[virtio-dev] Re: [virtio-comment] [PATCH v12] virtio-net: support inner header hash

[Heng Qi <hengqi@linux.alibaba.com>]

Hi, all.

Do you have any comments on this release?

Thanks.


在 2023/4/3 下午12:58, Heng Qi 写道:
> 1. Currently, a received encapsulated packet has an outer and an inner header, but
> the virtio device is unable to calculate the hash for the inner header. The same
> flow can traverse through different tunnels, resulting in the encapsulated
> packets being spread across multiple receive queues (refer to the figure below).
> However, in certain scenarios, we may need to direct these encapsulated packets of
> the same flow to a single receive queue. This facilitates the processing
> of the flow by the same CPU to improve performance (warm caches, less locking, etc.).
>
>                 client1                    client2
>                    |        +-------+         |
>                    +------->|tunnels|<--------+
>                             +-------+
>                                |  |
>                                v  v
>                        +-----------------+
>                        | monitoring host |
>                        +-----------------+
>
> To achieve this, the device can calculate a suitable hash based on the inner headers
> of this flow, for example using the Toeplitz combined with a symmetric hash key.
>
> 2. For legacy systems, they may lack entropy fields which modern protocols have in
> the outer header, resulting in multiple flows with the same outer header but
> different inner headers being directed to the same receive queue. This results in
> poor receive performance.
>
> To address this limitation, inner header hash can be used to enable the device to advertise
> the capability to calculate the hash for the inner packet, regaining better receive performance.
>
> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
> v11->v12:
> 	1. Add a command VIRTIO_NET_CTRL_MQ_TUNNEL_CONFIG.
> 	2. Refine the commit log. @Michael S . Tsirkin
> 	3. Add some tunnel types.
>
> v10->v11:
> 	1. Revise commit log for clarity for readers.
> 	2. Some modifications to avoid undefined terms. @Parav Pandit
> 	3. Change VIRTIO_NET_F_HASH_TUNNEL dependency. @Parav Pandit
> 	4. Add the normative statements. @Parav Pandit
>
> v9->v10:
> 	1. Removed hash_report_tunnel related information. @Parav Pandit
> 	2. Re-describe the limitations of QoS for tunneling.
> 	3. Some clarification.
>
> v8->v9:
> 	1. Merge hash_report_tunnel_types into hash_report. @Parav Pandit
> 	2. Add tunnel security section. @Michael S . Tsirkin
> 	3. Add VIRTIO_NET_F_HASH_REPORT_TUNNEL.
> 	4. Fix some typos.
> 	5. Add more tunnel types. @Michael S . Tsirkin
>
> v7->v8:
> 	1. Add supported_hash_tunnel_types. @Jason Wang, @Parav Pandit
> 	2. Change hash_report_tunnel to hash_report_tunnel_types. @Parav Pandit
> 	3. Removed re-definition for inner packet hashing. @Parav Pandit
> 	4. Fix some typos. @Michael S . Tsirkin
> 	5. Clarify some sentences. @Michael S . Tsirkin
>
> v6->v7:
> 	1. Modify the wording of some sentences for clarity. @Michael S. Tsirkin
> 	2. Fix some syntax issues. @Michael S. Tsirkin
>
> v5->v6:
> 	1. Fix some syntax and capitalization issues. @Michael S. Tsirkin
> 	2. Use encapsulated/encaptulation uniformly. @Michael S. Tsirkin
> 	3. Move the links to introduction section. @Michael S. Tsirkin
> 	4. Clarify some sentences. @Michael S. Tsirkin
>
> v4->v5:
> 	1. Clarify some paragraphs. @Cornelia Huck
> 	2. Fix the u8 type. @Cornelia Huck
>
> v3->v4:
> 	1. Rename VIRTIO_NET_F_HASH_GRE_VXLAN_GENEVE_INNER to VIRTIO_NET_F_HASH_TUNNEL. @Jason Wang
> 	2. Make things clearer. @Jason Wang @Michael S. Tsirkin
> 	3. Keep the possibility to use inner hash for automatic receive steering. @Jason Wang
> 	4. Add the "Tunnel packet" paragraph to avoid repeating the GRE etc. many times. @Michael S. Tsirkin
>
> v2->v3:
> 	1. Add a feature bit for GRE/VXLAN/GENEVE inner hash. @Jason Wang
> 	2. Chang \field{hash_tunnel} to \field{hash_report_tunnel}. @Jason Wang, @Michael S. Tsirkin
>
> v1->v2:
> 	1. Remove the patch for the bitmask fix. @Michael S. Tsirkin
> 	2. Clarify some paragraphs. @Jason Wang
> 	3. Add \field{hash_tunnel} and VIRTIO_NET_HASH_REPORT_GRE. @Yuri Benditovich
>
>   device-types/net/description.tex        | 143 ++++++++++++++++++++++++
>   device-types/net/device-conformance.tex |   1 +
>   device-types/net/driver-conformance.tex |   1 +
>   introduction.tex                        |  44 ++++++++
>   4 files changed, 189 insertions(+)
>
> diff --git a/device-types/net/description.tex b/device-types/net/description.tex
> index 0500bb6..121585e 100644
> --- a/device-types/net/description.tex
> +++ b/device-types/net/description.tex
> @@ -83,6 +83,9 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
>   \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
>       channel.
