| QUIC | M. Duke |
| Internet-Draft | F5 Networks, Inc. |
| Intended status: Standards Track | December 10, 2018 |
| Expires: June 13, 2019 |
QUIC-LB: Generating Routable QUIC Connection IDs
draft-duke-quic-load-balancers-03
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.
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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.
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.
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.
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.
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 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.
Though not an explicit goal of the QUIC-LB design, concealing the server mapping also complicates attempts to focus attacks on a specific server in the pool.
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.
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.
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 connection ID. The load balancer algorithms below apply to all incoming Handshake and 1-RTT packets.
There are situations where a server pool might be operating two or more routing algorithms or parameter sets simultaneously. The load balancer uses the first two bits of the connection ID to multiplex incoming SCIDs over these schemes.
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 MUST NOT select a routing mask that with more than 126 routing bits set to 1, which allows at least 2 bits for config rotation (see Section 5) and 16 for server purposes in a maximum-length connection ID.
The first two bits of an SCID MUST NOT be routing bits; these are reserved for config rotation.
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 divisor MUST be an odd integer so certain addition operations do not always produce an even number.
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, and SHOULD be distributed across the entire number space between zero and the divisor.
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.
The server chooses a connection ID length. This MUST contain all of the routing bits and MUST be at least 8 octets to provide adequate entropy.
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 except the config rotation bits. The non-routing bits SHOULD appear random to observers.
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.
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 load balancer also selects a nonce length and an 16-octet AES-CTR key to use for connection ID decryption. The nonce length MUST be at least eight octets and no more than 16 octets. The nonce length and server ID length MUST sum to 18 or fewer octets.
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 nonce length. The server ID immediately follows.
The load balancer decrypts the server ID using 128-bit AES in counter (CTR) mode, much like QUIC packet number decryption. The nonce octets are padded to 16 octets using the as many of the first octets of the token as necessary, and used as counter input to AES-CTR.
server_id = AES-CTR(key, padded-nonce, encrypted_server_id)
For example, if the nonce length is 10 octets and the server ID length is 2 octets, the connection ID can be as small as 12 octets. The load balancer uses the first 10 octets (including the config rotation bits) of the connection ID for the nonce, pads it to 16 octets using the first 6 octets of the token, and uses this to decrypt the server ID in the eleventh and twelfth octet.
The output of the decryption is the server ID that the load balancer uses for routing.
When generating a routable connection ID, the server writes arbitrary bits into its nonce octets, and its provided server ID into the server ID octets. Servers MAY opt to have a longer connection ID beyond the nonce and server ID. The nonce and additional bits MAY encode additional information, but SHOULD appear essentially random to observers. The first two bits of the first octet are reserved for config rotation Section 5, but form part of the nonce.
The server then encrypts the server ID octets using 128-bit AES in counter (CTR) mode, much like QUIC packet number encryption. The server pads its nonce to 16 octets using the earliest octets of the token, and uses the result as the counter input to AES-CTR.
encrypted_server_id = AES-CTR(key, padded-nonce, server-id)
The Block Cipher CID Algorithm, by using a full 16 octets of Plaintext and a 128-bit cipher, provides higher cryptographic protection and detection of spurious connection IDs. However, it also requires connection IDs of at least 17 octets, increasing overhead of client-to-server packets.
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 start in the second octet of the decrypted connection ID and occupy continuous octets beyond that.
The load balancer selects a zero-padding length. This SHOULD be at least four octets to allow detection of spurious connection IDs. The server ID and zero- padding length MUST sum to no more than 16 octets. They SHOULD sum to no more than 12 octets, to provide servers adequate space to encode their own opaque data.
The load balancer also selects an 16-octet AES-ECB key to use for connection ID decryption.
The load balancer shares these four 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 reads the first octet to obtain the config rotation bits. It then decrypts the subsequent 16 octets using AES-ECB decryption and the chosen key.
The decrypted plaintext contains the server id, zero padding, and opaque server data in that order. If the zero padding octets are not zero, the load balancer MUST drop the packet. The load balancer uses the server ID octets for routing.
When generating a routable connection ID, the server MUST choose a connection ID length of 17 or 18 octets. The server writes its provided server ID into the server ID octets, zeroes into the zero-padding octets, and arbitrary bits into the remaining bits. These arbitrary bits MAY encode additional information. Bits in the first and eighteenth octets SHOULD appear essentially random to observers. The first two bits of the first octet are reserved for config rotation Section 5.
The server then encrypts the second through seventeenth octets using the 128-bit AES-ECB cipher.
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 Stream Cipher CID Routing, this consists of the Server ID, Server ID Length, Key, and Nonce Length. The Server ID is unique to each server, but the others MUST be global. The authentication token MUST be distributed out of band for this algorithm to operate.
For Block Cipher CID Routing, this consists of the Server ID, Server ID Length, Key, and Zero-Padding Length. The Server ID is unique to each server, but the others MUST be global.
