The conguration of the maximum number of IP load sharing paths to a value more than 8 is determined by the maximum number of
ECMP paths dened at the system level using the system-max max-ecmp command. You cannot congure the maximum number of IP
load sharing paths higher than the value dened at the system level. Also, you cannot congure the maximum number of ECMP paths at
the system level to a value less than the congured IP load sharing value.
To dene the maximum number of ECMP paths at the system level, enter a command such as the following.
device(config)# system-max max-ecmp 20
device(config)# write memory
device(config)# exit
device# reload
Syntax: [no] system-max max-ecmp [ num ]
The num variable species the maximum number of ECMP paths and the value range can be from 8 through 32. This command is
supported only on the Brocade ICX 7750.
You must save the conguration and reload the device for the maximum ECMP value change to take eect.
ECMP load sharing for IPv6
The IPv6 route table selects the best route to a given destination from among the routes in the tables maintained by the congured
routing protocols (BGP4, OSPF, static, and so on). The IPv6 route table can contain more than one path to a given destination. When this
occurs, the Brocade device selects the path with the lowest cost for insertion into the routing table. If more than one path with the lowest
cost exists, all of these paths are inserted into the routing table, subject to the congured maximum number of load sharing paths (by
default 4). The device uses Equal-Cost Multi-Path (ECMP) load sharing to select a path to a destination.
When a route is installed by routing protocols or congured static route for the rst time, and the IPv6 route table contains multiple,
equal-cost paths to that route, the device checks the IPv6 neighbor for each next hop. Every next hop where the link layer address has
been resolved will be stored in hardware. The device will initiate neighbor discovery for the next hops whose link layer addresses are not
resolved. The hardware will hash the packet and choose one of the paths. The number of paths would be updated in hardware as the link
layer gets resolved for a next hop.
If the path selected by the device becomes unavailable, the IPv6 neighbor should change state and trigger the update of the destination
path in the hardware.
Brocade FastIron devices support network-based ECMP load-sharing methods for IPv6 trac. The Brocade device distributes trac
across equal-cost paths based on a XOR of some bits from the MAC source address, MAC destination address, IPv6 source address,
IPv6 destination address, IPv6 ow label, IPv6 next header. The software selects a path based on a calculation involving the maximum
number of load-sharing paths allowed and the actual number of paths to the destination network. This is the default ECMP load-sharing
method for IPv6.
You can manually disable or enable ECMP load sharing for IPv6 and specify the number of equal-cost paths the device can distribute
trac across. In addition, you can display information about the status of ECMP load-sharing on the device.
Disabling or re-enabling ECMP load sharing for IPv6
ECMP load sharing for IPv6 is enabled by default. To disable the feature, enter the following command.
device(config)#no ipv6 load-sharing
If you want to re-enable the feature after disabling it, you must specify the number of load-sharing paths. By entering a command such
as the following, iPv6 load-sharing will be re-enabled.
device(config)#ipv6 load-sharing 4
Syntax: [no] ipv6 load-sharing num
Conguring IP parameters - Layer 3 switches
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04 75
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