QUIC M. Duke Internet-Draft F5 Networks, Inc. Intended status: Standards Track September 17, 2018 Expires: March 21, 2019 QUIC-LB: Generating Routable QUIC Connection IDs draft-duke-quic-load-balancers-02 Abstract QUIC connection IDs allow continuation of connections across address/ port 4-tuple changes, and can store routing information for stateless or low-state load balancers. They also can prevent linkability of connections across deliberate address migration through the use of protected communications between client and server. This creates issues for load-balancing intermediaries. This specification standardizes methods for encoding routing information and proposes an optional protocol called QUIC_LB to exchange the parameters of that encoding. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on March 21, 2019. Copyright Notice Copyright (c) 2018 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect Duke Expires March 21, 2019 [Page 1] Internet-Draft QUIC-LB September 2018 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Protocol Objectives . . . . . . . . . . . . . . . . . . . . . 4 2.1. Simplicity . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Security . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3. Robustness to Middleboxes . . . . . . . . . . . . . . . . 5 2.4. Load Balancer Chains . . . . . . . . . . . . . . . . . . 5 3. Routing Algorithms . . . . . . . . . . . . . . . . . . . . . 5 3.1. Plaintext CID Algorithm . . . . . . . . . . . . . . . . . 6 3.1.1. Load Balancer Actions . . . . . . . . . . . . . . . . 6 3.1.2. Server Actions . . . . . . . . . . . . . . . . . . . 6 3.2. Encrypted CID Algorithm . . . . . . . . . . . . . . . . . 7 3.2.1. Load Balancer Actions . . . . . . . . . . . . . . . . 7 3.2.2. Server Actions . . . . . . . . . . . . . . . . . . . 8 4. Protocol Description . . . . . . . . . . . . . . . . . . . . 8 4.1. Out of band sharing . . . . . . . . . . . . . . . . . . . 8 4.2. QUIC-LB Message Exchange . . . . . . . . . . . . . . . . 8 4.2.1. Packet Header Format . . . . . . . . . . . . . . . . 9 4.2.2. Ack Payload . . . . . . . . . . . . . . . . . . . . . 9 4.2.3. Fail Payload . . . . . . . . . . . . . . . . . . . . 10 4.2.4. Routing Info Payload . . . . . . . . . . . . . . . . 11 4.2.5. Encrypted CID Payload . . . . . . . . . . . . . . . . 11 4.2.6. Server ID Payload . . . . . . . . . . . . . . . . . . 12 4.2.7. Modulus Payload . . . . . . . . . . . . . . . . . . . 13 5. Configuration Requirements . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6.1. Outside attackers . . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 8.1. Normative References . . . . . . . . . . . . . . . . . . 15 8.2. Informative References . . . . . . . . . . . . . . . . . 15 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 15 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 15 B.1. Since draft-duke-quic-load-balancers-00 . . . . . . . . . 15 B.2. Since draft-duke-quic-load-balancers-01 . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 Duke Expires March 21, 2019 [Page 2] Internet-Draft QUIC-LB September 2018 1. Introduction QUIC packets usually contain a connection ID to allow endpoints to associate packets with different address/port 4-tuples to the same connection context. This feature makes connections robust in the event of NAT rebinding. QUIC endpoints designate the connection ID which peers use to address packets. Server-generated connection IDs create a potential need for out-of-band communication to support QUIC. QUIC allows servers (or load balancers) to designate an initial connection ID to encode useful routing information for load balancers. It also encourages servers, in packets protected by cryptography, to provide additional connection IDs to the client. This allows clients that know they are going to change IP address or port to use a separate connection ID on the new path, thus reducing linkability as clients move through the world. There is a tension between the requirements to provide routing information and mitigate linkability. Ultimately, because new connection IDs are in protected packets, they must be generated at the server if the load balancer does not have access to the connection keys. However, it is the load balancer that has the context necessary to generate a connection ID that encodes useful routing information. In the absence of any shared state between load balancer and server, the load balancer must maintain a relatively expensive table of server-generated connection IDs, and will not route packets correctly if they use a connection ID that was originally communicated in a protected NEW_CONNECTION_ID frame. This specification provides a method of coordination between QUIC servers and low-state load balancers to support connection IDs that encode routing information. It describes desirable properties of a solution, and then specifies a protocol that provides those properties. This protocol supports multiple encoding schemes that increase in complexity as they address paths between load balancer and server with weaker trust dynamics. 