Robust Header Compression C. Bormann Internet-Draft Universitaet Bremen TZI Intended status: Standards Track July 13, 2009 Expires: January 14, 2010 Robust Header Compression (ROHC) over 802 networks draft-bormann-rohc-over-802-02 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 14, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract Various proposals have been submitted to the ROHC working group for enabling the use of ROHC [RFC3095] header compression over Ethernet, 802.11 and other 802-based links. Bormann Expires January 14, 2010 [Page 1] Internet-Draft ROHC over 802 July 2009 Previous proposals generally suffered from a lack of systems perspective on 802 networks. The present document attempts to supply some systems perspective and provides a rough outline for a solution. This is a submission to the IETF ROHC WG. Please direct discussion to its mailing list, rohc@ietf.org $Revision: 1.9 $ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Overall Requirements . . . . . . . . . . . . . . . . . . . 3 2.2. Elements of a Solution . . . . . . . . . . . . . . . . . . 4 2.3. Who Should Standardize? . . . . . . . . . . . . . . . . . 5 2.4. Why not just use PPPoE? . . . . . . . . . . . . . . . . . 6 3. Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Ethernet Minimum Frame Size . . . . . . . . . . . . . . . 6 3.2. Negotiation and the existing IP-over-802 model . . . . . . 7 4. Non-Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1. Reordering . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2. Padding a non-issue? . . . . . . . . . . . . . . . . . . . 8 5. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 8 5.1. ULE encapsulation . . . . . . . . . . . . . . . . . . . . 10 6. Negotiation . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . . 13 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15 Bormann Expires January 14, 2010 [Page 2] Internet-Draft ROHC over 802 July 2009 1. Introduction RFC 3095 [RFC3095] defines four ROHC profiles for the header compression of IP, UDP, RTP, ESP, and related protocol headers, as well as a framework that has been used to define a number of related profiles (such as IP ROHC [RFC3843] and UDP-lite based RTP ROHC [RFC4019]). Since, the framework has been extracted into RFC 4995 [RFC4995] and several "version 2" ROHC profiles have been defined [RFC4996] [RFC5225]. ROHC as a framework is also useful for transporting legacy compression formats where this is desirable [I-D.bormann-rohc-avt-crtp-profile]. To enable robust header compression over a specific link layer, the ROHC profile specifications have to be complemented by a link-layer specific specification, typically called "ROHC-over-X". One such specification has been defined in the IETF, ROHC over PPP [RFC3241]. Other ROHC-over-X specifications have been defined by the organizations defining specific link layers, such as 3GPP. No specification currently exists for applying robust header compression to IEEE 802 networks such as Ethernet, 802.11, or 802.16. A number of proposals have been made to the IETF ROHC WG , but it became obvious quickly that the solutions that seem to suggest themselves do not work at the desirable level of efficiency. The lack of a specification for IEEE 802 networks also impacts related IETF standards, such as IP over DVB [RFC4326]. While IP over DVB is not by itself an IEEE 802 network, actual implementations often are closely tied to Ethernets by technologies related to bridging, making some form of interoperability at the compressed level desirable. This document first discusses some issues about ROHC-over-802, then lists some potential non-issues, defines an encapsulation format for ROHC-over-802, and finally discusses an appropriate negotiation mechanism. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Discussion 2.1. Overall Requirements There is little need for robust header compression in a classical Ethernet (802.3) environment, which is both relatively high-speed and Bormann Expires January 14, 2010 [Page 3] Internet-Draft ROHC over 802 July 2009 (at least at the segment level) virtually error-free. However, WLAN (802.11) and WPAN (802.15) links are often bandwidth limited; the same will hold for WMAN (802.16) links. They also (depending on link quality and load) can exhibit loss and delay patterns that would motivate the use of ROHC in such scenarios. Since voice over IP is and will be commonly used in these networks, header compression will continue to be useful. In the ROHC framework, header compression is performed at the boundary between Layer 3 (IP) and Layer 2 (802, in the case of ROHC- over-802). 