| QUIC | M. Duke |
| Internet-Draft | F5 Networks, Inc. |
| Intended status: Standards Track | N. Banks |
| Expires: July 31, 2020 | Microsoft |
| January 28, 2020 |
QUIC-LB: Generating Routable QUIC Connection IDs
draft-ietf-quic-load-balancers-00
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. This framework also enables offload of other QUIC functions to trusted intermediaries, given the explicit cooperation of the QUIC server.
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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 usually 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.
Aside from load balancing, a QUIC server may also desire to offload other protocol functions to trusted intermediaries. These intermediaries might include hardware assist on the server host itself, without access to fully decrypted QUIC packets. For example, this document specifies a means of offloading stateless retry to counter Denial of Service attacks. It also proposes a system for self-encoding connection ID length in all packets, so that crypto offload can consistently look up key information.
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 encode routing information for each load balancer, this use case is out of scope for QUIC-LB.
The first octet of a Connection ID is reserved for two special purposes, one mandatory (config rotation) and one optional (length self-description).
Subsequent sections of this document refer to the contents of this octet as the “first octet.”
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 ‘11’ 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 ‘11’ MUST revert to 5-tuple routing.
Local hardware cryptographic offload devices may accelerate QUIC servers by receiving keys from the QUIC implementation indexed to the connection ID. However, on physical devices operating multiple QUIC servers, it is impractical to efficiently lookup these keys if the connection ID does not self-encode its own length.
Note that this is a function of particular server devices and is irrelevant to load balancers. As such, it is not negotiated between servers and load balancers. However, the remaining 6 bits in the first octet of the Connection ID are reserved to express the length of the following connection ID, not including the first octet.
A server not using this functionality SHOULD make the six bits appear to be random.
In QUIC-LB, load balancers do not generate 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.
As clients sometimes generate the DCIDs in long headers, these might not conform to the expectations of the routing algorithm. These are called “non-compliant DCIDs”:
Load balancers MUST forward packets with long headers with non-compliant DCIDs to an active server using an algorithm of its own choosing. It need not coordinate this algorithm with the servers. The algorithm SHOULD be deterministic over short time scales so that related packets go to the same server. For example, a non-compliant DCID might be converted to an integer and divided by the number of servers, with the modulus used to forward the packet. The number of servers is usually consistent on the time scale of a QUIC connection handshake.
Load balancers SHOULD drop packets with non-compliant DCIDs in a short header.
Load balancers MUST forward packets with compliant DCIDs to a server in accordance with the chosen routing algorithm.
The load balancer MUST NOT make the routing behavior dependent on any bits in the first octet of the QUIC packet header, except the first bit, which indicates a long header. All other bits are QUIC version-dependent and intermediaries should not build their design on version-specific templates.
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 DCIDs over these schemes.
This section describes two participants: the load balancer and the server. The load balancer, in this description, generates configuration parameters. Note that in practice a third party configuration agent MAY assume this responsibility.
The Plaintext CID Algorithm makes no attempt to obscure the mapping of connections to servers, significantly increasing linkability. The format is depicted in the figure below.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | First octet | Server ID (X=8..152) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Any (0..152-X) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Plaintext CID Format
The load balancer selects a number of bytes of the server connection ID (SCID) that it will use to route to a given server, called the “routing bytes”. The number of bytes MUST have enough entropy to have a different code point for each server.
The load balancer shares this value with servers, as explained in Section 7, along with the value that represents that server.
On each incoming packet, the load balancer extracts consecutive octets, beginning with the second byte. These bytes represent the server ID.
The server chooses a connection ID length. This MUST be at least one byte longer than the routing bytes.
When a server needs a new connection ID, it encodes its assigned server ID in consecutive octets beginning with the second. All other bits in the connection ID, except for the first octet, MAY be set to any other value. These other bits SHOULD appear random to observers.
The Obfuscated CID Algorithm makes an attempt to obscure the mapping of connections to servers to reduce linkability, while not requiring true encryption and decryption. The format is depicted in the figure below.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | First octet | Mixed routing and non-routing bits (64..152) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Obfuscated CID Format
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 with more than 136 routing bits set to 1, which allows for the first octet and up to 2 octets for server purposes in a maximum-length connection ID.
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 7.
Upon receipt of a QUIC packet, 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. These DCIDs are non-compliant as described above.
