MPLS Guide Label Distribution Protocol
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ECMP for LDP load-balances traffic across all equal-cost links based on the output
of the hashing algorithm using the allowed inputs, based on the service type. For
detailed information, refer to “LAG and ECMP Hashing” in the 7705 SAR Interface
Configuration Guide.
There is only one next-hop peer for a network link. To offer protection from a network
link or next-hop peer failure, multiple network links can be configured to connect to
different next-hop peers, or multiple links to the same peer. For example, an MLPPP
link and an Ethernet link can be connected to two peers, or two Ethernet links can be
connected to the same peer. ECMP occurs when the cost of each link reaching a
target IP prefix is equal.
The 7705 SAR uses a liberal label retention mode, which retains all labels for an IP
prefix from all next-hop peers. A 7705 SAR acting as an LSR load-balances the
MPLS traffic over multiple links using a hashing algorithm.
The 7705 SAR supports the following optional fields as hash inputs and supports
profiles for various combinations:
• hashing algorithms
- label-only option: hashing is done on the MPLS label stack, up to a
maximum of 10 labels (default)
- label-IP option: hashing is done on the MPLS label stack and the IPv4
source and destination IP address if an IPv4 header is present after the
MPLS labels
- Layer 4 header (source or destination UDP or TCP port number) and TEID:
hashing is done on the MPLS label stack, the IPv4 source and destination
IP address (if present), then on the Layer 4 source and destination UDP or
TCP port fields (if present) and the TEID in the GTP header (if present)
• label stack profile options on significance of the bottom-of-stack label (VC label)
- profile 1: favors better load balancing for pseudowires when the VC label
distribution is contiguous (default)
- profile 2: similar to profile 1 where the VC labels are contiguous, but
provides an alternate distribution
- profile 3: all labels have equal influence in hash key generation
• ingress LAG port at the LSR (default is disabled)
The use-ingress-port option, when enabled, specifies that the ingress port will
be used by the hashing algorithm at the LSR. This option should be enabled for
ingress LAG ports because packets with the same label stack can arrive on all
ports of a LAG interface. In this case, using the ingress port in the hashing
algorithm will result in better egress load balancing, especially for pseudowires.
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