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General IP Performance Measurement stamp The Simple Two-Way Active Measurement Protocol (STAMP) enables one-way and round-trip measurement of network metrics between IP hosts, and has a facility for defining optional extensions. This document defines a STAMP extension to enable the measurement of manipulation of the value of the explicit congestion notification (ECN) field of the IP header by middleboxes between two STAMP hosts, and to enable discovery and measurement of paths that provide differential treatment of packets depending on the value of their ECN field.

Introduction defines a "Class of Service TLV" extension for the STAMP protocol which enables bi-directional measurement of manipulation of the differentiated services code point (DSCP) field of the IP header by middleboxes but only allows one-way measurement of manipulation of the ECN field of the IP header by middleboxes. Since the ECN field of the IP header is separately meaningful in each direction, it is valuable to have the capability to perform bi-directional measurements of ECN traversal and to have the abilty to measure path characteristics that depend on the value of the ECN codepoint. In addition, bi-directional measurements are important to isolate traversal issues so that remediation actions can be taken appropriately.

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.

DSCP and ECN Traversal STAMP Extension The STAMP session-sender MAY include a DSCP and ECN TLV in the STAMP test packet. The format of the TLV is presented in .

DSCP and ECN Traversal TLV

The fields are defined as follows.

• STAMP TLV Flags: eight-bit field; format presented in .
• Type: one-octet field; value 179 allocated by this specification
• Length: two-octet field; set equal to the value 4 octets
• DSCP1: DSCP value intended by the session-sender to be used as the DSCP value of the reflected test packet
• EC1: ECN value intended by the session-sender to be used as the ECN value of the reflected test packet
• DSCP2: received value in the DSCP field at the ingress of the session-reflector
• EC2: received value in the ECN field at the ingress of the session-reflector
• RP (reverse path): two-bit field; a session-sender MUST set the value of the RP field to 0 on transmission
• Reserved: fourteen-bit field to be zeroed on transmission and ignored on receipt

A session-reflector that receives a test packet with the DSCP and ECN Traversal TLV MUST include the DSCP and ECN Traversal TLV in the reflected test packet. The session-reflector MUST copy the value of the DSCP and ECN fields of the IP header of the received STAMP test packet into the DSCP2 field and EC2 field in the reflected test packet. The session-reflector MUST set the value of the ECN field in the IP header of the reflected test packet equal to the value in the EC1 field of the received test packet. Finally, the session-reflector MUST use the local policy to verify whether the CoS corresponding to the value of the DSCP1 field is permitted in the domain. If the corresponding CoS is permitted in the domain, the session-reflector MUST set the DSCP field's value in the IP header of the reflected test packet equal to the value of the DSCP1 field of the received test packet. If the corresponding CoS is not permitted in the domain, the session-reflector MUST use the DSCP value of the received STAMP packet and set the value of the RP field to 1. Upon receiving the reflected packet, if the value of the RP field is 0, the session-sender will save the DSCP and ECN values for analysis of the CoS in the reverse direction. If the value of the RP field in the received reflected packet is 1, only CoS in the forward direction can be analyzed.

Implementation Status The author is aware of two independent implementations of this STAMP Extension TLV, one of which is publicly available here.

IANA Considerations Add this extension to the IANA STAMP TLV Types Registry.

• Value = 179
• Description = "DSCP and ECN Traversal"
• Reference = this document

Security Considerations This document should not affect the security of the Internet.

References Normative References Informative References

Acknowledgements TBD

Contributors Karthik Sundaresan, William Hawkins III