Cisco Routers Performance

In this blog post I will summarize available information on Cisco ISR and ASR performance. The following platforms will be covered: ISR G2, ISR 1100, ISR 4000, ASR 1000.

Update: check my new article on SD-WAN routers and platforms here.

ISR G2

Let’s start with ISR G2 performance numbers. ISR G2s are legacy products with Classic IOS, however, they are still around and it is important to know how they perform to properly size newer replacement routers.

Important: These are not real-world numbers. Please read further.

Model	Packets Per Second	Megabits Per Second
Cisco 860	25,000	197
Cisco 880	50,000	198
Cisco 890	100,000	1,400
Cisco 1921	290,000	2,770
Cisco 1941	330,000	2,932
Cisco 2901	330,000	3,114
Cisco 2911	352,000	3,371
Cisco 2921	479,000	3,502
Cisco 2951	579,000	5,136
Cisco 3925	833,000	6,903
Cisco 3925E	1,845,000	6,703
Cisco 3945	982,000	8,025
Cisco 3945E	2,924,000	8,675

Table 1. Cisco ISR G2 RFC 2544 Performance

The second column displays the number of packets per second that the platform can forward under maximum CPU utilization just before starting to drop the packets. For a router’s CPU it takes the same amount of effort to route the 64-byte packet as it would take for 1500-byte one. So it is usually a more reliable metric that removes packet size from the equation.

The third column displays the value in bytes per second (i.e. packet size in bytes x packets per second). As the results can differ more than 20x times based on the size of the packets selected, the specification must provide average packet size that was used during the test.

What is IMIX? The traffic doesn’t consist of packets of the same size, many tests are using packets of different sizes (called Internet Mix (IMIX)). For example, in a simple IMIX sample in every 12 packets transmitted – 7 will be 40 bytes long, 4 – 576, and 1 – 1500. The average packet size in this case will be 340 bytes.

Values provided in Table 1 are based only on IP packet routing without any additional processing, such as QoS, encryption, or NAT, so it is a maximum performance that a platform can deliver. The real-world number will be significantly smaller.

Another important thing to note is how a packet is counted, for example, it can be counted twice – as it enters an ingress interface and exits egress one. Cisco counts this is as a single packet, as it is seen by the forwarding engine. On the other hand, to select a router for a specific WAN interface bandwidth utilization in each direction must be added. For example, in the case of 10Mbps WAN with expected 9Mbps download and 3Mbps upload – calculation should be based on 12Mbps of the load.

For G2 platforms Cisco recommended WAN-link based sizing is as per the table below. Values are much smaller compared to normal IP forwarding. It is also expected that the router will not be running at 99% CPU and will be dropping packets.

Platform	WAN Link
860	4
880	8
890	15
1921	15
1941	25
2901	25
2911	35
2921	50
2951	75
3925	100
3945	150
3925E	250
3945E	350

Table 2. ISR G2 Recommended Sizing Based on WAN Link Speed

ISR 4000

ISR 4000s are running IOS-XE and have introduced performance-based licensing with 3 tiers:

Default
Performance (x2-3 of default throughput level)
Boost (removes shaping completely)

Cisco publishes the following statistics for basic IP routing without services with IMIX traffic (~330 bytes packets).

Model	Default (Mbps)	Performance (Mbps @ CPU %)	Boost (Mbps @ CPU %)	Boost (pps @ CPU %)	Encryption (Mbps, AES 256)
4221	35	75 @ 8% CPU	1,400 @ 94% CPU	530,000 @ 94% CPU	75
4321	50	100 @ 8% CPU	2,000 @ 68% CPU*	760,000 @ 68% CPU*	100
4331	100	300 @ 16% CPU	2,000 @ 53% CPU*	760,000 @ 53% CPU*	500
4351	200	400 @ 17% CPU	2,000 @ 45% CPU*	760,000 @ 45% CPU*	500
4431	500	1,000 @ 18% CPU	4,000 @ 62% CPU*	1,520,000 @ 62% CPU*	900
4451	1,000	2,000 @ 19% CPU	4,000 @ 35% CPU*	1,520,000 @ 35% CPU*	1,600
4461	1,500	3,000 @ not published	10,000+ @ not published	3,790,000+ @ not published	7,000

Table 3. ISR 4000 Performance (IP forwarding, IMIX 330 byte average packet size)

*- bottleneck was the physical interface speed, not forwarding CPU

As the routers are capable to forward significantly more traffic than default and performance license allows, the numbers in table 3 for these license tiers are close to real-life when services are getting added. It is safe to choose ISR 4000 with “factory default” and “performance” levels and in most cases lower models with a “performance” license if you plan to use multiple services.

Recently added boost license removes shaping completely. Table 3 displays PPS values for ISR 4000, however, most of the routers didn’t have high CPU utilization, as the bottleneck was at the interface clock speed. The calculation is based on an IMIX size of 330 Bytes.

The data provided should be used as an only approximation, as there are many variables that can affect actual device performance which also will not scale linearly with CPU load increase.

ISR 1100

ISR 1100 is a new branch office platform running IOS-XE and similar to Cisco 890 and 1921. Published performance numbers are listed in Table 4. IP forwarding of ISR 1100 is comparable to ISR 4221 with a boost license. Note that ISR 1100 doesn’t support voice features.

Platform	RFC-2544 (Mbps, IMIX)	RFC-2544 (pps, IMIX)	Encryption (Mbps, AES 256, IMIX)	NAT (Mbps, IMIX)	ACL + NAT + HQoS (Mbps, IMIX)
C1100-4P	1,252	475,000	230	660	330
C1100-8P	1,750	660,000	335	960	510

Table 4. ISR 1100 Performance

ASR 1000

In the cases when you need more than 10Gbps of throughput provided by ISR 4461, ASR 1000 will be the platform of choice. All models in the ASR 1000 range have 2 dedicated hardware components – RP (Route Processor) and ESP (Embedded Service Processor). RP is responsible for control-plane operations and ESP for data forwarding.

Lower-end models, such as ASR1001-X and ASR1002-X have RP and ESP integrated into chassis. The throughput of the system depends on ESP, which runs Cisco-proprietary programmable ASICs called Quantum Flow Processor (QFP).

The performance of 3 integrated models is shown in Table 5. For the models presented in Table 5, an incremental throughput license is required.

Model	ESP Bandwidth (Mbps)	Throughput (pps)
ASR1001-X	20,000	19,000,000
ASR1002-X	30,000	36,000,000
ASR1002-HX	100,000	58,000,000