Ecmp Load Sharing For Ipv6 - Brocade Communications Systems ICX 7250 Series Configuration Manual

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 configured
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 configured 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 configured static route for the first 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 traffic. The Brocade device distributes traffic
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 flow 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
traffic 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
The num variable specifies the number of paths and can be from 2-8. The default is 4. On the ICX 7750 device, the value of the num
variable can be from 2 through 32.
The configuration of the maximum number of IP load sharing paths to a value more than 8 is determined by the maximum number of
ECMP paths defined at the system level using the system-max max-ecmp command. You cannot configure the maximum number of IP
load sharing paths higher than the value defined at the system level.
To define 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 specifies the maximum number of ECMP paths and the value range can be from 8 through 32. This is supported only
on the ICX 7750 device.
Brocade FastIron Layer 3 Routing Configuration Guide
53-1003903-04
Configuring IP parameters - Layer 3 switches
75