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Transport MASQUE quic http datagram VPN proxy tunnels quic in udp in IP in quic turtles all the way down masque http-ng This document describes how to proxy IP packets in HTTP. This protocol is similar to UDP proxying in HTTP, but allows transmitting arbitrary IP packets. More specifically, this document defines a protocol that allows an HTTP client to create an IP tunnel through an HTTP server that acts as an IP proxy. This document updates RFC 9298. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the MASQUE Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction HTTP provides the CONNECT method (see ) for creating a TCP tunnel to a destination and a similar mechanism for UDP . However, these mechanisms cannot tunnel other IP protocols nor convey fields of the IP header. This document describes a protocol for tunnelling IP through an HTTP server acting as an IP-specific proxy over HTTP. This can be used for various use cases such as remote access VPN, site-to-site VPN, secure point-to-point communication, or general-purpose packet tunnelling. IP proxying operates similarly to UDP proxying , whereby the proxy itself is identified with an absolute URL, optionally containing the traffic's destination. Clients generate these URLs using a URI Template , as described in . This protocol supports all existing versions of HTTP by using HTTP Datagrams . When using HTTP/2 or HTTP/3 , it uses HTTP Extended CONNECT as described in and . When using HTTP/1.x , it uses HTTP Upgrade as defined in . This document updates to change the "masque" well-known URI, see .

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. In this document, we use the term "IP proxy" to refer to the HTTP server that responds to the IP proxying request. If there are HTTP intermediaries (as defined in ) between the client and the proxy, those are referred to as "intermediaries" in this document. This document uses terminology from . Where this document defines protocol types, the definition format uses the notation from . This specification uses the variable-length integer encoding from . Variable-length integer values do not need to be encoded in the minimum number of bytes necessary. Note that, when the HTTP version in use does not support multiplexing streams (such as HTTP/1.1), any reference to "stream" in this document represents the entire connection.

Configuration of Clients Clients are configured to use IP proxying over HTTP via a URI Template . The URI Template MAY contain two variables: "target" and "ipproto"; see . The optionality of the variables needs to be considered when defining the template so that either the variable is self-identifying or it is possible to exclude it in the syntax. Examples are shown below:

URI Template Examples

The following requirements apply to the URI Template:

• The URI Template MUST be a level 3 template or lower.
• The URI Template MUST be in absolute form, and MUST include non-empty scheme, authority and path components.
• The path component of the URI Template MUST start with a slash "/".
• All template variables MUST be within the path or query components of the URI.
• The URI Template MAY contain the two variables "target" and "ipproto" and MAY contain other variables. If the "target" or "ipproto" variables are included, their values MUST NOT be empty. Clients can instead use "*" to indicate wildcard or no-preference values; see .
• The URI Template MUST NOT contain any non-ASCII unicode characters and MUST only contain ASCII characters in the range 0x21-0x7E inclusive (note that percent-encoding is allowed; see Section 2.1 of ).
• The URI Template MUST NOT use Reserved Expansion ("+" operator), Fragment Expansion ("#" operator), Label Expansion with Dot- Prefix, Path Segment Expansion with Slash-Prefix, nor Path-Style Parameter Expansion with Semicolon-Prefix.

Clients SHOULD validate the requirements above; however, clients MAY use a general-purpose URI Template implementation that lacks this specific validation. If a client detects that any of the requirements above are not met by a URI Template, the client MUST reject its configuration and abort the request without sending it to the IP proxy. As with UDP proxying, some client configurations for IP proxies will only allow the user to configure the proxy host and proxy port. Clients with such limitations MAY attempt to access IP proxying capabilities using the default template, which is defined as: "https://$PROXY_HOST:$PROXY_PORT/.well-known/masque/ip/{target}/{ipproto}/", where $PROXY_HOST and $PROXY_PORT are the configured host and port of the IP proxy, respectively. IP proxy deployments SHOULD offer service at this location if they need to interoperate with such clients.

Tunnelling IP over HTTP To allow negotiation of a tunnel for IP over HTTP, this document defines the "connect-ip" HTTP upgrade token. The resulting IP tunnels use the Capsule Protocol (see ) with HTTP Datagrams in the format defined in . To initiate an IP tunnel associated with a single HTTP stream, a client issues a request containing the "connect-ip" upgrade token. When sending its IP proxying request, the client SHALL perform URI Template expansion to determine the path and query of its request, see . By virtue of the definition of the Capsule Protocol (see ), IP proxying requests do not carry any message content. Similarly, successful IP proxying responses also do not carry any message content.

IP Proxy Handling Upon receiving an IP proxying request:

• if the recipient is configured to use another HTTP proxy, it will act as an intermediary by forwarding the request to another HTTP server. Note that such intermediaries may need to re-encode the request if they forward it using a version of HTTP that is different from the one used to receive it, as the request encoding differs by version (see below).
• otherwise, the recipient will act as an IP proxy. The IP proxy can choose to reject the IP proxying request. Otherwise, it extracts the optional "target" and "ipproto" variables from the URI it has reconstructed from the request headers, decodes their percent-encoding, and establishes an IP tunnel.

IP proxies MUST validate whether the decoded "target" and "ipproto" variables meet the requirements in . If they do not, the IP proxy MUST treat the request as malformed; see and . If the "target" variable is a DNS name, the IP proxy MUST perform DNS resolution (to query the corresponding IPv4 and/or IPv6 addresses via A and/or AAAA records) before replying to the HTTP request. If errors occur during this process, the IP proxy MUST reject the request and SHOULD send details using an appropriate Proxy-Status header field . For example, if DNS resolution returns an error, the proxy can use the dns_error Proxy Error Type from . The lifetime of the IP forwarding tunnel is tied to the IP proxying request stream. The IP proxy MUST maintain all IP address and route assignments associated with the IP forwarding tunnel while the request stream is open. IP proxies MAY choose to tear down the tunnel due to a period of inactivity, but they MUST close the request stream when doing so. A successful response (as defined in Sections and ) indicates that the IP proxy has established an IP tunnel and is willing to proxy IP payloads. Any response other than a successful response indicates that the request has failed; thus, the client MUST abort the request. Along with a successful response, the IP proxy can send capsules to assign addresses and advertise routes to the client (). The client can also assign addresses and advertise routes to the IP proxy for network-to-network routing.