1.1. Terminology 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 RFC 2119 [RFC2119]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying significance described in RFC 2119. Duke Expires March 21, 2019 [Page 3] Internet-Draft QUIC-LB September 2018 In this document, "client" and "server" refer to the endpoints of a QUIC connection unless otherwise indicated. A "load balancer" is an intermediary for that connection that does not possess QUIC connection keys, but it may rewrite IP addresses or conduct other IP or UDP processing. Note that stateful load balancers that act as proxies, by terminating a QUIC connection with the client and then retrieving data from the server using QUIC or another protocol, are treated as a server with respect to this specification. When discussing security threats to QUIC-LB, we distinguish between "inside observers" and "outside observers." The former lie on the path between the load balancer and server, which often but not always lies inside the server's data center or cloud deployment. Outside observers are on the path between the load balancer and client. "Off-path" attackers, though not on any data path, may also be "inside" or "outside" depending on whether not they have network access to the server without intermediation by the load balancer and/ or other security devices. 2. Protocol Objectives 2.1. Simplicity QUIC is intended to provide unlinkability across connection migration, but servers are not required to provide additional connection IDs that effectively prevent linkability. If the coordination scheme is too difficult to implement, servers behind load balancers using connection IDs for routing will use trivially linkable connection IDs. Clients will therefore be forced choose between terminating the connection during migration or remaining linkable, subverting a design objective of QUIC. The solution should be both simple to implement and require little additional infrastructure for cryptographic keys, etc. 2.2. Security In the limit where there are very few connections to a pool of servers, no scheme can prevent the linking of two connection IDs with high probability. In the opposite limit, where all servers have many connections that start and end frequently, it will be difficult to associate two connection IDs even if they are known to map to the same server. QUIC-LB is relevant in the region between these extremes: when the information that two connection IDs map to the same server is helpful Duke Expires March 21, 2019 [Page 4] Internet-Draft QUIC-LB September 2018 to linking two connection IDs. Obviously, any scheme that transparently communicates this mapping to outside observers compromises QUIC's defenses against linkability. However, concealing this mapping from inside observers is beyond the scope of QUIC-LB. By simply observing Link-Layer and/or Network- Layer addresses of packets containing distinct connection IDs, it is trivial to determine that they map to the same server, even if connection IDs are entirely random and do not encode routing information. Schemes that conceal these addresses (e.g., IPsec) can also conceal QUIC-LB messages. Inside observers are generally able to mount Denial of Service (DoS) attacks on QUIC connections regardless of Connection ID schemes. However, QUIC-LB should protect against Denial of Service due to inside off-path attackers in cases where such attackers are possible. 2.3. Robustness to Middleboxes The path between load balancer and server may pass through middleboxes that could drop the coordination messages in this protocol. It is therefore advantageous to make messages resemble QUIC traffic as much as possible, as any viable path must obviously admit QUIC traffic. 2.4. Load Balancer Chains While it is possible to construct a scheme that supports multiple low-state load balancers in the path, by using different parts of the connection ID to encoding routing information for each load balancer, this use case is out of scope for QUIC-LB. 3. Routing Algorithms In QUIC-LB, load balancers do not send individual connection IDs to servers. Instead, they communicate the parameters of an algorithm to generate routable connection IDs. The algorithms differ in the complexity of configuration at both load balancer and server. Increasing complexity improves obfuscation of the server mapping. The load balancer SHOULD route Initial and 0-RTT packets from the client using an alternate algorithm. Note that the SCID in these packets may not be long enough to represent all the routing bits. This algorithm SHOULD generate consistent results for Initial and 0RTT packets that arrive with the same source and destination Duke Expires March 21, 2019 [Page 5] Internet-Draft QUIC-LB September 2018 connection ID. The load balancer algorithms below apply to all incoming Handshake and 1-RTT packets. 