H3C S5500-SI Series Operating instructions

Brand: H3C

Model: S5500-SI Series

Type: Operating instructions

Operation Manual – IPv6

H3C S5500-SI Series Ethernet Switches Table of Contents

Table of Contents

Chapter 1 IPv6 Basics Configuration..........................................................................................1-1

1.1 IPv6 Overview....................................................................................................................1-1

1.1.1 IPv6 Features..........................................................................................................1-2

1.1.2 Introduction to IPv6 Address...................................................................................1-3

1.1.3 Introduction to IPv6 Neighbor Discovery Protocol ..................................................1-7

1.1.4 IPv6 PMTU Discovery...........................................................................................1-10

1.1.5 Introduction to IPv6 DNS.......................................................................................1-11

1.1.6 Protocols and Standards.......................................................................................1-11

1.2 IPv6 Basics Configuration Task List................................................................................1-12

1.3 Configuring Basic IPv6 Functions....................................................................................1-12

1.3.1 Enabling the IPv6 Packet Forwarding Function....................................................1-12

1.3.2 Configuring an IPv6 Unicast Address ...................................................................1-13

1.4 Configuring IPv6 NDP......................................................................................................1-14

1.4.1 Configuring a Static Neighbor Entry......................................................................1-14

1.4.2 Configuring the Maximum Number of Neighbors Dynamically Learned............... 1-15

1.4.3 Configuring Parameters Related to an RA Message............................................1-16

1.4.4 Configuring the Number of Attempts to Send an NS Message for DAD...............1-19

1.5 Configuring PMTU Discovery ..........................................................................................1-19

1.5.1 Configuring a Static PMTU for a Specified IPv6 Address.....................................1-19

1.5.2 Configuring the Aging Time for PMTU..................................................................1-20

1.6 Configuring IPv6 TCP Properties.....................................................................................1-20

1.7 Configuring ICMPv6 Packet Sending..............................................................................1-21

1.7.1 Configuring the Maximum ICMPv6 Error Packets Sent in an Interval..................1-21

1.7.2 Enable Sending of Multicast Echo Replies...........................................................1-22

1.8 Configuring IPv6 DNS......................................................................................................1-22

1.8.1 Configuring Static IPv6 Domain Name Resolution ...............................................1-22

1.8.2 Configuring Dynamic IPv6 Domain Name Resolution ..........................................1-22

1.9 Displaying and Maintaining IPv6 Basics Configuration ...................................................1-23

1.10 IPv6 Configuration Example..........................................................................................1-25

1.11 Troubleshooting IPv6 Basics Configuration...................................................................1-28

Chapter 2 Dual Stack Configuration............................................................................................ 2-1

2.1 Dual Stack Overview .........................................................................................................2-1

2.2 Configuring Dual Stack......................................................................................................2-1

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Chapter 1 IPv6 Basics Configuration

When configuring IPv6 basics, go to these sections for information you are interested

in:

z IPv6 Overview

z IPv6 Basics Configuration Task List

z Configuring Basic IPv6 Functions

z Configuring IPv6 NDP

z Configuring PMTU Discovery

z Configuring IPv6 TCP Properties

z Configuring ICMPv6 Packet Sending

z Configuring IPv6 DNS

z Displaying and Maintaining IPv6 Basics Configuration

z IPv6 Configuration Example

z Troubleshooting IPv6 Basics Configuration

 Note:

The term “router” or the router icon in this document refers to a router in a generic

sense or a Layer 3 Ethernet switch running a routing protocol.

1.1 IPv6 Overview

Internet Protocol Version 6 (IPv6), also called IP next generation (IPng), was designed

by the Internet Engineering Task Force (IETF) as the successor to Internet Protocol

Version 4 (IPv4). The significant difference between IPv6 and IPv4 is that IPv6

increases the IP address size from 32 bits to 128 bits.This section covers the following:

z IPv6 Features

z Introduction to IPv6 Address

z Introduction to IPv6 Neighbor Discovery Protocol

z IPv6 PMTU Discovery

z Introduction to IPv6 DNS

z Protocols and Standards

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1.1.1 IPv6 Features

I. Header format simplification

IPv6 cuts down some IPv4 header fields or move them to the IPv6 extension headers to

reduce the length of the basic IPv6 header. IPv6 uses the basic header with a fixed

length, thus making IPv6 packet handling simple and improving the forwarding

efficiency. Although the IPv6 address size is four times that of IPv4 addresses, the size

of basic IPv6 headers is 40 bytes and is only twice that of IPv4 headers (excluding the

Options field).

