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Configuration Guide - IP Service

CloudEngine 12800 and 12800E V200R005C00

This document describes the configurations of IP Service, including IP address, ARP, DHCP, DNS, IP performance optimization, IPv6, DHCPv6, and IPv6 DNS.

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IPv6 Secure Neighbor Discovery

IPv6 Secure Neighbor Discovery

In the IPv6 protocol suite, ND is significant in ensuring availability of neighbors on the local link. As network security problems intensify, how to secure ND becomes a concern. RFC 3756 defines several threats to ND security, some of which are described as follows:

Table 7-3 IPv6 ND attacks

Attack Method


NS/NA spoofing

An attacker sends an authorized node (host or switch) an NS message with a bogus source link-layer address option, or an NA message with a bogus target link-layer address option. Then packets from the authorized node are sent to this link-layer address.

Neighbor Unreachability Detection (NUD) failure

An attacker repeatedly sends forged NA messages in response to an authorized node's NUD NS messages so that the authorized node cannot detect the neighbor unreachability. The consequences of this attack depend on why the neighbor became unreachable and how the authorized node would behave if it knew that the neighbor has become unreachable.

Duplicate Address Detection (DAD) attacks

An attacker responds to every DAD attempt made by a host that accesses the network, claiming that the address is already in use. Then the host will never obtain an address.

Spoofed Redirect message

An attacker uses the link-local address of the first-hop switch to send a Redirect message to an authorized host. The authorized host accepts this message because the host mistakenly considers that the message came from the first-hop switch.

Replay attacks

An attacker captures valid messages and replays them. Even if Neighbor Discovery Protocol (NDP) messages are cryptographically protected so that their contents cannot be forged, they are still prone to replay attacks.

Bogus address prefix

An attacker sends a bogus RA message specifying that some prefixes are on-link. If a prefix is on-link, a host will not send any packets that contain this prefix to the switch. Instead, the host will send NS messages to attempt address resolution, but the NS messages are not responded. As a result, the host is denied services.

Malicious last-hop switch

An attacker multicasts bogus RA messages or unicasts bogus RA messages in response to multicast RS messages to a host attempting to discover a last-hop switch. If the host selects the attacker as its default switch, the attacker is able to insert himself as a man-in-the-middle and intercepts all messages exchanged between the host and its destination.

To counter these threats, Secure Neighbor Discovery (SEND), defined in RFC 3971, specifies security mechanisms to extend ND. SEND defines Cryptographically Generated Addresses (CGAs), CGA option, and Rivest Shamir Adleman (RSA) option, which are used to ensure that the sender of an ND message is the owner of the message's source address. SEND also defines Timestamp and Nonce options to prevent replay attacks.

  • CGA: A CGA contains network prefix and interface identifier. Interface identifier is generated from a one-way hash of the public key and associated parameters.
  • CGA option: contains information used to verify the sender's CGA, including the public key of the sender. CGA is used to authenticate the validity of source IP addresses carried in ND messages.
  • RSA option: contains the hash value of the sender's public key and contains the digital signature generated from the sender's private key and ND messages. RSA is used to authenticate the completeness of ND messages and the identity of the ND message sender.
    For an attacker to use an address that belongs to an authorized node, the attacker must use the public key of the authorized node for encryption. Otherwise, the receiver can detect the attempted attack after checking the CGA option. Even if the attacker obtains the public key of the authorized node, the receiver can still detect the attempted attack after checking the digital signature, which is generated from the sender's private key.
  • Timestamp option: a 64-bit unsigned integer field containing a timestamp. The value indicates the number of seconds since January 1, 1970, 00:00 UTC. This option protects non-solicit notification messages and Redirect messages and ensures that the timestamp of the recently received message is the latest.
  • Nonce option: contains a random number selected by the sender of a solicitation message. This option prevents replay attacks during message exchange. For example, a sender sends an NS message carrying the Nonce option and receives an NA message as a response that also carries the Nonce option; the sender verifies the NA message based on the Nonce option.
Updated: 2019-04-18

Document ID: EDOC1100039535

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