Performance Measurement with Asymmetrical Traffic Using STAMP

Simple Two-way Active Measurement Protocol (STAMP) defined the STAMP base functionalities. STAMP Protocol Optional Extensions introduces a TLV structure that allows the Session-Sender to include optional instructions for Session-Reflector. New STAMP TLVs can be defined to support the scenarios in , which discusses the coordination of messaging between the source and destination to help deliver one of the fundamental principles of IP performance metric measurements, minimizing the test traffic effect on user flows. In some scenarios, e.g., rate measurements discussed in , it is beneficial not only to use a variable size of the test packets transmitted downstream while controlling length, number, and interpacket interval for reflected test packets. Measurement of performance metrics in a multicast network using an active measurement method has specific challenges compared to what operators experience monitoring in a unicast network. This document analyzes these challenges, and defines procedures and STAMP extensions to achieve more efficient measurements with a lesser impact on a network.

Abbreviations STAMP Simple Two-way Active Measurement Protocol DoS Denial-of-Service

Requirements Language 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 when, and only when, they appear in all capitals, as shown here.

Reflected Test Packet Control TLV This document defines a new optional STAMP extension, Reflected Test Packet Control TLV. The format of the Reflected Test Packet Control TLV is presented in .

Reflected Test Packet Control TLV Format The interpretation of the fields is as follows:

STAMP TLV Flags is a one-octet field.
Type is a one-octet field that identifies the Reflected Test Packet Control TLV. IANA is requested () to assign (TBA1) value.
Length is a two-octet field. The value is variable, not smaller than 12 octets.
Length of the Reflected Packet is a four-octet field. The value is an unsigned integer that is the requested length of a reflected test packet in octets.
Number of the Reflected Packets is a four-octet field. The value is an unsigned integer that is the number of reflected test packets the Session-Reflector is requested to transmit in response to receiving a STAMP test packet with the Reflected Test Packet Control TLV.
Interval Between the Reflected Packets is a four-octet field. The value is an unsigned integer set to the interval in nanoseconds between the transmission of the consecutive reflected test packets in response to receiving a STAMP test packet with the Reflected Test Packet Control TLV.
Sub-TLVs - an optional field that includes additional information communicated by a Session-Sender.

A Session-Sender MAY include the Reflected Test Packet Control TLV in a STAMP test packet. If the received STAMP test packet includes the Reflected Test Packet Control TLV, the Session-Reflector MUST transmit a sequence of reflected test packets according to the following rules:

The length of the reflected test packet MUST be the largest of the:

The length of a base Session-Reflector packet in the mode (unauthenticated or authenticated) of the received STAMP test packet, as defined in Section 4.3 of , including all STAMP extension TLVs , present in the received STAMP test packet but excluding any Extra Padding TLVs. The rationale to exclude any Extra Padding TLV present in combination with Reflected Test Packet Control TLV is to support a scenario when a Session-Reflector is requested to transmit a sequence of packets shorter than the received STAMP packet.
The value in the Length of the Reflected Packet field of the Reflected Test Packet Control TLV aligned at a four-octet boundary.

In such a case where the length of the reflected packet calculated by this rule is longer than the length of the reflected packet calculated by the rules in [RFC8972], the Session-Reflector MUST use the Extra Padding TLV (Section 4.1 of [RFC8972]) to increase the length of the reflected test packet.

The number of reflected test packets in the sequence MUST equal the value of the Number of the Reflected Test Packets.
If the value of the Number of the Reflected Packets is larger than one, the interval between the transmission of two consecutive reflected packets in the sequence MUST be equal to the value in the Interval Between the Reflected Packets in nanoseconds. If a Session-Reflector that recognizes the Reflected Test Control TLV cannot sustain the transmission of reflected test packets at the interval requested in the Interval Between the Reflected Packets field on the received TLV, the Session-Reflector MUST set the U flag to 1, and MUST transmit a single reflected packet. Otherwise, the Session-Reflector MUST set the U flag to 0 in each of reflected test packets.
If the value of the Number of the Reflected Packets equals zero, then the Session-Reflector MUST NOT send a reflected packet. Processing of the received STAMP test packet with the Reflected Test Packet Control TLV, in which the value of the Number of the Reflected Packets equals zero, is according to the local nodal policy. The received STAMP test packet is discarded if no policy to handle these cases is configured on the node.
Each reflected test packet in the sequence is formed according to Section 4.3 of .