Ver

0113

Traffic

class

Flow label

Payload length

header

Hop limit

Source address (128 bits)

Destination address (128 bits)

3115 23

Ver HL ToS Total length

0733115 23

Identification Fragment offsetF

TTL Protocol Header checksum

Source address (32 bits)

Destination address (32 bits)

Options Padding

IPv4 header

Basic IPv6 header

Figure 1-1 Comparison between IPv4 packet header format and basic IPv6 packet

header format

II. Adequate address space

The source and destination IPv6 addresses are both 128 bits (16 bytes) long. IPv6 can

provide 3.4 x 10

addresses to completely meet the requirements of hierarchical

address division as well as allocation of public and private addresses.

III. Hierarchical address structure

IPv6 adopts the hierarchical address structure to quicken route search and reduce the

system source occupied by the IPv6 routing table by means of route aggregation.

IV. Automatic address configuration

To simplify the host configuration, IPv6 supports stateful and stateless address

configuration.

z Stateful address configuration means that a host acquires an IPv6 address and

related information from a server (for example, DHCP server).

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z Stateless address configuration means that a host automatically configures an

IPv6 address and related information on basis of its own link-layer address and the

prefix information advertised by a router.

In addition, a host can generate a link-local address on basis of its own link-layer

address and the default prefix (FE80::/64) to communicate with other hosts on the link.

V. Built-in security

IPv6 uses IPSec as its standard extension header to provide end-to-end security. This

feature provides a standard for network security solutions and improves the

interoperability between different IPv6 applications.

VI. QoS support

The Flow Label field in the IPv6 header allows the device to label packets in a flow and

provide special handling for these packets.

VII. Enhanced neighbor discovery mechanism

The IPv6 neighbor discovery protocol is implemented through a group of Internet

Control Message Protocol Version 6 (ICMPv6) messages that manages the information

exchange between neighbor nodes on the same link. The group of ICMPv6 messages

takes the place of Address Resolution Protocol (ARP) message, Internet Control

Message Protocol version 4 (ICMPv4) router discovery message, and ICMPv4

redirection message to provide a series of other functions.

VIII. Flexible extension headers

IPv6 cancels the Options field in IPv4 packets but introduces multiple extension

headers. In this way, IPv6 enhances the flexibility greatly to provide scalability for IP

while improving the handling efficiency. The Options field in IPv4 packets contains 40

bytes at most, while the size of IPv6 extension headers is restricted by that of IPv6

packets.

1.1.2 Introduction to IPv6 Address

I. IPv6 address format

An IPv6 address is represented as a series of 16-bit hexadecimals, separated by

colons. An IPv6 address is divided into eight groups, and the 16 bits of each group are

represented by four hexadecimal numbers which are separated by colons, for example,

2001:0000:130F:0000:0000:09C0:876A:130B.

To simplify the representation of IPv6 addresses, zeros in IPv6 addresses can be

handled as follows:

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z Leading zeros in each group can be removed. For example, the above-mentioned

address can be represented in shorter format as

2001:0:130F:0:0:9C0:876A:130B.

z If an IPv6 address contains two or more consecutive groups of zeros, they can be

replaced by the double-colon :: option. For example, the above-mentioned

address can be represented in the shortest format as

2001:0:130F::9C0:876A:130B.

Caution:

The double-colon :: option can be used only once in an IPv6 address. Otherwise, the

device is unable to determine how many zeros double-colons represent when

converting them to zeros to restore a 128-bit IPv6 address.

An IPv6 address consists of two parts: address prefix and interface ID. The address

prefix and the interface ID are respectively equivalent to the network ID and the host ID

in an IPv4 address.

