Learn how the PTX12008 optimizes power consumption through automatic and operator-controlled mechanisms such as adaptive fan management, unused port shutdown, selective PFE offlining, MACsec clock gating, and dynamic fabric or line card power control to improve energy efficiency in high-capacity networks.
Introduction
The PTX12008 is a 8-slot modular chassis running Junos-EVO. It inherits the of power optimization/efficiency features introduced and validated on the Junos-EVO.
Power efficiency is increasingly important as network capacity is growing. The EVO platform integrates granular power control at every level of the forwarding pipeline from individual port SerDes to entire line cards so operators can match power draw to actual traffic demand without sacrificing availability.
Key principles:
- 1) Many optimizations are enabled by default and require no configuration.
- 2) Operator-driven optimizations allow further tuning for specific deployments.
- 3) PFE-level granularity in optimizations helps minimal blast radius.
- 4) All power-off operations on FRUs i.e. Fabric card/Line card/PFE can be applied/reversed without system reboot.
Power Consumers
The PTX12008 is a modular system. At high level, the major power consumers are Line cards, Optics, Fabric Cards, Cooling Fans and Routing Engines.
Here is power distribution across these components assuming each optics consumes 30W power (Typical 800G ZR optics power consumption)
Factors that increase power consumption:
- Higher ambient temperature (fans speed up to cool down system)
- Higher elevation
- More number of optics inserted
- High power optics i.e. ZR HP
- Higher traffic load in bps and pps
- Using MACsec on Wan Ports
- Fully populated FPC slots
Factors that decrease power consumption:
- Empty port slots (SerDes auto-shutdown)
- Ports configured "unused"
- PFEs powered off when not needed
- Fabric card/Line card offline in empty or temporarily unused slots
- Low traffic periods (PFE and fabric SerDes run at lower utilization)
Power Saving Features in PTX12008
Environment Management Policy - Controlling FAN speed to save Power
The Environmental Monitoring (EM) Policy is a built-in subsystem that continuously monitors thermal sensors distributed throughout the PTX12008 chassis and dynamically adjusts fan speed in real time. Because Fans are significant power consumers running them only as fast as thermals require is one of the most effective automatic power saving mechanisms in the platform.
How EM Policy Works:
- 1) Thermal sensors are placed at key locations inside the chassis: Line card inlet/exhaust, Fabric card, RE, CB, PSM, and fan tray zones.
- 2) The EM Policy daemon collects sensor readings at regular intervals and computes the required airflow.
- 3) Fan speed is set to the minimum level that keeps all components within their thermal operating limits.
- 4) As temperature rises due to higher ambient, more traffic load or more optics active, the EM Policy incrementally increases fan speed.
- 5) As temperature falls due to lower ambient, PFEs/optics powered off or traffic drops, fan speed is reduced automatically to save power.
- 6) This feedback loop runs continuously without any operator intervention.
As per EM Policy, FANs run at minimum speed required to keep system thermal within limits helps to save significant power.
Here is an example that shows the difference in power consumption when the Fan runs at ~60% vs. 100%.
