEID is present. If TEID is
present, it is included in hash algorithm inputs. TEID is used in addition to GTP tunnel IP hash
inputs: SA/DA and SPort/DPort (if L4 load balancing is enabled). If a non-GTP packet is received
on the GTP UDP ports above, the packets will be hashed as GTP.
Source-Only/Destination-Only Hash Inputs
This option allows an operator to only include source parameters or only include destination
parameters in the hash for inputs that have source/destination context (such as IP address and L4
port). Parameters that do not have source/destination context (such as TEID or System IP for
example) are also included in hash as per applicable hash configuration. The functionality allows,
among others, to ensure that both upstream and downstream traffic hash to the same ECMP path/
LAG port on system egress when traffic is sent to a hair-pinned appliance (by configuring source-
only hash for incoming traffic on upstream interfaces and destination-only hash for incoming
traffic on downstream interfaces).
7750 SR Interface Configuration Guide
Interface Configuration
Page 125