Each routing configuration also requires a unique two-bit config rotation codepoint (see Section 5) to identify it.
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.
QUIC-LB load balancers and servers exchange messages via the QUIC-LBv1 protocol, which uses the QUIC invariants with version number 0xF1000000. The QUIC-LB load balancers send the encoding parameters to servers and periodically retransmit until that server responds with an acknowledgement. Specifics of this retransmission are implementation-dependent.
A QUIC-LB packet uses a long header. It carries configuration information from the load balancer and acknowledgements from the servers. They are sent when a load balancer boots up, detects a new server in the pool or needs to update the server configuration.
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|C R| Reserved| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version (32) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x00 | 0x00 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Authentication Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Type | +-+-+-+-+-+-+-+-+
Figure 1: QUIC-LB Packet Format
The Version field allows QUIC-LB to use the Version Negotiation mechanism. All messages in this specification are specific to QUIC-LBv1. It should be set to 0xF1000000.
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 length of the DCIL and SCIL fields are 0x00.
As described in Section 4.3, QUIC-LB packets contain a single message. This section describes the format and semantics of the QUIC-LB message types.
A server uses the ACK_LB message (type=0x00) to acknowledge a QUIC-LB packet received from the load balancer. The ACK-LB message has no additional payload beyond the QUIC-LB packet header.
Load balancers SHOULD continue to retransmit a QUIC-LB packet until a valid ACK_LB message, FAIL message or Version Negotiation Packet is received from the server.
A server uses the FAIL message (type=0x01) to indicate the configuration received from the load balancer is unsupported.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Supp. Type | Supp. Type | ... +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Servers MUST send a FAIL message upon receipt of a message type which they do not support, or if they do not possess all of the implied out-of-band configuration to support a particular message type.
The payload of the FAIL message consists of a list of all the message types supported by the server.
Upon receipt of a FAIL message, Load Balancers MUST either send a QUIC-LB message the server supports or remove the server from the server pool.
A load balancer uses the ROUTING_INFO message (type=0x02) to exchange all the parameters for the plaintext CID algorithm.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Routing Bit Mask (144) + | | + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Modulus (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Divisor (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
These bits, along with the Modulus and Divisor, are chosen by the load balancer as described in Section 3.1.
A load balancer uses the STREAM_CID message (type=0x03) to exchange all the parameters for using Stream Cipher CIDs.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Nonce Len (8) | SIDL (8) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Server ID (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Key (128) + | | + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Stream CID Payload
A load balancer uses the BLOCK_CID message (type=0x04) to exchange all the parameters for using Stream Cipher CIDs.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ZP Len (8) | SIDL (8) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Server ID (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Key (128) + | | + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Block CID Payload
A load balancer uses the SERVER_ID message (type=0x05) to exchange explicit server IDs.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SIDL (8) | Server ID (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Load balancers send the SERVER_ID message when all global values for Stream or Block CIDs 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 Section 4.4.4 payload.
A load balancer uses the MODULUS message (type=0x06) to exchange just the modulus used in the plaintext CID algorithm.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Modulus (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Token (64) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 message.
The first two bits of any connection-ID MUST encode the configuration phase of that ID. QUIC-LB messages indicate the phase of the algorithm and parameters that they encode.
A new configuration may change one or more parameters of the old configuration, or change the algorithm used.
It is possible for servers to have mutually exclusive sets of supported algorithms, or for a transition from one algorithm to another to result in Fail Payloads. The four states encoded in these two bits allow two mutually exclusive server pools to coexist, and for each of them to transition to a new set of parameters.
When new configuration is distributed to servers, there will be a transition period when connection IDs reflecting old and new configuration coexist in the network. The rotation bits allow load balancers to apply the correct routing algorithm and parameters to incoming packets.
Servers MUST NOT generate new connection IDs using an old configuration when it has sent an Ack payload for a new configuration.
Load balancers SHOULD NOT use a codepoint to represent a new configuration until it takes precautions to make sure that all connections using IDs with an old configuration at that codepoint have closed or transitioned. They MAY drop connection IDs with the old configuration after a reasonable interval to accelerate this process.
If a server is configured to expect QUIC-LB messages, and it has not received these, it MUST generate connection IDs with the config rotation bits set to ‘0b11’ and MUST use the “disable_migration” transport parameter in all new QUIC connections. It MUST NOT send NEW_CONNECTION_ID frames with new values.
A load balancer that sees a connection ID with config rotation bits set to ‘0b11’ MUST revert to 5-tuple routing.
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. Endpoints that use Stream Cipher CIDs MUST have this token regardless of the configuration method.
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.
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.
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.
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.
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 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.
There are no IANA requirements.
| [QUIC-TRANSPORT] | Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed and Secure Transport", Internet-Draft draft-ietf-quic-transport-16 |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |