Chapter 11: Network Performance Considerations: Coexistence of IPv4 and IPv6

Cisco Press

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The IPv6 forwarding performance is at line rate below IMIX average packet sizes. On the other hand, mid-range routers from this family can maintain high forwarding performance even with advanced features enabled such as access control lists (ACLs). This is not always the case with mid-range hardware platforms available on the market. Table 11-3 shows the impact of ACLs on the performance of a Cisco 7200 router with an NPE-G1 processor. Unidirectional traffic was used and 100 ACLs were enabled on the ingress interface. The data is graphically represented in Figure 11-5.

Table 11-3 Cisco 7200 NPE-G1 Performance Between 2 Gigabit Ethernet Interfaces, Unidirectional, With and Without ACLs

Packet Size (Ethernet II)

IPv6 Without ACLs (pps)

IPv6 With ACLs (pps)

Maximum (pps)

64 bytes

561,209

287,377

1,225,490

128 bytes

558,280

288,403

753,012

256 bytes

425,170

288,988

425,170

512 bytes

227,272

227,272

227,273

1024 bytes

117,702

117,702

117,702

1280 bytes

94,840

94,840

94,841

1518 bytes

81,274

81,274

81,274

Figure 11-5

Figure 11-5

IPv6 Forwarding Performance With and Without ACLs (Cisco 7206)


Note - If a router is evaluated in a role that involves the extensive use of advanced features such as ACLs, it is important to evaluate the impact of these features on its forwarding performance.



Note - The router performance when running advanced features is of particular importance in the case of IPv6. Transition mechanisms such as IPv6 over IPv4 tunneling are falling in this category, so it is important to evaluate a router's performance in this context. Software platforms are well positioned in this case because packet switching is done in software for both native and tunneled IPv6 traffic. Hardware assist for IPv6 over IPv4 tunneling is not generally available.


When a mid-range platform is targeted for an aggregation role, a centralized, software forwarding design might be challenged by the high number of interfaces involved. In a distributed architecture, however, the forwarding performance is scaling linearly when interfaces are added to the system. An example of such a platform is the Cisco 7500 that leverages the distributed Cisco Express Forwarding (dCEF) feature. An example of forwarding performance numbers measured for the OC-3 interface of this router is shown in Table 11-4. Figure 11-6 also shows this data.

Table 11-4 Cisco 7500 RSP4 or RSP8 + VIP4-80 POSIP OC-3, Bidirectional, No ACL

Packet Size (Ethernet II)

OC-3 – IPv4 dCEF (pps)

OC-3 – IPv6 dCEF (pps)

Maximum (pps)

64 bytes

198,504

166,000

353,208

128 bytes

153,500

153,490

160,000

256 bytes

76,408

76,408

76,408

512 bytes

37,365

37,365

37,365

1024 bytes

18,480

18,480

18,480

1518 bytes

12,422

12,422

12,422

Figure 11-6

Figure 11-6

Example of IPv4 Versus IPv6 Forwarding Performance of a Mid-Range Router (Cisco 7500 – OC3).

Higher performance needs generally make hardware forwarding assistance necessary in high-end routers.

High-End Routers

Moving closer to the core of the network, routers need to support multiple very high-speed interfaces such as Gigabit Ethernet, 10 Gigabit Ethernet, OC-48, OC-192, and OC-768. To maintain line-rate forwarding, routers cannot rely on CPUs anymore; hardware assistance becomes necessary. To exemplify this need on high-end routers, Table 11-5 depicts the differences in performance on a Cisco Catalyst 6500 series switch and Cisco 7600 Series Router for various switching paths.

Table 11-5 Performance of Various Switching Paths on Catalyst 6500 / Cisco 7600

Switching Path

Performance

Process switched mode

10–30 Kpps

Software CEF switch mode

230 Kpps

Centralized PFC3 on a Supervisor Engine 720 for native IPv6 – Cisco IOS 12.2(17a)SX1

+20 Mpps

Supervisor Engine 720 with distributed PFC3 on linecards

+200 Mpps

This data clearly shows the performance enhancements that come through hardware assist. Actual performance numbers for another high-end Cisco router that performs IPv6 forwarding in hardware are shown in Table 11-6.

Table 11-6 Cisco 12000 Engine 3 POSIP OC-48 HDLC Encapsulation CRC32, Bidirectional, No ACL

Packet Size (Layer 2)

OC-48 – IPv4 (Mpps)

OC-48 – IPv6 (Mpps)

Maximum (Mpps)

64 bytes

3.846

3.846

4.103

128 bytes

2.321

2.321

2.321

256 bytes

1.156

1.156

1.156

512 bytes

0.579

0.579

0.579

1024 bytes

0.289

0.289

0.289

1500 bytes

0.198

0.198

0.198


Note - Consult Cisco documentation to identify the routers and router linecards that support hardware forwarding of IPv6.