>   
> +\item[VIRTIO_NET_F_HASH_TUNNEL(52)] Device supports inner header hash
> +    for tunnel-encapsulated packets.
> +
>   \item[VIRTIO_NET_F_NOTF_COAL(53)] Device supports notifications coalescing.
>   
>   \item[VIRTIO_NET_F_GUEST_USO4 (54)] Driver can receive USOv4 packets.
> @@ -139,6 +142,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
>   \item[VIRTIO_NET_F_NOTF_COAL] Requires VIRTIO_NET_F_CTRL_VQ.
>   \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
>   \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
> +\item[VIRTIO_NET_F_HASH_TUNNEL] Requires VIRTIO_NET_F_CTRL_VQ along with VIRTIO_NET_F_RSS and/or VIRTIO_NET_F_HASH_REPORT.
>   \end{description}
>   
>   \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
> @@ -198,6 +202,7 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device
>           u8 rss_max_key_size;
>           le16 rss_max_indirection_table_length;
>           le32 supported_hash_types;
> +        le32 supported_tunnel_hash_types;
>   };
>   \end{lstlisting}
>   The following field, \field{rss_max_key_size} only exists if VIRTIO_NET_F_RSS or VIRTIO_NET_F_HASH_REPORT is set.
> @@ -212,6 +217,12 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device
>   Field \field{supported_hash_types} contains the bitmask of supported hash types.
>   See \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash types} for details of supported hash types.
>   
> +Field \field{supported_tunnel_hash_types} only exists if the device
> +supports inner header hash, i.e. if VIRTIO_NET_F_HASH_TUNNEL is set.
> +
> +Filed \field{supported_tunnel_hash_types} contains the bitmask of supported tunnel hash types.
> +See \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled encapsulation hash types} for details of supported tunnel hash types.
> +
>   \devicenormative{\subsubsection}{Device configuration layout}{Device Types / Network Device / Device configuration layout}
>   
>   The device MUST set \field{max_virtqueue_pairs} to between 1 and 0x8000 inclusive,
> @@ -848,6 +859,7 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
>   If the feature VIRTIO_NET_F_RSS was negotiated:
>   \begin{itemize}
>   \item The device uses \field{hash_types} of the virtio_net_rss_config structure as 'Enabled hash types' bitmask.
> +\item The device uses \field{hash_tunnel_types} of the virtio_net_hash_tunnel_config structure as 'Enabled hash tunnel types' bitmask if VIRTIO_NET_F_HASH_TUNNEL was negotiated.
>   \item The device uses a key as defined in \field{hash_key_data} and \field{hash_key_length} of the virtio_net_rss_config structure (see
>   \ref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) / Setting RSS parameters}).
>   \end{itemize}
> @@ -855,6 +867,7 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
>   If the feature VIRTIO_NET_F_RSS was not negotiated:
>   \begin{itemize}
>   \item The device uses \field{hash_types} of the virtio_net_hash_config structure as 'Enabled hash types' bitmask.
> +\item The device uses \field{hash_tunnel_types} of the virtio_net_hash_tunnel_config structure as 'Enabled hash tunnel types' bitmask if VIRTIO_NET_F_HASH_TUNNEL was negotiated.
>   \item The device uses a key as defined in \field{hash_key_data} and \field{hash_key_length} of the virtio_net_hash_config structure (see
>   \ref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode / Hash calculation}).
