1072 BigIron RX Series Configuration Guide53-1001986-01ECMP load sharing for IPv643As an example, in a configuration where ftp6.companynet.com is a server with an IPv6 protocolstack, when a user pings ftp6.companynet.com, the Brocade device attempts to resolve the AAAADNS record. In addition, if the DNS server does not have an IPv6 address, as long as it is able toresolve AAAA records, it can still respond to DNS queries.ECMP load sharing for IPv6The IPv6 route table selects the best route to a given destination from among the routes in thetables maintained by the configured routing protocols (BGP4, OSPF, static, and so on). The IPv6route table can contain more than one path to a given destination. When this occurs, the Brocadedevice selects the path with the lowest cost for insertion into the routing table. If more than onepath with the lowest cost exists, all of these paths are inserted into the routing table, subject to theconfigured maximum number of load sharing paths (by default 4). The device uses Equal-CostMulti-Path (ECMP) load sharing to select a path to a destination.When the device receives traffic for a destination, and the IPv6 route table contains multiple,equal-cost paths to that destination, the device checks the IPv6 forwarding cache for a forwardingentry for the destination. The IPv6 forwarding cache provides a fast path for forwarding IPv6 traffic.The IPv6 forwarding cache contains entries that associate a destination host or network with apath (next-hop router).If the IPv6 forwarding cache contains a forwarding entry for the destination, the Brocade deviceuses the entry to forward the traffic. If the IPv6 forwarding cache does not contain a forwardingentry for the destination, the software selects a path from among the available equal-cost paths tothe destination, then creates an entry in the in the cache based on the calculation. Subsequenttraffic for the same destination uses the forwarding entry. Entries remain in the IPv6 forwardingcache for one minute, then are aged out.If the path selected by the device becomes unavailable, its entry in the IPv6 forwarding cache isremoved, a new path is selected from the remaining equal-cost paths to the destination, and anentry is created in the IPv6 forwarding cache using the new path.Brocade devices support the following ECMP load-sharing methods for IPv6 traffic:• Network-based – The Brocade device distributes traffic across equal-cost paths based ondestination network address. The software selects a path based on a calculation involving themaximum number of load-sharing paths allowed and the actual number of paths to thedestination network. This is the default ECMP load-sharing method for IPv6.• Host-based – The Brocade device uses a simple round-robin mechanism to distribute trafficacross the equal-cost paths based on destination host IP address. The device uses this ECMPload-sharing method for IPv6 if you explicitly configure it to do so.You can manually disable or enable ECMP load sharing for IPv6, specify the number of equal-costpaths the device can distribute traffic across, and configure the device to use the host-based ECMPload-sharing method instead of the network-based method. In addition, you can displayinformation about the status of ECMP load-sharing on the device, as well as the entries in the IPv6forwarding cache.Disabling or re-enabling ECMP load sharing for IPv6ECMP load sharing for IPv6 is enabled by default. To disable the feature, enter the followingcommand.BigIron RX(config)# no ipv6 load-sharing
