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Subject: Re: [virtio-dev] Re: [PATCH v11] virtio-net: support inner header hash



å 2023/3/21 äå3:43, Michael S. Tsirkin åé:

On Mon, Mar 20, 2023 at 07:18:40PM +0800, Heng Qi wrote:

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. Multiple
flows with the same outer header but different inner headers are steered to the
same receive queue. This results in poor receive performance.

To address this limitation, a new feature VIRTIO_NET_F_HASH_TUNNEL has been
introduced, which enables the device to advertise the capability to calculate the
hash for the inner packet header. Compared with the out header hash, it regains
better receive performance.

So this would be a very good argument however the cost would be it would
seem we have to keep extending this indefinitely as new tunneling
protocols come to light.
But I believe in fact we don't at least for this argument:
the standard way to address this is actually by propagating entropy
from inner to outer header.


Yes, we don't argue with this.



So I'd maybe reorder the commit log and give the explanation 2 below
then say "for some legacy systems
including entropy in IP header
as done in modern protocols is not practical, resulting in
bad performance under RSS".
I agree. But not necessarily the legacy system, some scenarios need to connect multiple tunnels, for compatibility, they will not use optional fields or choose the old tunnel protocol. 





2. 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, it becomes necessary 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
                       +-----------------+
                       | processing host |
                       +-----------------+

necessary is too strong a word I feel.
All this is, is an optimization, we don't really know how strong it is
even.

Here's how I understand this:

Imagine two clients client1 and client2 talking to each other.
A copy of all packets is sent to a processing host over a virtio device.
Two directions of the same flow between two clients might be
encapsulated in two different tunnels, with current RSS
strategies they would land on two arbitrary, unrelated queues.
As an optimization, some hosts might wish to make sure both directions
of the encapsulated flow land on the same queue.


Is this a good summary?


I think yes.




Now that things begin to be clearer, I kind of begin to agree with
Jason's suggestion that this is extremely narrow.  And what if I want
one direction on queue1 and another one queue2 e.g. adjacent numbers for


I don't understand why we need this, can you point out some usage scenarios?


the same flow?  If enough people agree this is needed we can accept this
but did you at all consider using something programmable like BPF for
I think the problem is that our virtio device cannot support ebpf, we can also ask Alvaro, Parav if their virtio devices can support ebpf offloading. :) 


this?  Considering we are putting not insignificant amount of work into
this, making this widely useful would be better than a narrow
optimization for a very specific usecase.



To achieve this, the device can calculate a symmetric hash based on the inner packet
headers of the flow. The symmetric hash disregards the order of the 5-tuple when
computing the hash.

when you say symmetric hash you really mean symmetric key for toeplitz, yes?
It's not that it disregards order, it just gives the same result if
you reverse source and destination, no?
Yes, symmetric hashes can use the key with 2 same bytes repeated, and only support reverse source and destination. 





Reviewed-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
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        | 119 +++++++++++++++++++++++-
  device-types/net/device-conformance.tex |   1 +
  device-types/net/driver-conformance.tex |   1 +
  introduction.tex                        |  24 +++++
  4 files changed, 144 insertions(+), 1 deletion(-)

diff --git a/device-types/net/description.tex b/device-types/net/description.tex
index 0500bb6..49dee2f 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 packet 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.
+The next field, \field{supported_tunnel_hash_types} only exists if the device 
+supports inner packet header hash, i.e. if VIRTIO_NET_F_HASH_TUNNEL is set.
+
+Field \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 tunnel 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_rss_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_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 +995,99 @@ \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 Packet Header Hash} 
+If the driver negotiates the VIRTIO_NET_F_HASH_TUNNEL feature, it can configure the
+hash parameters (including \field{hash_tunnel_types}) for inner packet header hash
+through the VIRTIO_NET_CTRL_MQ_HASH_CONFIG or the VIRTIO_NET_CTRL_RSS_CONFIG command.
+If multiple commands are sent, the device configuration will be defined by the last command received.
+
+If a specific encapsulation type is set in \field{hash_tunnel_types}, the device will calculate the
+hash on the inner packet header of the encapsulated packet (See \ref{sec:Device Types
+/ Network Device / Device OperatiHn / Processing of Incoming Packets /
+Hash calculation for incoming packets / Tunnel/Encapsulated packet}). If the encapsulation
+type is not included in \field{hash_tunnel_types} or the value of \field{hash_tunnel_types}
+is VIRTIO_NET_HASH_TUNNEL_TYPE_NONE, the device calculates the hash on the outer header.
+
+\field{hash_tunnel_types} is set to VIRTIO_NET_HASH_TUNNEL_TYPE_NONE by the device for non-encapsulated packets.
+
+\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.
+
+When the feature 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 encapsulation types are listed
+in \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming
+Packets / Hash calculation for incoming packets / Supported/enabled hash tunnel types}.
+
+Some encapsulated packet types: \hyperref[intro:GRE]{[GRE]}, \hyperref[intro:VXLAN]{[VXLAN]},
+\hyperref[intro:GENEVE]{[GENEVE]}, \hyperref[intro:IPIP]{[IPIP]} and \hyperref[intro:NVGRE]{[NVGRE]}.
+
+\subparagraph{Supported/enabled tunnel hash types}
+\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled tunnel hash types}
+If the feature VIRTIO_NET_F_HASH_TUNNEL is negotiated and \field{hash_tunnel_types}
+is set to VIRTIO_NET_HASH_TUNNEL_TYPE_NONE, the device calculates the hash using the
+outer header of the encapsulated packet.
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_NONE        (1 << 0)
+\end{lstlisting}
+
+The encapsulation hash type below indicates that the hash is calculated over the
+inner packet header:
+Hash type applicable for inner payload of the gre-encapsulated packet
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE         (1 << 1)
+\end{lstlisting}
+Hash type applicable for inner payload of the vxlan-encapsulated packet
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_VXLAN       (1 << 2)
+\end{lstlisting}
+Hash type applicable for inner payload of the geneve-encapsulated packet
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_GENEVE      (1 << 3)
+\end{lstlisting}
+Hash type applicable for inner payload of the ip-encapsulated packet
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_IPIP        (1 << 4)
+\end{lstlisting}
+Hash type applicable for inner payload of the nvgre-encapsulated packet
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_NVGRE       (1 << 5)
+\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 packet 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 packer header hash.
+
+\devicenormative{\subparagraph}{Inner Packet Header Hash}{Device Types / Network Device / Device Operation / Control Virtqueue / Inner Packet Header Hash}
+
+The device MUST calculate the outer packet hash if the received encapsulated packet has an encapsulation type not in \field{supported_tunnel_hash_types}.
+
+The device MUST drop the encapsulated packet if the destination receive queue is being reset.

I'm not sure how this last one got here. It seems to have nothing to do
with encapsulation - if we want to we should require this for all
packets or none at all.


Yes, you are right. It works for all packets.





+\drivernormative{\subparagraph}{Inner Packet Header Hash}{Device Types / Network Device / Device Operation / Control Virtqueue / Inner Packet Header Hash}
+
+If the driver does not negotiate the VIRTIO_NET_F_HASH_TUNNEL feature, it MUST set \field{hash_tunnel_types}
+to VIRTIO_NET_HASH_TUNNEL_TYPE_NONE before issuing the command VIRTIO_NET_CTRL_MQ_HASH_CONFIG or VIRTIO_NET_CTRL_RSS_CONFIG.
+
+The driver MUST set \field{hash_tunnel_types} to the encapsulation types supported by the device.

unclear. seems to mean all types must be approved
where you really mean "only those types". original for non tunnel is:

A driver MUST NOT set any VIRTIO_NET_HASH_TYPE_ flags that are not supported by a device.

which is clear though a bit verbose with two negations.


Yes, we can use the same sentence structure to illustrate.