At 60%, around 800W
root@ptx12008> show chassis fan
Item Status % RPM Measurement
Fan Tray 0 Fan 0 OK 56% 5700 RPM
Fan Tray 0 Fan 1 OK 62% 7200 RPM
Fan Tray 0 Fan 2 OK 55% 5550 RPM
Fan Tray 0 Fan 3 OK 62% 7200 RPM
Fan Tray 0 Fan 4 OK 55% 5550 RPM
Fan Tray 0 Fan 5 OK 63% 7350 RPM
Fan Tray 0 Fan 6 OK 55% 5550 RPM
Fan Tray 0 Fan 7 OK 62% 7200 RPM
Fan Tray 0 Fan 8 OK 55% 5550 RPM
Fan Tray 0 Fan 9 OK 62% 7200 RPM
Fan Tray 1 Fan 0 OK 56% 5700 RPM
Fan Tray 1 Fan 1 OK 62% 7200 RPM
Fan Tray 1 Fan 2 OK 56% 5700 RPM
Fan Tray 1 Fan 3 OK 62% 7200 RPM
Fan Tray 1 Fan 4 OK 56% 5700 RPM
Fan Tray 1 Fan 5 OK 62% 7200 RPM
Fan Tray 1 Fan 6 OK 55% 5550 RPM
Fan Tray 1 Fan 7 OK 62% 7200 RPM
Fan Tray 1 Fan 8 OK 56% 5700 RPM
Fan Tray 1 Fan 9 OK 61% 7050 RPM
Fan Tray 2 Fan 0 OK 56% 5700 RPM
Fan Tray 2 Fan 1 OK 62% 7200 RPM
Fan Tray 2 Fan 2 OK 55% 5550 RPM
Fan Tray 2 Fan 3 OK 62% 7200 RPM
Fan Tray 2 Fan 4 OK 56% 5700 RPM
Fan Tray 2 Fan 5 OK 61% 7050 RPM
Fan Tray 2 Fan 6 OK 55% 5550 RPM
Fan Tray 2 Fan 7 OK 62% 7200 RPM
Fan Tray 2 Fan 8 OK 56% 5700 RPM
Fan Tray 2 Fan 9 OK 62% 7200 RPM
root@ptx12008> show chassis power detail | match FAN
Fan Tray 0 269
Fan Tray 1 254
Fan Tray 2 265
At 100% speed, around 4,100W
root@ptx12008> show chassis fan
Item Status % RPM Measurement
Fan Tray 0 Fan 0 OK 100% 10200 RPM
Fan Tray 0 Fan 1 OK 100% 11700 RPM
Fan Tray 0 Fan 2 OK 100% 10200 RPM
Fan Tray 0 Fan 3 OK 100% 11700 RPM
Fan Tray 0 Fan 4 OK 100% 10200 RPM
Fan Tray 0 Fan 5 OK 100% 11700 RPM
Fan Tray 0 Fan 6 OK 100% 10050 RPM
Fan Tray 0 Fan 7 OK 100% 11700 RPM
Fan Tray 0 Fan 8 OK 100% 10050 RPM
Fan Tray 0 Fan 9 OK 100% 11700 RPM
Fan Tray 1 Fan 0 OK 100% 10200 RPM
Fan Tray 1 Fan 1 OK 100% 11700 RPM
Fan Tray 1 Fan 2 OK 100% 10200 RPM
Fan Tray 1 Fan 3 OK 100% 11700 RPM
Fan Tray 1 Fan 4 OK 100% 10050 RPM
Fan Tray 1 Fan 5 OK 100% 11700 RPM
Fan Tray 1 Fan 6 OK 100% 10200 RPM
Fan Tray 1 Fan 7 OK 100% 11550 RPM
Fan Tray 1 Fan 8 OK 100% 10050 RPM
Fan Tray 1 Fan 9 OK 100% 11550 RPM
Fan Tray 2 Fan 0 OK 100% 10050 RPM
Fan Tray 2 Fan 1 OK 100% 11700 RPM
Fan Tray 2 Fan 2 OK 100% 10200 RPM
Fan Tray 2 Fan 3 OK 100% 11700 RPM
Fan Tray 2 Fan 4 OK 100% 10200 RPM
Fan Tray 2 Fan 5 OK 100% 11700 RPM
Fan Tray 2 Fan 6 OK 100% 10200 RPM
Fan Tray 2 Fan 7 OK 100% 11550 RPM
Fan Tray 2 Fan 8 OK 100% 10200 RPM
Fan Tray 2 Fan 9 OK 100% 11550 RPM
root@ptx12008> show chassis power detail | match FAN
Fan Tray 0 1363
Fan Tray 1 1343
Fan Tray 2 1375
All three fan trays info collected via telemetry:
This example shows how running Fan as least as required helps to save system power significantly.
WAN Ports “unused” Configuration
A port populated with a transceiver but not in service can be disabled via the "unused" keyword. This shuts down the forwarding path of the transceiver and help to save power. This “unused” configuration removes the interface from all "show interfaces" output, but optic module remains powered for inventory/monitoring purposes.
Here is an example that shows the power saving by marking ports “unused”.
root@ptx12008# set interfaces et-0/0/0 unused
root@ptx12008# set interfaces et-0/0/1 unused
root@ptx12008# set interfaces et-0/0/2 unused
root@ptx12008# set interfaces et-0/0/3 unused
root@ptx12008# commit
re0:
configuration check succeeds
re1:
configuration check succeeds
commit complete
re0:
commit complete
root@ptx12008>
Here is an other example that shows the power saving by marking 4 ports “unused”.
By marking 4 ports as unused, the Line card's power consumption came down from 2.21 kW to 2.14 kW. This example shows power saving by marking the FR optics unused. If ZR optics is marked unused, power savings per optics will be more.
This behavior is reversible with “delete interface et-x/y/z unused” and it just takes a few seconds to restore the port in its original state, without any impact on the other ports of the system.
Selective PFE Power off
Each PFE (Packet Forwarding Engine ASIC) on an Line card can be powered off independently without affecting other PFEs on the same Line card or in the system. This is one of the most impactful power-saving features available to operators.
Use cases:
- a) Pay-As-You-Grow: Only the PFEs needed for current port count are powered on. Unused PFEs remain off until capacity is expanded.
- b) Off-peak scheduling: Power off idle PFEs during low-traffic window (e.g., nights/weekends). Use traffic engineering to keep traffic away from those PFEs before powering down.
PFE Power off help to save Line card power by turning off PFE completely. Also, it helps save power consumed by Fabric Cards by turning off Fabric serdes that map to the offlining PFE.
Here is an example that displays power saving with PFE Power off
root@ptx12008> show chassis fpc 0 pfe-instance all
FPC 0
PFE-Instance PFE PFE-State
0 0 ONLINE
0 1 ONLINE
1 2 ONLINE
1 3 ONLINE
2 4 ONLINE
2 5 ONLINE
root@ptx12008> show chassis power detail | match FPC
FPC 0 2620
FPC 1 2102
FPC 2 2723
FPC 3 1943
FPC 4 2061
FPC 5 1462
FPC 6 2043
FPC 7 2321
root@ptx12008> show chassis power detail | match SIB
SIB 0 609
SIB 1 609
SIB 2 620
SIB 3 613
SIB 4 627
SIB 5 622
SIB 6 613
SIB 7 614
SIB 8 613
root@ptx12008> request chassis fpc slot 0 pfe-instance 0 offline
Fru Block offline initiated!
root@ptx12008> show chassis fpc 0 pfe-instance all
FPC 0
PFE-Instance PFE PFE-State
0 0 Offlined by CLI
0 1 Offlined by CLI
1 2 ONLINE
1 3 ONLINE
2 4 ONLINE
2 5 ONLINE
root@ptx12008> show chassis power detail | match FPC
FPC 0 1859
FPC 1 2097
FPC 2 2724
FPC 3 1935
FPC 4 2064
FPC 5 1460
FPC 6 2042
FPC 7 2325
root@ptx12008>
root@ptx12008> show chassis power detail | match SIB
SIB 0 577
SIB 1 572
SIB 2 588
SIB 3 581
SIB 4 594
SIB 5 590
SIB 6 580
SIB 7 582
SIB 8 579
Or in another example represented on the Grafana dashboards:
Above examples clearly shows that PFE Power off not just bring down Line card power consumption significantly but also helps to save power consumed by Fabric cards by turning off Fabric card side serdes’es that are mating with PFE.
More Details on saving power using PFE power of can be found on following TechPost article
https://community.juniper.net/blogs/ramdas-machat/2023/07/27/saving-energy-on-ptx-with-pfe-power-off
MACSEC Block Clock Gating
MACsec encryption/decryption Security block resides inside the forwarding ASIC. It operates on a per-Port-Group (PG) basis. Each forwarding ASIC has 9 Port Groups.
