Catalyst 2960 Switch Software Configuration Guide, Rel. 12.2(40)SE

Configuring IPv6 Host Functions

Internet Protocol Version 6 (IPv6) is the network-layer Internet Protocol intended to replace Version 4 (IPv4) in the TCP/IP suite of protocols. This chapter describes how to configure IPv6host functions on the Catalyst 2960 switch.

For information about configuring IPv6 Multicast Listener Discovery (MLD) snooping, see Chapter 30, "Configuring IPv6 MLD Snooping."

To enable dual stack environments (supporting both IPv4 and IPv6), you must configure a switch database management (SDM) template to a dual IPv4 and IPv6 template. See the "SDM Templates" section.

Note For complete syntax and usage information for the commands used in this chapter, see the Cisco IOS documentation referenced in the procedures

This chapter consists of these sections:

•"Understanding IPv6" section

•"Configuring IPv6" section

•"Displaying IPv6" section

Understanding IPv6

The primary reason for using IPv6 is to increase Internet global address space to accommodate the rapidly increasing number of users and applications that require unique global IP addresses. IPv4 uses 32-bit addresses to provide approximately 4 billion available addresses. Large blocks of these addresses are allocated to government agencies and large organizations, and the number of available IP addresses is rapidly decreasing. IPv6 incorporates 128-bit source and destination addresses and can provide significantly more globally unique IP addresses than IPv4.

The architecture of IPv6 allows existing IPv4 users to transition easily to IPv6, and provides services such as end-to-end security, quality of service (QoS), and globally unique addresses. The flexibility of the IPv6 address space reduces the need for private addresses and the use of Network Address Translation (NAT) processing by border routers at the edge of networks. IPv6 provides newer unicast methods, introduces hexadecimal values into the IP address, and uses colons (:) instead of periods (.) as delimiters.

IPv6 also provides these advantages over IPv4:

•Easier address management and delegation

•Easy address autoconfiguration with stateless autoconfiguration, which is similar to DHCP but does not require a specified DHCP application or server

•Embedded IPsec (encrypted security)

•Routing optimized for mobile devices

•Duplicate Address Detection (DAD) feature

For information about how Cisco Systems implements IPv6, go to this URL:

http://www.cisco.com//warp/public/732/Tech/ipv6/

This section describes IPv6 implementation on the switch. These sections are included:

•IPv6 Addresses

•Supported IPv6 Unicast Routing Features

•SDM Templates

IPv6 Addresses

IPv6 supports three types of addresses: unicast (one-to-one), multicast (one-to-many), and anycast (one-to-nearest). Multicast addresses replace the use of broadcast addresses. The switch supports only IPv6 unicast addresses. The switch does not support site-local unicast addresses, anycast addresses, or multicast addresses in this release.

The IPv6 128-bit addresses are represented as a series of eight 16-bit hexadecimal fields separated by colons in the format: x:x:x:x:x:x:x:x. This is an example of an IPv6 address:

2031:0000:130F:0000:0000:09C0:080F:130B

For easier implementation, leading zeros in each field are optional. This is the same address without leading zeros:

2031:0:130F:0:0:9C0:80F:130B

You can also use two colons (::) to represent successive hexadecimal fields of zeros, but you can use this short version only once in each address:

2031:0:130F::09C0:080F:130B

For more information about IPv6 address formats, address types, and the IPv6 packet header, go to the "Implementing Addressing and Basic Connectivity" section of "The Cisco IOS IPv6 Configuration Library" at this URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00807fcf4b.html

In the "Implementing Addressing and Basic Connectivity" chapter, these sections apply to the Catalyst 2960 switch:

•IPv6 Address Formats

•IPv6 Address Output Display

•Simplified IPv6 Packet Header

Supported IPv6 Unicast Routing Features

These sections describe the IPv6 protocol (RFC 2460) features supported by the switch:

•128-Bit Wide Unicast Addresses

•ICMPv6

•Neighbor Discovery

•IPv6 Stateless Autoconfiguration and Duplicate Address Detection

•IPv6 Applications

•Dual IPv4 and IPv6 Protocol Stacks

Support on the switch includes expanded address capability, header format simplification, improved support of extensions and options, and hardware parsing of the extension header. The switch supports hop-by-hop extension header packets, which are routed or bridged in software.