802 networks are often bridged, i.e. multiple 802 technologies may contribute to a Layer 2 path that constitutes what is considered to be "the link" from a ROHC framework point of view. In practical implementation, nodes such as routers (often one end of a ROHC channel) in many cases don't connect directly to 802.11 links, but send packets on 802.3 (Ethernet) links that then are bridged by "Access Points" to 802.11 links. System architectures for other 802 technologies also often make use of bridging. (In this document, we use the term "bridging" for any kind of interconnection of IEEE 802 LANs above the physical layer but below the MAC service boundary, i.e. whenever an L3-visible hop is built from multiple L2 constituents by interconnection with bridge-like devices -- even if not all these L2 intermediate systems are completely compliant to the definitions of the term "bridge" in section 6.3.2 of IEEE 802 and in IEEE 802.1D.) One can conclude: It is not sufficient to just look at the wireless links -- ROHC-over-802 also needs to work on 802.3 (and other fixed- line 802) networks. In effect, a single solution for applying ROHC to all 802 (and related) environments needs to be defined independent of the physical layer technology. By staying above the MAC service interface, the solution can be largely oblivious of the specifics of the 802 technologies employed. A nice side effect is that this will simplify both standardization and implementation. 2.2. Elements of a Solution A ROHC-over-X specification needs to define two elements: o An encapsulation for ROHC framework packets, and o a negotiation mechanism for agreeing on the use of ROHC and on the parameters of the ROHC channel. (While a negotiation mechanism is not strictly needed for every ROHC- over-X document, it is clearly too late for the alternative, i.e. making ROHC mandatory and defining fixed channel parameter values for any use of IP over 802.) Bormann Expires January 14, 2010 [Page 4] Internet-Draft ROHC over 802 July 2009 2.3. Who Should Standardize? (This section is not intended to become part of any standards document resulting from this work.) In previous discussions, the question was raised which body should standardize ROHC-over-802. As mentioned in the introduction, one ROHC-over-X protocol has been defined in the IETF, other ones have been defined in the standards bodies defining the link layers under consideration. In the view of the author, a good test would be to see who has defined the IP-over-X specification. The ROHC-over-PPP specification clearly fits in the IETF as both the IP-over-PPP specification and the PPP specification itself are IETF specifications. For 802 networks, the IETF also has specified the link layer mapping of IP, including a number of ancillary protocols (ARP and ND) necessary for these mappings. If these protocols need to be extended, it would be more appropriate for the IETF to do so. The system issues of complex 802 networks do have a bearing on ROHC-over-802 and are in the domain of the IEEE; on the other hand, no good arguments exist currently that would call for an extension to the 802 protocols for ROHC. In summary, the author believes that IETF is the right body to work on ROHC-over-802. Related questions are: a) Who is the community of interest? Which standards meetings do they attend? b) Which body has the required expertise? c) What existing work is underway? Are there conflicts between that work and the proposed work? For question a) the answer appears to be the group of people who participate within the IETF ROHC WG. This group also has demonstrated expertise in header compression issues, but not necessarily in the details of link layer capabilities negotiation that may need to be part of a solution. (If work is required on the subject of link layer capabilities negotiation, e.g. use of ROHC, this would fit within the charter of existing IEEE 802 groups; however, staying above the MAC service interface would avoid the architectural need for this. Otherwise, while the ROHC over 802 component seems best suited to IETF, there may be link layer components to the work that are best done in IEEE 802.) In any case, close review of this work by IEEE 802 experts is advisable. Bormann Expires January 14, 2010 [Page 5] Internet-Draft ROHC over 802 July 2009 2.4. Why not just use PPPoE? An informational RFC specifies a widely deployed specification for PPP over Ethernet (PPPoE [RFC2516]), and, as mentioned there is a specification for ROHC over PPP [RFC3241]. For a number of reasons, just combining these as a ROHC-over-802 solution would be suboptimal: 1. PPPoE's encapsulation together with the PPP encapsulation has a fixed overhead of eight bytes per packet, negating some of the savings provided by header compression. 