| Internet-Draft | pcapng-extras | November 2024 |
| Tuexen, et al. | Expires 28 May 2025 | [Page] |
This document contains a number of extensions to the PCAPng file format which are outside of the IETF networking mandate.¶
This note is to be removed before publishing as an RFC.¶
Discussion of this document takes place on the OPSAWG Working Group mailing list (opsawg@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/opsawg/.¶
Source for this draft and an issue tracker can be found at https://github.com/IETF-OPSAWG-WG/draft-ietf-opsawg-pcap.¶
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Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The systemd Journal Export Block is a lightweight container for systemd Journal Export Format entry data.¶
One of the primary components of the systemd System and Service Manager is the "Journal", a message logging system that uses arrays of key-value pairs. Journal entries are stored in a database-like file on disk but can be serialized to easily parseable "Journal Export Format" data or to a JSON object. The block described here is limited to Journal Export Format data only.¶
A systemd Journal Export Block contains a single systemd Journal Export Format entry. Each entry MUST contain a __REALTIME_TIMESTAMP= field. If a timestamp for the block is required it can be derived from this field. Each entry MUST be zero-padded to 32 bits. Although the primary use of this block is intended for importing data from systemd, it could potentially be used to include arbitrary key-value data in a capture file.¶
Figure 1 shows the format of the Journal Export Block.¶
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 | Block Type = 0x00000009 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 / /
/ Journal Entry /
/ variable length, padded to 32 bits /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The systemd Journal Export Block has the following fields:¶
Block Type: The block type of the Journal Export Block is 9.¶
Block Total Length: total size of this block, as described in [I-D.tuexen-opsawg-pcapng], section "Section Blocks".¶
Journal Entry: A journal entry as described in the Journal Export Format documentation. Entries consist of a series of field names followed by text or binary field data. Common field names can be found in the systemd.journal-fields documentation. The __REALTIME_TIMESTAMP= field MUST be present and valid as described above. Entries are not guaranteed to be a multiple of four octets and must be zero-padded. This allows the length of the entry to be determined by finding the last non-zero octet in the Journal Entry data. An entry may contain an entry separator (trailing newline) as described in the Journal Export Format specification¶
Can some other packet blocks (besides the ones described in the previous paragraphs) be useful?¶
The Compression Block is optional. A file can contain an arbitrary number of these blocks. A Compression Block, as the name says, is used to store compressed data. Its format is shown in Figure 2.¶
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 | Block Type = ? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Compr. Type | /
+-+-+-+-+-+-+-+-+ /
/ /
/ Compressed Data /
/ /
/ variable length, octet-aligned and padded to end on a 32-bit /
/ boundary /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields have the following meaning:¶
Block Type: The block type of the Compression Block is not yet assigned.¶
Block Total Length: total size of this block, as described in [I-D.tuexen-opsawg-pcapng], section "Section Blocks".¶
Compression Type (8 bits): an unsigned value that specifies the compression algorithm. Possible values for this field are 0 (uncompressed), 1 (Lempel-Ziv), 2 (Gzip), other?? Probably some kind of dumb and fast compression algorithm could be effective with some types of traffic (for example web), but which?¶
Compressed Data: data of this block. Once decompressed, it is made of other blocks.¶
The Encryption Block is optional. A file can contain an arbitrary number of these blocks. An Encryption Block is used to store encrypted data. Its format is shown in Figure 3.¶
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 | Block Type = ? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Encr. Type | /
+-+-+-+-+-+-+-+-+ /
/ /
/ Encrypted Data /
/ /
/ variable length, octet-aligned /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields have the following meaning:¶
Block Type: The block type of the Encryption Block is not yet assigned.¶
Block Total Length: total size of this block, as described in [I-D.tuexen-opsawg-pcapng], section "Section Blocks".¶
Encryption Type (8 bits): an unsigned value that specifies the encryption algorithm. Possible values for this field are ??? (TODO) NOTE: this block should probably contain other fields, depending on the encryption algorithm. To be defined precisely.¶
Encrypted Data: data of this block. Once decrypted, it originates other blocks.¶
The Fixed Length Block is optional. A file can contain an arbitrary number of these blocks. A Fixed Length Block can be used to optimize the access to the file. Its format is shown in Figure 4. A Fixed Length Block stores records with constant size. It contains a set of Blocks (normally Enhanced Packet Blocks or Simple Packet Blocks), of which it specifies the size. Knowing this size a priori helps to scan the file and to load some portions of it without truncating a block, and is particularly useful with cell-based networks like ATM.¶
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 | Block Type = ? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Cell Size | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
/ /
/ Fixed Size Data /
/ /
/ variable length, octet-aligned /
/ /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Block Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields have the following meaning:¶
Block Type: The block type of the Fixed Length Block is not yet assigned.¶
Block Total Length: total size of this block, as described in [I-D.tuexen-opsawg-pcapng], section "Section Blocks".¶
Cell size (16 bits): an unsigned value that indicates the size of the blocks contained in the data field.¶
Fixed Size Data: data of this block.¶
If present, this block contains the following information:¶
A directory block MUST be followed by at least N packets, otherwise it MUST be considered invalid. It can be used to efficiently load portions of the file to memory and to support operations on memory mapped files. This block can be added by tools like network analyzers as a consequence of file processing.¶
One or more blocks could be defined to contain network statistics or traffic monitoring information. They could be use to store data collected from RMON or Netflow probes, or from other network monitoring tools.¶
This block could be used to store events. Events could contain generic information (for example network load over 50%, server down...) or security alerts. An event could be:¶
skipped, if the application doesn't know how to do with it¶
processed independently by the packets. In other words, the applications skips the packets and processes only the alerts¶
processed in relation to packets: for example, a security tool could load only the packets of the file that are near a security alert; a monitoring tool could skip the packets captured while the server was down.¶
TBD.¶
[Open issue: decide whether the block types, option types, NRB Record types, etc. should be IANA registries. And if so, what the IANA policy for each should be (see RFC 5226)]¶
Loris Degioanni and Gianluca Varenni were coauthoring this document before it was submitted to the IETF.¶
The authors wish to thank Anders Broman, Ulf Lamping, Richard Sharpe and many others for their invaluable comments.¶