128-Bit Wide Unicast Addresses

The switch supports aggregatable global unicast addresses and link-local unicast addresses (RFC 2373). It does not support site-local unicast addresses.

•Aggregatable global unicast addresses are IPv6 addresses from the aggregatable global unicast prefix. The address structure enables strict aggregation of routing prefixes and limits the number of routing table entries in the global routing table. These addresses are used on links that are aggregated through organizations and eventually to the Internet service provider.

These addresses are defined by a global routing prefix, a subnet ID, and an interface ID. Current global unicast address allocation uses the range of addresses that start with binary value 001 (2000::/3). Addresses with a prefix of 2000::/3(001) through E000::/3(111) must have 64-bit interface identifiers in the extended universal identifier (EUI)-64 format.

•Link local unicast addresses can be automatically configured on any interface by using the link-local prefix FE80::/10(1111 1110 10) and the interface identifier in the modified EUI format. Link-local addresses are used in the neighbor discovery protocol and the stateless autoconfiguration process. Nodes on a local link use link-local addresses and do not require globally unique addresses to communicate. IPv6 routers do not forward packets with link-local source or destination addresses to other links.

See the section on IPv6 Unicast Addresses in the "Implementing Addressing and Basic Connectivity for IPv6" chapter in the Cisco IOS IPv6 Configuration Library at this URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00807fcf4b.html

Each IPv6 host interface can support up to three addresses in hardware (one aggregatable global unicast address, one link-local unicast address, and zero or more privacy addresses).

DNS for IPv6

IPv6 introduces new Domain Name System (DNS) record types that are supported in the DNS name-to-address and address-to-name lookup processes. The new DNS AAAA resource record types support IPv6 addresses and are equivalent to an A address record in IPv4. The switch supports DNS resolution for IPv4 and IPv6.

ICMPv6

The Internet Control Message Protocol (ICMP) in IPv6 (RFC 2463) functions the same as in IPv4. ICMP generates error messages, such as ICMP destination unreachable messages, to report errors during processing and other diagnostic functions. In IPv6, ICMP packets are also used in the neighbor discovery protocol and path MTU discovery. A value of 58 in the Next Header field of the basic IPv6 packet header identifies an IPv6 ICMP packet.

Neighbor Discovery

The switch supports Neighbor Discovery Protocol (NDP) for IPv6 (RFC 2461), a protocol running on top of ICMPv6, and Static Neighbor Discovery for IPv6 stations that do not support NDP. The IPv6 neighbor discovery process uses ICMP messages and solicited-node multicast addresses to determine the link-layer address of a neighbor on the same network (local link), verify the reachability of the neighbor, and keep track of neighboring routers.

A value of 135 in the Type field of the ICMP packet header identifies a neighbor solicitation message. These messages are sent on the local link when a node needs to determine the link-layer address of another node on the same local link. When a destination node receives a neighbor solicitation message, it replies by sending a neighbor advertisement message, which has a value of 136 in the ICMP packet header Type field.

A value of 137 in the ICMP packet header Type field identifies an IPv6 neighbor redirect message. The switch supports ICMPv6 redirect (RFC 2463) for routes with mask lengths less than 64. ICMP redirect is not supported for host routes or for summarized routes with mask lengths greater than 64. Routers send neighbor-redirect messages to inform hosts of better first-hop nodes on the path to a destination. A router does not update its routing tables after receiving a neighbor-redirect message and hosts do not originate neighbor-redirect messages.

Neighbor discovery throttling ensures that the switch CPU is not unnecessarily burdened while it is in the process of obtaining the next hop forwarding information to route an IPv6 packet. The switch performs a drop in hardware of any additional IPv6 packets whose next hop is the same neighbor the CPU is actively resolving. Performing this drop avoids adding further load on the CPU and results in a more efficient use of the switch CPU in an IPv6 routed environment.

IPv6 Stateless Autoconfiguration and Duplicate Address Detection

IPv6 supports two types of autoconfiguration:

•Stateless autoconfiguration (RFC 2462), where a host autonomously configures its own link-local address, and booting nodes send router solicitations to request router advertisements for configuring interfaces

•Stateful autoconfiguration using Dynamic Host Configuration Protocol (DHCP) v6.