Address Group Sub-TLVs

Layer 2 Address Group Sub-TLV Layer 2 Address Group sub-TLV: A 16-octet sub-TLV that includes the EUI-48 Address Group Mask and EUI-48 Address Group. The Type value is TBA2 (). The value of the Length field MUST be equal to 12. The format of Layer 2 Address Group sub-TLV is presented in .

Layer 2 Address Group Sub-TLV Format The Value field consists of the following fields:

EUI-48 Address Group Mask: A six-octet field that represents the bitmask to be applied to the Session-Reflector MAC Address.
EUI-48 Address Group: A six-octet field that represents the group this TLV is addressed to. If the Session-Reflector applies the EUI-48 Address Group Mask to its MAC Address and the result is different from the EUI-48 Address Group, then the Session-Reflector MUST stop processing the received test packet.

Layer 3 Address Group Sub-TLV Layer 3 Address Group sub-TLV: A variable-length sub-TLV that includes the IP Address Family, IP Network Prefix, and IP Prefix Length. The Type value is TBA3 (). The value of the Length field MUST be equal to 8 if the value of the Address Family family is set to IPv4. The value of the Length field MUST be equal to 20 if the value of the Address Family field is set to IPv6. The format of Layer 3 Address Group sub-TLV is presented in .

Layer 3 Address Group Sub-TLV Format The Value field consists of the following fields:

Address Family: A one-octet field that indicates the type of IP address contained in the IP Network Prefix field. If that is IPv4 address, then the value MUST be set to 1. For the IPv6 address, the value MUST be set to 2. Other values MUST be considered invalid.
Prefix Length: A one-octet unsigned integer field that contains the length, in bits, of the network prefix part of the value in the IP Network Prefix field.
Reserved: A two-octet field. The field MUST be zeroed on transmission and ignored on receipt.
IP Network Prefix: A variable-length field. Depending on the value of the Address Family field, the field contains either IPv4 or IPv6 address. If the former, the length is four octets; if the latter - 16 octets.

Theory of Operation

Rate Measurement defines the problem of access rate measurement in access networks. Essential requirements identified for a test protocol are the ability to control packet characteristics on the tested path, such as asymmetric rate and asymmetric packet size. The Reflected Test Packet Control TLV, defined in , conforms to the requirements for measuring access rate by providing optional controls of the number of reflected test packets, the size of the reflected packet(s), and the time interval, i.e., rate, in transmitting the sequence of the reflected test packets. The UDP Speed Test ( and ) also allows for the measurement of access bandwidth.

Active Performance Measurement in Multicast Environment For performance measurements using STAMP in a multicast environment, a Session-Sender is expected to be the root and Session-Reflectors leaves of the same multicast distribution tree. The mechanism of constructing the multicast tree is outside the scope of this document. According to , a STAMP Session is demultiplexed by a Session-Reflector by the tuple that consists of source and destination IP addresses, source and destination UDP port numbers, or the source IP address and STAMP Session Identifier. That is also the case when monitoring performance of a multicast flow, despite the fact that the destination IP address is a multicast address. Therefore, the behavior of a Session-Reflector upon receiving a STAMP test packet over a multicast tree is as defined in and . The Session-Reflector MUST use the source IP address of the received STAMP test packet as the destination IP address of the reflected test packet, and MUST use one of the IP addresses associated with the node as the source IP address for that packet. The Session-Sender has to pay more attention when sending a multicast STAMP packet. Instead of possibly receiving a reply from a single Session-Reflector, the Session-Sender may now receive multiple replies from multiple counterparts: its STAMP Session has a 1:N relation. Network traffic is another aspect that needs attention: network congestion may happen if a single packet can generate millions of concurrent replies, all directed to the same endpoint. Depending on the multicast-implementation, adding a Reflected Test Packet Control TLV allows Session-Sender to limit the number of replies. If a multicast environment allows selecting Session-Reflectors, this may, for example, be done by

Randomly by specifying a Layer 2 Address Group Sub-TLV: for example, setting the EUI-48 Address Group Mask to 0xF and the EUI-48 Address Group to 0x1. As a result, only 1 out of 16 reflectors will reply;
Having a specific vendor NIC by specifying a Layer 2 Address Group Sub-TLV with the EUI-48 Address Group Mask set to 0xFFFFFF000000;
Belonging to specific IP networks, for example, a subnet dedicated to IPv6 over IPv4 encapsulation by specifying the appropriate Layer 3 Address Group Sub-TLV.

Multicast traffic is also intrinsically asymmetrical, and focus on the return path is usually limited. The Length of the Reflected Packet value can be used to ensure the reflected packet transports all the timestamps and requested information, crucial for the underlying measure, but is as short as possible so as not to flood the network with useless data.

