This document contains Frequently Asked Questions(FAQ's) about Internet Protocol Version 6(IPv6).
Q. How to limit clients getting an IPv6 address without using a DHCP server ?
A. Use the command"ipv6nd prefix <prefix> no-advertise".This will set a bit in theIPv6 NA packets to tell hosts not to use this prefix for autoconfiguration.
Q. When configuring Dual Stack VRF,IPv6 address family is not listed as shown in the example
ipv4 Address family Router(config)#interface GigabitEthernet0/0.901 Router(config-subif)#ipv6 en Router(config-subif)#ipv6 enable %GigabitEthernet0/0.901 is linked to a VRF. Enable IPv6 on thatVRF first.
A.In ""show version"", check if the Data license is activated.
Router# show version
Technology Package License Information for Module:'c2900'
Q. Getting Error Message when creating address-family for IPv6 on the 7600 as shown in the example:
Example : Router(config-vrf)#address-family ipv6 % VRF address family ipv6 is not supported or not enabled % Can't activate address-family 'ipv6'
A. In order to enable IPv6 in a VRF, enter the ""mls ipv6 vrf"" command in global configuration mode. If this command is not used, a VRF is supported only for the IPv4 address family. Example: Router(config)# mls ipv6 vrf.For further information on this command refer:
To use these features,change the feature set to Advanced Enterprise Services.
Q. How to configure IPv6 netflow?
A. Configuring IPv6 netflow means configuring collection of hardware-routed IPv6 flows. IPv6 netflow is independent of IPv4 netflow except for export configuration, which is same for both. For commands and configuration example, check: How to configure Netflow v9 for IPv6
Q. When configuring IPv6 Netflow on Catalyst 6500 at the interface level,there is no ability to specify the direction of flow export !
Q.How to configure ICMP rate limiting in an IPv6 environment?
A. ICMP rate limiting is enabled by default with a default interval between error messages of 100 milliseconds and a bucket size (maximum number of tokens to be stored in a bucket) of 10. The command is "ipv6 icmp error-interval". This can be checked by giving "show ip interface <Interface Type> and the output is shown as below:
Q. What is the feature on IPv6 on Catalyst 6500 similar to ip-helper address?
A. A DHCP relay agent, which may reside on the client's link, is used to relay messages between the client and server. DHCP relay agent operation is transparent to the client. A client locates a DHCP server using a reserved, link-scoped multicast address. Therefore, it is a requirement for direct communication between the client and the server that the client and the server be attached to the same link. However, in some situations in which ease of management, economy, or scalability is a concern, it is desirable to allow a DHCP client to send a message to a DHCP server that is not connected to the same link.
Perform this task to enable the DHCPv6 relay agent function and specify relay destination addresses on an interface.
Q. What is the command that can be used to re-sequence IPv6 access control list (ACL)?
A. IPv6 acl re-sequence feature is not available in IOS.
Q. What are the ICMPv6 messages used by the neighbor discovery protocol?
A. There are 5 ICMPv6 messages used by the neighbor discovery protocol. They are listed as below:
Router Solicitation (RS)
Router Advertisement (RA)
Neighbor Solicitation (NS)
Neighbor Advertisement (NA)
Q. IPv4 to IPv6. What happened to IPv5?
A. According to Wikipedia, Internet Protocol Version 5 was used by the Internet Stream Protocol, an experimental streaming protocol. The second version (of Internet Stream Protocol), known variously as ST-II or ST2, distinguishes its own packets with an Internet Protocol version number 5, although it was never known as IPv5. The Internet Stream Protocol family was never introduced for public use, but many of the concepts available in ST are similar to later Asynchronous Transfer Mode protocols and can be found in Multiprotocol Label Switching (MPLS). They also presaged Voice over IP. Since the number 5 was already allocated, this number was not considered for the successor to IPv4. Several proposals were suggested as the IPv4 successor, and each was assigned a number. In the end, it happened that the one with version number 6 was selected.
Q. Not able to configure IPv6 on a WS-SUP32-GE-3B with IP Services Cisco IOS. Does Sup32 supports IPv6?
% Unrecognized command
A. Sup32 does support IPv6 but on 12.2(33) SXI or later then you can use IP services.
Q. Does the Cisco IPSec VPN Client support IPv6 ?
A.The IPSEC client can only form tunnels between IPv4 endpoints, and will only transport IPv4 packets inside the tunnel.If you are using something that will tunnel IPv6 inside IPv4 (ISATAP,6in4),the IPv6 will be transported but only because it looks like an IPv4 packet at the driver layer. The classic Cisco VPN client only carries IPv6 over IPSEC if the IPv6 is tunneled inside IPv4.For native IPv6 transport, you can use Cisco AnyConnect VPN client.
Q. What is the reason for a dedicated link local address for each VLAN?
A. One of the advantages of IPv6 is the fact that every link has a link local addresses that are significant only for that link, in addition to having at least one global address. The fact that the same link-local address can appear on multiple different links should be embraced as a benefit.
The ability to have many different addresses on an interface is one of the useful traits of IPv6 that can provide an advantage over IPv4