IPC Terminology Fundamentals

Background Information

The Cisco IOS software Inter-Process Communication (IPC) module provides a communication infrastructure by which processes in a distributed system can interact with each other. It also provides transparent communication across backplanes, networks and shared memory.
IPC services serve as the means by which line cards (LCs) and the central route processor (RP) in a distributed system communicate with each other through an exchange of IPC messages sent from the RP to the LCs, and also between active and standby RPs. These messages include configuration commands and responses to those commands, and also "events" that need to be reported by an LC to the RP.
The Cisco 12000 Series, Cisco 10000 Series, Cisco 7600 Series, and the Cisco 7500 Series use a distributed architecture based on IPC messages. Under rare conditions, these routers may report these IPC-related log messages:

• Cisco 12000 Series – %IPC-3-NOBUFF: The main IPC message header cache has emptied
  
• Cisco 7500 Series – %IPC_RSP_CBUS-3-NOBUF: No more IPC memd buffers to transmit IPC message
  

Note: IPC is also used on Cisco 6400 series and Cisco 7304 series.

IPC Terminology Fundamentals

The more common IPC terminologies are:

• IPC – Inter-Process Communication.
  
• IPC Address – A 32-bit word that is composed of a 16-bit seat ID and a 16-bit port ID.
  
• IPC Client – A software module that uses IPC services.
  
• IPC Port – A communication endpoint within IPC used as the source and destination of all communication.
  
• IPC Seat – An IPC seat is a computational element, such as a processor, that can be communicated with the help of IPC. An IPC seat is where IPC clients and ports reside.
  
• IPC Session – An IPC session is an active simplex communication channel between two IPC ports.
  

All communication that uses IPC happens between IPC ports. A port is a communication endpoint in IPC. Each IPC port is associated with a logical address called an IPC address. IPC uses the IPC address of an IPC port as a return address when it sends IPC messages, or a destination address when it receives IPC messages.
Reference:Cisco 12000, 10000, 7600, and 7500 Series Routers: Troubleshooting IPC-3-NOBUFF Messages