Internet DRAFT - draft-bennett-ippm-ipmp
draft-bennett-ippm-ipmp
IP Measurement Protocol March 2003
Internet Draft J. C. R. Bennett
Document: draft-bennett-ippm-ipmp-01.txt Harvard
Expires: September 2003 March 2003
IP Measurement Protocol (IPMP)
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026
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Abstract
The practice and need for active network measurement is well
established, however current tools are not well suited to this task,
mostly because the protocols which they employ have not been designed
for measurement of the modern Internet.
The IP Measurement Protocol (IPMP) is based on packet-probes, and is
designed to allow routers to participate in measurements by the
insertion of path information as the probe passes between a pair of
hosts.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119
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v
Table of Contents
1. Introduction...................................................2
1.1 IPMP Redirection..............................................4
2. Packet Formats.................................................4
2.1 IPMP Echo Request and Echo Reply..............................4
2.1.1 Echo Request Header.........................................4
2.1.2 IPMP Options................................................5
2.1.3 Header Fields...............................................6
2.1.4 Path Record formats.........................................7
2.1.5 Optional Data Section Formats..............................14
2.1.6 Defined Data Section Types.................................14
2.2 IPMP Information Request and Information Reply...............17
2.2.1 Information Request Header.................................17
2.2.2 Information Reply Header...................................18
3. IP Protocol Header Values.....................................22
4. Processing of IPMP packets....................................22
4.1.1 Measurement host processing................................22
4.2 Echoing System Processing....................................23
4.3 Forwarding System Processing.................................24
4.3.1 Path Record................................................24
5. Discussion....................................................24
5.1 Checksums....................................................24
5.1.1 Checksum update at a forwarding router.....................25
5.2 Timestamps...................................................25
5.2.1 NTP Timestamp format.......................................25
5.2.2 IPMP Timestamp Format......................................26
5.2.3 Inferred Real Time.........................................26
5.3 Minimum Implementations......................................27
5.3.1 Echoing System.............................................27
5.3.2 Forwarding System..........................................27
6. Security Considerations.......................................27
6.1 Denial of Service Attacks....................................28
7. References....................................................28
Acknowledgments..................................................29
Author's Addresses...............................................29
1. Introduction
The practice and need for active network measurement is well
established, however current tools are not well suited to this task,
mostly because the protocols which they employ have not been designed
for measurement of the modern Internet.
ICMP, for example, is widely used for measurement despite its well
known limitations for this task. These limitations include it being
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treated different to other IP protocols at routers and hosts. ICMP
has also received bad press from denial of service attacks and
because of the number of sites generating monitoring traffic. As a
consequence some ISPs disable ICMP even though this potentially
causes poor performance and does not comply with RFC1009 [1].
The protocol operates as an echo protocol allowing packet loss, path
length, route, RTT and in some cases, one-way delay measurements to
be taken. Packets are generated by a measurement host and returned
by an echoing router or host, known as an echoing system in this
memo. The translation of router time stamps to real time, time
stamps is supported through a separate information request and reply
exchange between the measurement system and systems that insert time
stamps into the echo request or reply.
Current packet probing techniques are not suited to measuring packet
delay at the router level. Routers often make bad measurement
targets because they are optimized for the relatively simple task of
forwarding packets. Routers may process tasks that are resource
intensive and therefore an opportunity for a denial of service attack
at low priority or not at all. Some measurement techniques construct
measurement traffic that can be difficult to efficiently detect and
respond to amongst other network traffic. This type of measurement
traffic precludes measuring to a router and makes the task of
identifying where delay occurs in the network difficult.
IPMP addresses these issues by providing a measurement protocol that
is tightly constrained, efficient and easy to implement. The protocol
has been designed so measurement packets can be processed with about
the same level of computation as IP packet forwarding. The protocol
is intended to allow for easy implementation in hardware/firmware so
as to provide for highly accurate measurements.
It should be noted that only the TTL and Timestamp fields in the Path
Records are dynamic, all the other fields are likely to be the same
for all the Path Records inserted at a particular stamping location.
As a result it will be possible to precompute and/or cache the static
portions of the Path Record as well as partial checksum update
computations.
