ip load-sharing

Syntax

ip load-sharing 2 - 4

no ip load-sharing 2 - 4

Description

When OSPF is enabled and multiple, equal-cost, next-hop routes are available for traffic destinations on different subnets, this feature, by default, enables load-sharing among up to four next-hop routes.

Specifiers

2 - 4

Specifies the maximum number of equal-cost next-hop paths the router allows.

Default: Enabled with four equal-cost, next-hop routes allowed

The no form of the command disables this load-sharing so that only one route in a group of multiple, equal-cost, next-hop routes are used for traffic that could otherwise be load-shared across multiple routes.

NOTE:

Disabling load-sharing means that router "1" selects only one next-hop router for traffic that is actually eligible for load-sharing through different next-hop routers.

In the default configuration, load-sharing is enabled by default for both IPv4 and IPv6. However, it has no effect unless routing and OSPF are enabled.

Example

In the figure, the next-hop routers "B," "C," and "D" are available for equal-cost load-sharing of eligible traffic. Disabling IP load-sharing means that router "A" selects only one next-hop router for traffic that is actually eligible for load-sharing through different next-hop routers. The ECMP inter-area routes to destination network 2001:db8:0:e::/64 consist of the following next-hop gateway addresses:

  • 2001:db8:0:b::b:101

  • 2001:db8:0:c::c:101

  • 2001:db8:0:d::d:101

OSPFv3 ECMP multiple next-hop routing (inter-area)

However, the forwarding software distributes traffic across the three possible next-hop routes in such a way that all traffic for a specific host is sent to the same next-hop router.

As shown in the figure, one possible distribution of traffic to host devices is:

  • Traffic to host "A" passes through next-hop router "3"

  • Traffic to host "B" passes through next-hop router "2"

  • Traffic to host "C" passes through next-hop router "3"

  • Traffic to host "D" passes through next-hop router "4"

    IP packet destination

    Next hop used

    2001:db8:0:e::100 2001:db8:0:b::b:10
    2001:db8:0:e::110 2001:db8:0:c::c:20
    2001:db8:0:e::120 2001:db8:0:b::b:10
    2001:db8:0:e::130 2001:db8:0:d::d:30