3.1. Plaintext CID Algorithm 3.1.1. Load Balancer Actions The load balancer selects an arbitrary set of bits of the server connection ID (SCID) that it will use to route to a given server, called the "routing bits". The number of bits MUST have enough entropy to have a different code point for each server, and SHOULD have enough entropy so that there are many codepoints for each server. The load balancer selects a divisor that MUST be larger than the number of servers. It SHOULD be large enough to accommodate reasonable increases in the number of servers. The load balancer also assigns each server a "modulus", an integer between 0 and the divisor minus 1. These MUST be unique for each server. The load balancer shares these three values with servers, as explained in Section 4. Upon receipt of a QUIC packet that is not of type Initial or 0-RTT, the load balancer extracts the selected bits of the SCID and expresses them as an unsigned integer of that length. The load balancer then divides the result by the chosen divisor. The modulus of this operation maps to the modulus for the destination server. . Note that any SCID that contains a server's modulus, plus an arbitrary integer multiple of the divisor, in the routing bits is routable to that server regardless of the contents of the non-routing bits. Outside observers that do not know the divisor or the routing bits will therefore have difficulty identifying that two SCIDs route to the same server. Note also that not all Connection IDs are necessarily routable, as the computed modulus may not match one assigned to any server. Load balancers SHOULD drop these packets if not a QUIC Initial or 0-RTT packet. 3.1.2. Server Actions The server may choose any connection ID length that can represent all of the routing bits. Duke Expires March 21, 2019 [Page 6] Internet-Draft QUIC-LB September 2018 When a server needs a new connection ID, it adds an arbitrary nonnegative integer multiple of the divisor to its modulus, without exceeding the maximum integer value implied by the number of routing bits. The choice of multiple should appear random within these constraints. The server encodes the result in the routing bits. It MAY put any other value into the non-routing bits. The non-routing bits SHOULD appear random to observers. 3.2. Encrypted CID Algorithm The Encrypted CID algorithm provides true cryptographic protection, rather than mere obfuscation, at the cost of additional per-packet processing at the load balancer to decrypt every incoming connection ID except for Initial and 0RTT packets. 3.2.1. Load Balancer Actions The load balancer assigns a server ID to every server in its pool, and determines a server ID length (in octets) sufficiently large to encode all server IDs, including potential future servers. The server ID will be encoded in the first octets of the connection ID. The load balancer also selects a connection ID length that all servers must use, and an 16-octet AES-CTR key to use for connection ID decryption. The load balancer shares these three values with servers, as explained in Section 4. Upon receipt of a QUIC packet that is not of type Initial or 0-RTT, the load balancer extracts as many of the earliest octets from the destination connection ID as necessary to match the server ID length. The load balancer decrypts the server ID using 128-bit AES in counter (CTR) mode, much like QUIC packet number decryption. The counter input to AES-CTR is the bytes of the connection ID that do not constitute the encrypted server ID. server_id = AES-CTR(key, non-server-id-bytes, encrypted_server_id) The output of the decryption is the server ID that the load balancer uses for routing. Duke Expires March 21, 2019 [Page 7] Internet-Draft QUIC-LB September 2018 3.2.2. Server Actions When generating a routable connection ID, the server writes its provided server ID into the server ID octets, and arbitrary bits into the remaining required connection ID octets. These arbitrary bits MAY encode additional information, but SHOULD appear essentially random to observers. The server then encrypts the server ID bytes using 128-bit AES in counter (CTR) mode, much like QUIC packet number encryption. The counter input to AES-CTR is the bytes of the connection ID that do not constitute the encrypted server ID. encrypted_server_id = AES-CTR(key, non_server_id_bytes, server-id) 4. Protocol Description The fundamental protocol requirement is to share the choice of routing algorithm, and the relevant parameters for that algorithm, between load balancer and server. For Plaintext CID Routing, this consists of the Routing Bits, Divisor, and Modulus. The Modulus is unique to each server, but the others MUST be global. For Encrypted CID Routing, this consists of the Server ID, Server ID Length, Key, and Connection ID Length. The Server ID is unique to each server, but the others MUST be global. 4.1. Out of band sharing When there are concerns about the integrity of the path between load balancer and server, operators may share routing information using an out-of-band technique, which is out of the scope of this specification. To simplify configuration, the global parameters can be shared out- of-band, while the load balancer sends the unique server IDs via the truncated message formats presented below. 