Users Guide

Restrictions and limitations
When the port is operating in CT mode, you can observe the following restrictions, depending on the configuration or timing of
the incoming packet, PFC message, or port speed configurations.
● Layer 2/Layer 1/Layer 0, and queue level maximum shaper configurations are not considered. For example, if a queue within
a port has a shaper that is configured to a rate that is less than the rate of the port, the queue can violate the shaper limit
and can grow to the port rate, if the traffic rate is out of the profile.
● The following table lists the CT mode support on existing OS10 platforms:
Table 36. Cut-Through mode support
Platform CT Mode Support
Z9100-ON No
S4048-ON Yes
S6000-ON Yes (only 40G ports)
S4000-ON Yes (only 40G ports)
S6010-ON Yes (only 40G ports)
S4100-ON Series Yes (only 40G ports)
MX7000 Yes
Z9264-ON Yes
S4200-ON No
S5148-ON No
S5200-ON Series Yes
S3048-ON No
Z9300-ON Series Yes
N-Series No
● The destination port cannot use Link Level Flow Control (LLFC) Pause as flow control (PFC). However, PFC can co-exist
with CT mode, but the response time can be delayed depending on the size of the on-the-fly packet.
● CT mode is not allowed for multicast packets. This limitation is specific to Z9300-ON Series switches.
● CT mode is not supported for egress encapsulations such as VXLAN, ERSPAN, and any other tunneling the knowledge of the
full packet length.
● Fast-to-slow CT mode support is available only when the maximum port speed ratio is 4:1; for example, 40G to 10G or 400G
to 100G. Fast-to-slow CT mode support is available on S5200-ON Series, Z9200-ON Series, and Z9300-ON Series switches.
Table 37. Fast-to-slow CT mode support
Ingress Port speed range (Min-
Max)
Egress Port speed Combinations (SRC-DEST)
10G-50G 10G (25G-10G), (40G-10G), (50G-10G)
25G-50G 25G (40G-25G), (50G-25G)
40G-100G 40G (50G-40G), (100G-40G)
50G-100G 50G (100G-50G)
System management 351