An IPv6 address prefix is written in IPv6-address/prefix-length notation, where

IPv6-address is an IPv6 address in any of the notations and prefix-length is a decimal

number indicating how many bits from the utmost left of an IPv6 address are the

address prefix.

II. IPv6 address classification

IPv6 addresses fall into three types: unicast address, multicast address, and anycast

address.

z Unicast address: An identifier for a single interface, similar to an IPv4 unicast

address. A packet sent to a unicast address is delivered to the interface identified

by that address.

z Multicast address: An identifier for a set of interfaces (typically belonging to

different nodes), similar to an IPv4 multicast address. A packet sent to a multicast

address is delivered to all interfaces identified by that address.

z Anycast address: An identifier for a set of interfaces (typically belonging to

different nodes). A packet sent to an anycast address is delivered to one of the

interfaces identified by that address (the nearest one, according to the routing

protocols’ measure of distance).

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 Note:

There are no broadcast addresses in IPv6. Their function is superseded by multicast

addresses.

The type of an IPv6 address is designated by the first several bits called format prefix.

Table 1-1 lists the mappings between address types and format prefixes.

Table 1-1 Mapping between address types and format prefixes

Type Format prefix (binary) IPv6 prefix ID

Unassigned

address

00...0 (128 bits) ::/128

Loopback

address

00...1 (128 bits) ::1/128

Link-local

address

1111111010 FE80::/10

Site-local

address

1111111011 FEC0::/10

Unicast

address

Global unicast

address

other forms —

Multicast address 11111111 FF00::/8

Anycast address

Anycast addresses are taken from unicast address

space and are not syntactically distinguishable from

unicast addresses.

III. Unicast address

There are several forms of unicast address assignment in IPv6, including aggregatable

global unicast address, link-local address, and site-local address.

z The aggregatable global unicast address, equivalent to an IPv4 public address, is

provided for network service providers. The type of address allows efficient route

prefix aggregation to restrict the number of global routing entries.

z The link-local address is used for communication between link-local nodes in

neighbor discovery and stateless autoconfiguration. Routers must not forward any

packets with link-local source or destination addresses to other links.

z IPv6 unicast site-local addresses are similar to private IPv4 addresses. Routers

must not forward any packets with site-local source or destination addresses

outside of the site (equivalent to a private network).

z Loopback address: The unicast address 0:0:0:0:0:0:0:1 (represented in the

shortest format as ::1) is called the loopback address and may never be assigned

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to any physical interface. Like the loopback address in IPv4, it may be used by a

node to send an IPv6 packet to itself.

z Unassigned address: The unicast address "::” is called the unassigned address

and may not be assigned to any node. Before acquiring a valid IPv6 address, a

node may fill this address in the source address field of an IPv6 packet, but may

not use it as a destination IPv6 address.

IV. Multicast address

IPv6 multicast addresses listed in Table 1-2 are reserved for special purpose.

Table 1-2 Reserved IPv6 multicast addresses

Address Application

FF01::1 Node-local scope all-nodes multicast address

FF02::1 Link-local scope all-nodes multicast address

FF01::2 Node-local scope all-routers multicast address

FF02::2 Link-local scope all-routers multicast address

FF05::2 Site-local scope all-routers multicast address

Besides, there is another type of multicast address: solicited-node address. A

solicited-node multicast address is used to acquire the link-layer addresses of neighbor

nodes on the same link and is also used for duplicate address detection (DAD). Each

IPv6 unicast or anycast address has one corresponding solicited-node address. The

format of a solicited-node multicast address is as follows:

FF02:0:0:0:0:1:FFXX:XXXX

Where, FF02:0:0:0:0:1 FF is permanent and consists of 104 bits, and XX:XXXX is the

last 24 bits of an IPv6 unicast or anycast address.

V. Interface identifier in IEEE EUI-64 format

Interface identifiers in IPv6 unicast addresses are used to identify interfaces on a link

and they are required to be unique on that link. Interface identifiers in IPv6 unicast

addresses are currently required to be 64 bits long. An interface identifier in IEEE

EUI-64 format is derived from the link-layer address of that interface. Interface

identifiers in IPv6 addresses are 64 bits long, while MAC addresses are 48 bits long.

