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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
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Chapter 39 Configuring IPv6 Unicast Routing
Understanding IPv6
Note To route IPv6 packets in a stack, all switches in the stack should be running the advanced IP services
feature set.
If a new switch becomes the stack master, the new master recomputes the IPv6 routing tables and
distributes them to the member switches. While the new stack master is elected and is resetting, the
switch stack does not forward IPv6 packets. If a new switch becomes the stack master, the stack MAC
address also changes. When the IPv6 address of the stack is specified with an extended universal
identifier (EUI) by using the ipv6 address ipv6-prefix/prefix length eui-64 interface configuration
command, the address is based on the interface MAC address, and changing the MAC address changes
the IPv6 address. See the “Configuring IPv6 Addressing and Enabling IPv6 Routing” section on
page 39-11.
Note If you configure the persistent MAC address feature on the stack and the stack master changes, the stack
MAC address does not change for approximately four minutes. If the previous stack master rejoins the
stack as a member switch during that time period, the stack MAC address remains the MAC address of
the previous stack master. See the “Enabling Persistent MAC Address” section on page 5-20 in
Chapter 5, “Managing Switch Stacks.”
These are the functions of IPv6 stack master and members:
• Stack master:
–
runs IPv6 routing protocols
–
generates routing tables
–
distributes CEFv6 routing tables to stack members that use dCEFv6
–
runs IPv6 host functionality and IPv6 applications
• Stack member (must be running the advanced IP services feature set):
–
receives CEFv6 routing tables from the stack master
–
programs the routes into hardware
Note IPv6 packets are routed in hardware across the stack provided the packet does not have
exceptions (IPv6Options) and the switches in the stack have not run out of hardware
resources.
–
flushes the CEFv6 tables on master re-election
With IPv4 unicast routing, if the stack detects that the stack master is down and elects one of the stack
members to be the new stack master, except for a momentary interruption, the hardware continues to
forward packets with no protocols active. With IPv6, the switch does not continue forwarding packets.
On election of a new stack master, the stack might need up to 60 seconds to recover all routes and resume
forwarding traffic.
IPv6 host functionality is supported on the stack master, and all IPv6 applications run on the stack
master.