HTTP/1.1 Request When using HTTP/1.1 , an IP proxying request will meet the following requirements:

• the method SHALL be "GET".
• the request SHALL include a single Host header field containing the host and optional port of the IP proxy.
• the request SHALL include a Connection header field with value "Upgrade" (note that this requirement is case-insensitive as per ).
• the request SHALL include an Upgrade header field with value "connect-ip".

An IP proxying request that does not conform to these restrictions is malformed. The recipient of such a malformed request MUST respond with an error and SHOULD use the 400 (Bad Request) status code. For example, if the client is configured with URI Template "https://example.org/.well-known/masque/ip/{target}/{ipproto}/" and wishes to open an IP forwarding tunnel with no target or protocol limitations, it could send the following request:

Example HTTP/1.1 Request

HTTP/1.1 Response The server indicates a successful response by replying with the following requirements:

• the HTTP status code on the response SHALL be 101 (Switching Protocols).
• the response SHALL include a Connection header field with value "Upgrade" (note that this requirement is case-insensitive as per ).
• the response SHALL include a single Upgrade header field with value "connect-ip".
• the response SHALL meet the requirements of HTTP responses that start the Capsule Protocol; see .

If any of these requirements are not met, the client MUST treat this proxying attempt as failed and close the connection. For example, the server could respond with:

Example HTTP/1.1 Response

HTTP/2 and HTTP/3 Requests When using HTTP/2 or HTTP/3 , IP proxying requests use HTTP Extended CONNECT. This requires that servers send an HTTP Setting as specified in and and that requests use HTTP pseudo-header fields with the following requirements:

• The :method pseudo-header field SHALL be "CONNECT".
• The :protocol pseudo-header field SHALL be "connect-ip".
• The :authority pseudo-header field SHALL contain the authority of the IP proxy.
• The :path and :scheme pseudo-header fields SHALL NOT be empty. Their values SHALL contain the scheme and path from the URI Template after the URI Template expansion process has been completed; see . Variables in the URI Template can determine the scope of the request, such as requesting full-tunnel IP packet forwarding, or a specific proxied flow; see .

An IP proxying request that does not conform to these restrictions is malformed; see and . For example, if the client is configured with URI Template "https://example.org/.well-known/masque/ip/{target}/{ipproto}/" and wishes to open an IP forwarding tunnel with no target or protocol limitations, it could send the following request:

Example HTTP/2 or HTTP/3 Request

HTTP/2 and HTTP/3 Responses The server indicates a successful response by replying with the following requirements:

• the HTTP status code on the response SHALL be in the 2xx (Successful) range.
• the response SHALL meet the requirements of HTTP responses that start the Capsule Protocol; see .

If any of these requirements are not met, the client MUST treat this proxying attempt as failed and abort the request. As an example, any status code in the 3xx range will be treated as a failure and cause the client to abort the request. For example, the server could respond with:

Example HTTP/2 or HTTP/3 Response

Limiting Request Scope Unlike UDP proxying requests, which require specifying a target host, IP proxying requests can allow endpoints to send arbitrary IP packets to any host. The client can choose to restrict a given request to a specific IP prefix or IP protocol by adding parameters to its request. When the IP proxy knows that a request is scoped to a target prefix or protocol, it can leverage this information to optimize its resource allocation; for example, the IP proxy can assign the same public IP address to two IP proxying requests that are scoped to different prefixes and/or different protocols. The scope of the request is indicated by the client to the IP proxy via the "target" and "ipproto" variables of the URI Template; see . Both the "target" and "ipproto" variables are optional; if they are not included, they are considered to carry the wildcard value "*".

target:

The variable "target" contains a hostname or IP prefix of a specific host to which the client wants to proxy packets. If the "target" variable is not specified or its value is "*", the client is requesting to communicate with any allowable host. "target" supports using DNS names, IPv6 prefixes and IPv4 prefixes. Note that IPv6 scoped addressing zone identifiers () are not supported. If the target is an IP prefix (IP address optionally followed by a percent-encoded slash followed by the prefix length in bits), the request will only support a single IP version. If the target is a hostname, the IP proxy is expected to perform DNS resolution to determine which route(s) to advertise to the client. The IP proxy SHOULD send a ROUTE_ADVERTISEMENT capsule that includes routes for all addresses that were resolved for the requested hostname, that are accessible to the IP proxy, and belong to an address family for which the IP proxy also sends an Assigned Address.

ipproto:

The variable "ipproto" contains an IP protocol number, as defined in the "Assigned Internet Protocol Numbers" IANA registry . If present, it specifies that a client only wants to proxy a specific IP protocol for this request. If the value is "*", or the variable is not included, the client is requesting to use any IP protocol.

Using the terms IPv6address, IPv4address, and reg-name from , the "target" and "ipproto" variables MUST adhere to the format in , using notation from . Additionally:

• if "target" contains an IPv6 literal or prefix, the colons (":") MUST be percent-encoded. For example, if the target host is "2001:db8::42", it will be encoded in the URI as "2001%3Adb8%3A%3A42".
• If present, the IP prefix length in "target" SHALL be preceded by a percent-encoded slash ("/"): "%2F". The IP prefix length MUST represent a decimal integer between 0 and the length of the IP address in bits, inclusive.
• If "target" contains an IP prefix and the prefix length is strictly less than the length of the IP address in bits, the lower bits of the IP address that are not covered by the prefix length MUST all be set to 0.
• "ipproto" MUST represent a decimal integer between 0 and 255 inclusive, or the wildcard value "*".

URI Template Variable Format

IP proxies MAY perform access control using the scoping information provided by the client: if the client is not authorized to access any of the destinations included in the scope, then the IP proxy can immediately fail the request. Note that IP protocol numbers represent both upper layers (as defined in , examples include TCP and UDP) and IPv6 extension headers (as defined in , examples include Fragment and Options headers). IP proxies MAY reject requests to scope to protocol numbers that are used for extension headers. Upon receiving packets, implementations that support scoping by IP protocol number MUST walk the chain of extensions to find the matching IP protocol number.

Capsules This document defines multiple new capsule types that allow endpoints to exchange IP configuration information. Both endpoints MAY send any number of these new capsules.