Therefore, the hexadecimal number FFFE needs to be inserted in the middle of MAC

addresses (behind the 24 high-order bits). To ensure the interface identifier obtained

from a MAC address is unique, it is necessary to set the universal/local (U/L) bit (the

seventh high-order bit) to “1”. Thus, an interface identifier in IEEE EUI-64 format is

obtained.

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Figure 1-2 Convert a MAC address into an EUI-64 interface identifier

1.1.3 Introduction to IPv6 Neighbor Discovery Protocol

IPv6 Neighbor Discovery Protocol (NDP) uses five types of ICMPv6 messages to

implement the following functions:

z Address resolution

z Neighbor reachability detection

z Duplicate address detection

z Router/prefix discovery and address autoconfiguration

z Redirection

Table 1-3 lists the types and functions of ICMPv6 messages used by the NDP.

Table 1-3 Types and functions of ICMPv6 messages

ICMPv6 message Number Function

Used to acquire the link-layer address of a

neighbor

Used to verify whether the neighbor is

reachable

Neighbor solicitation

(NS) message

135

Used to perform a duplicate address

detection

Used to respond to an NS message

Neighbor

advertisement (NA)

message

136

When the link layer changes, the local node

initiates an NA message to notify neighbor

nodes of the node information change.

Router solicitation

(RS) message

133

After started, a node sends an RS message

to request the router for an address prefix and

other configuration information for the

purpose of autoconfiguration.

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ICMPv6 message Number Function

Used to respond to an RS message

Router advertisement

(RA) message

134

With the RA message suppression disabled,

the router regularly sends an RA message

containing information such as prefix

information options and flag bits.

Redirect message 137

When a certain condition is satisfied, the

default gateway sends a redirect message to

the source host so that the host can reselect a

correct next hop router to forward packets.

The NDP mainly provides the following functions:

I. Address resolution

Similar to the ARP function in IPv4, a node acquires the link-layer addresses of

neighbor nodes on the same link through NS and NA messages.

Figure 1-3 shows how

node A acquires the link-layer address of node B.

Figure 1-3 Address resolution

The address resolution procedure is as follows:

1) Node A multicasts an NS message. The source address of the NS message is the

IPv6 address of an interface of node A and the destination address is the

solicited-node multicast address of node B. The NS message contains the

link-layer address of node A.

2) After receiving the NS message, node B judges whether the destination address

of the packet corresponds to the solicited-node multicast address. If yes, node B

can learn the link-layer address of node A, and unicasts an NA message

containing its link-layer address.

3) Node A acquires the link-layer address of node B from the NA message.

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II. Neighbor reachability detection

After node A acquires the link-layer address of its neighbor node B, node A can verify

whether node B is reachable according to NS and NA messages.

1) Node A sends an NS message whose destination address is the IPv6 address of

node B.

2) If node A receives an NA message from node B, node A considers that node B is

reachable. Otherwise, node B is unreachable.

III. Duplicate address detection

After node A acquires an IPv6 address, it will perform duplicate address detection (DAD)

to determine whether the address is being used by other nodes (similar to the

gratuitous ARP function of IPv4). DAD is accomplished through NS and NA messages.

Figure 1-3 shows the DAD procedure.

Figure 1-4 Duplicate address detection

The DAD procedure is as follows:

1) Node A sends an NS message whose source address is the unassigned address ::

and destination address is the corresponding solicited-node multicast address of

the IPv6 address to be detected. The NS message contains the IPv6 address.

2) If node B uses this IPv6 address, node B returns an NA message. The NA

message contains the IPv6 address of node B.

3) Node A learns that the IPv6 address is being used by node B after receiving the

NA message from node B. Otherwise, node B is not using the IPv6 address and

node A can use it.

IV. Router/prefix discovery and address autoconfiguration

Router/prefix discovery means that a node locates the neighboring routers, and learns

the prefix of the network where the host is located, and other configuration parameters

from the received RA message.

Stateless address autoconfiguration means that a node automatically configures an

IPv6 address according to the information obtained through router/prefix discovery.