2. PPPoE does not solve the minimum-size padding problem (see below). 3. PPPoE has a different model than the usual IP-over-802 model, with discovery and session stages, and possibly multiple PPP sessions. This complexity is often not required. On the other hand, if PPPoE is in active use on an 802 link, adding ROHC-over-PPP may be a simple way to add robust header compression. 3. Issues 3.1. Ethernet Minimum Frame Size Due to its roots in the CSMA/CD protocol, Ethernet (IEEE 802.3) defines a minimum frame size of 64 bytes. Of these, 14 bytes are used for the MAC header and 4 are used for the MAC trailer (frame check sequence), which means that the minimum payload of an Ethernet packet is 46 bytes. The existing IPv4-over-802 [RFC1042] specification uses the "total size" field in the IP packet to indicate how much of the 802 packet payload is actually an IP packet; this indirectly indicates the presence of padding, if any. ROHC compresses away the "total size" field. Instead, it relies on the link layer (or the ROHC-over-X protocol) to provide a packet size. A ROHC-over-802 encapsulation could use a number of ways to provide this packet size: 1. It still could rely on the link layer size and use ROHC padding schemes to always inflate the size to at least 46 bytes. 2. It could add a length field. 3. It could make use of the length-field variant of the 802 MAC header format; this requires a different way of demultiplexing ROHC packets from other LLC packets. Note that solutions 1 and 2 mean that ROHC-compressed packets shorter Bormann Expires January 14, 2010 [Page 6] Internet-Draft ROHC over 802 July 2009 than 46 bytes will be padded out to this length if they ever go over an 802.3 link. Worse, there will be no way for an 802.3-to-802.x bridge to identify this padding and remove it, so the padding will remain on any wireless segments of the link layer path. Given that many voice over IP packets will have payloads of 10 to 20 bytes and headers often can be compressed down to 3 bytes or less, this entails a significant overhead. So, apart from the issue of properly indicating padding, a more interesting property of a ROHC-over-802 encapsulation is whether it allows 802.3-to-802.x bridges to remove any padding inserted on the 802.3 segments. 3.2. Negotiation and the existing IP-over-802 model In the existing IP-over-802 model (as exemplified by IPv4-over-802 [RFC1042]) assumes that once the MAC (link layer) address of a node is known, packets can be sent to it. No channel setup/teardown is provided for. In particular, a node can lose its state (be rebooted) and packets can still be sent to it based on the knowledge of the MAC address. (Note that channel setup/teardown procedures that may be available with specific 802 technologies such as 802.11 are often not end-to- end with respect to the L2 path. E.g., a router connected to an 802.3 segment connected to an 802.11 AP may not notice when the 802.11 station goes away and comes back.) The ROHC channel model [RFC3759] assumes that channel state is maintained explicitly, at least if the more advanced O- and R-modes are to be used. In addition, this channel setup is used to negotiate parameters of the channel (such as variants of the encapsulation format or the maximum number of compression contexts supported). Also, while there is a ROHC channel for each direction, each ROHC channel itself is bidirectional in the sense that (at least if not just U-mode is to be used) there needs to be a way to return feedback. Finally, only the receiving end of a packet flow may be aware that there is a benefit in using header compression (for illustration, consider a VoWLAN phone that is receiving packets from a router that is different than the router it chose as its default router and thus for the reverse packet flow). Therefore, there should be a way to initiate the setup of a ROHC channel from the receiving end. Bormann Expires January 14, 2010 [Page 7] Internet-Draft ROHC over 802 July 2009 4. Non-Issues 4.1. Reordering Fortunately, 802 links are sequence-preserving, so there is no need to re-sequence packets to avoid reordering (as would be required by unmodified use of the current ROHC framework and profiles). (The sequence preservation property holds as long as all packets of a context are sent on the same 802.1p priority group. The author is unable to imagine good reasons for using multiple 802.1p priority groups for one ROHC context.) (See also ROHC over PPP [RFC3241], section 1, which says:) ROHC assumes that the link layer delivers packets in sequence. PPP normally does not reorder packets. When using reordering mechanisms such as multiclass multilink PPP [RFC2686], care must be taken so that packets that share the same compression context are not reordered. (Note that in certain cases, reordering may be acceptable to ROHC, such as within a sequence of packets that all do not change the decompression context.) 