>   \end{itemize}
> @@ -870,6 +883,8 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
>   
>   \subparagraph{Supported/enabled hash types}
>   \label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash types}
> +This paragraph relies on definitions from \hyperref[intro:IP]{[IP]},
> +\hyperref[intro:UDP]{[UDP]} and \hyperref[intro:TCP]{[TCP]}.
>   Hash types applicable for IPv4 packets:
>   \begin{lstlisting}
>   #define VIRTIO_NET_HASH_TYPE_IPv4              (1 << 0)
> @@ -980,6 +995,133 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
>   (see \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / IPv6 packets without extension header}).
>   \end{itemize}
>   
> +\paragraph{Inner Header Hash}
> +\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Inner Header Hash}
> +
> +If VIRTIO_NET_F_HASH_TUNNEL has been negotiated, the device supports inner header hash and
> +the driver can configure the inner header hash calculation for encapsulated packets \ref{sec:Device Types / Network Device / Device OperatiHn / Processing of Incoming Packets / Hash calculation for incoming packets / Tunnel/Encapsulated packet}
> +by issuing the command VIRTIO_NET_CTRL_MQ_TUNNEL_CONFIG from the class VIRTIO_NET_CTRL_MQ.
> +The command sets \field{hash_tunnel_types} in the structure virtio_net_hash_tunnel_config.
> +
> +struct virtio_net_hash_tunnel_config {
> +    le32 hash_tunnel_types;
> +};
> +
> +Filed \field{hash_tunnel_types} contains a bitmask of supported hash tunnel types as
> +defined in \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash tunnel types}.
> +
> +\subparagraph{Tunnel/Encapsulated packet}
> +\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Tunnel/Encapsulated packet}
> +
> +A tunnel packet is encapsulated from the original packet based on the tunneling
> +protocol (only a single level of encapsulation is currently supported). The
> +encapsulated packet contains an outer header and an inner header, and the device
> +calculates the hash over either the inner header or the outer header.
> +
> +If VIRTIO_NET_F_HASH_TUNNEL is negotiated and a received encapsulated packet's
> +outer header matches one of the supported \field{hash_tunnel_types}, the hash
> +of the inner header is calculated.
> +
> +Supported encapsulated packet types:
> +\begin{itemize}
> +\item \hyperref[intro:gre_rfc2784]{[GRE_rfc2784]}
> +\item \hyperref[intro:gre_rfc2890]{[GRE_rfc2890]}
> +\item \hyperref[intro:gre_rfc7676]{[GRE_rfc7676]}
> +\item \hyperref[intro:gre_in_udp_rfc8086]{[GRE-in-UDP]}
> +\item \hyperref[intro:vxlan]{[VXLAN]}
> +\item \hyperref[intro:vxlan_gpe]{[VXLAN-GPE]}
> +\item \hyperref[intro:geneve]{[GENEVE]}
> +\item \hyperref[intro:ipip]{[IPIP]}
> +\item \hyperref[intro:nvgre]{[NVGRE]}
> +\item \hyperref[intro:sit]{[STT]}
> +\end{itemize}
> +
> +If VIRTIO_NET_HASH_TUNNEL_TYPE_NONE is set or the encapsulation type is not included in
> +\field{hash_tunnel_types}, the hash of the outer header is calculated for the received encapsulated packet.
> +
> +The hash is calculated for the received non-encapsulated packet as if VIRTIO_NET_F_HASH_TUNNEL was not negotiated.