When no port in a Port Group has MACsec configured, the MACsec block for that Port Group is automatically disabled and doesn’t consume power.
- Automatic. No configuration needed to save power.
- MACsec is activated only when explicitly configured on a port:
set security macsec interfaces et-X/Y/Z
- This is fully automatic and reversible: adding or removing MACsec configuration enables or disables the block transparently.
Fabric Card Power Off
The PTX12008 fabric card consists of multiple Switch Asics and the associated Fabric SerDes that form the full-mesh interconnect between all PFEs in the chassis.
An entire Fabric card can be taken offline. This is appropriate when:
- Reducing fabric power during sustained low-traffic periods when full fabric bandwidth is not required.
- Partial optic population per PFE: If fewer than the maximum number of optics are inserted per PFE, the fabric bandwidth requirement is proportionally lower and one or more SIBs can be kept offline. Example- If 8 out of 9 optics are inserted on all PFEs for PTX12008, the Fabric card does not need to carry full line-rate. 1 SIB can be kept offline without oversubscribing the remaining fabric.
- Lower bandwidth optics on WAN ports: If operators install lower-speed optics instead of the maximum supported rate, the aggregate bandwidth injected into the fabric is reduced, allowing some Fabric cards to be kept offline. Example - If 400G optics are installed on all PTX12008 Line card ports, the total fabric demand is halved. 4 Fabric cards can be offlined while the remaining SIBs carry the full traffic load without oversubscription.
- Scheduled Fabric card maintenance or replacement.
On Fabric Card offline, all Fabric ASICs and SerDes’es on Fabric card go to zero power. Along with this, Line card fabric serdes which are mating to the offlined fabric card, are also brought down and helps to save power online card as well.
Here is an example that displays power saving with Fabric Card Power off
root@ptx12008> show chassis sibs
Slot State Fabric links Errors
0 Online Active None
1 Online Active None
2 Online Active None
3 Online Active None
4 Online Active None
5 Online Active None
6 Online Active None
7 Online Active None
8 Online Active None
root@ptx12008> show chassis power detail | match SIB
SIB 0 609
SIB 1 611
SIB 2 621
SIB 3 613
SIB 4 627
SIB 5 622
SIB 6 613
SIB 7 614
SIB 8 612
root@ptx12008> show chassis power detail | match FPC
FPC 0 2619
FPC 1 2099
FPC 2 2723
FPC 3 1942
FPC 4 2065
FPC 5 1460
FPC 6 2036
FPC 7 2326
root@ptx12008> request chassis sib slot 0 offline
Offline initiated, use "show chassis sibs" to verify
root@ptx12008> show chassis sibs
Slot State Fabric links Errors
0 Offline Unused None
1 Online Active None
2 Online Active None
3 Online Active None
4 Online Active None
5 Online Active None
6 Online Active None
7 Online Active None
8 Online Active None
root@ptx12008> show chassis power detail | match SIB
SIB 0 0
SIB 1 606
SIB 2 621
SIB 3 613
SIB 4 626
SIB 5 622
SIB 6 613
SIB 7 613
SIB 8 612
root@ptx12008> show chassis power detail | match FPC
FPC 0 2497
FPC 1 1965
FPC 2 2603
FPC 3 1814
FPC 4 1931
FPC 5 1371
FPC 6 1908
FPC 7 2186
Another example collected in graphical manner:
Above examples clearly show that Fabric card Power off not just bring down fabric card power consumption to 0 but also helps to save power consumed by Line cards by turning off linecard side SerDes’es that are mating with the offlined fabric card.
Line Card Power Off
An entire Line card can be taken offline. This is appropriate when:
- Planning maintenance on a line card.
- Decommissioning capacity.
All PFEs, SerDes, PHYs and optics on the card go to zero power. Along with this, Fabric card SerDes’es which are mating to the offlined Line card, are also brought down and it helps to save power on fabric card as well.
