IOS Software

Packet Switching Architecture

This chapter covers the following key topics A multiprotocol router's primary purpose is, of course, to switch packets from one network segment to another. If the scheduler and memory manager are the router's software infrastructure, then the IOS switching architecture is the router's very foundation. The switching methods and structures used by IOS essentially dictate how well the router performs its primary task so, as you can imagine, a great deal of effort has been put into designing and...

Routing 101 Process Switching

Process switching was the first switching method implemented in IOS. Basically, it uses the brute-force method to switch packets. Although process switching contains the least amount of performance optimizations and can consume large amounts of CPU time, it does have the advantage of being platform-independent, making it universally available across all Cisco IOS-based products. Process switching also provides some traffic load sharing capabilities not found in most of the other switching...

Buffer Management Using Particles

Particle buffering uses a scatter-gather approach for packet buffer memory management. Instead of allocating one piece of contiguous memory for a buffer, particle buffering allocates dis-contiguous (scattered) pieces of memory, called particles, and then links them together (gathers) to form one logical packet buffer, called a particle buffer. With this scheme, a single packet can be spread across multiple physical buffers. Particle buffers are built that is, individual particles are linked...

Example 15 show process cpu Command Output

Router show process cpu CPU utilization for five seconds 90 82 one minute 60 five minutes 40 PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process 1 1356 2991560 0 0.00 0.00 0.00 0 BGP Router 2 100804 7374 13670 0.00 0.02 0.00 0 Check heaps 3 0 1 0 0.00 0.00 0.00 0 Pool Manager 4 0 2 0 0.00 0.00 0.00 0 Timers 5 6044 41511000 0.00 0.00 0.00 0 OIR Handler 6 0 1 0 0.00 0.00 0.00 0 IPC Zone Manager 7 0 1 0 0.00 0.00 0.00 0 IPC Realm Manager 8 7700 36331 211 8.00 0.00 0.00 0 IP Input The first...

Route Switch Processor

The Route Switch Processor, more commonly called the RSP, performs centralized routing and switching functions (what a surprise ). The RSP is often considered the heart of a 7500 series router because it makes switching decisions, runs routing protocols, and performs maintenance tasks. The RSP is essentially equivalent to a combined Route Processor (RP) and Switch Processor (SP) from the Cisco 7000 router. Combining the RP and SP function on a single board eliminates the relatively slow...

Watchdog Timer

To reduce the impact of runaway processes, IOS employs a process watchdog timer to allow the scheduler to periodically poll the current running process. This feature is not the same as preemption but is instead a failsafe mechanism to prevent the system from becoming unresponsive or completely locking up due to a process consuming all of the CPU. If a process appears to be hung (for example, it's been running for a long time), the scheduler can force the process to terminate. Each time the...

Flow Cache Maintenance

The size and the number of entries in the flow cache are platform dependent. Table A-1 lists the default values. Table A.1. Flow Cache Entry Default Values Table A.1. Flow Cache Entry Default Values Platform Default Cache Entries Default Memory for NetFlow Cache AS5800, 4x00, 3600, 2600, 2500, 1600, 1400 4000 256 KB 7200, RSP7000 64,000 4 MB VIP with 16 MB DRAM 2000 128 KB VIP with 32 MB DRAM 32,000 2 MB VIP with 64 MB DRAM 64,000 4 MB VIP with 128 MB DRAM 128,000 8 MB Each time a new flow is...

Device Drivers

One of the primary functions of an operating system is to provide hardware abstraction between platform hardware and the programs that run on it. This hardware abstraction typically occurs in device drivers that are part of the operating system, making those components an integral part of the system. IOS is no different in that regard. IOS contains device drivers for a range of platform hardware devices, such as Flash cards and NVRAM, but most notable are its device drivers for network...