ADDRESS_ASSIGN Capsule The ADDRESS_ASSIGN capsule (see for the value of the capsule type) allows an endpoint to inform its peer of the list of IP addresses or prefixes it has assigned to it. Every capsule contains the full list of IP prefixes currently assigned to the receiver. Any of these addresses can be used as the source address on IP packets originated by the receiver of this capsule.

ADDRESS_ASSIGN Capsule Format

The ADDRESS_ASSIGN capsule contains a sequence of zero or more Assigned Addresses.

Assigned Address Format

Each Assigned Address contains the following fields:

Request ID:

Request identifier, encoded as a variable-length integer. If this address assignment is in response to an Address Request (see ), then this field SHALL contain the value of the corresponding field in the request. Otherwise, this field SHALL be zero.

IP Version:

IP Version of this address assignment, encoded as an unsigned 8-bit integer. MUST be either 4 or 6.

IP Address:

Assigned IP address. If the IP Version field has value 4, the IP Address field SHALL have a length of 32 bits. If the IP Version field has value 6, the IP Address field SHALL have a length of 128 bits.

IP Prefix Length:

The number of bits in the IP address that are used to define the prefix that is being assigned, encoded as an unsigned 8-bit integer. This MUST be less than or equal to the length of the IP Address field, in bits. If the prefix length is equal to the length of the IP address, the receiver of this capsule is allowed to send packets from a single source address. If the prefix length is less than the length of the IP address, the receiver of this capsule is allowed to send packets from any source address that falls within the prefix. If the prefix length is strictly less than the length of the IP address in bits, the lower bits of the IP Address field that are not covered by the prefix length MUST all be set to 0.

If any of the capsule fields are malformed upon reception, the receiver of the capsule MUST follow the error handling procedure defined in . If an ADDRESS_ASSIGN capsule does not contain an address that was previously transmitted in another ADDRESS_ASSIGN capsule, that indicates that the address has been removed. An ADDRESS_ASSIGN capsule can also be empty, indicating that all addresses have been removed. In some deployments of IP proxying in HTTP, an endpoint needs to be assigned an address by its peer before it knows what source address to set on its own packets. For example, in the Remote Access VPN case () the client cannot send IP packets until it knows what address to use. In these deployments, the endpoint that is expecting an address assignment MUST send an ADDRESS_REQUEST capsule. This isn't required if the endpoint does not need any address assignment, for example when it is configured out-of-band with static addresses. While ADDRESS_ASSIGN capsules are commonly sent in response to ADDRESS_REQUEST capsules, endpoints MAY send ADDRESS_ASSIGN capsules unprompted.

ADDRESS_REQUEST Capsule The ADDRESS_REQUEST capsule (see for the value of the capsule type) allows an endpoint to request assignment of IP addresses from its peer. The capsule allows the endpoint to optionally indicate a preference for which address it would get assigned.

ADDRESS_REQUEST Capsule Format

The ADDRESS_REQUEST capsule contains a sequence of one or more Requested Addresses.

Requested Address Format

Each Requested Address contains the following fields:

Request ID:

Request identifier, encoded as a variable-length integer. This is the identifier of this specific address request. Each request from a given endpoint carries a different identifier. Request IDs MUST NOT be reused by an endpoint, and MUST NOT be zero.

IP Version:

IP Version of this address request, encoded as an unsigned 8-bit integer. MUST be either 4 or 6.

IP Address:

Requested IP address. If the IP Version field has value 4, the IP Address field SHALL have a length of 32 bits. If the IP Version field has value 6, the IP Address field SHALL have a length of 128 bits.

IP Prefix Length:

Length of the IP Prefix requested, in bits, encoded as an unsigned 8-bit integer. MUST be less than or equal to the length of the IP Address field, in bits. If the prefix length is strictly less than the length of the IP address in bits, the lower bits of the IP Address field that are not covered by the prefix length MUST all be set to 0.

If the IP address is all-zero (0.0.0.0 or ::), this indicates that the sender is requesting an address of that address family but does not have a preference for a specific address. In that scenario, the prefix length still indicates the sender's preference for the prefix length it is requesting. If any of the capsule fields are malformed upon reception, the receiver of the capsule MUST follow the error handling procedure defined in . Upon receiving the ADDRESS_REQUEST capsule, an endpoint SHOULD assign one or more IP addresses to its peer, and then respond with an ADDRESS_ASSIGN capsule to inform the peer of the assignment. For each Requested Address, the receiver of the ADDRESS_REQUEST capsule SHALL respond with an Assigned Address with a matching Request ID. If the requested address was assigned, the IP Address and IP Prefix Length fields in the Assigned Address response SHALL be set to the assigned values. If the requested address was not assigned, the IP address SHALL be all-zero and the IP Prefix Length SHALL be the maximum length (0.0.0.0/32 or ::/128) to indicate that no address was assigned. These address rejections SHOULD NOT be included in subsequent ADDRESS_ASSIGN capsules. Note that other Assigned Address entries that do not correspond to any Request ID can also be contained in the same ADDRESS_ASSIGN response. If an endpoint receives an ADDRESS_REQUEST capsule that contains zero Requested Addresses, it MUST abort the IP proxying request stream. Note that the ordering of Requested Addresses does not carry any semantics. Similarly, the Request ID is only meant as a unique identifier, it does not convey any priority or importance.

ROUTE_ADVERTISEMENT Capsule The ROUTE_ADVERTISEMENT capsule (see for the value of the capsule type) allows an endpoint to communicate to its peer that it is willing to route traffic to a set of IP address ranges. This indicates that the sender has an existing route to each address range, and notifies its peer that if the receiver of the ROUTE_ADVERTISEMENT capsule sends IP packets for one of these ranges in HTTP Datagrams, the sender of the capsule will forward them along its preexisting route. Any address which is in one of the address ranges can be used as the destination address on IP packets originated by the receiver of this capsule.

ROUTE_ADVERTISEMENT Capsule Format

The ROUTE_ADVERTISEMENT capsule contains a sequence of zero or more IP Address Ranges.

IP Address Range Format

Each IP Address Range contains the following fields:

IP Version:

IP Version of this range, encoded as an unsigned 8-bit integer. MUST be either 4 or 6.