> +
> +\subparagraph{Supported/enabled encapsulation hash types}
> +\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled encapsulation hash types}
> +
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_NONE        (1 << 0)
> +\end{lstlisting}
> +
> +Supported encapsulation hash types:
> +Hash type applicable for inner payload of the \hyperref[intro:gre_rfc2784]{[GRE_rfc2784]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_2784    (1 << 1)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:gre_rfc2890]{[GRE_rfc2890]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_2890    (1 << 2)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:gre_rfc7676]{[GRE_rfc7676]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_7676    (1 << 3)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:gre_in_udp_rfc8086]{[GRE-in-UDP]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_UDP     (1 << 4)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:vxlan]{[VXLAN]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_VXLAN       (1 << 5)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:vxlan_gpe]{[VXLAN-GPE]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_VXLAN_GPE   (1 << 6)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:geneve]{[GENEVE]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_GENEVE      (1 << 7)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:ipip]{[IPIP]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_IPIP        (1 << 8)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:nvgre]{[NVGRE]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_NVGRE       (1 << 9)
> +\end{lstlisting}
> +Hash type applicable for inner payload of the \hyperref[intro:stt]{[STT]} packet:
> +\begin{lstlisting}
> +#define VIRTIO_NET_HASH_TUNNEL_TYPE_STT         (1 << 10)
> +\end{lstlisting}
> +
> +\subparagraph{Tunnel QoS limitation}
> +When a specific receive queue is shared by multiple tunnels to receive encapsulated packets,
> +there is no quality of service (QoS) for these packets. For example, when the packets of certain
> +tunnels are spread across multiple receive queues, these receive queues may have an unbalanced
> +amount of packets. This can cause a specific receive queue to become full, resulting in packet loss.
> +
> +Possible mitigations:
> +\begin{itemize}
> +\item Use a tool with good forwarding performance to keep the receive queue from filling up.
> +\item If the QoS is unavailable, the driver can set \field{hash_tunnel_types} to VIRTIO_NET_HASH_TUNNEL_TYPE_NONE
> +      to disable inner header hash for encapsulated packets.
> +\item Choose a hash key that can avoid queue collisions.
> +\item Perform appropriate QoS before packets consume the receive buffers of the receive queues.
> +\end{itemize}
> +
> +The limitations mentioned above exist with/without the inner header hash.
> +
> +\devicenormative{\subparagraph}{Inner Header Hash}{Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
> +
> +The device MUST calculate the outer header hash if the received encapsulated packet has an encapsulation type not in \field{supported_tunnel_hash_types}.
> +
> +The device MUST respond to the VIRTIO_NET_CTRL_MQ_TUNNEL_CONFIG command with VIRTIO_NET_ERR if the device
> +received an unrecognized or unsupported VIRTIO_NET_HASH_TUNNEL_TYPE_ flag.
> +
> +Upon reset, the device MUST initialize \field{hash_tunnel_type} to 0.
> +
> +\drivernormative{\subparagraph}{Inner Header Hash}{Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
> +
> +The driver MUST have negotiated the feature VIRTIO_NET_F_HASH_TUNNEL when issuing the command VIRTIO_NET_CTRL_MQ_TUNNEL_CONFIG.
> +
> +The driver MUST NOT set any VIRTIO_NET_HASH_TUNNEL_TYPE_ flags that are not supported by the device.
> +
>   \paragraph{Hash reporting for incoming packets}
>   \label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash reporting for incoming packets}
>   
> @@ -1308,6 +1450,7 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
>    #define VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET        0 (for automatic receive steering)
>    #define VIRTIO_NET_CTRL_MQ_RSS_CONFIG          1 (for configurable receive steering)
>    #define VIRTIO_NET_CTRL_MQ_HASH_CONFIG         2 (for configurable hash calculation)
> + #define VIRTIO_NET_CTRL_MQ_TUNNEL_CONFIG       3 (for configurable inner header hash)
>   \end{lstlisting}
>   
>   If more than one multiqueue mode is negotiated, the resulting device configuration is defined by the last command sent by the driver.
> diff --git a/device-types/net/device-conformance.tex b/device-types/net/device-conformance.tex
> index 54f6783..f88f48b 100644
> --- a/device-types/net/device-conformance.tex
> +++ b/device-types/net/device-conformance.tex
> @@ -14,4 +14,5 @@
>   \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode}
>   \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) / RSS processing}
>   \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing}
> +\item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
>   \end{itemize}
> diff --git a/device-types/net/driver-conformance.tex b/device-types/net/driver-conformance.tex
> index 97d0cc1..9d853d9 100644
> --- a/device-types/net/driver-conformance.tex
> +++ b/device-types/net/driver-conformance.tex
> @@ -14,4 +14,5 @@
>   \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Offloads State Configuration / Setting Offloads State}
>   \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) }
>   \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing}
> +\item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
>   \end{itemize}
> diff --git a/introduction.tex b/introduction.tex
> index 287c5fc..36b620f 100644
> --- a/introduction.tex
> +++ b/introduction.tex
> @@ -99,6 +99,50 @@ \section{Normative References}\label{sec:Normative References}
>       Standards for Efficient Cryptography Group(SECG), ``SEC1: Elliptic Cureve Cryptography'', Version 1.0, September 2000.
