Junos OS

Hi there!

I wonder what kind of packets are handled by RE and PFE.

For example, Routing protocols such as OSPF, IS-IS, and BGP are handled by RE. Inline ppmd such as BFD and LACP is handled by PFE. Right?

Could you please let me know about this?

Thank you for reading me

Best Regards,

Seunghyun Lee

Hello,

Good day!

You are correct in your understanding  "For example, Routing protocols such as OSPF, IS-IS, and BGP are handled by RE. Inline BFD is handled by PFE. Right?" [though Inline BFD handling is platform and junos version specific.

Refer links for more info on Inline BFD:https://www.juniper.net/documentation/en_US/junos/topics/concept/bfd-distributed.html and for BFD inline feature support for MX960 refer https://apps.juniper.net/feature-explorer/parent-feature-info.html?pFName=Bidirectional%20Forwarding%20Detection%20(BFD)]

All Juniper Networks devices that run on the Junos operating system share the same common design philosophy, which is to have a clean separation of the control and forwarding planes. In the high-end devices (for example, M-series routers, MX edge devices, and Data Center SRXs), this separation is created in hardware, whereas the other devices (J-series routers and Branch Office SRXs) maintain this division in software. The forwarding plane is referred to as the Packet Forwarding Engine (PFE), and the control plane is called the Routing Engine (RE).

The RE’s primary functions are to manage the PFE, control the device’s software (Junos operating system), manage the command-line interface (CLI), provide troubleshooting tools, and maintain the route tables (both the route table and the route forwarding table). The forwarding table, a subset of the route table, is passed down to the PFE and is used to forward traffic. In this way, the RE never has to be directly involved in packet forwarding, which allows more resources for the actual control functions.

You may also visit the below mentioned link for a detailed explanation:

https://www.juniper.net/documentation/en_US/junos/topics/concept/junos-software-architecture.html

Hope this helps!

Regards,

Yeshas

Thanks for the reply.

Do you happen to know that there are any data or page that specifies traffic that is processed by the Inline ppmd?

Best Regards,

Seunghyun Lee

Hi,

Distributed PPM processing is enabled for all protocols that use PPM such as:

• Bidirectional Forwarding Detection (BFD)

• Connectivity Fault Management (CFM)

• Link Aggregation Control Protocol (LACP)

• Link Fault Management (LFM)

• Real-time Performance Monitoring (RPM)

• Spanning Tree Protocol (STP)

• Synchronous Ethernet (SYNCE)

• Virtual Router Redundancy Protocol (VRRP)

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/ppm-edit-routing-options-rp.html

You can also disable the distributed PPM for the PFE. If you do so, PPM continues to run only on the RE.

Vishal

Thanks for the reply.

May I ask you one more question?

I saw the contents of the link below.

https://www.juniper.net/documentation/en_US/junos/topics/reference/general/hw-cos-default-re-queues-reference-cos-config-guide.html

Table 1(Default Queue Assignments for Packets Generated by the Routing Engine) shows that BFD, LACP, VRRP, and RPM are handled by the Routing Engine, which is sure to be PFE processing is possible via distributed ppmmd?

I look forward to hearing from you.

Best Regards,

Seunghyun Lee

The link you shared in the above post explains how traffic generated by the routing engine are assigned to different queues available.

By default, PPM will ensure it handles the packet processing for it's client processes at the linecard level. Only if the linecard CPU is busy, Routing engine will come into the picture and handle packet processing.

"The responsibility for PPM processing on the switch is distributed between the Routing Engine and the access interfaces for all protocols that use PPM by default. This distributed model provides a faster response time for protocols that use PPM than the response time provided by the nondistributed model."

https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/routing-distributed-periodic-packet-management-qfx-series-cli.html

-Vishal

PS: Please accept my response as solution if it answers you query, kudos are appreciated too!

Hopefully, I'm not too far off-topic, but I have found this article to be useful:

https://forums.juniper.net/t5/Routing/An-Informal-Guide-to-the-Engines-of-Packet-Forwarding/ta-p/401192

Thanks for the reply.

Thank you everyone for all your help on this topic.

My curiosity has been solved.

Best Regards,

Seunghyun Lee