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The router/prefix discovery is implemented through RS and RA messages. The

router/prefix discovery procedure is as follows:

1) After started, a node sends an RS message to request the router for the address

prefix and other configuration information for the purpose of autoconfiguration.

2) The router returns an RA message containing information such as prefix

information option. (The router also regularly sends an RA message.)

3) The node automatically configures an IPv6 address and other information for its

interface according to the address prefix and other configuration parameters in the

RA message.

 Note:

z In addition to an address prefix, the prefix information option also contains the

preferred lifetime and valid lifetime of the address prefix. After receiving a periodic

RA message, the node updates the preferred lifetime and valid lifetime of the

address prefix accordingly.

z An automatically generated address is applicable within the valid lifetime and will be

removed when the valid lifetime times out.

V. Redirection

When a host is started, its routing table may contain only the default route to the

gateway. When certain conditions are satisfied, the gateway sends an ICMPv6 redirect

message to the source host so that the host can select a better next hop to forward

packets (similar to the ICMP redirection function in IPv4).

The gateway will send an IPv6 ICMP redirect message when the following conditions

are satisfied:

z The receiving interface is the forwarding interface.

z The selected route itself is not created or modified by an IPv6 ICMP redirect

message.

z The selected route is not the default route.

z The forwarded IPv6 packet does not contain any routing header.

1.1.4 IPv6 PMTU Discovery

The links that a packet passes from the source to the destination may have different

MTUs. In IPv6, when the packet size exceeds the link MTU, the packet will be

fragmented at the source end so as to reduce the processing pressure of the

forwarding device and utilize network resources rationally.

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The path MTU (PMTU) discovery mechanism is to find the minimum MTU of all links in

the path from the source to the destination.

Figure 1-5 shows the working procedure of

the PMTU discovery.

Figure 1-5 Working procedure of the PMTU discovery

The working procedure of the PMTU discovery is as follows:

1) The source host uses its MTU to fragment packets and then sends them to the

destination host.

2) If the MTU supported by the forwarding interface is less than the packet size, the

forwarding device will discard the packet and return an ICMPv6 error packet

containing the interface MTU to the source host.

3) After receiving the ICMPv6 error packet, the source host uses the returned MTU to

fragment the packet again and then sends it.

4) Step 2 to step 3 are repeated until the destination host receives the packet. In this

way, the minimum MTU of all links in the path from the source host to the

destination host is determined.

1.1.5 Introduction to IPv6 DNS

In the IPv6 network, a Domain Name System (DNS) supporting IPv6 converts domain

names into IPv6 addresses, instead of IPv4 addresses.

However, just like an IPv4 DNS, an IPv6 DNS also covers static domain name

resolution and dynamic domain name resolution. The function and implementation of

these two types of domain name resolution are the same as those of an IPv4 DNS. For

details, refer to DNS Configuration.

Usually, the DNS server connecting IPv4 and IPv6 networks not only contain A records

(IPv4 addresses), but also AAAA records (IPv6 addresses). The DNS server can

convert domain names into IPv4 addresses or IPv6 addresses. In this way, the DNS

server implements the functions of both IPv6 DNS and IPv4 DNS.

1.1.6 Protocols and Standards

Protocols and standards related to IPv6 include:

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z RFC 1881: IPv6 Address Allocation Management

z RFC 1887: An Architecture for IPv6 Unicast Address Allocation

z RFC 1981: Path MTU Discovery for IP version 6

z RFC 2375: IPv6 Multicast Address Assignments

z RFC 2460: Internet Protocol, Version 6 (IPv6) Specification.

z RFC 2461: Neighbor Discovery for IP Version 6 (IPv6)

z RFC 2462: IPv6 Stateless Address Autoconfiguration

z RFC 2463: Internet Control Message Protocol (ICMPv6) for the Internet Protocol

Version 6 (IPv6) Specification

z RFC 2464: Transmission of IPv6 Packets over Ethernet Networks

z RFC 2526: Reserved IPv6 Subnet Anycast Addresses

z RFC 3307: Allocation Guidelines for IPv6 Multicast Addresses

z RFC 3513: Internet Protocol Version 6 (IPv6) Addressing Architecture

z RFC 3596: DNS Extensions to Support IP Version 6

1.2 IPv6 Basics Configuration Task List

Complete the following tasks to perform IPv6 basics configuration:

Task Remarks

Configuring Basic IPv6 Functions Required

Configuring IPv6 NDP Optional

Configuring PMTU Discovery Optional

Configuring IPv6 TCP Properties Optional

Configuring ICMPv6 Packet Sending Optional

Configuring IPv6 DNS Optional

1.3 Configuring Basic IPv6 Functions

1.3.1 Enabling the IPv6 Packet Forwarding Function

Before IPv6-related configurations, you must enable the IPv6 packet forwarding

function. Otherwise, an interface cannot forward IPv6 packets even if an IPv6 address

is configured, resulting in communication failures in the IPv6 network.

Follow these steps to enable the IPv6 packet forwarding function:

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To do... Use the command... Remarks

Enter system view

system-view

—

Enable the IPv6 packet

forwarding function

ipv6

Required

Disabled by default.

1.3.2 Configuring an IPv6 Unicast Address

IPv6 site-local addresses and aggregatable global unicast addresses can be

configured in the following ways:

z EUI-64 format: When the EUI-64 format is adopted to form IPv6 addresses, the

IPv6 address prefix of an interface is the configured prefix and the interface

identifier is derived from the link-layer address of the interface.

z Manual configuration: IPv6 site-local addresses or aggregatable global unicast

addresses are configured manually.

IPv6 link-local addresses can be configured in either of the following ways:

z Automatic generation: The device automatically generates a link-local address for

an interface according to the link-local address prefix (FE80::/64) and the

link-layer address of the interface.

z Manual assignment: IPv6 link-local addresses can be assigned manually.

Follow these steps to configure an IPv6 unicast address:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter interface view

interface interface-type

interface-number

—

Manually assign

an IPv6 address

ipv6 address

{ ipv6-address

prefix-length |

ipv6-address/prefix-lengt

h }

Configure

an IPv6

aggregatabl

e global

unicast

address or

site-local

address

Adopt the EUI-64

format to form an

IPv6 address

ipv6 address

ipv6-address/prefix-lengt

h eui-64

Required to use

either command.

By default, no

site-local address or

aggregatable global

unicast address is

configured for an

interface.

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To do... Use the command... Remarks

Automatically

generate a

link-local

address

ipv6 address auto

link-local

Configure

an IPv6

link-local

address

Manually assign

a link-local

address for an

interface

ipv6 address

ipv6-address link-local

Optional

By default, after an

IPv6 site-local

address or

aggregatable global

unicast address is

configured for an

interface, a link-local

address will be

generated

automatically.

 Note:

z After an IPv6 site-local address or aggregatable global unicast address is

configured for an interface, a link-local address will be generated automatically. The

automatically generated link-local address is the same as the one generated by

using the ipv6 address auto link-local command. If a link-local address is

manually assigned to an interface, this link-local address takes effect. If the

manually assigned link-local address is removed, the automatically generated

link-local address takes effect.

z The manual assignment takes precedence over the automatic generation. That is, if

you first adopt the automatic generation and then the manual assignment, the

manually assigned link-local address will overwrite the automatically generated one.

If you first adopt the manual assignment and then the automatic generation, the

automatically generated link-local address will not take effect and the link-local

address of an interface is still the manually assigned one. If you delete the manually

assigned address, the automatically generated link-local address is validated.

z You need to execute the ipv6 address auto link-local command before the undo

ipv6 address auto link-local command. However, if an IPv6 site-local address or

aggregatable global unicast address is already configured for an interface, the

interface still has a link-local address because the system automatically generates

one for the interface. If no IPv6 site-local address or aggregatable global unicast

address is configured, the interface has no link-local address.

1.4 Configuring IPv6 NDP

1.4.1 Configuring a Static Neighbor Entry

The IPv6 address of a neighbor node can be resolved into a link-layer address

dynamically through NS and NA messages or through a manually configured neighbor

entry.