4.2. Padding a non-issue? One argument could be that the padding issue outlined in Section 3.1 can be ignored for most 802 networks, either because the payloads will be larger than for the most heavily compressing voice codecs or because the header overhead is already rather high (e.g., for 802.11b, the link-layer header overhead in typical configurations is about as large as that of three-digit numbers of bytes in the payload). The author takes the viewpoint that a solution that is intended to be used universally through the 802 space does need to address padding. 5. Encapsulation Based on the considerations above, this document proposes to use LLC encapsulation of ROHC packets. Several approaches would have been possible: 1. An SAP value (Logical Link Control Address) is allocated to ROHC. The per-packet overhead is reduced to three bytes. Note that this means the negotiation protocol needs to fix the small-CID vs. large-CID choice (alternatively, ROHC-over-802 could simply always use large CIDs, or even a pair of SAP values could be allocated). Bormann Expires January 14, 2010 [Page 8] Internet-Draft ROHC over 802 July 2009 2. SAP 0xAA is used. By setting the first byte of the OUI to a value illegal for an OUI (multicast/private), the rest of the frame can be used for the ROHC packet, reducing the overhead to four bytes. The first (illegal OUI) byte can be used to demultiplex variants, e.g. small-CID and large-CID ROHC packets as well as possible negotiation protocol packets (see below). What would be the second and third OUI bytes are already used for the ROHC packet. 3. A full SNAP header is used. (From an overhead perspective, for 802.3 networks this is not better than the PPPoE case, but, like the previous proposals, it does allow the removal of padding by bridges.) Note that, to maintain reliable padding removal even over multiple header conversions between 802.3 and other types of 802 links, this could NOT be a basic ethertype-carrying SNAP header -- this would be converted to an 802.3 header on the first conversion to 802.3 and would lose its padding-removal property on any further conversions. To prevent this, a non-zero OUI could be used. Of these theoretically possible approaches, this document chooses variant 1. The actual SAP (SSAP/DSAP) value (Logical Link Control Address) to be used is to be defined (preferably one allocated by the registration authority [refauth]); for testing until the SAP value is assigned, the unreserved value of AC (hex) should be used. In summary, the frame format including an Ethernet MAC header could look like in Figure 1 (the CRC in the MAC trailer is not shown). The Ethernet MAC header includes the length field, which is the length of the ROHC header and payload plus the static LLC header. This means the total per-packet overhead is 21 bytes, 18 bytes for the Ethernet MAC header and trailer and three bytes for the LLC header carrying the ROHC identification. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination MAC Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Source MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ROHC Length + 3 | ROHC SAP | ROHC SAP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x03 (UI) | ROHC header and payload... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: ROHC packet including Ethernet MAC header Bormann Expires January 14, 2010 [Page 9] Internet-Draft ROHC over 802 July 2009 5.1. ULE encapsulation For IP over DVB, bridged frame encapsulation (type 0x0001) can be used unchanged. If a more compact encoding (more like the ethertype compatible formats) is required, the encapsulation as defined in Figure 2 and Figure 3 can be used. (The type value is provisional and needs to be defined in the ULE type registry.) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Length (15b) | Type = 0x00AC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Receiver Destination NPA Address (6B) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | = ROHC header and payload... = | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (CRC-32) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: ROHC packet in ULE (D=0) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Length (15b) | Type = 0x00AC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | = ROHC header and payload... = | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (CRC-32) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: ROHC packet in ULE (D=1) 6. Negotiation Negotiation of ROHC channels can either be piggy-backed on the existing address resolution/neighbor discovery protocols or a completely separate negotiation protocol can be used. Bormann Expires January 14, 2010 [Page 10] Internet-Draft ROHC over 802 July 2009 For IPv4, extending ARP sounds rather difficult at this point in the evolution of this protocol. For IPv6, while ND is probably a more extensible protocol, it is not clear that it is the right place for negotiating link-layer characteristics. Instead, a simple negotiation protocol should be defined that is based on regularly probing the peer node for ROHC capability and offering a capability set. A magic number scheme can be used both to ensure liveness of the peer state assumed and as a basic security measure. The negotiation protocol should preferably share its encapsulation with the ROHC encapsulation itself to ensure probes only arrive if there is no obstacle to LLC-style frames. Additional checking could be made part of the protocol that would detect common mistakes when implementing IEEE 802 framing. This specification therefore uses the ROHC encapsulation for also carrying the negotiation payload. This is achieved by hijacking the ROHC Add-CID packet types 11100001 to 11101111, see Figure 4; note that R cannot be 0 (this would indicate a ROHC Padding byte). Remaining_length gives the length of the negotiation payload and thus echoes the LLC length (ROHC Length + 3) minus the 6 bytes consumed; this serves as a check that the length was not damaged by a faulty IEEE 802 implementation. (The ULE encapsulations are defined analogously.) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination MAC Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Source MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ROHC Length + 3 | ROHC SAP | ROHC SAP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x03 (UI) |1|1|1|0| R | Remaining_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | negotiation payload... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: ROHC negotiation packet including Ethernet MAC header The negotiation payload defined in this specification looks exactly like an RFC 3241 Robust Header Compression (ROHC) Option [RFC3241]. If R is odd, it indicates the receiving capability of the originator Bormann Expires January 14, 2010 [Page 11] Internet-Draft ROHC over 802 July 2009 of the negotiation payload. If R is even, it indicates the actual values that will be used in sending ROHC packets by the originator. For unicast packets and where bidirectional connectivity is available, a ROHC capable receiver SHOULD occasionally send negotiation solicitation packets with R=1 to known neighbors, e.g. triggered by the reception of ARP or ND packets or of actual data packets (these negotiation solicitation packets MUST be strictly rate limited and MUST NOT be sent unless activity is detected from a neighbor). A ROHC capable sender MAY then send negotiation advertisement packets with R=2; once bidirectional advertisement has been achieved, the ROHC capable receiver SHOULD answer with its own actual values used in sending ROHC packets in negotiation advertisement packets with R=4 (no longer sending any R=2 packets). Only when the negotiation advertisement packet exchange has been completed SHOULD the ROHC capable sender start sending actual ROHC packets instead of IP packets encapsulated the usual way. In the spirit of IPv6 Neighbor Unreachability Detection (NUD [RFC4861]), the negotiation exchanges should be repeated whenever it is unclear whether the ROHC packets are successfully decompressed. For multicast packets or for unidirectional connectivity, a ROHC capable sender SHOULD send packets with R=6 to the MAC-layer multicast address. ROHC receivers MUST NOT answer. There is no way for a multicast/unidirectional sender to ascertain its receivers indeed all support ROHC and are reached by ROHC packets. (Extensions to IGMP/MLD could be defined to remedy this.) For ROHC over 802, LARGE_CIDS is always set. ROHC capability is always indicated for both IPv4 and IPv6. 