The IPMP protocol has a number of options to allow it to measure a
number of different properties of the links and devices on a path
between two endpoints. It is intended that it should be practical to
process IPMP packets in the same forwarding path as normal(non-IPMP)
packets without any (significant) performance impact. To achieve this
it is anticipated that a device will pre-compute all but one or two
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of the components of the path record and insert some combination of
these components based on the options field of the packet.
The option fields of the IPMP request packet are defined with the
objective of allowing a forwarding device to determine what if any
path records should be inserted with the minimum amount of logic
complexity.
S
1.1 IPMP Redirection
To allow for measurement of paths that do not originate at the
measurement host IPMP there are hooks defined to allow the addition
of a redirection mode of operation.
2. Packet Formats
2.1 IPMP Echo Request and Echo Reply
2.1.1 Echo Request Header
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Faux Source Port | Faux Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPMP Options | Start TTL | Faux P-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version |Info Req Flags | Path Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet ID | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) Data Section |
: .... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) Path Record(s) |
: .... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding (if required) |
: .... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version = 0
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2.1.2 IPMP Options
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| P |R|F|T|D|A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P = Packet Type : 4 bits
Value Packet Type
0000 Echo Request
0001 Echo Reply
0010 Information Request
0011 Information Reply
0100- Reserved for Redirection Packet Types
0111
1000- Reserved for Future use
1111
R = Record Path Record : 1 bit
F = Fastpath ONLY Records Requested : 1 bit
T = Timestamps Requested : 1 bit
D = Data Section Present : 1 bit
A = turnAround Options : 1 bit
Record Path Record
If this field is 1 then a Path Record SHOULD be inserted by any
device that forwards this packet. If the field is 0 then a device
forwarding the packet MUST NOT insert a Path Record into the packet.
The echoing host MAY insert a Path Record on reception or
transmission of the packet even if doing so would otherwise be
prohibited by this option.
Fastpath ONLY Records Requested
If this field is 1 then a Path Record SHOULD NOT be inserted unless
it can be done in the same processing path that would be taken by a
regular data packet. The objective of this option is to allow
measurement to be restricted to those points where inserting the path
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record will not affect the forwarding of the IPMP packet with respect
to non-IPMP packets. This may be of use if the IPMP packet is being
inserted periodically into a stream of packets so that the position
of the IPMP packet in the data stream is not disturbed.
Timestamp Requested
If this field is 1 then any Path Records inserted into the packet
SHOULD include a timestamp in the Path Record. If this field is 0
then any Path Records inserted into the packet SHOULD NOT contain a
timestamp. This field allows the IPMP packet to be used to perform a
function similar to traceroute, without the need to collect timing
data.
Data Section Present
If this field is 1 then it indicates that the optional data section
is present and contains at least one data element. All data elements
are specified as TLVs. The data section if present MUST end on a word
alignment and MUST be terminated with the æEndÆ TLV.
Turnaround Options
If this field is 0 then there are no elements in the Data section
which require processing by the Echo Host. If this field is 1 and and
the Data Section Present field is 1 then there MAY be elements in the
Data section which if present MUST be processed by the Echo Host.
2.1.3 Header Fields
Faux Source Port, Faux Destination Port
In order for IPMP to be used to monitor the characteristics of the
path being taken by the data packets of an application it will be
necessary for the IPMP packets to be filtered and queued in a manner
identical to that of user data packets. In order to allow such
filtering to be performed, In the location where the source and
destination port fields of a TCP/UDP packet are located an IPMP
packet contains two "faux" port fields which allow it to be matched
any per flow filters that might be in use. The real source and
destination port fields used by the IPMP protocol are found further
down in the IPMP header.
Faux P-Type (Packet Type)
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For those devices with packet filters that include the packet type
field of the IP header in determining how to process a packet, and
are IPMP aware, this field SHOULD be used by the filter in place of
the actual packet type field which will always contain the IPMP
packet type.
Checksum
The checksum is the 16-bit one's complement of the one's complement
sum of the IPMP message starting with the Faux Source Port. For
computing the checksum, the checksum is initialized to zero.
Path Pointer
The position, in 32 bit words from the beginning of the IP packet, of
the next available path record location.
Info Request Flags
These flags allow for hosts to request additional information (if
available, and at the option of the stamping device) to be added to
the Path Records.
