TWAMP Light is an optional model included in the TWAMP standard RFC5357 that uses standard TWAMP test packets but provides a lightweight approach to gathering ongoing IP delay performance data for base router and per-VPRN statistics. Full details are described in Appendix I of RFC 5357 (Active Two Way Measurement Protocol). The 7210 SAS implementation supports the TWAMP Light model for gathering delay and loss statistics.
For TWAMP Light, the TWAMP Client/Server model is replaced with the Session Controller/Responder model. In general terms, the Session Controller is the launch point for the test packets and the Responder performs the reflection function.
TWAMP Light maintains the TWAMP test packet exchange but eliminates the TWAMP TCP control connection with local configurations; however, not all negotiated control parameters are replaced with local configuration. For example, CoS parameters communicated over the TWAMP control channel are replaced with a reply-in-kind approach. The reply-in-kind model reflects back the received CoS parameters, which are influenced by the reflector’s QoS policies.
The responder function is configured under the config>router>twamp-light command hierarchy for base router reflection, and under the config>service>vprn>twamp-light command hierarchy for per VPRN reflection. The TWAMP Light reflector function is configured per context and must be activated before reflection can occur; the function is not enabled by default for any context. The reflector requires the operator to define the TWAMP Light UDP listening port that identifies the TWAMP Light protocol and the prefixes that the reflector will accept as valid sources for a TWAMP Light request. If the configured TWAMP Light listening UDP port is in use by another application on the system, a Minor OAM message will be presented indicating that the port is unavailable and that the activation of the reflector is not allowed.
f the source IP address in the TWAMP Light packet arriving on the responder does not match a configured IP address prefix, the packet is dropped. Multiple prefix entries may be configured per context on the responder. An inactivity timeout under the config>oam-test>twamp>twamp-light hierarchy defines the amount of time the reflector will keep the individual reflector sessions active in the absence of test packets. A responder requires CPM3 or better hardware.
TWAMP Light test packet launching is controlled by the OAM Performance Monitoring (OAM-PM) architecture and adheres to those rules; this includes the assignment of a test Id. TWAMP Light does not carry the 4-byte test ID in the packet to remain locally significant and uniform with other protocols under the control of the OAM-PM architecture. The OAM-PM construct allow the various test parameters to be defined. These test parameters include the IP session-specific information which allocates the test to the specific routing instance, the source and destination IP address, the destination UDP port (which must match the listening UDP port on the reflector) and a number of other options that allow the operator to influence the packet handling. The probe interval and padding size can be configured under the specific session. The size of the all ‟0” padding can be included to ensure that the TWAMP packet is the same size in both directions. The TWAMP PDU definition does not accomplish symmetry by default. A pad size of 27 bytes will accomplish symmetrical TWAMP frame sizing in each direction.
The OAM-PM architecture does not perform any validation of the session information. The test will be allowed to be activated regardless of the validity of this information. For example, if the configured source IP address is not local within the router instance to which the test is allocated, the test will start sending TWAMP Light packets but will not receive any responses.
The OAM Performance Monitoring (OAM-PM) section of this guide provides more information describing the integration of TWAMP Light and the OAM-PM architecture, including hardware dependencies.
The following is a summary of supported TWAMP Light functions.
base router instances for network interfaces and IES services:
IPv6 addresses are supported only with IP interfaces that support IPv6, such as an IES IP interface in access-uplink and network mode. IPv6 is not supported for IP interfaces that do not support IPv6; for example, routed VPLS services in access-uplink mode do not support IPv6, and therefore TWAMP Light IPv6 sessions are not supported with it.
per-VPRN service context
IPv4 and IPv6:
must be unicast
for IPv6, addresses cannot be a reserved or link local address
reflector prefix definition for acceptable TWAMP Light sources:
Prefix list may be added and removed without shutting down the reflector function.
If no prefixes are defined, the reflector will drop all TWAMP Light packets.
integration with OAM-PM architecture capturing delay and loss measurement statistics:
Not available from interactive CLI.
Multiple test sessions can be configured between the same source and destination IP endpoints. The tuple of Source IP, Destination IP, Source UDP, and Destination UDP provide a unique index for each test.
The following example shows a basic configuration using TWAMP Light to monitor two IP endpoints in a VPRN, including the default TWAMP Light values that were not overridden with configuration entries.
The following is a sample reflector configuration output.
config>test-oam>twamp>twamp-light# info detail
--------------------------------------------------------------------------
(default) inactivity-timeout 100
--------------------------------------------------------------------------
config>service>vprn# info
---------------------------------------------------------------------------
route-distinguisher 65535:500
auto-bind ldp
vrf-target target:65535:500
interface "to-cpe31" create
address 10.1.1.1/30
sap 1/1/2:500 create
exit
exit
static-route 192.168.1.0/24 next-hop 10.1.1.2
bgp
no shutdown
exit
twamp-light
reflector udp-port 15000 create
description "TWAMP Light reflector VPRN 500"
prefix 10.2.1.1/32 create
description "Process only 10.2.1.1 TWAMP Light Packets"
exit
prefix 172.16.1.0/24 create
description "Process all 172.16.1.0 TWAMP Light packets"
exit
no shutdown
exit
exit
no shutdown
------------------------------------------------------------------------------
The following is a sample session controller configuration output.
config>service>vprn# info
-------------------------------------------------------------------------
route-distinguisher 65535:500
auto-bind ldp
vrf-target target:65535:500
interface "to-cpe28" create
address 10.2.1.1/30
sap 1/1/4:500 create
exit
exit
static-route 192.168.2.0/24 next-hop 10.2.1.2
no shutdown
-------------------------------------------------------------------------
config>oam-pm>session# info detail
-------------------------------------------------------------------------
bin-group 2
meas-interval 15-mins create
intervals-stored 8
exit
ip
dest-udp-port 15000
destination 10.1.1.1
fc "l2"
(default) no forwarding
profile in
router 500
source 10.2.1.1
(default) ttl 255
twamp-light test-id 500 create
(default) interval 100
(default) pad-size 0
(default) no test-duration
no shutdown
exit
exit
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