Start IP Address and End IP Address:

Inclusive start and end IP address of the advertised range. If the IP Version field has value 4, these fields SHALL have a length of 32 bits. If the IP Version field has value 6, these fields SHALL have a length of 128 bits. The Start IP Address MUST be less than or equal to the End IP Address.

IP Protocol:

The Internet Protocol Number for traffic that can be sent to this range, encoded as an unsigned 8-bit integer. If the value is 0, all protocols are allowed. ICMP traffic is always allowed, regardless of the value of this field.

If any of the capsule fields are malformed upon reception, the receiver of the capsule MUST follow the error handling procedure defined in . Upon receiving the ROUTE_ADVERTISEMENT capsule, an endpoint MAY update its local state regarding what its peer is willing to route (subject to local policy), such as by installing entries in a routing table. Each ROUTE_ADVERTISEMENT contains the full list of address ranges. If multiple ROUTE_ADVERTISEMENT capsules are sent in one direction, each ROUTE_ADVERTISEMENT capsule supersedes prior ones. In other words, if a given address range was present in a prior capsule but the most recently received ROUTE_ADVERTISEMENT capsule does not contain it, the receiver will consider that range withdrawn. If multiple ranges using the same IP protocol were to overlap, some routing table implementations might reject them. To prevent overlap, the ranges are ordered; this places the burden on the sender and makes verification by the receiver much simpler. If an IP Address Range A precedes an IP Address Range B in the same ROUTE_ADVERTISEMENT capsule, they MUST follow these requirements:

• IP Version of A MUST be less than or equal to IP Version of B
• If the IP Version of A and B are equal, the IP Protocol of A MUST be less than or equal to IP Protocol of B.
• If the IP Version and IP Protocol of A and B are both equal, the End IP Address of A MUST be strictly less than the Start IP Address of B.

If an endpoint receives a ROUTE_ADVERTISEMENT capsule that does not meet these requirements, it MUST abort the IP proxying request stream. Since setting the IP protocol to zero indicates all protocols are allowed, the requirements above make it possible for two routes to overlap when one has IP protocol set to zero and the other set to non-zero. Endpoints MUST NOT send a ROUTE_ADVERTISEMENT capsule with routes that overlap in such a way. Validating this requirement is OPTIONAL, but if an endpoint detects the violation, it MUST abort the IP proxying request stream.

Context Identifiers The mechanism for proxying IP in HTTP defined in this document allows future extensions to exchange HTTP Datagrams that carry different semantics from IP payloads. Some of these extensions can augment IP payloads with additional data or compress IP header fields, while others can exchange data that is completely separate from IP payloads. In order to accomplish this, all HTTP Datagrams associated with IP proxying request streams start with a Context ID field; see . Context IDs are 62-bit integers (0 to 2⁶²-1). Context IDs are encoded as variable-length integers; see . The Context ID value of 0 is reserved for IP payloads, while non-zero values are dynamically allocated. Non-zero even-numbered Context IDs are client-allocated, and odd-numbered Context IDs are proxy-allocated. The Context ID namespace is tied to a given HTTP request; it is possible for a Context ID with the same numeric value to be simultaneously allocated in distinct requests, potentially with different semantics. Context IDs MUST NOT be re-allocated within a given HTTP request but MAY be allocated in any order. The Context ID allocation restrictions to the use of even-numbered and odd-numbered Context IDs exist in order to avoid the need for synchronization between endpoints. However, once a Context ID has been allocated, those restrictions do not apply to the use of the Context ID; it can be used by either the client or the IP proxy, independent of which endpoint initially allocated it. Registration is the action by which an endpoint informs its peer of the semantics and format of a given Context ID. This document does not define how registration occurs. Future extensions MAY use HTTP header fields or capsules to register Context IDs. Depending on the method being used, it is possible for datagrams to be received with Context IDs that have not yet been registered. For instance, this can be due to reordering of the packet containing the datagram and the packet containing the registration message during transmission.

HTTP Datagram Payload Format When associated with IP proxying request streams, the HTTP Datagram Payload field of HTTP Datagrams (see ) has the format defined in . Note that when HTTP Datagrams are encoded using QUIC DATAGRAM frames, the Context ID field defined below directly follows the Quarter Stream ID field which is at the start of the QUIC DATAGRAM frame payload:

IP Proxying HTTP Datagram Format

The IP Proxying HTTP Datagram Payload contains the following fields:

Context ID:

A variable-length integer that contains the value of the Context ID. If an HTTP/3 datagram which carries an unknown Context ID is received, the receiver SHALL either drop that datagram silently or buffer it temporarily (on the order of a round trip) while awaiting the registration of the corresponding Context ID.

Payload:

The payload of the datagram, whose semantics depend on value of the previous field. Note that this field can be empty.

IP packets are encoded using HTTP Datagrams with the Context ID set to zero. When the Context ID is set to zero, the Payload field contains a full IP packet (from the IP Version field until the last byte of the IP Payload).

IP Packet Handling Clients MAY optimistically start sending proxied IP packets before receiving the response to its IP proxying request, noting however that those may not be processed by the IP proxy if it responds to the request with a failure, or if the datagrams are received by the IP proxy before the request. Since receiving addresses and routes is required in order to know that a packet can be sent through the tunnel, such optimistic packets might be dropped by the IP proxy if it chooses to provide different addressing or routing information than what the client assumed. When an endpoint receives an HTTP Datagram containing an IP packet, it will parse the packet's IP header, perform any local policy checks (e.g., source address validation), check their routing table to pick an outbound interface, and then send the IP packet on that interface or pass it to a local application. The endpoint can also choose to drop any received packets instead of forwarding them. If a received IP packet fails any correctness or policy checks, that is a forwarding error, not a protocol violation as far as IP proxying is concerned; see . In the other direction, when an endpoint receives an IP packet, it checks to see if the packet matches the routes mapped for an IP tunnel, and performs the same forwarding checks as above before transmitting the packet over HTTP Datagrams. When IP proxying endpoints forward IP packets between different links, they will decrement the IP Hop Count (or TTL) upon encapsulation, but not upon decapsulation. In other words, the Hop Count is decremented right before an IP packet is transmitted in an HTTP Datagram. This prevents infinite loops in the presence of routing loops, and matches the choices in IPsec . This does not apply to IP packets generated by the IP proxying endpoint itself. Note that the IP forwarding tunnels described in this document are not fully featured "interfaces" in the IPv6 addressing architecture sense . In particular, they do not necessarily have IPv6 link-local addresses. Additionally, IPv6 stateless autoconfiguration or router advertisement messages are not used in such interfaces, and neither is neighbor discovery. Implementers need to ensure that they do not forward any link-local traffic beyond the IP proxying interface that it was received on. IP proxying endpoints also need to properly reply to packets destined to link-local multicast addresses. IPv6 requires that every link have an MTU of at least 1280 bytes . Since IP proxying in HTTP conveys IP packets in HTTP Datagrams and those can in turn be sent in QUIC DATAGRAM frames which cannot be fragmented , the MTU of an IP tunnel can be limited by the MTU of the QUIC connection that IP proxying is operating over. This can lead to situations where the IPv6 minimum link MTU is violated. IP proxying endpoints that support IPv6 MUST ensure that the IP tunnel link MTU is at least 1280 (i.e., that they can send HTTP Datagrams with payloads of at least 1280 bytes). This can be accomplished using various techniques:

• if both IP proxying endpoints know for certain that HTTP intermediaries are not in use, the endpoints can pad the QUIC INITIAL packets of the outer QUIC connection that IP proxying is running over. (Assuming QUIC version 1 is in use, the overhead is 1 byte type, 20 bytes maximal connection ID length, 4 bytes maximal packet number length, 1 byte DATAGRAM frame type, 8 bytes maximal quarter stream ID, one byte for the zero Context ID, and 16 bytes for the AEAD authentication tag, for a total of 51 bytes of overhead which corresponds to padding QUIC INITIAL packets to 1331 bytes or more.)
• IP proxying endpoints can also send ICMPv6 echo requests with 1232 bytes of data to ascertain the link MTU and tear down the tunnel if they do not receive a response. Unless endpoints have an out-of-band means of guaranteeing that the previous techniques is sufficient, they MUST use this method. If an endpoint does not know an IPv6 address of its peer, it can send the ICMPv6 echo request to the link local all nodes multicast address (ff02::1).

If an endpoint is using QUIC DATAGRAM frames to convey IPv6 packets, and it detects that the QUIC MTU is too low to allow sending 1280 bytes, it MUST abort the IP proxying request stream. Endpoints MAY implement additional filtering policies on the IP packets they forward. Note that it is possible for multiple proxied IP packets to be encapsulated in the same outer packet, for example because a QUIC packet can carry two QUIC DATAGRAM frames. It is also possible for a proxied IP packet to span multiple outer packets, because a DATAGRAM capsule can be split across multiple QUIC or TCP packets.

Error Signalling Since IP proxying endpoints often forward IP packets onwards to other network interfaces, they need to handle errors in the forwarding process. For example, forwarding can fail if the endpoint does not have a route for the destination address, or if it is configured to reject a destination prefix by policy, or if the MTU of the outgoing link is lower than the size of the packet to be forwarded. In such scenarios, IP proxying endpoints SHOULD use ICMP to signal the forwarding error to its peer by generating ICMP packets and sending them using HTTP Datagrams. Endpoints are free to select the most appropriate ICMP errors to send. Some examples that are relevant for IP proxying include:

• For invalid source addresses, send Destination Unreachable () with code 5, "Source address failed ingress/egress policy".
• For unroutable destination addresses, send Destination Unreachable () with a code 0, "No route to destination", or code 1, "Communication with destination administratively prohibited".
• For packets that cannot fit within the MTU of the outgoing link, send Packet Too Big ().

In order to receive these errors, endpoints need to be prepared to receive ICMP packets. If an endpoint does not send ROUTE_ADVERTISEMENT capsules, such as a client opening an IP flow through an IP proxy, it SHOULD process proxied ICMP packets from its peer in order to receive these errors. Note that ICMP messages can originate from a source address different from that of the IP proxying peer, and also from outside the target if scoping is in use (see ).

Examples IP proxying in HTTP enables many different use cases that can benefit from IP packet proxying and tunnelling. These examples are provided to help illustrate some of the ways in which IP proxying in HTTP can be used.

Remote Access VPN The following example shows a point-to-network VPN setup, where a client receives a set of local addresses, and can send to any remote host through the IP proxy. Such VPN setups can be either full-tunnel or split-tunnel.

VPN Tunnel Setup IP D | +--------------------+ IP | IP C | | Client | IP Subnet C <--> ? | Proxy +-----------+---> IP E | +--------------------+ | | +--------+ +--------+ +---> IP ... ]]>

In this case, the client does not specify any scope in its request. The IP proxy assigns the client an IPv4 address (192.0.2.11) and a full-tunnel route of all IPv4 addresses (0.0.0.0/0). The client can then send to any IPv4 host using a source address in its assigned prefix.

VPN Full-Tunnel Example

A setup for a split-tunnel VPN (the case where the client can only access a specific set of private subnets) is quite similar. In this case, the advertised route is restricted to 192.0.2.0/24, rather than 0.0.0.0/0.

VPN Split-Tunnel Capsule Example

Site-to-Site VPN The following example shows how to connect a branch office network to a corporate network such that all machines on those networks can communicate. In this example, the IP proxying client is attached to the branch office network 192.0.2.0/24, and the IP proxy is attached to the corporate network 203.0.113.0/24. There are legacy clients on the branch office network that only allow maintenance requests from machines on their subnet, so the IP Proxy is provisioned with an IP address from that subnet.

Site-to-site VPN Example 203.0.113.9 | | +-------------+ IP | | 192.0.2.2 <--+---+ Client | IP Proxying | Proxy +---+---> 203.0.113.8 | | +-------------+ | | 192.0.2.3 <--+ +--------+ +-------+ +---> 203.0.113.7 ]]>

In this case, the client does not specify any scope in its request. The IP proxy assigns the client an IPv4 address (203.0.113.100) and a split-tunnel route to the corporate network (203.0.113.0/24). The client assigns the IP proxy an IPv4 address (192.0.2.200) and a split-tunnel route to the branch office network (192.0.2.0/24). This allows hosts on both networks to communicate with each other, and allows the IP proxy to perform maintenance on legacy hosts in the branch office. Note that IP proxying endpoints will decrement the IP Hop Count (or TTL) when encapsulating forwarded packets, so protocols that require that field be set to 255 will not function.