Data
The data field is used to contain additional information about the
IPMP packet either for use by the echoing host and/or by the
measurement host.
2.1.4 Path Record formats
Without Timestamp
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|1|1| Flags | Reserved | TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proxy Address |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| Extensions |
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
With Timestamp
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp | TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proxy Address |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| Extensions |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Extensions Format
0 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 (Pad) |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+
| 255 (End) |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Type | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Base Extension Types
Type# Length Field Name
0 No (L=1) Pad
1 No (L=13)IPv6 Proxy Address (partial)
255 No (L=1) End
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Flags
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TT |F|AT | L |Accuracy |T|E|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flag Fields
TT = Timestamp Type
0 = Undefined
1 = Local source
2 = External (Stratum ?) source
3 = Reserved
4 = Reserved
5 = ~UTC
6 = UTC
7 = No Timestamp
F = Processed in "Fastpath"
0 No
1 Yes
AT = Address Type
0 = IP address of interface
1 = IP address of interface (non-responsive)
2 = IP address of interface + IPMP proxy Address
3 = Non-IP address
L = Stamping Location
0 = Packet RX
1 = Packet TX
2 = Internal processing
3 = Unspecified
A = Accuracy
0-31, most accurate bit position in timestamp, compared to 'real
time clock' on the device, this will be the worst of the number of
bits of resolution of the device's clock and the maximum time
difference between the real time clock at the time the packet is
stamped and the value of the timestamp placed in the packet.
T = Tunnel [De/En]capsulation Point
0 = No
1 = Yes
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E = Extensions
0 = No
1 = Yes
R = Reserved
TTL
The value of the TTL field in the Path Record is set to the value of
the TTL in the packet when transmitted by the device which inserted
the Path Record.
By comparing the TTL field of consecutive Path Records it can be
determined if the time delta between two consecutive Path Records
measures the time between two directly connected devices or if there
are intermediate (non-IPMP aware) devices between the those that
inserted the Path Records.
Stamping Location
The Stamping Location field indications where in the device the Path
Record was inserted into the Echo Request packet.
If the field value is 0 then the Path Record was inserted at the
interface where the packet was received.
If the field value is 1 then the Path Record was inserted at the
interface where the packet was transmitted.
If the field value is 2 then the Path Record was inserted at an
internal location in the device.
If the field value is 3 then the Path Record was inserted at an
unknown/unspecified location in the device.
Usage Example:
+--------+ +---------+ +----------+ +----------+
| | | | | | | |
| A |---|rx B tx|---|rx C tx|---| D |
| | | | | | | |
+--------+ +---------+ +----------+ +----------+
If host A sends an Echo Request to D with a TTL of 255 and both B and
C insert Path Records, with TTLs of 254 and 253, then when the Echo
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Request returns to A it can determine that there are no devices
between B and C. But without knowing the stamping location it does
not know what was measured. Suppose that B stamped at the 'rx'
location and C stamped at the 'rx' location then the difference in
the timestamps would be due to the processing at B and the
propagation delay of the B->C link, and any variation in the
difference seen over repeated measurements would be due entirely to
variations in delay within B. However if C stamped at 'tx' instead of
'rx' than any variation between measurement may be caused by either B
or C or both.
By marking the stamping location it is possible to determine what was
or was not measured by the difference in two consecutive timestamps.
Address
If the value of the Address Type field is 0, the Address field MUST
contain the address of the interface at which the packet was
processed by the system that inserted the Path Record into the Echo
Request or Echo Reply packet, as well as the address to which any
Information Request packets should be sent to.
If the value of the Address Type field is 1, the Address field MUST
contain the address of the interface at which the packet was
processed by the system that inserted the Path Record into the Echo
Request or Echo Reply packet. Unlike the case above, if the field
value is 1 the system will NOT respond to Information Request packets
at this address.
If the value of the Address Type field is 2, the Address field MUST
contain the address of the interface at which the packet was
processed by the system that inserted the Path Record into the Echo
Request or Echo Reply packet. As in the case of Type 1 the system
will not respond to Information Request packets at this address.
However in this case the optional Proxy Address field is present and
MUST contain the address of an IPMP proxy that will respond in place
of the stamping interface.