>   	\newline\url{https://www.secg.org/sec1-v2.pdf}\\
>   
> +	\phantomsection\label{intro:gre_rfc2784}\textbf{[GRE_rfc2784]} &
> +    Generic Routing Encapsulation. This protocol is only specified for IPv4 and used as either the payload or delivery protocol.
> +	\newline\url{https://datatracker.ietf.org/doc/rfc2784/}\\
> +	\phantomsection\label{intro:gre_rfc2890}\textbf{[GRE_rfc2890]} &
> +    Key and Sequence Number Extensions to GRE \ref{intro:gre_rfc2784}. This protocol describes extensions by which two fields, Key and
> +    Sequence Number, can be optionally carried in the GRE Header \ref{intro:gre_rfc2784}.
> +	\newline\url{https://www.rfc-editor.org/rfc/rfc2890}\\
> +	\phantomsection\label{intro:gre_rfc7676}\textbf{[GRE_rfc7676]} &
> +    IPv6 Support for Generic Routing Encapsulation (GRE). This protocol is specified for IPv6 and used as either the payload or
> +    delivery protocol. Note that this does not change the GRE header format or any behaviors specified by RFC 2784 or RFC 2890.
> +	\newline\url{https://datatracker.ietf.org/doc/rfc7676/}\\
> +	\phantomsection\label{intro:gre_in_udp_rfc8086}\textbf{[GRE-in-UDP]} &
> +    GRE-in-UDP Encapsulation. This specifies a method of encapsulating network protocol packets within GRE and UDP headers.
> +    This GRE-in-UDP encapsulation allows the UDP source port field to be used as an entropy field. This protocol is specified for IPv4 and IPv6,
> +    and used as either the payload or delivery protocol.
> +	\newline\url{https://www.rfc-editor.org/rfc/rfc8086}\\
> +	\phantomsection\label{intro:vxlan}\textbf{[VXLAN]} &
> +    Virtual eXtensible Local Area Network.
> +	\newline\url{https://datatracker.ietf.org/doc/rfc7348/}\\
> +	\phantomsection\label{intro:vxlan-gpe}\textbf{[VXLAN-GPE]} &
> +    Generic Protocol Extension for VXLAN. This protocol describes extending Virtual eXtensible Local Area Network (VXLAN) via changes to the VXLAN header.
> +	\newline\url{https://www.ietf.org/archive/id/draft-ietf-nvo3-vxlan-gpe-12.txt}\\
> +	\phantomsection\label{intro:geneve}\textbf{[GENEVE]} &
> +    Generic Network Virtualization Encapsulation.
> +	\newline\url{https://datatracker.ietf.org/doc/rfc8926/}\\
> +	\phantomsection\label{intro:ipip}\textbf{[IPIP]} &
> +    IP Encapsulation within IP.
> +	\newline\url{https://www.rfc-editor.org/rfc/rfc2003}\\
> +	\phantomsection\label{intro:nvgre}\textbf{[NVGRE]} &
> +    NVGRE: Network Virtualization Using Generic Routing Encapsulation
> +	\newline\url{https://www.rfc-editor.org/rfc/rfc7637.html}\\
> +	\phantomsection\label{intro:stt}\textbf{[STT]} &
> +    Stateless Transport Tunneling. STT is particularly useful when some tunnel endpoints are in end-systems, as it utilizes the capabilities
> +    of the network interface card to improve performance.
> +	\newline\url{https://www.ietf.org/archive/id/draft-davie-stt-08.txt}\\
> +	\phantomsection\label{intro:IP}\textbf{[IP]} &
> +    INTERNET PROTOCOL
> +	\newline\url{https://www.rfc-editor.org/rfc/rfc791}\\
> +	\phantomsection\label{intro:UDP}\textbf{[UDP]} &
> +    User Datagram Protocol
> +	\newline\url{https://www.rfc-editor.org/rfc/rfc768}\\
> +	\phantomsection\label{intro:TCP}\textbf{[TCP]} &
> +    TRANSMISSION CONTROL PROTOCOL
> +	\newline\url{https://www.rfc-editor.org/rfc/rfc793}\\
>   \end{longtable}
>   
>   \section{Non-Normative References}


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