The switch supports stateless autoconfiguration to manage link, subnet, and site addressing changes, such as management of host and mobile IP addresses.

All interfaces on IPv6 nodes must have a link-local address, which is automatically configured from the identifier (router MAC address) for an interface and the link-local prefix FE80::/10. A link-local address enables a node to communicate with other nodes on the link and can be used to further configure the node. Nodes can connect to a network and automatically generate global IPv6 addresses without the need for manual configuration or the help of a server, such as a DHCP server. With IPv6, a router on the link uses router advertisement messages to advertise global prefixes and its ability to act as a default router for the link. A node on the link can automatically configure global IPv6 addresses by appending its interface identifier (64-bits) to the prefixes (64 bits) included in the router advertisement messages.

The 128-bit IPv6 addresses configured by a node are then subjected to duplicate-address detection (RFC 2462) to ensure their uniqueness on the link. If the advertised prefixes are globally unique, the IPv6 addresses configured by the node are guaranteed to be globally unique. Router solicitation messages, which have a value of 133 in the ICMP packet header Type field, are sent by hosts at system startup so that the host can be immediately autoconfigured without waiting for the next scheduled router advertisement message. IPv6 duplicate-address detection is performed on unicast addresses before they are assigned to an interface. The switch does not support automatically generated site-local IPv6 addresses.

IPv6 Applications

The switch has IPv6 support for these applications:

•Ping, traceroute, Telnet, TFTP, and FTP

•Secure Shell (SSH) over an IPv6 transport

•HTTP server access over IPv6 transport

•DNS resolver for AAAA over IPv4 transport

•Cisco Discovery Protocol (CDP) support for IPv6 addresses

For more information about managing these applications with Cisco IOS, see the "Managing Cisco IOS Applications over IPv6" section in the Cisco IOS IPv6 Configuration Library at this URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00807fcf4b.html

Dual IPv4 and IPv6 Protocol Stacks

One technique for transitioning to IPv6 is by using dual IPv4 and IPv6 protocol stacks. Using dual stacks enables gradual, one-by-one upgrades to applications running on nodes. Applications that are upgraded to IPv6 use the IPv6 protocol stack, and applications that are not upgraded and support only IPv4 can coexist with upgraded applications on the same node. New and upgraded applications can use both IPv4 and IPv6 protocol stacks.

The Cisco IOS software supports the dual IPv4 and IPv6 protocol stack technique. When both IPv4 and IPv6 routing are enabled and an interface is configured with both an IPv4 and IPv6 address, the interface forwards both IPv4 and IPv6 traffic.

Figure 29-1 shows a router forwarding both IPv4 and IPv6 traffic through the same interface, based on the IP packet and destination addresses.

Figure 29-1 Dual IPv4 and IPv6 Support on an Interface

The switch uses ternary content addressable memory (TCAM) to store unicast routes, MAC addresses, access control lists (ACLs), and other features, and provides the switch database management (SDM) templates to allocate memory resources depending on how the switch is used. You must use the dual IPv4 and IPv6 template templates to allocate TCAM usage to both IPv4and IPv6 protocols. See the "SDM Templates" section.

SDM Templates

Catalyst 2960 switches have one TCAM to store unicast routes, MAC addresses, ACLs, and other features. To allocate TCAM resources for different usages, the switch SDM templates prioritize system resources to optimize support for certain features. You select the template that best suits the switch environment by entering the sdm prefer global configuration command. For more information about SDM templates, see "Configuring SDM Templates."

The dual IPv4 and IPv6 templates allow the switch to be used in dual stack environments (supporting both IPv4 and IPv6).

Note If you try to configure IPv6 without first selecting a dual IPv4 and IPv6 template, a warning message is generated.

•In IPv4-only environments, the switch applies IPv4 QoS and ACLs in hardware. IPv6 packets are not supported.

•In dual IPv4 and IPv6 environments, the switch applies IPv4 QoS and ACLs in hardware.

Note If you do not plan to use IPv6, do not use the dual stack template because this template results in less TCAM capacity for each resource.