The proxy address option is designed to allow a system operator to
support the IPMP protocol without requiring the processing of
Information Request packets by the router interfaces that inserted
the Path Records.
The proxy address option also allows for information about stamping
interfaces located behind firewalls/NATs/ALGs etc to be made
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available to hosts which could not otherwise reach them with an
Information Request packet.
If the value of the Address Type field is 3, the Address field
contains a non-IP address value, more accurately it contains a value
which is not the IP address of the interface which inserted the Path
Record, since it may be any 32 bit value it MAY by chance be an IP
address of some other system. The value of the Address field SHOULD
be static while a system is up. The value SHOULD be static across
system restarts. The value is not guaranteed to be globally unique,
but SHOULD be unique at least amongst systems belonging to the same
AS.
This value is designed to allow a system operator to support the IPMP
protocol without being required to expose the addresses of their
systems to the protocol while still providing a unique identifier to
be associated with the interface which inserted the Path Record. If
the value in the Address field is not the IP address of the receiving
interface or of an IPMP 'proxy' this value MUST be used. This value
SHOULD also be used if the IP address of the interface is a 'private'
address, e.g. 10.0.0.1 .
Timestamp
The time at which the Path Record is inserted into the packet is
recorded as a reduced size form (see section 4.3) of an RFC1305 NTP
format [2] timestamp. The relationship between this timestamp and
real time, if there is one, may be derived using information from an
IPMP Information Reply (see section 4.3), or it may be inferred from
a combination of the Fastpath, Timestamp Type and Accuracy fields.
This reduced size timestamp is designed to allow the entire Path
Record to fit into 3 words, or 4 words for Path Records with a Proxy
Address.
Timestamp Type
The Timestamp Type field gives an indication of the clock source that
the timestamp was derived from.
If the Timestamp Type is 0 then the clock source is of undefined
quality and/or may be subject to arbitrary amounts of drift. An
example case would be a PC router using the OS clock for the
timestamp, in this case the software performing the stamping may have
no knowledge of the quality of the clock source and the value of the
OS clock may be subject to large adjustments.
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If the Timestamp Type is 1 then the clock source is a local
oscillator which may drift but which is not subject to adjustments.
Different stamping points on a device with a Type 1 source are
neither guaranteed to have the same rate of drift nor to have
identical values.
If the Timestamp Type is 2 then the clock source is an external clock
signal of (NOTE what level accuracy is required here?) quality and is
not subject to adjustments. Different stamping points on a device
with a Type 2 source are not guaranteed to have identical values, but
they are guaranteed to have the same drift rate.
If the Timestamp Type is 5 then the clock source is an external clock
signal of (Stratum 1/GPS?) quality (i.e. it doesn't drift because it
IS the reference time) which is not subject to adjustments. Further
the second's value in at least the 3 highest order bits of the
timestamp, corresponding to bits 16-18 of an NTP timestamp, MUST have
a value which differs by no more than +/- 2 from the value of bits
16-18 of an NTP timestamp from a station at (+0 GMT). This allows the
'missing' upper bits to be determined if the receiver knows the
correct value of real time (+0 GMT). Different stamping points on a
device with a Type 5 source are not guaranteed to have identical
values, but they are guaranteed to have the same (~0) drift rate.
If the Timestamp Type is 6 then the device inserting the Path Record
asserts that the value in the Timestamp IS the UTC time value for +0
GMT, within the accuracy as defined by the Accuracy flag. Different
stamping points on a device with a Type 6 source are guaranteed to
have the same time value (+/- Accuracy) and the same (~0) drift rate.
Fastpath
If the Fastpath field value is 1, aside from the alterations to
contents of the IPMP packet the IPMP packet was processed and routed
identically to a normal data packet containing the same IP header
fields (addresses,ports,DSCP). This field allows the measurement host
to determine how close the reported times reflect the delays seen by
regular data packets.
Tunnel
If the Tunnel Encapsulation field is 1 then the device inserting the
Path Record is an de/en-capsulation point for the packet. This may be
any form of encapsulation that will prevent the insertion of Path
Records and results in transmission over equipment with variable
delays. For example IPSEC tunnels, MPLS encapsulation, IP-over-ATM,
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etc. The flag deliberately does not indicate if the stamping device
is the source or end point of a tunnel since unless all devices along
the path are IPMP aware it might be possible to have two records the
first indicating an encapsulation followed by one indicating a
decapsulation making it appear that there was a tunnel between the
two points, when in fact there was more than one tunnel between the
two points.