The server chooses a connection ID length. This MUST contain all of the routing bits and MUST be at least 9 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 bits that used neither for routing nor config rotation. These bits SHOULD appear random to observers.
The Stream Cipher 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. The CID format is depicted below.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | First Octet | Nonce (X=64..144) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Encrypted Server ID (Y=8..152-X) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | For server use (0..152-X-Y) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Stream Cipher CID Format
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-ECB key to use for connection ID decryption. The nonce length MUST be at least 8 octets and no more than 16 octets. The nonce length and server ID length MUST sum to 19 or fewer octets.
The load balancer shares these three values with servers, as explained in Section 7.
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 Electronic Codebook (ECB) mode, much like QUIC header protection. The nonce octets are zero-padded to 16 octets. AES-ECB encrypts this nonce using its key to generate a mask which it applies to the encrypted server id.
server_id = encrypted_server_id ^ AES-ECB(key, padded-nonce)
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 13 octets. The load balancer uses the the second through eleventh of the connection ID for the nonce, zero-pads it to 16 octets using the first 6 octets of the token, and uses this to decrypt the server ID in the twelfth and thirteenth 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 server decrypts the server ID using 128-bit AES Electronic Codebook (ECB) mode, much like QUIC header protection. The nonce octets are zero-padded to 16 octets using the as many of the first octets of the token as necessary. AES-ECB encrypts this nonce using its key to generate a mask which it applies to the server id.
encrypted_server_id = server_id ^ AES-ECB(key, padded-nonce)
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 non-compliant connection IDs. However, it also requires connection IDs of at least 17 octets, increasing overhead of client-to-server packets.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | First octet | Encrypted server ID (X=8..144) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Encrypted Zero Padding (Y=0..144-X) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Encrypted bits for server use (144-X-Y) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Unencrypted bits for server use (0..24) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Block Cipher CID Format
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 non-compliant DCIDs. 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 7.
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. The load balancer uses the server ID octets for routing.
When generating a routable connection ID, the server MUST choose a connection ID length between 17 and 20 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, eighteenth, nineteenth, and twentieth octets SHOULD appear essentially random to observers. The first octet is reserved as described in Section 3.
The server then encrypts the second through seventeenth octets using the 128-bit AES-ECB cipher.
When a server is under load, QUICv1 allows it to defer storage of connection state until the client proves it can receive packets at its advertised IP address. Through the use of a Retry packet, a token in subsequent client Initial packets, and the original_connection_id transport parameter, servers verify address ownership and clients verify that there is no “man in the middle” generating Retry packets.
As a trusted Retry Service is literally a “man in the middle,” the service must communicate the original_connection_id back to the server so that in can pass client verification. It also must either verify the address itself (with the server trusting this verification) or make sure there is common context for the server to verify the address using a service-generated token.
There are two different mechanisms to allow offload of DoS mitigation to a trusted network service. One requires no shared state; the server need only be configured to trust a retry service, though this imposes other operational constraints. The other requires shared key, but has no such constraints.
Retry services MUST forward all non-Initial QUIC packets, as well as Initial packets from the server.
Regardless of mechanism, a retry service has an active mode, where it is generating Retry packets, and an inactive mode, where it is not, based on its assessment of server load and the likelihood an attack is underway. The choice of mode MAY be made on a per-packet basis, through a stochastic process or based on client address.
A retry service MUST forward all packets for a QUIC version it does not understand. Note that if servers support versions the retry service does not, this may unacceptably increase loads on the servers. However, dropping these packets would introduce chokepoints to block deployment of new QUIC versions. Note that future versions of QUIC might not have Retry packets, or require different information.
The no-shared-state retry service requires no coordination, except that the server must be configured to accept this service. The scheme uses the first bit of the token to distinguish between tokens from Retry packets (codepoint ‘0’) and tokens from NEW_TOKEN frames (codepoint ‘1’).
A no-shared-state retry service MUST be present on all paths from potential clients to the server. These paths MUST fail to pass QUIC traffic should the service fail for any reason. That is, if the service is not operational, the server MUST NOT be exposed to client traffic. Otherwise, servers that have already disabled their Retry capability would be vulnerable to attack.
The path between service and server MUST be free of any potential attackers. Note that this and other requirements above severely restrict the operational conditions in which a no-shared-state retry service can safely operate.
Retry tokens generated by the service MUST have the format below.
