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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 43 Configuring IPv6 Unicast Routing Understanding IPv6
The switch as a tunnel endpoint supporting IPv4-to-IPv6 or IPv6-to-IPv4 tunneling protocols
IPv6 unicast reverse-path forwarding
IPv6 general prefixes
Limitations
Because IPv6 is implemented in switch hardware, some limitations occur due to the IPv6 compressed
addresses in the hardware memory. These hardware limitations result in some loss of functionality and
limits some features.
These are feature limitations.
ICMPv6 redirect functionality is not supported for IPv6 host routes (routes used to reach a specific
host) or for IPv6 routes with masks greater than 64 bits. The switch cannot redirect hosts to a better
first-hop router for a specific destination that is reachable through a host route or through a route
with masks greater than 64 bits.
Load balancing using equal cost and unequal cost routes is not supported for IPv6 host routes or for
IPv6 routes with a mask greater than 64 bits.
The switch cannot forward SNAP-encapsulated IPv6 packets.
Note There is a similar limitation for IPv4 SNAP-encapsulated packets, but the packets are
dropped at the switch and are not forwarded.
The switch routes IPv6-to-IPv4 and IPv4-to-IPv6 packets in hardware, but the switch cannot be an
IPv6-to-IPv4 or IPv4-to-IPv6 tunnel endpoint.
Bridged IPv6 packets with hop-by-hop extension headers are forwarded in software. In IPv4, these
packets are routed in software, but bridged in hardware.
In addition to the normal SPAN and RSPAN limitations defined in the software configuration guide,
these limitations are specific to IPv6 packets:
When you send RSPAN IPv6-routed packets, the source MAC address in the SPAN output
packet can be incorrect.
When you send RSPAN IPv6-routed packets, the destination MAC address can be incorrect.
Normal traffic is not affected.
The switch cannot apply QoS classification or policy-based routing on source-routed IPv6 packets
in hardware.
The switch cannot generate ICMPv6 Packet Too Big messages for multicast packets.
IPv6 and Switch Stacks
The switch supports IPv6 forwarding across the stack and IPv6 host functionality on the stack master.
The stack master runs the IPv6 unicast routing protocols and computes the routing tables. Using
distributed CEF (dCEF), the stack master downloads the routing table to the stack member switches.
They receive the tables and create hardware IPv6 routes for forwarding. The stack master also runs all
IPv6 applications.
Note To route IPv6 packets in a stack, all switches in the stack should be running the IP services feature set.