2.1.5 Optional Data Section Formats
0 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 (Pad) |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+
| 255 (End) |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Type | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
2.1.6 Defined Data Section Types
Type# Length Field Name
0 Fixed (1)Pad
1 Variable Error Return
240- Reserved for Redirect Options
251
252 Variable Echo Host Options (future use)
253 Fixed (3) Echo Host Std Options
254 Fixed (1)End Echo Host Options
255 Fixed (1)End
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Echo Host Standard Options
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 11111101 | Flags | TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Echo Host Standard Options Flags
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| P |F|T|R| Res |
+-+-+-+-+-+-+-+-+
P = Path Records Requested
F = Swap Faux Ports
T = TTL Reset
R = Record Route Set
Path Records Requested
Specifies the number (0-2) of Path Records that the echo host SHOULD
insert into the packet.
If 0, the host SHOULD NOT insert any Path Records.
If 1, the host SHOULD insert one (1) Path Record. The record SHOULD
be inserted when the packet is received if the Record Route bit is
set when the packet is received. If the Record Route bit is not set
when the packet is received the record SHOULD be inserted when the
packet is transmitted.
If 2, the host SHOULD insert a first record when the packet is
received and a second record when the packet is transmitted. If the
host implementation can not insert a record on either reception or
transmission then only one (1) record SHOULD be inserted.
The value 3 is invalid and SHOULD be treated as 0.
Swap Faux Ports
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If this field is 1 then the echoing host MUST swap the values in the
Faux Src/Dst Port fields when returning the packet. This allows both
forward and backward paths of a flow to be measured by one packet.
The swapping of the ports is needed to insure that any packet filters
act on the packet as if it were part of the flow being measured.
Record Route Set
The echoing host MUST set the value of the Record Path Record field
to the value of this field before echoing the packet. This allows for
path records to be recorded in only one direction by turning on or
off the stamping process when the packet reaches the echoing host.
TTL Reset
If this field is 1 then the echoing host MUST set the TTL field of
the IP header in the echoed packet to be equal to the TTL field of
the Echo Host Options data element.
End Echo Host Options
This option tells the echo host that there are no more TLVs in the
data section for it to process. This allows the echo host to avoid
having to process the entire data section once all of itÆs options
have been reached.
Error Return Option
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 00000001 | Length | Error Type | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Value
- - - - - - - - - - - - - - - -
Error Types
Value Error
1 Invalid Field/Option
2 Missing Data Element
3 Security Option Required
4 Security Option Rejected
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2.2 IPMP Information Request and Information Reply
2.2.1 Information Request Header
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0000000000000000 | 0000000000000000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPMP Options | 0000000000000000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0000000000000000 | 0000000000000000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Info Flags | 0000000000000000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet ID | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proxy Address |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| Extensions |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| 0000000000000000 | Timestamp |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| Timestamp | Last |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Info Flags
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|P|T|I|Reserved |
+-+-+-+-+-+-+-+-+
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P = Proxy Address Present
If this flag is 1 then the information request packet contains a
Proxy Address.
T = Timestamps Present
If this flag is 1 than the information request packet contains one or
more Timestamps.
I = Information Request Extensions Present
The Extensions section exists and contains Information Request TLVs
requesting additional information about the forwarding address
specified.
2.2.2 Information Reply Header
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0000000000000000 | 0000000000000000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPMP Options | Precision Hi | Precision Lo |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Info Flags | Performance Data Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet ID | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proxy Address |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| Accuracy |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPMP Processing Overhead |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) Real Time Reference Points |
| |
| |
| |
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: .... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) Performance Data |
: .... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Real Time Reference Point
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Real Time |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reported Time |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version = 0.
Flags
The Flags field indicates the presence of optional elements in the
information request. The information reply MUST contain the same
value in the Flags field as the request packet contained.
Last
If there is a timestamp included in the information request the Last
field indicates which is the last timestamp. If the Last field is 0
then another timestamp follows, if the Last field is any non-zero
value then there are no more timestamps.
Checksum
The checksum is the 16-bit one's complement of the one's complement
sum of the IPMP message starting with the version number. For
computing the checksum, the checksum and returned checksum fields are
zero.
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Precision Hi
The number of bits in the whole seconds part of timestamps that are
valid. A Precision Hi of N, means that the timestamps wrap around
every 2^N seconds.
Precision Lo
The number of bits in the fractional part of timestamps that are
valid.
Length
The total length, in bytes, of the IPMP packet. The length should
not normally exceed 556 bytes. That is the Real Time Reference
Points and Performance Data fields should not exceed 524 bytes.
Longer packets risk being discarded if they need to be forwarded of a
path with a MTU less that 576. If no performance data is included 32
Real Time Reference Points may be included in the packet.
The IPMP packet MAY be the MTU size supported by the path, so
equipment MUST be prepared to process IPMP packets as large as their
supported MTU size.
Performance Data Pointer
The position, in bytes from the beginning of the IPMP packet, of the
performance data field if it exists. If there is no performance data
this field is 0.
Forwarding IP Address
The address of the interface to which the Information Request was
sent.
Accuracy
The maximum difference between actual real time and the inferred real
time (see section 4.3.2) of any timestamp generated by this
interface. If there is no relationship between real time and the
timestamps recorded by the interface or the extent of the difference
from real time is unknown accuracy is set to 0.
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IPMP Processing Overhead
The maximum difference between the time taken to process and forward
an IPMP packet and the time taken to forward an IP packet with the
same characteristics. If the overhead is unknown this is reported as
MAX_TIME, i.e. all bits to 1.
Real Time Reference Point
A real time reference point gives the relationship between real time
and the timestamp that would have been placed in a Path Record by the
interface at that time. If there is no relationship between real
time and timestamps no reference points are included in the
Information Reply.
If there were any timestamps present in the information request
packet then the reply packet SHOULD contain a real time reference
point corresponding to each timestamp in the request packet. If the
host does not believe that a valid reference point can be returned,
for example if the host recently restarted and believes the timestamp
was taken before the restart, it MAY return a reference point with a
real time of 0, for the reported timestamp.
Performance Data
The Performance Data field allows arbitrary information from the MIB
of the system or the interface to optionally be included in the
Information Reply. It is formatted as a VarBindList from the SNMPv2-
PDU defined in [6]. In this context ObjectSyntax is the only valid
choice within VarBind.
I.E.
IPMP-PERFORMANCE-DATA DEFINITIONS ::= BEGIN
IMPORTS
ObjectName, ObjectSyntax,
FROM SNMPv2-SMI;
-- IPMP simplified list element
IPMPVarBind ::=
SEQUENCE {
name
ObjectName,
value
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ObjectSyntax
}
-- variable-binding list
VarBindList ::=
SEQUENCE (SIZE (0..max-bindings)) OF
IPMPVarBind
END
3. IP Protocol Header Values
Version = 4
IHL = 5
Identification = unspecified
Flags = DF
Fragment offset = 0
IP Protocol type = TO BE ASSIGNED.
IP options are forbidden.
4. Processing of IPMP packets
4.1.1 Measurement host processing
A measurement host constructs an IPMP request, encapsulates it in an
IP datagram and the appropriate link layer protocol and sends it into
the network. Performance information is gleaned from the presence or
absence of a reply, the delay between the request and the reply the
value of TTL and the path record(s) if present and possibly the
presence of errors.
The measurement host, when constructing the echo request, MUST set
all words from the end of the data field to the end of the echo
request (the space allocated for path records) to zero.
When an IPMP echo reply arrives the checksum is recomputed. Unless
further protection is provided in the data field an IPMP echo reply
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with an incorrect checksum SHOULD be discarded because of the risk of
data corruption causing incorrect matching with the echo request, or
the reporting of invalid measurement data.
4.2 Echoing System Processing
The IPMP Echo Request and Echo Reply packet formats are designed to
make processing at the stamping points simple and efficient, at the
echoing point however there are a number of more complex functions
that an echoing system may have to perform.
On receipt of the IPMP Echo Request (IPMP Option Packet Type = 0 or
4) the echoing system constructs the echo reply from the echo request
by:
1. Exchanging the IP source and destination addresses
2. Check the IPMP checksum, if checksum invalid, either add Error
Return data section with value 1 (Bad Checksum), may require
moving any path records already present or drop the packet.