Dual IPv4-and-IPv6 SDM Templates

These SDM templates support IPv4 and IPv6 environments:

Note This release does not support IPv6 multicast routing or QoS. This release does support IPv6 Multicast Listener Discovery (MLD) snooping.

•Dual IPv4 and IPv6 default SDM template—supports Layer 2, QoS, and ACLs for IPv4; and Layer 2 and ACLs for IPv6 on the switch.

Note An IPv4 route requires only one TCAM entry. Because of the hardware compression scheme used for IPv6, an IPv6 route can take more than one TCAM entry, reducing the number of entries forwarded in hardware.

Table 29-1 defines the approximate feature resources allocated by each new template.

Configuring IPv6

These sections contain this IPv6 forwarding configuration information:

•Default IPv6 Configuration

•Configuring IPv6 ICMP Rate Limiting

•Configuring Static Routes for IPv6

Default IPv6 Configuration

Table 29-2 shows the default IPv6 configuration.

Configuring IPv6 ICMP Rate Limiting

IPv6 ICMP rate limiting uses a token-bucket algorithm for limiting the rate at which IPv6 ICMP error messages are sent to the network. The interval between error messages is specified in a time interval and a bucket size. Because some applications, such as traceroute, sometimes require replies to a group of requests to be sent out in rapid succession, specifying only the interval between error messages can cause the application to fail. The token bucket allows a number of tokens, each representing the ability to send one error message, to be stored in virtual buckets. For every message to be sent, one token is removed from the bucket. If a series of error messages is generated, error messages can be sent until the bucket is empty. When the bucket is empty, IPv6 ICMP error messages are not sent until a new token is placed in the bucket. This method does not increase the average rate-limiting time interval, but it provides more flexibility than fixed-time intervals.

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.

Beginning in privileged EXEC mode, follow these steps to change the ICMP rate-limiting parameters:

To return to the default configuration, use the no ipv6 icmp error-interval global configuration command.

This example shows how to configure an IPv6 ICMP error message interval of 50 milliseconds and a bucket size of 20 tokens.

Switch(config)#ipv6 icmp error-interval 50 20

Configuring Static Routes for IPv6

Static routes are manually configured and define an explicit route between two networking devices. The benefits of static routes include security and resource efficiency. Static routes use less bandwidth than dynamic routing protocols because there is no requirement for routes to be calculated and communicated. The main disadvantage of using static routes is that static routes are not automatically updated, as with a dynamic routing protocol, and must be manually reconfigured if the network topology changes. Static routes are useful for smaller networks with only one path to an outside network or to provide security for a larger network for certain types of traffic.

There are types of static routes:

•Directly attached static routes—Only the output interface is specified because the destination is assumed to be directly attached to this interface. The packet destination is used as the next hop address. A directly attached static route is valid only when the specified interface is IPv6-enabled and is up.

•Recursive static routes—Only the next hop is specified, and the output interface is derived from the next hop. A recursive static route is valid only when the specified next hop results in a valid IPv6 output interface, the route does not self-recur, and the recursion depth does not exceed the maximum IPv6 forwarding recursion depth.

•Fully specified static routes—Both the output interface and the next hop are specified. The next hop is assumed to be directly attached to the specified output interface. A fully specified route is valid when the specified IPv6 interface is IPv6-enabled and up.

•Floating static routes—Any of the three types of static routes can be floating static routes, used to back up dynamic routes learned through configured routing protocols. A floating static route is configured with a less efficient administrative distance than the routing protocol it is backing up. Therefore, the dynamic route is always used for routing traffic in preference to the floating static route. If the dynamic route is lost, the floating static route is used in its place.

Beginning in privileged EXEC mode, follow these steps to configure an IPv6 static route:

To remove a configured static route, use the no ipv6 route ipv6-prefix/prefix length {ipv6-address | interface-id [ipv6-address]} [administrative distance] global configuration command.

This example shows how to configure a floating static route to an interface with an administrative distance of 130:

Switch(config)# ipv6 route 2001:0DB8::/32 gigabitethernet0/1 130

For more information about configuring static IPv6 routing, see the "Implementing Static Routes for IPv6" chapter in the Cisco IOS IPv6 Configuration Library at this URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00807fcf4b.html

Displaying IPv6

Table 29-3 shows the privileged EXEC commands for monitoring IPv6 on the switch.