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| ODCIL (7) | Original Destination Connection ID (0..160) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Original Destination Connection ID (...) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opaque Data (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Format of non-shared-state retry service tokens
The first bit of retry tokens generated by the service must be zero. The token has the following additional fields:
ODCIL: The length of the original destination connection ID from the triggering Initial packet. This is in cleartext to be readable for the server, but authenticated later in the token.
Original Destination Connection ID: This also in cleartext and authenticated later.
Opaque Data: This data MUST contain encrypted information that allows the retry service to validate the client’s IP address, in accordance with the QUIC specification. It MUST also encode a secure hash of the original destination connection ID field to verify that this field has not been edited.
Upon receipt of an Initial packet with a token that begins with ‘0’, the retry service MUST validate the token in accordance with the QUIC specification. It must also verify that the secure hash of the Connect ID is correct. If incorrect, the token is invalid.
In active mode, the service MUST issue Retry packets for all Client initial packets that contain no token, or a token that has the first bit set to ‘1’. It MUST NOT forward the packet to the server. The service MUST validate all tokens with the first bit set to ‘0’. If successful, the service MUST forward the packet with the token intact. If unsuccessful, it MUST drop the packet.
Note that this scheme has a performance drawback. When the retry service is in active mode, clients with a token from a NEW_TOKEN frame will suffer a 1-RTT penalty even though it has proof of address with its token.
In inactive mode, the service MUST forward all packets that have no token or a token with the first bit set to ‘1’. It MUST validate all tokens with the first bit set to ‘0’. If successful, the service MUST forward the packet with the token intact. If unsuccessful, it MUST either drop the packet or forward it with the token removed. The latter requires decryption and re-encryption of the entire Initial packet to avoid authentication failure. Forwarding the packet causes the server to respond without the original_connection_id transport parameter, which preserves the normal QUIC signal to the client that there is an unauthorized man in the middle.
A server behind a non-shared-state retry service MUST NOT send Retry packets.
Tokens sent in NEW_TOKEN frames MUST have the first bit be set to ‘1’.
If a server receives an Initial Packet with the first bit set to ‘1’, it could be from a server-generated NEW_TOKEN frame and should be processed in accordance with the QUIC specification. If a server receives an Initial Packet with the first bit to ‘0’, it is a Retry token and the server MUST NOT attempt to validate it. Instead, it MUST assume the address is validated and MUST extract the Original Destination Connection ID, assuming the format described in Section 5.2.1.
A shared-state retry service uses a shared key, so that the server can decode the service’s retry tokens. It does not require that all traffic pass through the Retry service, so servers MAY send Retry packets in response to Initial packets that don’t include a valid token.
Both server and service must have access to Universal time, though tight synchronization is not necessary.
All tokens, generated by either the server or retry service, MUST use the following format. This format is the cleartext version. On the wire, these fields are encrypted using an AES-ECB cipher and the token key. If the token is not a multiple of 16 octets, the last block is padded with zeroes.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ODCIL | Original Destination Connection ID (0..160) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Client IP Address (128) + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + + | date-time (160) | + + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opaque Data (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Cleartext format of shared-state retry tokens
The tokens have the following fields:
ODCIL: The original destination connection ID length. Tokens in NEW_TOKEN frames SHOULD set this field to zero.
Original Destination Connection ID: This is copied from the field in the client Initial packet.
Client IP Address: The source IP address from the triggering Initial packet. The client IP address is 16 octets. If an IPv4 address, the last 12 octets are zeroes.
date-time: The date-time string is a total of 20 octets and encodes the time the token was generated. The format of date-time is described in Section 5.6 of [RFC3339]. This ASCII field MUST use the “Z” character for time-offset.
Opaque Data: The server may use this field to encode additional information, such as congestion window, RTT, or MTU. Opaque data SHOULD also allow servers to distinguish between retry tokens (which trigger use of the original_connection_id transport parameter) and NEW_TOKEN frame tokens.
The service MUST share a “token key” with all supported servers.
When in active mode, the service MUST generate Retry tokens with the format described above when it receives a client Initial packet with no token.
In active mode, the service SHOULD decrypt incoming tokens. The service SHOULD drop packets with an IP address that does not match, and SHOULD forward packets that do, regardless of the other fields.
In inactive mode, the service SHOULD forward all packets to the server so that the server can issue an up-to-date token to the client.