3. Optionally inserting a path record (as described in section
4.3.1).
4. If the IPMP option Toggle Record Path is set to 1, then toggle the
value of the Record Path Record field of the IPMP options.
5. If the IPMP option Swap Faux Ports is set to 1, then swap the
values of the Fax Src/Dst Port fields.
6. If the Packet Type field is 0, set it to 1, if 4, set it to 5.
7. Set TTL according to Reverse Path TTL option.
8. Calculate the IPMP checksum.
9. Schedule the packet for forwarding taking account of the Faux P-
type field if appropriate.
Processing IPMP Information Request packets requires more resources
than an Echo Request. Direct measurements are not made from
Information Request packets. Consequently an implementer may choose
to processes Information Request packets off the interface card
and/or at low priority.
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4.3 Forwarding System Processing
A forwarding router does not need to be IPMP aware. In the simplest
case IPMP is forwarded like any other IP protocol.
If the router forwards schedules packets based (perhaps in part) on
the value of the IP protocol field, from the IP header, then the
forwarding router SHOULD use the Faux P-type field of the IPMP header
for scheduling instead of the IP protocol field.
A forwarding router may include a path record as described below.
4.3.1 Path Record
Inclusion of path records is optional. A path record MAY be inserted
by forwarding routers (on the forward or reverse path) and the
echoing system.
A system which adds a path record MUST increase the Path Pointer by
the size of the inserted path record, which MUST be a multiple of 4
bytes in length and MUST update the Checksum field. The length of
the packet is not changed. Before inserting the path record the path
pointer plus the size of the path record MUST be compared with the
packet length to ensure that sufficient space is available for the
new path record.
A system that adds a path record MAY include a timestamp in the path
record using the IPMP timestamp format described in section 5.2.2.
If it does not include a timestamp the timestamp field in the path
record is left unaltered.
5. Discussion
5.1 Checksums
The IPMP checksum is calculated by the measurement host when it
creates the echo request packet. It is updated (as described in
section 5.1.1) by forwarding routers that insert a route record into
the IPMP packet. The checksum MUST be checked by the echoing host,
and by the redirecting host (if any). Packets with bad IPMP checksum
SHOULD be discarded, but hosts MAY choose to return a Bad Checksum
Error Return instead.
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5.1.1 Checksum update at a forwarding router.
A forwarding router that does not include a path record does not
check or modify the IPMP checksum. (Normal IP forwarding occurs
including decrementing TTL and updating the IP header checksum.)
A forwarding router that includes a path pointer must update the IPMP
checksum. This MAY be done in two ways:
1. Absolute. Check that the checksum matches for the received
packet. If it does not set the checksum in the forwarded packet to
0. If the checksum in the received packet does match add the Route
Record to the packet and recalculate the checksum.
2. Relative. Form the checksum of the path record (this will be a
constant for a particular interface if timestamps are not used) and
the previous checksum.
Option #1 or #2 is selected on the basis of efficiency.
If possible option #2 SHOULD be used as option #1 allows for errors
to be introduced and then covered up.
5.2 Timestamps
The timestamp field is coded following the conventions described in
RFC1305 NTP [4] but using reduced number of bits.
5.2.1 NTP Timestamp format
Summarizing from RFC1305:
In conformance with standard Internet practice, timestamps are
specified as integer or fixed-point quantities, with bits numbered in
big-endian fashion from 0 starting at the left, or high-order,
position. All quantities are unsigned and may occupy the full field
width with an implied 0 preceding bit 0.
Timestamps are represented as a 64-bit unsigned fixed-point number,
in seconds relative to 0h on 1 January 1900. The integer part is in
the first 32 bits and the fraction part in the last 32 bits. In the
fraction part, the non-significant low order can be set to 0.
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0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds Fraction (0-padded) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This format allows convenient multiple-precision arithmetic and
conversion to UDP/TIME representation (seconds), but does complicate
the conversion to ICMP Timestamp message representation, which is in
milliseconds. The most future time that can be represented is
4,294,967 (some time in the year 2036) with a precision of about 200
picoseconds, which should be adequate for even the most demanding
measurements. RFC 2030 [5] contains a proposal for extending
timestamps beyond the year 2036.
