This document is intended to assist in troubleshooting hardware-related issues for Routing Engines (RE) on Juniper platforms. It outlines a systematic approach to identifying and resolving problems with RE modules, covering typical symptoms such as the RE not booting up, no response on the console, and various CLI-reported errors including ECC errors, parity errors, hard disk failures, I2C errors, and other related hardware faults.
Before starting troubleshooting, ensure the device is receiving proper power and verify the status of all the SYS (System/Chassis) LED’s to be functional.
Juniper Routing Engines (RE) contain Dynamic Random Access Memory (DRAM), while various Packet Forwarding Engine (PFE) components utilize Synchronous DRAM (SDRAM). All of this memory is protected by Error-Correcting Code (ECC), which helps detect and in some cases correct bit-level errors during normal operation. ECC errors typically indicate faulty memory on a specific hardware component and are crucial for identifying memory degradation or failure.
ECC errors are classified into two main types: correctable and uncorrectable, and they can involve either single-bit or multi-bit faults.
Correctable Errors: These are typically single-bit errors that the system can detect and automatically correct, with no impact to functionality. However, if such errors occur frequently, they may indicate a failing memory module and warrant further investigation from JTAC.
Uncorrectable Errors: Often associated with multi-bit failures, these errors cannot be automatically corrected by the system. If such messages persist even after a reboot, the memory is likely faulty, and RMA of the affected component is recommended.
Single-Bit Errors: These are minor and generally correctable by the ECC mechanism.
Multi-Bit Errors: These are more serious and often result in uncorrectable errors that can cause system instability or crashes.
Note: Before proceeding with an RMA, it's advisable to perform a restart and reseat of the RE or affected FPC during a maintenance window, as this can sometimes resolve transient hardware issues.
Examples of ECC Errors
user@lab-router> show log chassisd | match "ECC"Apr 1 01:01:01 labrouter -RE0 : %USER-3: (FPC Slot 9, PIC Slot 3) ms93 kernel: svcs_ms2_ddr_mon: ECC errors uncorrectable 6301 correctable 6301 chA 1 chB 0Apr 1 01:01:01 labrouter -RE0 : %USER-3: (FPC Slot 9, PIC Slot 3) ms93 kernel: svcs_ms2_ddr_mon: ECC errors uncorrectable 6361 correctable 6361 chA 1 chB 0Apr 1 01:01:01 labrouter -RE0 : %USER-3: (FPC Slot 9, PIC Slot 3) ms93 kernel: svcs_ms2_ddr_mon: ECC errors uncorrectable 6421 correctable 6421 chA 1 chB 0user@lab-router> show log chassisd | match "ECC"Apr 1 01:01:01 CHASSISD_SBE_DETECTED: Too many single bit ECC errors in routing engine DRAMApr 1 01:01:01 send: red alarm set, device Routing Engine 0, reason Host 0 memory ECC S
ECC errors on the Compact Forwarding Engine Board (CFEB):
user@lab-router> show log messages | match "ECC"Apr 1 01:01:01 labrouter cfeb BCHIP 1: multiple correctable ECC errorsApr 1 01:01:01 labrouter cfeb BCHIP 1: ECC from SDRAM bank 1, at bit 39 was correctedApr 1 01:01:01 labrouter cfeb CM: Slot 1: Recoverable error detected; multiple ECC errorsApr 1 01:01:01 labrouter cfeb BCHIP 1: multiple correctable ECC errorsApr 1 01:01:01 labrouter cfeb BCHIP 1: ECC from SDRAM bank 1, at bit 39 was corrected
ECC errors on the Flexible PIC Concentrator (FPC) in slot 2, as reported by the System Control Board (SCB):
user@lab-router> show log messages | match "ECC"Apr 1 01:01:01 lab-router scb BCHIP 2: correctable ECC errorApr 1 01:01:01 lab-router scb BCHIP 2: ECC from SDRAM bank 0, at bit 62 was correctedApr 1 01:01:01 lab-router scb CM: Slot 2: Recoverable error detected; ECC errorApr 1 01:01:01 lab-router scb BCHIP 2: correctable ECC errorApr 1 01:01:01 lab-router scb BCHIP 2: ECC from SDRAM bank 0, at bit 62 was correctedApr 1 01:01:01 lab-router scb CM: Slot 2: Recoverable error detected; ECC error
Reference KB - KB35412 - [MX] ECC uncorrectable and correctable errors [juniper.net]
Reference Doc - https://www.juniper.net/documentation/us/en/software/junos/chassis/topics/topic-map/chassis-guide-tm-error-handling-alarms.html
Parity errors in Juniper routing engines can occur due to various reasons, including environmental conditions like humidity, electro static discharge, magnetic interference and so on, hardware faults, and transient issues.
Soft Parity Errors: These can be cleared by rebooting the RE. They are transient and do not indicate a permanent hardware fault.
Hard Parity Errors: These errors persist even after rebooting and indicate a hardware fault that may require component replacement.
In Juniper Routing Engines, I2C (Inter-Integrated Circuit) errors are hardware-related and typically involve communication failures over the I2C bus - a serial bus used to connect various internal components on the RE. These errors may manifest as read or write failures when the RE attempts to communicate with onboard devices.
When such issues occur, the RE may log I2C error messages. As per the current router implementation, I2C alarms are not cleared immediately and may persist for up to 24 hours. If the alarm remains active beyond this period, a reboot is recommended as a corrective action. If the issue continues even after reboot, an RMA may be required as a last resort.
Reference KB - KB91717 - [PTX] I2C readback error messages for the CB after the routing-engine is inserted on the CB [juniper.net].
Reference KB - KB75406 [juniper.net] -KB75406 - Minor RE0 IIC access Error [juniper.net]
For additional assistance from Juniper Support, open a case with all the relevant files such as RSI/Logs, and include the answers to the following questions:
2025-06-17 - Article created
2025-06-25: Minor non-technical and formatting changes made