ASR1000 Series Memory Allocation Between Linux and IOSd

Introduction

This document describes the memory allocation between Linux and IOSd on the Cisco 1000 Series Aggregation Services Router (ASR).

Memory Allocation

Cisco IOS^® runs as a process, Cisco IOS daemon (IOSd), on top of a Linux kernel on the ASR1000 platform. Linux is the memory manager and allocates a fixed portion of memory for IOSd to use. The amount of memory is split roughly half and half between the Linux kernel and IOSd.

In order to verify how much physical memory is installed, check the output from the show version command. In this output, there is 4GB (4194304K) of DRAM installed with 1.7GB (1732016K) allocated to IOSd.

cisco ASR1002 (2RU) processor with 1732016K/6147K bytes of memory.
4 Gigabit Ethernet interfaces
32768K bytes of non-volatile configuration memory.
4194304K bytes of physical memory.

Check the Processor Pool with the show process memory command in order to verify the total processor IOSd memory. This is the only pool of concern in IOSd:  

------------------ show process memory ------------------
Processor Pool Total: 1773498940 Used: 1069637628 Free:  703861312

There is 1.77GB available for use, as expected. However, this amount is a little less than half because a sizeable portion is used in order to store the large decompressed IOS-XE images.

Memory Usage in SSO Mode for Single RP Chassis

Single Route Processor?only chassis, such as the ASR1001, ASR1002, and ASR1004, can run Software Stateful Switchover (SSO) virtually and provide software redundancy. There is no hardware Route Processor (RP) redundancy with these platforms.

In this example, there is 4GB of DRAM installed with an RP1 processor.

cisco ASR1004 (RP1) processor with 680124K/6147K bytes of memory.
Processor board ID FOX1537G88Y
5 Gigabit Ethernet interfaces
32768K bytes of non-volatile configuration memory.
4194304K bytes of physical memory.

However, the router is configured for SSO.

redundancy
mode sso

The output from the show platform command confirms that the single RP (R0) is split into two software RPs (R0/0 and R0/1).

------------------ show platform ------------------
Chassis type: ASR1004
Slot      Type                State                 Insert time (ago)
--------- ------------------- --------------------- ----------------- 
0         ASR1000-SIP10       ok                    18w0d          
0/0       SPA-5X1GE-V2        ok                    18w0d         
R0        ASR1000-RP1         ok                    18w0d          
R0/0                          ok, active            18w0d          
R0/1                          ok, standby           18w0d    

When you check the Processor Pool, you can see that the memory is split in half again, with 1GB to each RP. After you subtract the decompressed IOS-XE image, there is now only approximately 696MB of total memory left for one instance of IOSd.

------------------ show process memory ------------------
Processor Pool Total:  696361580 Used:  676707244 Free:   19654336

In order to run a full Border Gateway Protocol (BGP) table stably, more than 696MB might be needed. The recommended minimum in order to run SSO is 8GB total DRAM.

Note: The maximum DRAM supported for an RP1 is 4GB. For more details, reference the Cisco ASR1000 Series Route Processor Data Sheet.

Memory Usage with ASR1001

For platforms like the ASR1001, with both the RP and Embedded Services Processor (ESP) integrated, the total initial Processor Memory starts off lower than expected.

As with the other examples, this output shows 4GB of DRAM installed.

cisco ASR1001 (1RU) processor with 1207128K/6147K bytes of memory.
4 Gigabit Ethernet interfaces
32768K bytes of non-volatile configuration memory.
4194304K bytes of physical memory.

Notice that the router only has 1.23GB of Processor Pool memory available, whereas an ASR1002 has approximately 1.77GB.

------------------ show process memory ------------------
Processor Pool Total: 1235972656 Used:  983365712 Free:  252606944

The ESP is generally a separate module with its own physical memory. However, for the ASR1001, the RP and ESP are both integrated and must share the DRAM. For this reason, the router starts off with with less memory.

Note: The memory values listed in this document might differ slightly due to configuration variations.