5.2.2 IPMP Timestamp Format
The IPMP Timestamp Format includes bits [16:31] of the 'seconds' word
of an NTP timestamp and bits [0:23] of the 'seconds fraction' of an
NTP timestamp. This format reduces the overall size of the Path
Records. This reduced timestamp should be sufficient for all purposes
of the IPMP protocol being accurate to about 50 nanoseconds, and
taking 18 hours for the seconds field to wrap around. If archival
time stamps are needed then the sending host can use IPMP info
request messages, if needed, to determine the values of the high
order seconds bits.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds Fraction (0-padded) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.2.3 Inferred Real Time
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The real time of the timestamp may be inferred when a system provides
an IPMP Information Reply with at least one Real Time Reference Point
earlier and one later than the timestamp. For the purpose of this
inference the clock drift of the interfaces clock is assumed to be
linear and linear interpolation is used between the two nearest Real
Time Reference Points where one is greater than and one is less than,
the timestamp.
The accuracy field of an Information Reply reports the greatest
difference between an inferred real time, calculated using linear
interpolation, and true real time.
5.3 Minimum Implementations.
5.3.1 Echoing System
The simplest echoing system implementation returns the IPMP echo
request without a path record. As described in section 4.2 this only
requires that the IP source and destination addresses be exchanged,
the type field changed and the packet scheduled for forwarding.
Because of the format of the IPMP echo request and echo reply packets
this can be implemented with a very small number of instructions. A
system that does not insert path records does not need to processes
IPMP Echo Requests.
Systems which just provide this level of implementation allow a
number of measurements to be made that are not currently possible,
particularly if they are routers that processes ICMP at a low
priority to avoid DOS attacks.
5.3.2 Forwarding System
Forwarding systems do not need to be IPMP aware.
A forwarding system that is IPMP aware MAY include path records with
only the Forwarding IP Address set. This requires writing the
address to the packet and updating the checksum and Path Pointer in
the packet as described in section 4.3.1 and 5.1.1. In this case the
forwarding system does not need to process IPMP Information Request
packets.
6. Security Considerations
Info request amplification and CPU use
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6.1 Denial of Service Attacks
Because IPMP echo request packets are processed with about the same
effort as forwarding an IP packet they do not introduce any new
denial of service opportunities.
IPMP Information Request packets require more processing and may be
used as the basis of a denial of service attack in the same way as
any information request on a router or host. Because Information
Request packets are not used to make measurements an designer may
implement protection against denial of service attacks made with
these packets in the same way as other information requests. This
might involve processing IPMP Information Requests at a low priority
or regulating the maximum flow of packets.
Since the IPMP Information Request packet is echoed by the responding
interface it could be used as a reflector in a DOS attack by a host
which sent packets with false source addresses. The use of a proxy
host to respond to Information Request packets should make it
possible to detect and stop such attacks. Also since the volume of
legitimate IPMP Information Request traffic should be low, the proxy
may simply limit how many requests it processes.
The use of the redirection function for a denial of service attack is
addressed in the Security Considerations section.
7. References
[1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
[3] Braden, R., and J. Postel, "Requirements for Internet Gateways",
STD 4, RFC 1009, USC/Information Sciences Institute, June 1987.
[4] Mills, D., "Network Time Protocol (Version 3) Specification,
Implementation and analysis", RFC 1305, March 1992.
[5] Mills, D. "Simple Network Time Protocol (SNTP) Version 4 for
IPv4, IPv6 and OSI", RFC 2030, October 1996.
[6] Case, J., et al. "Protocol Operations for Version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC 1905, October 1996.
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Acknowledgments
This draft draws very heavily, and in some cases draws verbatim from
the text of the IPMP draft by Anthony J. McGregor as well as drawing
from the experiences presents by the implementation and use of the
protocol. This draft would not have been produced if not for those
efforts.
Author's Addresses
Jon C. R. Bennett
Harvard University
Maxwell Dworkin
33 Oxford Street
Cambridge, MA 02138
jcrb@yahoo.com
Full Copyright Statement
Copyright (c) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
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or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Bennett Expires - September 2003 [Page 29]