The server MUST validate all tokens that arrive in Initial packets, as they may have bypassed the Retry service. It SHOULD use the date-time field to apply its expiration limits for tokens. This need not be synchronized with the retry service. However, servers MAY allow retry tokens marked as being a few seconds in the future, due to possible clock synchronization issues.
A server MUST NOT send a Retry packet in response to an Initial packet that contains a retry token.
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.
If there is any in-band communication, servers MUST be explicitly configured with the token of the load balancer they expect to interface with.
The load balancer and server MUST agree on a routing algorithm and the relevant parameters for that algorithm.
For Plaintext CID Routing, this consists of the Server ID and the routing bytes. The Server ID is unique to each server, and the routing bytes are global.
For Obfuscated 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.
A full QUIC-LB configuration MUST also specify the information content of the first CID octet and the presence and mode of any Retry Service.
The following pseudocode depicts the data items necessary to store a full QUIC-LB configuration at the server. It is meant to describe the conceptual range and not specify the presentation of such configuration in an internet packet. The comments signify the range of acceptable values where applicable.
uint2 config_rotation_bits;
enum { in_band_config, out_of_band_config } config_method;
select (config_method) {
case in_band_config: uint64 config_token;
case out_of_band_config: null;
} config-method
boolean first_octet_encodes_cid_length;
enum { none, non_shared_state, shared_state } retry_service;
select (retry_service) {
case none: null;
case non_shared_state: null;
case shared_state: uint8 key[16];
} retry_service_config;
enum { none, plaintext, obfuscated, stream_cipher, block_cipher }
routing_algorithm;
select (routing_algorithm) {
case none: null;
case plaintext: struct {
uint8 server_id_length; /* 1..19 */
uint8 server_id[server_id_length];
} plaintext_config;
case obfuscated: struct {
uint8 routing_bit_mask[19];
uint16 divisor; /* Must be odd */
uint16 modulus; /* 0..(divisor - 1) */
} obfuscated_config;
case stream_cipher: struct {
uint8 nonce_length; /* 8..16 */
uint8 server_id_length; /* 1..(19 - nonce_length) */
uint8 server_id[server_id_length];
uint8 key[16];
} stream_cipher_config;
case block_cipher: struct {
uint8 server_id_length;
uint8 zero_padding_length; /* 0..(16 - server_id_length) */
uint8 server_id[server_id_length];
uint8 key[16];
} block_cipher_config;
} routing_algorithm_config;
This specification allows for out-of-band dissemination of this configuration items, but also provides an in-band method for deployment models that need it.
There are multiple means of configuration that correspond to differing deployment models and increasing levels of concern about the security of the load balancer-server path.
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 7: 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 7.3, 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 Obfuscated 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 (152) + | | + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Modulus (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Divisor (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
These bits, along with the Modulus and Divisor, are chosen by the load balancer as described in Section 4.2.
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 8: 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 9: 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. It also provides all necessary paramters for Plaintext CIDs. The fields are identical to their counterparts in the Section 7.4.4 payload.
A load balancer uses the MODULUS message (type=0x06) to exchange just the modulus used in the Obfuscated 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) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Load balancers send the MODULUS when all global values for Obfuscated 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.
A load balancer uses the PLAINTEXT message (type=0x07) to exchange all parameters needed 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SIDL (8) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Server ID (variable) + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The SIDL field indicates the length of the server ID field. The Server ID field indicates the encoding that represents the destination server.
A no-shared-state retry service uses this message (type=0x08) to notify the server of the existence of this service. This message has no fields.
A shared-state retry service uses this message (type=0x09) to tell the server about its existence, and share the key needed to decrypt server-generated retry tokens.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Key (128) + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
QUIC-LB is intended to preserve routability and prevent linkability. Attacks on the protocol would compromise at least one of these objectives.
Note that the Plaintext CID algorithm makes no attempt to obscure the server mapping, and therefore does not address these concerns. It exists to allow consistent CID encoding for compatibility across a network infrastructure. Servers that are running the Plaintext CID algorithm SHOULD only use it to generate new CIDs for the Server Initial Packet and SHOULD NOT send CIDs in QUIC NEW_CONNECTION_ID frames. Doing so might falsely suggest to the client that said CIDs were generated in a secure fashion.
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 Obfuscated 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 |
| [RFC3339] | Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |