Label Distribution Protocol
380
MPLS Guide
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The option should be disabled for LDP ECMP so that the ingress port is not used
by the hashing algorithm. For ingress LDP ECMP, if the ingress port is used by
the hashing algorithm, the hash distribution could be biased, especially for
pseudowires.
• system IP address – hashing on the system IP address is enabled and disabled
at the system level only
All of the above options can be configured with the lsr-load-balancing command, with
the exception of the system IP address, which is configured with the system-ip-load-
balancing command.
LSR load balancing can be configured at the system level or interface level.
Configuration at the interface level overrides the system-level settings for the specific
interface. Configuration must be done on the ingress network interface (that is, the
interface on the LDP LSR node that the packet is received on).
Configuration of load balancing at the interface level provides some control to the
user; for example, the label-IP option can be disabled on a specific interface if
labeled packets received on the interface include non-IP packets that can be
confused by the hash routine for IP packets. Disabling the label-IP option can be
used in cases where the first nibble of a non-IP packet is a 4, which would result in
the packet being hashed incorrectly if the label-IP option was enabled.
If ECMP is not enabled, the label from only one of the next-hop peers is selected and
installed in the forwarding plane. In this case, the algorithm used to distribute the
traffic flow looks up the route information, and selects the network link with the lowest
IP address. If the selected network link or next-hop peer fails, another next-hop peer
is selected, and LDP reprograms the forwarding plane to use the label sent by the
newly selected peer.
ECMP is supported on all Ethernet ports in network mode, and is also supported on
the 4-port OC3/STM1 Clear Channel Adapter card when it is configured for POS
(ppp-auto) encapsulation and network mode.
For information on configuring the 7705 SAR for LSR ECMP, refer to the
lsr-load-balancing and system-ip-load-balancing commands in the
7705 SAR Basic System Configuration Guide, “System Information and General
Commands” and the lsr-load-balancing command in the 7705 SAR Router
Configuration Guide, “Router Interface Commands”.
Note: The global IF index is no longer a hash input for LSR ECMP load balancing. It has
been replaced with the use-ingress-port configurable option in the lsr-load-balancing
command. As well, the default treatment of the MPLS label stack has changed to focus on
the bottom-of-stack label (VC label). In previous releases, all labels had equal influence.
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