Site-to-site VPN Capsule Example

IP Flow Forwarding The following example shows an IP flow forwarding setup, where a client requests to establish a forwarding tunnel to target.example.com using SCTP (IP protocol 132), and receives a single local address and remote address it can use for transmitting packets. A similar approach could be used for any other IP protocol that isn't easily proxied with existing HTTP methods, such as ICMP, ESP, etc.

Proxied Flow Setup D | Proxy +---------> IP D | +-------------------+ | +--------+ +--------+ ]]>

In this case, the client specfies both a target hostname and an IP protocol number in the scope of its request, indicating that it only needs to communicate with a single host. The IP proxy is able to perform DNS resolution on behalf of the client and allocate a specific outbound socket for the client instead of allocating an entire IP address to the client. In this regard, the request is similar to a regular CONNECT proxy request. The IP proxy assigns a single IPv6 address to the client (2001:db8:1234::a) and a route to a single IPv6 host (2001:db8:3456::b), scoped to SCTP. The client can send and receive SCTP IP packets to the remote host.

Proxied SCTP Flow Example

Proxied Connection Racing The following example shows a setup where a client is proxying UDP packets through an IP proxy in order to control connection establishment racing through an IP proxy, as defined in Happy Eyeballs . This example is a variant of the proxied flow, but highlights how IP-level proxying can enable new capabilities even for TCP and UDP.

Proxied Connection Racing Setup IP E | Client | IP C <--> E | IP | | | D <--> F | Proxy | | +-------------------+ |<------------> IP F +--------+ +--------+ IP D ]]>

As with proxied flows, the client specifies both a target hostname and an IP protocol number in the scope of its request. When the IP proxy performs DNS resolution on behalf of the client, it can send the various remote address options to the client as separate routes. It can also ensure that the client has both IPv4 and IPv6 addresses assigned. The IP proxy assigns both an IPv4 address (192.0.2.3) and an IPv6 address (2001:db8:1234::a) to the client, as well as an IPv4 route (198.51.100.2) and an IPv6 route (2001:db8:3456::b), which represent the resolved addresses of the target hostname, scoped to UDP. The client can send and receive UDP IP packets to either one of the IP proxy addresses to enable Happy Eyeballs through the IP proxy.

Proxied Connection Racing Example

Extensibility Considerations Extensions to IP proxying in HTTP can define behavior changes to this mechanism. Such extensions SHOULD define new capsule types to exchange configuration information if needed. It is RECOMMENDED for extensions that modify addressing to specify that their extension capsules be sent before the ADDRESS_ASSIGN capsule and that they do not take effect until the ADDRESS_ASSIGN capsule is parsed. This allows modifications to address assignment to operate atomically. Similarly, extensions that modify routing SHOULD behave similarly with regard to the ROUTE_ADVERTISEMENT capsule.

Performance Considerations Bursty traffic can often lead to temporally-correlated packet losses; in turn, this can lead to suboptimal responses from congestion controllers in protocols running inside the tunnel. To avoid this, endpoints SHOULD strive to avoid increasing burstiness of IP traffic; they SHOULD NOT queue packets in order to increase batching beyond the minimal amount required to take advantage of hardware offloads. When the protocol running inside the tunnel uses congestion control (e.g., or ), the proxied traffic will incur at least two nested congestion controllers. The outer HTTP connection MAY disable congestion control if it knows that the inner packets belong to congestion-controlled connections. Implementers will benefit from reading the guidance in . When the protocol running inside the tunnel uses loss recovery (e.g., or ), and the outer HTTP connection runs over TCP, the proxied traffic will incur at least two nested loss recovery mechanisms. This can reduce performance as both can sometimes independently retransmit the same data. To avoid this, IP proxying SHOULD be performed over HTTP/3 to allow leveraging the QUIC DATAGRAM frame.

MTU Considerations When using HTTP/3 with the QUIC Datagram extension , IP packets are transmitted in QUIC DATAGRAM frames. Since these frames cannot be fragmented, they can only carry packets up to a given length determined by the QUIC connection configuration and the Path MTU (PMTU). If an endpoint is using QUIC DATAGRAM frames and it attempts to route an IP packet through the tunnel that will not fit inside a QUIC DATAGRAM frame, the IP proxy SHOULD NOT send the IP packet in a DATAGRAM capsule, as that defeats the end-to-end unreliability characteristic that methods such as Datagram Packetization Layer PMTU Discovery (DPLPMTUD) depend on . In this scenario, the endpoint SHOULD drop the IP packet and send an ICMP Packet Too Big message to the sender of the dropped packet; see .

ECN Considerations If a client or IP proxy with a connection containing an IP Proxying request stream disables congestion control, it cannot signal Explicit Congestion Notification (ECN) support on that outer connection. That is, the QUIC sender MUST mark all IP headers with the Not-ECT codepoint for QUIC packets which are outside of congestion control. The endpoint can still report ECN feedback via QUIC ACK_ECN frames or the TCP ECE bit, as the peer might not have disabled congestion control. Conversely, if congestion control is not disabled on the outer congestion, the guidance in about transferring ECN marks between inner and outer IP headers does not apply because the outer connection will react correctly to congestion notifications if it uses ECN. The inner traffic can also use ECN, independently of whether it is in use on the outer connection.

