Dell BigIron RX Series, Configuration Manual

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1092 BigIron RX Series Configuration Guide
53-1002253-01
ECMP load sharing for IPv6
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As an example, in a configuration where ftp6.companynet.com is a server with an IPv6 protocol
stack, when a user pings ftp6.companynet.com, the Brocade device attempts to resolve the AAAA
DNS record. In addition, if the DNS server does not have an IPv6 address, as long as it is able to
resolve AAAA records, it can still respond to DNS queries.
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 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 forwarding
entry 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 a
path (next-hop router).
If the IPv6 forwarding cache contains a forwarding entry for the destination, the Brocade device
uses the entry to forward the traffic. If the IPv6 forwarding cache does not contain a forwarding
entry for the destination, the software selects a path from among the available equal-cost paths to
the destination, then creates an entry in the in the cache based on the calculation. Subsequent
traffic for the same destination uses the forwarding entry. Entries remain in the IPv6 forwarding
cache for one minute, then are aged out.
If the path selected by the device becomes unavailable, its entry in the IPv6 forwarding cache is
removed, a new path is selected from the remaining equal-cost paths to the destination, and an
entry 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 on
destination network address. 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.
•
Host-based – The Brocade device uses a simple round-robin mechanism to distribute traffic
across the equal-cost paths based on destination host IP address. The device uses this ECMP
load-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-cost
paths the device can distribute traffic across, and configure the device to use the host-based ECMP
load-sharing method instead of the network-based method. In addition, you can display
information about the status of ECMP load-sharing on the device, as well as the entries in the IPv6
forwarding cache.
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.
BigIron RX(config)# no ipv6 load-sharing