Flow Monitoring Version 5 Format Output Fields

date_range 13-Jan-21

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A detailed explanation of version 5 packet formats and fields is shown in the following figures and tables:

Figure 1
Table 1
Figure 2
Table 2

Figure 1: Version 5 Packet Header Format

Table 1: Export Version 5 Packet Header Fields
Field	Description	Comments
`Version`	5	–
Count	The number of records in the Protocol Data Unit (PDU) or packet	–
sysUptime	Current time elapsed, in milliseconds, since the router started	–
UNIX seconds	Current seconds since 0000 UTC 1970	NTP synchronized time; the clock on each services PIC is autonomous (200–400 msec jitter) across PICs in a chassis
UNIX nanoseconds	Residual nanoseconds since 0000 UTC 1970	See Comments above for UNIX seconds
Flow sequence number	Sequence number of total flows received	–
Engine type	User-configured 8-bit value	Also known as VIP type on other vendors’ equipment
Engine ID	User-configured 8-bit value	–

Figure 2: Version 5 Flow-Export Flow Header Format

Table 2: Export Version 5 Flow-Export Flow Header Fields
Field	Description	Comments
Source IP address	Source IP address of the flow	–
Destination IP address	Destination IP address of the flow	–
Next-hop IP address	IP address of the router where flows are forwarded	–
Input ifIndex	SNMP index value for the input interface where the router receives flows	Junos OS Release 5.7 and later—Dynamically inserted, but overridden by manual configuration Junos OS Release 5.5—Manually set Junos OS Release 5.4—Set to zero
Output ifIndex	SNMP index value for the output interface where the router forwards flows	Junos OS Release 5.7 and later—Dynamically inserted, but overridden by manual configuration Junos OS Release 5.5—Manually set Junos OS Release 5.4—Set to zero
Packets	Total number of packets received in a flow	–
Bytes	Total number of bytes received in a flow	–
Start time of flow	System up time, in seconds, at the start of the flow	System up time for the services PIC accepting flows
End time of flow	System up time, in seconds, at the end of the flow	System up time for the services PIC accepting flows
Source port	Source application port	–
Destination port	Destination application port	The ICMP type is placed in the high-order byte and the ICMP type code is placed in the low-order byte of this field
TCP flags	TCP flags set in the flow	–
IP protocol	IP protocol number	–
TOS	IP type of service	–
Source AS	AS number of the source address	Junos OS Release 5.7 and later—Dynamically inserted if AS information is available
Destination AS	AS number of the destination address	Junos OS Release 5.7 and later—Dynamically inserted if AS information is available
Source mask length	Source address network mask length	–
Dest. mask length	Destination address network mask length	–
Padding	Bytes available to ensure a minimum packet length	–

Useful formulas for flow monitoring are:

start flow timestamp absolute = unixTime x 1000 – (sysUptime – start flow timestamp)
end flow timestamp absolute = unixTime x 1000 – (sysUptime – end flow timestamp)

Note:
In the 2-byte destination port field of the export version 5 flow-export flow format, the following information can be derived:
High-order byte—ICMP type
Low-order byte—ICMP type code

For example, if the ICMP type is 3 (00000011 in binary) and the ICMP type code is network unreachable (Type Code 0, or 00000000 in binary), the resulting destination port field value is 00000011 00000000 (768 in decimal).

For more information on ICMP type and type code, see RFC 792 at http://www.ietf.org.

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Flow Monitoring Version 5 Format Output Fields

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