7. Security Considerations Making a node believe its peer node is ROHC capable when it isn't is one way to stage a denial of service attack, as is maliciously tearing down ROHC state. The ROHC negotiation protocol probably needs to have security that is commensurate to that of the address resolution/neighbor discovery protocol in use. (Extensions to ICMPv6/SEND could be defined to make ROHC negotiation more secure.) The ROHC protocol itself is quite susceptible to attacks. To quote RFC 3095 [RFC3095]: Denial-of-service attacks are possible if an intruder can introduce (for example) bogus STATIC, DYNAMIC or FEEDBACK packets onto the link and thereby cause compression efficiency to be reduced. However, an intruder having the ability to inject Bormann Expires January 14, 2010 [Page 12] Internet-Draft ROHC over 802 July 2009 arbitrary packets at the link layer in this manner raises additional security issues that dwarf those related to the use of header compression. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3241] Bormann, C., "Robust Header Compression (ROHC) over PPP", RFC 3241, April 2002. [RFC4995] Jonsson, L-E., Pelletier, G., and K. Sandlund, "The RObust Header Compression (ROHC) Framework", RFC 4995, July 2007. 8.2. Informative References [RFC3095] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H., Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le, K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K., Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header Compression (ROHC): Framework and four profiles: RTP, UDP, ESP, and uncompressed", RFC 3095, July 2001. [RFC3242] Jonsson, L-E. and G. Pelletier, "RObust Header Compression (ROHC): A Link-Layer Assisted Profile for IP/UDP/RTP", RFC 3242, April 2002. [RFC3408] Liu, Z. and K. Le, "Zero-byte Support for Bidirectional Reliable Mode (R-mode) in Extended Link-Layer Assisted RObust Header Compression (ROHC) Profile", RFC 3408, December 2002. [RFC3843] Jonsson, L-E. and G. Pelletier, "RObust Header Compression (ROHC): A Compression Profile for IP", RFC 3843, June 2004. [RFC4019] Pelletier, G., "RObust Header Compression (ROHC): Profiles for User Datagram Protocol (UDP) Lite", RFC 4019, April 2005. [RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D., and R. Wheeler, "A Method for Transmitting PPP Over Ethernet (PPPoE)", RFC 2516, February 1999. Bormann Expires January 14, 2010 [Page 13] Internet-Draft ROHC over 802 July 2009 [RFC1042] Postel, J. and J. Reynolds, "Standard for the transmission of IP datagrams over IEEE 802 networks", STD 43, RFC 1042, February 1988. [RFC3759] Jonsson, L-E., "RObust Header Compression (ROHC): Terminology and Channel Mapping Examples", RFC 3759, April 2004. [RFC5225] Pelletier, G. and K. Sandlund, "RObust Header Compression Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and UDP-Lite", RFC 5225, April 2008. [RFC4996] Pelletier, G., Sandlund, K., Jonsson, L-E., and M. West, "RObust Header Compression (ROHC): A Profile for TCP/IP (ROHC-TCP)", RFC 4996, July 2007. [RFC4326] Fairhurst, G. and B. Collini-Nocker, "Unidirectional Lightweight Encapsulation (ULE) for Transmission of IP Datagrams over an MPEG-2 Transport Stream (TS)", RFC 4326, December 2005. [RFC2686] Bormann, C., "The Multi-Class Extension to Multi-Link PPP", RFC 2686, September 1999. [I-D.bormann-rohc-avt-crtp-profile] Bormann, C., "A ROHC Profile for CRTP (ROHC-CRTP)", draft-bormann-rohc-avt-crtp-profile-00 (work in progress), March 2007. [refauth] "IEEE Logical Link Control Address & Standard Group MAC Address Registration Authority", . [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. Appendix A. Acknowledgements The issue of enabling robust header compression over 802 networks has been brought up repeatedly, e.g. by Kris Fleming in a contribution called ROHCoWEM (draft-fleming-rohc-wireless-ethernet-med). The participant comments at the Atlanta IETF ROHC WG meeting (November 2002) provided the basis for the analytical part of this document. I would like to thank Bernard Aboba, Pedro Fortuna, Stephen McCann, and Mike Morton for reviewing earlier versions of this document and Bormann Expires January 14, 2010 [Page 14] Internet-Draft ROHC over 802 July 2009 suppyling extremely useful comments. In particular, Bernard provided a number of comments that proved useful for fleshing out Section 2.3. (All errors, however, are mine.) Author's Address Carsten Bormann Universitaet Bremen TZI Postfach 330440 Bremen D-28334 Germany Phone: +49 421 218 63921 Fax: +49 421 218 7000 Email: cabo@tzi.org Bormann Expires January 14, 2010 [Page 15]