Juniper Networks

USA rbonica@juniper.net

INT Area 6man IPv6 This document deprecates the IPv6 Router Alert Option. Protocols that use the Router Alert Option may continue to do so, even in future versions. However, new protocols that are standardized in the future must not use the Router Alert Option. This document updates RFC 2711.

In IPv6, optional internet-layer information is encoded in separate headers that may be placed between the IPv6 header and the upper-layer header in a packet. There is a small number of such extension headers, each one identified by a distinct Next Header value. One of these extension headers is called the Hop-by-Hop Options header. The Hop-by-Hop Options header is used to carry optional information that may be examined and processed by every node along a packet's delivery path. The Hop-by-Hop Options header can carry one or more options. Among these is the Router Alert Option . The Router Alert Option provides a mechanism whereby routers can know when to intercept datagrams not addressed to them without having to extensively examine every datagram. The semantic of the Router Alert Option is, "routers should examine this datagram more closely". Excluding this option tells the router that there is no need to examine this datagram more closely. As explained below, the Router Alert Option introduces many issues. This document updates . Implementers of protocols that continue to use the Router Option can continue to reference for Router Alert Option details.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

identifies security considerations associated with the Router Alert Option. In a nutshell, the IP Router Alert Option does not provide a universal mechanism to accurately and reliably distinguish between IP Router Alert packets of interest and unwanted IP Router Alerts. This creates a security concern, because, short of appropriate router-implementation-specific mechanisms, the router's control plane is at risk of being flooded by unwanted traffic. NOTE: Many routers maintain separation between forwarding and control plane hardware. The forwarding plane is implemented on high-performance Application Specific Integrated Circuits (ASIC) and Network Processors (NP), while the control plane is implemented on general-purpose processors. Given this difference, the control plane is more susceptible to a Denial-of-Service (DoS) attack than the forwarding plane. demonstrates how a network operator can deploy Access Control Lists (ACL) that protect the control plane from DoS attack. These ACLs are effective and efficient when they select packets based upon information that can be found in a fixed position. However, they become less effective and less efficient when they must parse an IPv6 Hop-by-Hop Options header, searching for the Router Alert Option. So, network operators can address the security considerations raised in by: Deploying the operationally complex and computationally expensive ACLs described in . Configuring their routers to ignore the Router Alert Option. Dropping or severely rate limiting packets that contain the IPv6 Hop-by-hop Options header at the network edge. These options become less viable as protocol designers continue to design protocols that use the Router Alert Option. seeks to eliminate Hop-by-Hop processing on the control plane. However, because of its unique function, the Router Alert option is granted an exception to this rule. One approach would be to deprecate the Router Alert option, because current usage beyond the local network appears to be limited, and packets containing Hop-by-Hop options are frequently dropped. Deprecation would allow current implementations to continue using it, but its use could be phased out over time.

This document deprecates the IPv6 Router Alert Option. Protocols that use the Router Alert Option MAY continue to do so, even in future versions. However, new protocols that are standardized in the future MUST NOT use the Router Alert Option. contains an exhaustive list of protocols that may continue to use the Router Alert Option. This document updates .

As listed in , there are a number of protocols that use the Router Alert option. The only protocols in the Appendix that have wide spread deployment are Multicast Listener Discovery Version 2 (MLDv2) and Multicast Router Discovery (MRD) . The other protocols have either limited deployment, are Experimental, or have no known implementation. It is left for future work to develop new versions of MLDv2 and MRD that do not rely on the Router Alert option. That task is out of scope for this document.

This document mitigates all security considerations associated with the IPv6 Router Alert Option. These security considerations can be found in , and .

IANA is requested to mark the Router Alert Option as "Deprecated" in the Destination Options and Hop-by-hop Options Registry ( https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtml#ipv6-parameters-2) and add a pointer to this document. Please include a note describing how this document uses the word "deprecate". Text can be take from the abstract of this document. IANA is also requested to make a note in the IPv6 Router Alert Option Values Registry (https://www.iana.org/assignments/ipv6-routeralert-values/ipv6-routeralert-values.xhtml?) stating that allocations from this registry are no longer available. Please mark all unused and experimental codepoints in this registry as "reserved".

Thanks to Zafar Ali, Brian Carpenter, Toerless Eckert, David Farmer, Adrian Farrel, Bob Hinden and Jen Linkova for their reviews of this document.

contains an exhaustive list of protocols that use the IPv6 Router Alert Option. There are no known IPv6 implementations of MPLS PING. Neither INTSERV nor NSIS are widely deployed. All NSIS protocols are EXPERIMENTAL. Pragmatic Generic Multicast (PGM) is EXPERIMENTAL and there are no known IPv6 implementations. Protocol References Application Multicast Listener Discovery Version 2 (MLDv2) IPv6 Multicast Multicast Router Discovery (MRD) IPv6 Multicast Pragmatic General Multicast (PGM) IPv6 Multicast MPLS PING (Use of router alert deprecated) MPLS OAM Resource Reservation Protocol (RSVP): Both IPv4 and IPv6 implementations Integrated Services (INTSERV) and Multiprotocol Label Switching (MPLS) Next Steps In Signaling (NSIS) NSIS