Overview

In modern data center architectures, every microsecond of processing latency directly impacts application performance and transaction speeds. This FAQ addresses critical pre-sales and post-sales technical questions about high-performance switches engineered for deterministic, low-latency packet forwarding. Whether you are validating optical module compatibility, troubleshooting redundant power failover, or verifying line-rate throughput, the answers below provide immediate, actionable insights for network architects and infrastructure engineers.

Frequently Asked Questions

Q1: What is the maximum switching throughput and processing latency in microseconds for a data center core switch?

The maximum switching capacity is 12.8 Tbps with a forwarding rate of 4.2 Bpps (billion packets per second), delivering a port-to-port processing latency of just 0.6 microseconds for 100GbE interfaces. This cut-through forwarding architecture bypasses store-and-forward delays on standard frames. For jumbo frames (9K bytes), latency remains below 1.2 microseconds across all 48 ports simultaneously active.

Q2: Which optical transceivers (SFP, SFP+, QSFP28) are compatible with low-latency data center switches, and do third-party optics affect microsecond performance?

The switch supports all MSA-compliant SFP, SFP+, QSFP28, and QSFP56-DD transceivers without vendor lock-in, and third-party optics do not degrade the sub-microsecond processing latency. However, you must manually disable DOM polling intervals longer than 100ms to prevent management bus contention. Compatible types include: SR4 for 100m multimode, LR4 for 10km single-mode, and AOC direct-attach cables for under 5m. Third-party coded optics with standard I2C interface add no more than 0.02 microseconds of latency overhead.

Q3: What is the backplane capacity and per-slot bandwidth for modular chassis in this data center series?

The backplane provides 30 Tbps of non-blocking crossbar switching fabric with 480 Gbps per slot on a 28-slot chassis. Each line card slot connects via two 240 Gbps SerDes channels operating at 28G NRZ. This architecture guarantees that adding or removing modules does not trigger fabric recalculations, preserving sub-microsecond deterministic latency. Backplane oversubscription is 0:1, meaning no single slot ever bottlenecks aggregate throughput.

Q4: What are the main differences in processing latency and buffer depth between this generation and the previous ASIC-based model?

This generation reduces average port-to-port latency by 73% (from 2.2 microseconds to 0.6 microseconds) while increasing shared buffer memory from 32 MB to 128 MB per ASIC. Key improvements include: dynamic threshold buffer allocation (vs static thresholds), programmable pipeline stages reduced from 6 to 3, and introduction of P4-programmable match-action tables. Unlike the previous generation, current model supports in-band telemetry insertion without adding latency probes.

Q5: How do I perform basic CLI configuration for low-latency cut-through mode and disable store-and-forward on a per-port basis?

To enable cut-through mode globally, enter ‘set forwarding-mode cut-through’ in global config mode, then apply ‘set port cut-through enable’ on each interface. For verification, use ‘show interface latency-stats’. Example workflow: configure terminal, interface ethernet 1/1/1, forwarding-mode cut-through, no store-and-forward, latency-buffer 0, end. Disabling internal head-of-line blocking prevention is also required for deterministic sub-microsecond forwarding; use ‘no qos arbitration’. Save with ‘write memory’.

Q6: How do I stack multiple data center switches for low-latency leaf-spine topologies, and what is the inter-switch stacking latency?

Stack up to 8 switches using dedicated 400GbE stacking ports, achieving inter-switch processing latency of 2.8 microseconds across a 5-meter passive copper cable. Configure virtual chassis by setting ‘stack role master’ on the primary switch and ‘stack member’ on subordinates, then assign unique stack member IDs (1-8). Stacking links automatically form a ring topology with sub-50ms failover. For lowest latency, use VLT (Virtual Link Trunking) instead of traditional stacking to eliminate control plane synchronization delays.

Q7: How do I troubleshoot redundant power supply failover that is causing microsecond-level packet drops?

Packet drops during power failover almost always stem from the PSU hot-swap controller’s hold-up time being shorter than the switching power supply ramp-up. First, confirm both PSUs are in active-active mode via ‘show power redundancy’. If one PSU fails, check syslog for ‘voltage droop on bus 0’. To fix, adjust the power threshold using ‘power-supply droop-tolerance 12ms’ (default is 5ms). Then verify capacitor health on failed PSU and replace if hold-up time is below 10ms. Always use PSUs with same firmware revision to avoid mismatched inrush currents.

Q8: What is the maximum throughput in Gbps for mixed 10G/25G/100G port configurations without exceeding microsecond latency?

At full line rate, the switch forwards 6.4 Tbps mixed traffic (e.g., 24x100G + 48x25G + 24x10G) while maintaining maximum processing latency of 1.5 microseconds at 100% load. The shared buffer dynamically allocates up to 32 MB per 100G port group, preventing microburst drops. Throughput remains non-blocking as long as no oversubscription exceeds 4:1 per port group. Use ‘show interface utilization’ and ‘show buffer microburst’ to confirm latency remains under 2 microseconds even with 80% random small-packet (64-byte) traffic.