4.2. QUIC-LB Message Exchange QUIC-LB load balancers send the encoding parameters to servers as they discover the servers, using a single packet to each that resembles QUIC. They periodically retransmit this packet to each server until that server responds with a QUIC-LB ack. Specifics of this retransmission are implementation-dependent. Duke Expires March 21, 2019 [Page 8] Internet-Draft QUIC-LB September 2018 These message formats are specific to QUICv2 and experimental versions leading up to QUICv2. They may require revision for future versions of QUIC. 4.2.1. Packet Header Format 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 +-+-+-+-+-+-+-+-+ | Type = 0xfb | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version (32) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x00 | +-+-+-+-+-+-+-+-+ Figure 1: QUIC-LB Header QUIC-LB messages are QUIC packets with a long header and zero length connection IDs. They are sent when a load balancer boots up, or detects a new server in the pool. QUIC-LB packets are delivered in a UDP datagram. The type field is 0xfb, which is otherwise unused in QUICv2. The Version field allows QUIC-LB to use the Version Negotiation mechanism. All messages in this specification are specific to QUICv2, as future QUIC versions may use the 0xfb packet type for other purposes. Therefore, the Version field should be set as the codepoint for QUICv2 as defined in [QUIC-TRANSPORT]. Load balancers MUST cease sending QUIC-LB packets of this version to a server when that server sends a Version Negotiation packet that does not advertise the version. The 0x00 byte indicates that there are no connection IDs present in the header. The remainder of the packet is the payload. This has multiple formats. 4.2.2. Ack Payload Duke Expires March 21, 2019 [Page 9] Internet-Draft QUIC-LB September 2018 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x00 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Ack Payload The Ack Payload consists of nine octets. Servers send this payload after receipt of any acceptable QUIC-LB packet from a load balancer. The token field echoes the token field from the acknowledged packet. Load balancers MUST retransmit a QUIC-LB packet if not followed by a valid Ack Payload or Version Negotiation Packet from the destination after a reasonable interval. 4.2.3. Fail Payload 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x01 | Supp. Type | Supp. Type | ... +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Fail Payload Servers MUST send a Fail Payload upon receipt of a payload type which they do not support, or if they do not possess all of the implied out-of-band configuration to support a particular payload type. After the type octet, servers append additional octets to list all payload types they support. The token field echoes the token field from the acknowledged packet. Upon receipt of a Fail Payload, Load Balancers MUST either send a QUIC-LB payload the server supports, or remove the server from the server pool. Duke Expires March 21, 2019 [Page 10] Internet-Draft QUIC-LB September 2018 4.2.4. Routing Info Payload 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Routing Bit Mask (144) + | | + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Modulus (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Divisor (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Routing Info Payload The Type Octet indicates that this is a Routing Info Payload, which contains all parameters for the plaintext CID algorithm. The Token is an 8-octet field that both entities obtain at configuration time. It is used to verify that the sender is not an inside off-path attacker. Servers SHOULD silently drop QUIC-LB packets with an incorrect token. The Routing Bit Mask encodes a '1' at every bit position in the server connection ID that will encode routing information. These bits, along with the Modulus and Divisor, are chosen by the load balancer as described in Section 3.1. 4.2.5. Encrypted CID Payload Duke Expires March 21, 2019 [Page 11] Internet-Draft QUIC-LB September 2018 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x03 | CIDL (8) | SIDL (8) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Server ID (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Key (128) + | | + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: Encrypted CID Payload The CIDL field is a one-octet unsigned integer that describes the server connection ID length necessary to use this routing algorithm, in octets. The SIDL field is a one-octet unsigned integer that describes the server ID length necessary to use this routing algorithm, in octets. The server ID is the unique value assigned to the receiving server. Its length is determined by the SIDL field. The key is an 16-octet field that contains the key that the load balancer will use to decrypt server IDs on QUIC packets. See Section 6 to understand why sending keys in plaintext may be a safe strategy. 