This is an example of the output from the show ipv6 interface privileged EXEC command:

Switch# show ipv6 interface

Vlan1 is up, line protocol is up

  IPv6 is enabled, link-local address is FE80::20B:46FF:FE2F:D940

  Global unicast address(es):

    3FFE:C000:0:1:20B:46FF:FE2F:D940, subnet is 3FFE:C000:0:1::/64 [EUI]

  Joined group address(es):

    FF02::1

    FF02::2

    FF02::1:FF2F:D940

  MTU is 1500 bytes

  ICMP error messages limited to one every 100 milliseconds

  ICMP redirects are enabled

  ND DAD is enabled, number of DAD attempts: 1

  ND reachable time is 30000 milliseconds

  ND advertised reachable time is 0 milliseconds

  ND advertised retransmit interval is 0 milliseconds

  ND router advertisements are sent every 200 seconds

  ND router advertisements live for 1800 seconds

<output truncated>

This is an example of the output from the show ipv6 protocols privileged EXEC command:

Switch# show ipv6 protocols

IPv6 Routing Protocol is "connected"

IPv6 Routing Protocol is "static"

IPv6 Routing Protocol is "rip fer"

  Interfaces:

    Vlan6

    FastEthernet0/4

    FastEthernet0/11

    FastEthernet0/12

  Redistribution:

    None

This is an example of the output from the show ipv6 static privileged EXEC command:

Switch# show ipv6 static

IPv6 Static routes

Code: * - installed in RIB

* ::/0 via nexthop 3FFE:C000:0:7::777, distance 1

This is an example of the output from the show ipv6 neighbor privileged EXEC command:

Switch# show ipv6 neighbors

IPv6 Address                              Age Link-layer Addr State Interface

3FFE:C000:0:7::777                          - 0007.0007.0007  REACH Vl7

3FFE:C101:113:1::33                         - 0000.0000.0033  REACH Fa1/0/13

This is an example of the output from the show ipv6 route privileged EXEC command:

Switch# show ipv6 route

IPv6 Routing Table - Default - 1 entries

Codes: C - Connected, L - Local, S - Static, U - Per-user Static route

L   FF00::/8 [0/0]

     via Null0, receive

This is an example of the output from the show ipv6 traffic privileged EXEC command.

Switch# show ipv6 traffic

IPv6 statistics:

  Rcvd:  1 total, 1 local destination

         0 source-routed, 0 truncated

         0 format errors, 0 hop count exceeded

         0 bad header, 0 unknown option, 0 bad source

         0 unknown protocol, 0 not a router

         0 fragments, 0 total reassembled

         0 reassembly timeouts, 0 reassembly failures

  Sent:  36861 generated, 0 forwarded

         0 fragmented into 0 fragments, 0 failed

         0 encapsulation failed, 0 no route, 0 too big

         0 RPF drops, 0 RPF suppressed drops

  Mcast: 1 received, 36861 sent

ICMP statistics:

  Rcvd: 1 input, 0 checksum errors, 0 too short

        0 unknown info type, 0 unknown error type

        unreach: 0 routing, 0 admin, 0 neighbor, 0 address, 0 port

        parameter: 0 error, 0 header, 0 option

        0 hopcount expired, 0 reassembly timeout,0 too big

        0 echo request, 0 echo reply

        0 group query, 0 group report, 0 group reduce

        1 router solicit, 0 router advert, 0 redirects

        0 neighbor solicit, 0 neighbor advert

  Sent: 10112 output, 0 rate-limited

        unreach: 0 routing, 0 admin, 0 neighbor, 0 address, 0 port

        parameter: 0 error, 0 header, 0 option

        0 hopcount expired, 0 reassembly timeout,0 too big

        0 echo request, 0 echo reply

        0 group query, 0 group report, 0 group reduce

        0 router solicit, 9944 router advert, 0 redirects

        84 neighbor solicit, 84 neighbor advert

UDP statistics:

  Rcvd: 0 input, 0 checksum errors, 0 length errors

        0 no port, 0 dropped

  Sent: 26749 output

TCP statistics:

  Rcvd: 0 input, 0 checksum errors

  Sent: 0 output, 0 retransmitted