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The device uniquely identifies a static neighbor entry according to the IPv6 address and

the layer 3 interface ID. Currently, there are two configuration methods:

z Configure an IPv6 address and link-layer address for a Layer 3 interface.

z Configure an IPv6 address and link-layer address for a port in a VLAN.

Follow these steps to configure a static neighbor entry:

To do... Use the command... Remarks

Enter system view

system-view

—

Configure a static

neighbor entry

ipv6 neighbor ipv6-address

mac-address { vlan-id port-type

port-number | interface interface-type

interface-number }

Required

Caution:

You can adopt either of the two methods above to configure a static neighbor entry for

a VLAN interface.

z After a static neighbor entry is configured by using the first method, the device

needs to resolve the corresponding Layer 2 port information of the VLAN interface.

z If you adopt the second method to configure a static neighbor entry, you should

ensure that the corresponding VLAN interface exists and that the layer 2 port

specified by port-type port-number belongs to the VLAN specified by vlan-id. After a

static neighbor entry is configured, the device relates the VLAN interface to an IPv6

address to uniquely identify a static neighbor entry.

1.4.2 Configuring the Maximum Number of Neighbors Dynamically Learned

The device can dynamically acquire the link-layer address of a neighbor node and add

it into the neighbor table through NS and NA messages. Too large a neighbor table from

which neighbor entries can be dynamically acquired may lead to the forwarding

performance degradation of the device. Therefore, you can restrict the size of the

neighbor table by setting the maximum number of neighbors that an interface can

dynamically learn. When the number of dynamically learned neighbors reaches the

threshold, the interface will stop learning neighbor information.

Follow these steps to configure the maximum number of neighbors dynamically

learned:

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To do… Use the command… Remarks

Enter system view

system-view

—

Enter interface view

interface interface-type

interface-number

—

Configure the maximum

number of neighbors

dynamically learned by an

interface

ipv6 neighbors

max-learning-num number

Optional

1.4.3 Configuring Parameters Related to an RA Message

You can configure whether the interface sends an RA message, the interval for sending

RA messages, and parameters in RA messages. After receiving an RA message, a

host can use these parameters to perform corresponding operations.

Table 1-4 lists the

configurable parameters in an RA message and their descriptions.

Table 1-4 Parameters in an RA message and their descriptions

Parameters Description

Cur hop limit

When sending an IPv6 packet, a host uses the value of this

parameter to fill the Cur Hop Limit field in IPv6 headers.

Meanwhile, the value of this parameter is equal to the value

of the Cur Hop Limit field in response messages of the

device.

Prefix information

options

After receiving the prefix information advertised by the

device, the hosts on the same link can perform stateless

autoconfiguration operations.

M flag

This field determines whether hosts use the stateful

autoconfiguration to acquire IPv6 addresses.

If the M flag is set to 1, hosts use the stateful

autoconfiguration to acquire IPv6 addresses. Otherwise,

hosts use the stateless autoconfiguration to acquire IPv6

addresses, that is, hosts configure IPv6 addresses

according to their own link-layer addresses and the prefix

information issued by the router.

O flag

This field determines whether hosts use the stateful

autoconfiguration to acquire information other than IPv6

addresses.

If the O flag is set to 1, hosts use the stateful

autoconfiguration (for example, DHCP server) to acquire

information other than IPv6 addresses. Otherwise, hosts use

the stateless autoconfiguration to acquire information other

than IPv6 addresses.

Operation Manual – IPv6

H3C S5500-SI Series Ethernet Switches Chapter 1 IPv6 Basics Configuration

1-17

Parameters Description

Router lifetime

This field is used to set the lifetime of the router that sends

RA messages to serve as the default router of hosts.

According to the router lifetime in the received RA

messages, hosts determine whether the router sending RA

messages can serve as the default router of hosts.

Retrans timer

If the device fails to receive a response message within the

specified time after sending an NS message, the device will

retransmit it.

Reachable time

After the neighbor reachability detection shows that a

neighbor is reachable, the device considers the neighbor is

reachable within the reachable time. If the device needs to

send a packet to a neighbor after the reachable time expires,

the device will again confirm whether the neighbor is

reachable.