4.2.6. Server ID Payload 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x04 | SIDL (8) | Server ID (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Server ID Payload Duke Expires March 21, 2019 [Page 12] Internet-Draft QUIC-LB September 2018 Load balancers send the Server ID when all global values for CID encryption are sent out-of-band, so that only the server-unique values must be sent in-band. The fields are identical to their counterparts in the Encrypted CID payload. 4.2.7. Modulus Payload 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x05 | Modulus (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: Modulus Payload Load balancers send the Modulus when all global values for Plaintext CIDs are sent out-of-band, so that only the server- unique values must be sent in-band. The Modulus field is identical to its counterpart in the Routing Info payload. 5. Configuration Requirements QUIC-LB strives to minimize the configuration load to enable, as much as possible, a "plug-and-play" model. However, there are some configuration requirements based on algorithm and protocol choices above. There are three levels of configuration that correspond to increasing levels of concern about the security of the load balancer-server path. The complete information requirements are described in Section 4. Load balancers MUST have configuration for all parameters of each routing algorithm they support. If there is any in-band communication, servers MUST be explicitly configured with the token of the load balancer they expect to interface with. Optionally, servers MAY be configured with the global parameters of supported routing algorithms. This allows load balancers to use Server ID and Modulus Payloads, limiting the information sent in- band. Duke Expires March 21, 2019 [Page 13] Internet-Draft QUIC-LB September 2018 Finally, servers MAY be directly configured with their unique server IDs or modulus, eliminating need for in-band messaging at all. In this case, servers and load balancers MUST enable only one routing algorithm, as there is no explicit message to agree on one or the other. 6. Security Considerations QUIC-LB is intended to preserve routability and prevent linkability. Attacks on the protocol would compromise at least one of these objectives. A routability attack would inject QUIC-LB messages so that load balancers incorrectly route QUIC connections. A linkability attack would find some means of determining that two connection IDs route to the same server. As described above, there is no scheme that strictly prevents linkability for all traffic patterns, and therefore efforts to frustrate any analysis of server ID encoding have diminishing returns. 6.1. Outside attackers For an outside attacker to break routability, it must inject packets that correctly guess the 64-bit token, and servers must be reachable from these outside hosts. Load balancers SHOULD drop QUIC-LB packets that arrive on its external interface. Off-path outside attackers cannot observe connection IDs, and will therefore struggle to link them. On-path outside attackers might try to link connection IDs to the same QUIC connection. The Encrypted CID algorithm provides robust entropy to making any sort of linkage. The Plaintext CID obscures the mapping and prevents trivial brute-force attacks to determine the routing parameters, but does not provide robust protection against sophisticated attacks. ## Inside Attackers As described above, on-path inside attackers are intrinsically able to map two connection IDs to the same server. The QUIC-LB algorithms do prevent the linkage of two connection IDs to the same individual connection if servers make reasonable selections when generating new IDs for that connection. On-path inside attackers can break routability for new and migrating connections by copying the token from QUIC-LB messages. From this Duke Expires March 21, 2019 [Page 14] Internet-Draft QUIC-LB September 2018 privileged position, however, there are many other attacks that can break QUIC connections to the server during the handshake. Off-path inside attackers cannot observe connection IDs to link them. To successfully break routability, they must correctly guess the token. 7. IANA Considerations There are no IANA requirements. 8. References 8.1. Normative References [QUIC-TRANSPORT] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", draft-ietf-quic- transport-14 (work in progress). 8.2. Informative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Appendix A. Acknowledgments Appendix B. Change Log *RFC Editor's Note:* Please remove this section prior to publication of a final version of this document. B.1. Since draft-duke-quic-load-balancers-00 o Converted to markdown o Added variable length connection IDs B.2. Since draft-duke-quic-load-balancers-01 o Complete rewrite o Supports multiple security levels o Lightweight messages Duke Expires March 21, 2019 [Page 15] Internet-Draft QUIC-LB September 2018 Author's Address Martin Duke F5 Networks, Inc. Email: martin.h.duke@gmail.com Duke Expires March 21, 2019 [Page 16]