Using Reflected Test Packet Control TLV in Combination with Other TLVs defines the Return Path TLV that, when used in combination with the Return Address Sub-TLV, allows a Session-Sender to request the reflected packet be sent to a different address from the Session-Sender one. These STAMP extensions could be used in combination with the Reflected Packet Control TLV, defined in this document, to direct the reflected STAMP test packets to a collector of measurement data (according to ) for further processing and network analytics. An example of the use case could be used in the multicast scenario when, for example, the Session-Sender is close to the actual multicast frames generator (for example, a camera transmitting live video) so that the test packets follow the same path as the video stream packets in one direction. The data center where the test data are analyzed could be far away, and it would be better to have reflected packets return there. For compatibility with , a Session-Sender MUST NOT include a Return Path Control Code Sub-TLV with the Control Code flag set to No Reply Requested in the same test packet as the Reflected Test Packet Control TLV is non-zero. A Session-Reflector that supports both TLVs MUST set the U flag in Return Path and Reflected Test Packet Control TLVs in the reflected STAMP packet. Furthermore, the Session-Reflector SHOULD log a notification to inform an operator about the misconstructed STAMP packet. Reflected Test Packet Control TLV can be combined with the Class of Service TLV to augment rate testing or testing in a multicast network with monitoring the onsistency of Differentiated Services Code Point and Explicit Congestion Notification values in forward and reverse directions of the particular STAMP test session.

Security Considerations Security considerations discussed in ,, and apply to this document. Furthermore, spoofed STAMP test packets with the Reflected Test Packet Control TLV can be exploited to conduct a Denial-of-Service (DoS) attack. Hence, implementations MUST use an identity protection mechanism. For example, the Session-Reflector could verify the information about the source of the STAMP packet against a pre-defined list of trusted nodes. Also, either STAMP authentication mode or HMAC TLV SHOULD be used for a STAMP test session containing the Reflected Test Packet Control TLV. Furthermore, a DoS attack using the Reflected Test Packet Control TLV might target the STAMP Session-Reflector by overloading it with test packet reflection, e.g., extremely small intervals and/or too many concurrent test sessions. To mitigate that, an implementation that supports the new TLV MUST control the rate and volume of reflection of STAMP test packets by the Session-Reflector. Considering the potential number of reflected packets generated by a single test packet sent to a multicast address, parameters in the first STAMP test packet with the Reflected Test Packet Control TLV MUST be selected conservatively. Consider the Number of the Reflected Packets field value set to one. As a result, a Session-Sender, by counting the packets reflected after originating a first STAMP test packet with the Reflected Test Packet Control TLV, can evaluate the load caused by using the Reflected Test Packet Control TLV in which more than a single reflected packet to the same multicast destination is requested. To mitigate the risk of using the Reflected Test Packet Control TLV in a multicast network further, a Session-Sender SHOULD sign packets using the HMAC TLV when sending such messages in unauthenticated mode . But even with the HMAC TLV, the Reflected Test Packet Control TLV could be exploited by a replay attack. To mitigate that risk, a STAMP Session-Reflector SHOULD use the value of the Sequence Number field of the received STAMP test packet. If that value compared to the received in the previous test packet of the same STAMP test session is not increasing, then the Session-Reflector MUST respond with a single reflected packet, setting the U flag to 1 . A Session-Sender SHOULD NOT send the next STAMP test packet with the Reflected Test Packet Control TLV before the Session-Reflector is expected to complete transmitting all reflected packets in response to the Reflected Test Packet Control TLV in the previous test packet.

Acknowledgments The authors thank Zhang Li and Ruediger Geib for their thorough reviews and helpful suggestions, which improved the document.

IANA Considerations

Reflected Test Packet Control TLV Type The IANA is requested to assign a new value for the Reflected Test Packet Control TLV from the STAMP TLV Types registry according to . New Reflected Test Packet Control Type TLV

Value	Description	Reference
TBA1	Reflected Test Packet Control	This document

Layer 2 and Layer 3 Address Group Sub-TLV Types The IANA is requested to assign new values for the Layer 2 and Layer 3 Address Group sub-TLV Types from the STAMP Sub-TLV Types registry according to . STAMP sub-TLV Types for the Reflected Test Packet Control TLV

Value	Description	TLV Used	Reference
TBA2	Layer 2 Address Group	Reflected Test Packet Control	This document
TBA3	Layer 3 Address Group	Reflected Test Packet Control	This document