 Note:

The values of the Retrans Timer field and the Reachable Time field configured for an

interface are sent to hosts via RA messages. Furthermore, this interface sends NS

messages at intervals of Retrans Timer and considers a neighbor reachable within the

time of Reachable Time.

Follow these steps to configure parameters related to an RA message:

To do… Use the command… Remarks

Enter system view

system-view

—

Configure the current hop

limit

ipv6 nd hop-limit value

Optional

64 by default.

Enter interface view

interface interface-type

interface-number

—

Disable the RA message

suppression

undo ipv6 nd ra halt

Optional

By default, RA messages

are suppressed.

Operation Manual – IPv6

H3C S5500-SI Series Ethernet Switches Chapter 1 IPv6 Basics Configuration

1-18

To do… Use the command… Remarks

Configure the maximum

and minimum intervals for

sending RA messages

ipv6 nd ra interval

max-interval-value

min-interval-value

Optional

By default, the maximum

interval for sending RA

messages is 600

seconds, and the

minimum interval is 200

seconds.

The device sends RA

messages at intervals of a

random value between

the maximum interval and

the minimum interval.

The minimum interval

should be less than or

equal to 0.75 times the

maximum interval.

Configure the prefix

information options in RA

messages

ipv6 nd ra prefix

{ ipv6-address

prefix-length |

ipv6-address/prefix-lengt

h } valid-lifetime

preferred-lifetime

[ no-autoconfig

[ off-link ]*

Optional

By default, no prefix

information is configured

in RA messages and the

IPv6 address of the

interface sending RA

messages is used as the

prefix information.

Set the M flag bit to 1

ipv6 nd autoconfig

managed-address-flag

Optional

By default, the M flag bit is

set to 0, that is, hosts

acquire IPv6 addresses

through stateless

autoconfiguration.

Set the O flag bit to 1.

ipv6 nd autoconfig

other-flag

Optional

By default, the O flag bit is

set to 0, that is, hosts

acquire other information

through stateless

autoconfiguration.

Configure the router

lifetime in RA messages

ipv6 nd ra

router-lifetime value

Optional

1,800 seconds by default.

Set the retrans timer

ipv6 nd ns retrans-timer

value

Optional

By default, the local

interface sends NS

messages at intervals of

1,000 milliseconds and

the Retrans Timer field in

RA messages sent by the

local interface is equal to

Operation Manual – IPv6

H3C S5500-SI Series Ethernet Switches Chapter 1 IPv6 Basics Configuration

1-19

To do… Use the command… Remarks

Set the reachable time

ipv6 nd nud

reachable-time value

Optional

By default, the neighbor

reachable time on the

local interface is 30,000

milliseconds and the

Reachable Timer field in

RA messages is 0.

Caution:

The maximum interval for sending RA messages should be less than or equal to the

router lifetime in RA messages.

1.4.4 Configuring the Number of Attempts to Send an NS Message for DAD

An interface sends a neighbor solicitation (NS) message for DAD after acquiring an

IPv6 address. If the interface does not receive a response within a specified time

(determined by the ipv6 nd ns retrans-timer command), it continues to send an NS

message. If it still does not receive a response after the number of attempts to send an

NS message reaches the maximum, the acquired address is considered available.

Follow these steps to configure the attempts to send an NS message for DAD:

To do… Use the command… Remarks

Enter system view

system-view

—

Enter interface view

interface interface-type

interface-number

—

Configure the number of

attempts to send an NS

message for DAD

ipv6 nd dad attempts

value

Optional

1 by default. When the

value argument is set to 0,

DAD is disabled.

1.5 Configuring PMTU Discovery

1.5.1 Configuring a Static PMTU for a Specified IPv6 Address

You can configure a static PMTU for a specified destination IPv6 address. When a

source host sends packets through an interface, it compares the interface MTU with the

static PMTU of the specified destination IPv6 address. If the packet size is larger than

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H3C S5500-SI Series Operating instructions

H3C S5500-SI Series Operating instructions

H3C S5500-SI Series Operating instructions

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