Here is an example that displays power saving with Fabric Card Power off
root@ptx12008> show chassis fpc
Temp CPU Utilization (%) CPU Utilization (%) Memory Utilization (%)
Slot State (C) Total Interrupt 1min 5min 15min DRAM (MB) Heap Buffer
0 Online 48 5 0 5 5 5 65536 16 0
1 Online 39 4 0 4 4 4 65536 15 0
2 Online 45 4 0 4 4 4 65536 15 0
3 Online 38 4 0 4 4 4 65536 15 0
4 Online 40 4 0 4 4 4 65536 15 0
5 Online 36 4 0 4 4 4 65536 15 0
6 Online 36 4 0 4 4 4 65536 15 0
7 Online 42 4 0 4 4 4 65536 15 0
root@ptx12008> show chassis power detail | match SIB
SIB 0 609
SIB 1 604
SIB 2 621
SIB 3 613
SIB 4 626
SIB 5 622
SIB 6 613
SIB 7 613
SIB 8 612
root@ptx12008> show chassis power detail | match FPC
FPC 0 2618
FPC 1 2097
FPC 2 2727
FPC 3 1938
FPC 4 2055
FPC 5 1459
FPC 6 2034
FPC 7 2321
root@ptx12008> request chassis fpc slot 0 offline
Offline initiated, use "show chassis fpc" to verify
{master}
root@ptx12008> show chassis fpc
Temp CPU Utilization (%) CPU Utilization (%) Memory Utilization (%)
Slot State (C) Total Interrupt 1min 5min 15min DRAM (MB) Heap Buffer
0 Offline ---Offlined by cli command---
1 Online 39 4 0 4 4 4 65536 15 0
2 Online 45 4 0 4 4 4 65536 15 0
3 Online 38 4 0 4 4 4 65536 15 0
4 Online 40 4 0 4 4 4 65536 15 0
5 Online 36 4 0 4 4 4 65536 15 0
6 Online 36 4 0 4 4 4 65536 15 0
7 Online 42 4 0 4 4 4 65536 15 0
root@ptx12008> show chassis power detail | match SIB
SIB 0 514
SIB 1 513
SIB 2 524
SIB 3 518
SIB 4 530
SIB 5 527
SIB 6 517
SIB 7 520
SIB 8 518
root@ptx12008> show chassis power detail | match FPC
FPC 0 0
FPC 1 2103
FPC 2 2728
FPC 3 1941
FPC 4 2060
FPC 5 1459
FPC 6 2042
FPC 7 2317
Line card can also be configured offline using the following config command
root@ptx12008# set chassis fpc 0 power off
root@ptx12008# commit
re0:
configuration check succeeds
re1:
configuration check succeeds
commit complete
re0:
commit complete
Another case, from the telemetry collector perspective:
Above examples clearly shows that Line card Power off not just bring down Line card power consumption to 0 but also helps to save power consumed by Fabric cards by turning off Fabric card fabric SerDes’es that are mating with the offlined Line card.
Conclusion
The PTX12008 demonstrates that significant power savings can be achieved without compromising availability. The platform's layered approach, combining automatic mechanisms like Environmental Monitoring-driven fan control with operator-driven controls like Fabric Card/Line Card/PFE power-off, gives network operators fine-grained flexibility to match power draw to actual traffic demand. Cascading SerDes shutdown between Line cards and Fabric cards (and vice versa) ensures power savings propagate across the system rather than being isolated to a single component. Together, these capabilities make the PTX12008 a power-efficient platform well-suited for modern high-capacity networks where energy optimization is as critical requirement.
Useful links
Glossary
- ASIC: Application Specific Integrated Circuit
- CPU: Central Processing Unit
- DDR: Double Data Rate
- EM: Environmental Monitoring
- FPC: Flexible PIC Concentrator
- IFD: Physical Interface
- PFE: Packet Forwarding Engine
- PG: Port Group
- PM: Power Management
- PSM: Power Supply Module
- SerDes: Serializer/Deserializer
- SIB: Switch Interface Board
- WAN: Wide Area Network
Acknowledgements
Thanks to Nicolas Fevrier and David Roy for their participation and review comments on this document.