Security Considerations There are significant risks in allowing arbitrary clients to establish a tunnel that permits sending to arbitrary hosts, regardless of whether tunnels are scoped to specific hosts or not. Bad actors could abuse this capability to send traffic and have it attributed to the IP proxy. HTTP servers that support IP proxying SHOULD restrict its use to authenticated users. Depending on the deployment, possible authentication mechanisms include mutual TLS between clients and proxies, HTTP-based authentication via the HTTP Authorization header , or even bearer tokens. Proxies can enforce policies for authenticated users to further constrain client behavior or deal with possible abuse. For example, proxies can rate limit individual clients that send an excessively large amount of traffic through the proxy. As another example, proxies can restrict address (prefix) assignment to clients based on certain client attributes such as geographic location. Address assignment can have privacy implications for endpoints. For example, if a proxy partitions its address space by the number of authenticated clients and then assigns distinct address ranges to each client, target hosts could use this information to determine when IP packets correspond to the same client. Avoiding such tracking vectors may be important for certain proxy deployments. Proxies SHOULD avoid persistent per-client address (prefix) assignment when possible. Falsifying IP source addresses in sent traffic has been common for denial of service attacks. Implementations of this mechanism need to ensure that they do not facilitate such attacks. In particular, there are scenarios where an endpoint knows that its peer is only allowed to send IP packets from a given prefix. For example, that can happen through out-of-band configuration information, or when allowed prefixes are shared via ADDRESS_ASSIGN capsules. In such scenarios, endpoints MUST follow the recommendations from to prevent source address spoofing. Limiting request scope (see ) allows two clients to share one of the proxy's external IP addresses if their requests are scoped to different IP protocol numbers. If the proxy receives an ICMP packet destined for that external IP address, it has the option to forward it back to the clients. However, some of these ICMP packets carry part of the original IP packet that triggered the ICMP response. Forwarding such packets can accidentally divulge information about one client's traffic to another client. To avoid this, proxies that forward ICMP on shared external IP addresses MUST inspect the invoking packet included in the ICMP packet and only forward the ICMP packet to the client whose scoping matches the invoking packet. Implementers will benefit from reading the guidance in . Since there are known risks with some IPv6 extension headers (e.g., ), implementers need to follow the latest guidance regarding handling of IPv6 extension headers.

IANA Considerations

HTTP Upgrade Token This document will request IANA to register "connect-ip" in the HTTP Upgrade Token Registry maintained at <>.

Value:

connect-ip

Description:

Proxying of IP Payloads

Expected Version Tokens:

None

References:

This document

Creation of the MASQUE URI Suffixes Registry This document requests that IANA create a new "MASQUE URI Suffixes" registry maintained at IANA_URL_TBD. This new registry governs the path segment that immediately follows "masque" in paths that start with "/.well-known/masque/", see <> for the registration of "masque" in the "Well-Known URIs" registry. This new registry contains three columns:

Path Segment:

An ASCII string containing only characters allowed in tokens; see . Entries in this registry MUST all have distinct entries in this column.

Description:

A description of the entry.

Reference:

An optional reference defining the use of the entry.

The registration policy for this registry is Expert Review; see . There are initially two entries in this registry: New MASQUE URI Suffixes

Path Segment	Description	Reference
udp	UDP Proxying	RFC 9298
ip	IP Proxying	This Document

Designated experts for this registry are advised that they should approve all requests as long as the expert believes that both (1) the requested Path Segment will not conflict with existing or expected future IETF work and (2) the use case is relevant to proxying.

Updates to masque Well-Known URI This document will request IANA to update the entry for the "masque" URI suffix in the "Well-Known URIs" registry maintained at <>. IANA is requested to update the "Reference" field to include this document in addition to previous values from that field. IANA is requested to replace the "Related Information" field with "For sub-suffix allocations, see registry at IANA_URL_TBD." where IANA_URL_TBD is the URL of the new registry described in .

Capsule Type Registrations This document requests IANA to add the following values to the "HTTP Capsule Types" registry maintained at <>. New Capsules

Value	Capsule Type	Description
0x01	ADDRESS_ASSIGN	Address Assignment
0x02	ADDRESS_REQUEST	Address Request
0x03	ROUTE_ADVERTISEMENT	Route Advertisement

All of these new entries use the following values for these fields:

Status:

provisional (permanent when this document is approved)

Reference:

This Document

Change Controller:

IETF

Contact:

masque@ietf.org

Notes:

Empty

RFC Editor: please remove the rest of this subsection before publication. Since this document has not yet been published, it might still change before publication as RFC. Any implementer that wishes to deploy IP proxying in production before publication MUST use the following temporary codepoints instead: 0x2575D601 for ADDRESS_ASSIGN, 0x2575D602 for ADDRESS_REQUEST, and 0x2575D603 for ROUTE_ADVERTISEMENT.