Also here it says "supported" but below it says "allowed".




  \paragraph{Hash reporting for incoming packets}
  \label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash reporting for incoming packets}
@@ -1392,12 +1500,17 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi 
      le16 reserved[4];
      u8 hash_key_length;
      u8 hash_key_data[hash_key_length];
+    le32 hash_tunnel_types;
  };

Hmm this fixed type after variable type is problematic - might
become unaligned. We could use some of reserved[4]
for this ...
This is a problem, and perhaps Parav's proposal of using a separate command and structure for inner hash is correct. 




  \end{lstlisting}
  Field \field{hash_types} contains a bitmask of allowed hash types as
  defined in
  \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash types}.
-Initially the device has all hash types disabled and reports only VIRTIO_NET_HASH_REPORT_NONE.
+
+Field \field{hash_tunnel_types} contains a bitmask of allowed 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}.
+
+Initially the device has all hash types and hash tunnel types disabled and reports only VIRTIO_NET_HASH_REPORT_NONE.
Field \field{reserved} MUST contain zeroes. It is defined to make the structure to match the layout of virtio_net_rss_config structure, 
  defined in \ref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS)}.
@@ -1421,6 +1534,7 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
      le16 max_tx_vq;
      u8 hash_key_length;
      u8 hash_key_data[hash_key_length];
+    le32 hash_tunnel_types;


Same alignment problem here but I'm not sure how to solve it.
Suggestions?


  };
  \end{lstlisting}
  Field \field{hash_types} contains a bitmask of allowed hash types as
@@ -1441,6 +1555,9 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
Fields \field{hash_key_length} and \field{hash_key_data} define the key to be used in hash calculation. +Field \field{hash_tunnel_types} contains a bitmask of allowed 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}.
+
  \drivernormative{\subparagraph}{Setting RSS parameters}{Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) }
A driver MUST NOT send the VIRTIO_NET_CTRL_MQ_RSS_CONFIG command if the feature VIRTIO_NET_F_RSS has not been negotiated. 
diff --git a/device-types/net/device-conformance.tex b/device-types/net/device-conformance.tex
index 54f6783..0ff5944 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 Packet Header Hash}
  \end{itemize}
diff --git a/device-types/net/driver-conformance.tex b/device-types/net/driver-conformance.tex
index 97d0cc1..951be89 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 Packet Header Hash}
  \end{itemize}
diff --git a/introduction.tex b/introduction.tex
index 287c5fc..25c9d48 100644
--- a/introduction.tex
+++ b/introduction.tex
@@ -99,6 +99,30 @@ \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}\textbf{[GRE]} & 
+    Generic Routing Encapsulation
+	\newline\url{https://datatracker.ietf.org/doc/rfc2784/}\\

This is GRE over IPv4.
So we are not supporting GRE over IPv6?


Yes. Do we need to add it?
https://datatracker.ietf.org/doc/rfc7676/



And we do not support optional keys?


We did not disallow optional fields.

Thanks.






+	\phantomsection\label{intro:VXLAN}\textbf{[VXLAN]} &
+    Virtual eXtensible Local Area Network
+	\newline\url{https://datatracker.ietf.org/doc/rfc7348/}\\
+	\phantomsection\label{intro:GENEVE}\textbf{[GENEVE]} &
+    Generic Network Virtualization Encapsulation
+	\phantomsection\label{intro:IPIP}\textbf{[IPIP]} &
+    IP Encapsulation within IP
+	\newline\url{https://www.rfc-editor.org/rfc/rfc2003}\\
+	\phantomsection\label{intro:IPIP}\textbf{[NVGRE]} &
+    NVGRE: Network Virtualization Using Generic Routing Encapsulation
+	\newline\url{https://www.rfc-editor.org/rfc/rfc7637.html}\\
+	\newline\url{https://datatracker.ietf.org/doc/rfc8926/}\\
+	\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} 
--
2.19.1.6.gb485710b


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