References Normative References The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document specifies the HTTP/1.1 message syntax, message parsing, connection management, and related security concerns. This document obsoletes portions of RFC 7230. This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced latency by introducing field compression and allowing multiple concurrent exchanges on the same connection. This document obsoletes RFCs 7540 and 8740. The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC. This document also identifies HTTP/2 features that are subsumed by QUIC and describes how HTTP/2 extensions can be ported to HTTP/3. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. This document specifies the Transmission Control Protocol (TCP). TCP is an important transport-layer protocol in the Internet protocol stack, and it has continuously evolved over decades of use and growth of the Internet. Over this time, a number of changes have been made to TCP as it was specified in RFC 793, though these have only been documented in a piecemeal fashion. This document collects and brings those changes together with the protocol specification from RFC 793. This document obsoletes RFC 793, as well as RFCs 879, 2873, 6093, 6429, 6528, and 6691 that updated parts of RFC 793. It updates RFCs 1011 and 1122, and it should be considered as a replacement for the portions of those documents dealing with TCP requirements. It also updates RFC 5961 by adding a small clarification in reset handling while in the SYN-RECEIVED state. The TCP header control bits from RFC 793 have also been updated based on RFC 3168. A URI Template is a compact sequence of characters for describing a range of Uniform Resource Identifiers through variable expansion. This specification defines the URI Template syntax and the process for expanding a URI Template into a URI reference, along with guidelines for the use of URI Templates on the Internet. [STANDARDS-TRACK] This document describes HTTP Datagrams, a convention for conveying multiplexed, potentially unreliable datagrams inside an HTTP connection. In HTTP/3, HTTP Datagrams can be sent unreliably using the QUIC DATAGRAM extension. When the QUIC DATAGRAM frame is unavailable or undesirable, HTTP Datagrams can be sent using the Capsule Protocol, which is a more general convention for conveying data in HTTP connections. HTTP Datagrams and the Capsule Protocol are intended for use by HTTP extensions, not applications. This document defines a mechanism for running the WebSocket Protocol (RFC 6455) over a single stream of an HTTP/2 connection. The mechanism for running the WebSocket Protocol over a single stream of an HTTP/2 connection is equally applicable to HTTP/3, but the HTTP-version-specific details need to be specified. This document describes how the mechanism is adapted for HTTP/3. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] This document defines the Proxy-Status HTTP response field to convey the details of an intermediary's response handling, including generated errors. This document describes how the zone identifier of an IPv6 scoped address, defined as <zone_id> in the IPv6 Scoped Address Architecture (RFC 4007), can be represented in a literal IPv6 address and in a Uniform Resource Identifier that includes such a literal address. It updates the URI Generic Syntax specification (RFC 3986) accordingly. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. This document defines an extension to the QUIC transport protocol to add support for sending and receiving unreliable datagrams over a QUIC connection. This document describes the format of a set of control messages used in ICMPv6 (Internet Control Message Protocol). ICMPv6 is the Internet Control Message Protocol for Internet Protocol version 6 (IPv6). [STANDARDS-TRACK] This memo specifies the incorporation of ECN (Explicit Congestion Notification) to TCP and IP, including ECN's use of two bits in the IP header. [STANDARDS-TRACK] This paper discusses a simple, effective, and straightforward method for using ingress traffic filtering to prohibit DoS (Denial of Service) attacks which use forged IP addresses to be propagated from 'behind' an Internet Service Provider's (ISP) aggregation point. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. Informative References IANA This document describes how to proxy UDP in HTTP, similar to how the HTTP CONNECT method allows proxying TCP in HTTP. More specifically, this document defines a protocol that allows an HTTP client to create a tunnel for UDP communications through an HTTP server that acts as a proxy. This document describes an updated version of the "Security Architecture for IP", which is designed to provide security services for traffic at the IP layer. This document obsoletes RFC 2401 (November 1998). [STANDARDS-TRACK] This specification defines the addressing architecture of the IP Version 6 (IPv6) protocol. The document includes the IPv6 addressing model, text representations of IPv6 addresses, definition of IPv6 unicast addresses, anycast addresses, and multicast addresses, and an IPv6 node's required addresses. This document obsoletes RFC 3513, "IP Version 6 Addressing Architecture". [STANDARDS-TRACK] Many communication protocols operating over the modern Internet use hostnames. These often resolve to multiple IP addresses, each of which may have different performance and connectivity characteristics. Since specific addresses or address families (IPv4 or IPv6) may be blocked, broken, or sub-optimal on a network, clients that attempt multiple connections in parallel have a chance of establishing a connection more quickly. This document specifies requirements for algorithms that reduce this user-visible delay and provides an example algorithm, referred to as "Happy Eyeballs". This document obsoletes the original algorithm description in RFC 6555. The User Datagram Protocol (UDP) provides a minimal message-passing transport that has no inherent congestion control mechanisms. This document provides guidelines on the use of UDP for the designers of applications, tunnels, and other protocols that use UDP. Congestion control guidelines are a primary focus, but the document also provides guidance on other topics, including message sizes, reliability, checksums, middlebox traversal, the use of Explicit Congestion Notification (ECN), Differentiated Services Code Points (DSCPs), and ports. Because congestion control is critical to the stable operation of the Internet, applications and other protocols that choose to use UDP as an Internet transport must employ mechanisms to prevent congestion collapse and to establish some degree of fairness with concurrent traffic. They may also need to implement additional mechanisms, depending on how they use UDP. Some guidance is also applicable to the design of other protocols (e.g., protocols layered directly on IP or via IP-based tunnels), especially when these protocols do not themselves provide congestion control. This document obsoletes RFC 5405 and adds guidelines for multicast UDP usage. This document specifies Datagram Packetization Layer Path MTU Discovery (DPLPMTUD). This is a robust method for Path MTU Discovery (PMTUD) for datagram Packetization Layers (PLs). It allows a PL, or a datagram application that uses a PL, to discover whether a network path can support the current size of datagram. This can be used to detect and reduce the message size when a sender encounters a packet black hole. It can also probe a network path to discover whether the maximum packet size can be increased. This provides functionality for datagram transports that is equivalent to the PLPMTUD specification for TCP, specified in RFC 4821, which it updates. It also updates the UDP Usage Guidelines to refer to this method for use with UDP datagrams and updates SCTP. The document provides implementation notes for incorporating Datagram PMTUD into IETF datagram transports or applications that use datagram transports. This specification updates RFC 4960, RFC 4821, RFC 6951, RFC 8085, and RFC 8261. This document redefines how the explicit congestion notification (ECN) field of the IP header should be constructed on entry to and exit from any IP-in-IP tunnel. On encapsulation, it updates RFC 3168 to bring all IP-in-IP tunnels (v4 or v6) into line with RFC 4301 IPsec ECN processing. On decapsulation, it updates both RFC 3168 and RFC 4301 to add new behaviours for previously unused combinations of inner and outer headers. The new rules ensure the ECN field is correctly propagated across a tunnel whether it is used to signal one or two severity levels of congestion; whereas before, only one severity level was supported. Tunnel endpoints can be updated in any order without affecting pre-existing uses of the ECN field, thus ensuring backward compatibility. Nonetheless, operators wanting to support two severity levels (e.g., for pre-congestion notification -- PCN) can require compliance with this new specification. A thorough analysis of the reasoning for these changes and the implications is included. In the unlikely event that the new rules do not meet a specific need, RFC 4774 gives guidance on designing alternate ECN semantics, and this document extends that to include tunnelling issues. [STANDARDS-TRACK] A number of security concerns with IP tunnels are documented in this memo. The intended audience of this document includes network administrators and future protocol developers. The primary intent of this document is to raise the awareness level regarding the security issues with IP tunnels as deployed and propose strategies for the mitigation of those issues. [STANDARDS-TRACK] The functionality provided by IPv6's Type 0 Routing Header can be exploited in order to achieve traffic amplification over a remote path for the purposes of generating denial-of-service traffic. This document updates the IPv6 specification to deprecate the use of IPv6 Type 0 Routing Headers, in light of this security concern. [STANDARDS-TRACK] Google LLC Google LLC Google LLC There is interest among MASQUE working group participants in designing a protocol that can proxy IP traffic over HTTP. This document describes the set of requirements for such a protocol. Discussion of this work is encouraged to happen on the MASQUE IETF mailing list masque@ietf.org or on the GitHub repository which contains the draft: https://github.com/ietf-wg-masque/draft-ietf- masque-ip-proxy-reqs.

Acknowledgments The design of this method was inspired by discussions in the MASQUE working group around . The authors would like to thank participants in those discussions for their feedback. Additionally, , , and provided valuable feedback on the document. Most of the text on client configuration is based on the corresponding text in .