Figure 11-7 shows the forwarding performance improvement at low packet sizes because of its implementation in hardware. The other advantage of hardware forwarding is that IPv4 and IPv6 traffic will not compete for processor resources. Turning IPv6 on is not going to impact the forwarding of existent IPv4 traffic.

Figure 11-7

Figure 11-7

Example of IPv4 Versus IPv6 Forwarding Performance of a High-End Router (Cisco 12000 – OC48)

Cisco CRS-1 is its flagship of core routers, and it represents the most compelling example of high performance achieved through advanced hardware forwarding design. Independent studies by the European Advanced Networking Test Center show that it can forward IPv4 and IPv6 traffic at line rate through OC-768 (40 Gbps) interfaces with and without advanced features enabled. The system throughput for the single chassis configuration is 640 Gbps, although the multichassis configuration is 1.28 terabits per second. It also achieves line rate at these speeds for traffic mixes (85 percent IPv4, and 15 percent IPv6).

6PE Forwarding Performance

6PE and 6VPE are key migration options in the deployment of IPv6. See the section "IPv6 over 6PE" in Chapter 3, "Delivering IPv6 Unicast Services," and Chapter 7, "VPN IPv6 Architecture and Services," for details about these technologies. IPv6 forwarding performance through a 6PE environment is an important factor when weighing a certain deployment strategy. A Multiprotocol Label Switching (MPLS)-enabled core has high forwarding performance, close to line rate, of labeled traffic irrespective of the IP version of the packets. It is thus up to the PE routers to avoid reducing the end-to-end forwarding performance of IPv6 in a 6PE deployment.

In the case of 6PE and 6VPE, there is a level of asymmetry in terms of forwarding performance. Routers will exhibit a certain performance when traffic flows from the IPv6 side toward the MPLS core (router performs label imposition) and when it flows in the opposite direction (router performs label disposition). For this reason, a simple bidirectional traffic test is not fully revealing because the forwarding performance result is shaped by the lowest of the performances in each individual direction. In this case, the right testing approach is to use unidirectional streams and analyze each direction separately.


Note - The same approach should be applied when evaluating the forwarding performance over IPv6 tunnels.


Table 11-7 lists the 6PE forwarding performance data for the OC-48 ISE card of the Cisco 12000. Forwarding is hardware assisted for this platform. The performance in the "label imposition" direction shapes the overall performance on the path. In the Cisco implementation of 6PE, a different label is usually associated with each prefix, so no IPv6 lookup is performed on the egress 6PE. For this reason, the expected performance in the "label disposition" direction is the usual MPLS performance (line rate on this card). This forwarding data is represented graphically in Figure 11-8.

Table 11-7 Unidirectional 6PE Traffic on Cisco 12000 with OC-48 Engine 3 Linecard

Packet size (IP)

Imposition - OC-48 (Mpps)

Disposition - OC-48 (Mpps)

64 bytes

3.8

3.84

128 bytes

1.91

1.95

256 bytes

1.11

1.11

512 bytes

0.570

0.570

1024 bytes

0.289

0.289

1500 bytes

0.198

0.198

Figure 11-8

Figure 11-8

6PE Forwarding Performance in the Label Imposition and Label Disposition Directions (Cisco 12000 – OC48)

The forwarding performance for 6PE is close to line rate for most (and the relevant) packet sizes. Similar high performance is also available with software-switched platforms, and that certainly qualifies the 6PE solution for large-scale, high-performance deployments.

IPv6 Router Performance Evaluation Checklist

For the time being, the IPv6 networks are small compared with IPv4, and the IPv6 traffic most likely represents a fraction of the existent IPv4 traffic. For these reasons, operators would tend to look at IPv6 performance in terms of its impact on the revenue-generating IPv4 services. As focus moves toward large-scale deployments, router IPv6 performance becomes an important factor in network planning and design.

This chapter underlines the relevant aspects of router performance while showing the importance of keeping in balance all the other factors relevant in router selection, such as feature richness and cost. It also discusses the impact of IPv6 protocol specificities on router performance. The chapter provides guidelines on practical and objective evaluation methodologies of router IPv6 performance. From a practical perspective, this information can be summarized in a checklist of major items to be verified when evaluating a router's IPv6 performance. Table 11-8 shows this list.

Table 11-8 IPv6 Router Performance Evaluation Checklist

Test Scope

Test Targets

Control plane

Evaluate the CPU impact of targeted IPv6 features. For routers that will operate in dual-stack mode, add the result to the operational CPU values (generated by IPv4) to see whether it will lead to comfortable overall CPUs (typically below 60 percent under regular traffic loads).

Evaluate the memory needs for the IPv6 routing tables. For routers that will operate in dual-stack mode, add to IPv4 memory use to see whether it leads to comfortable overall memory use.

Data plane

Measure unicast interface-to-interface and system-level throughput performance for basic IPv6 traffic and no advanced router features enabled. Pay particular attention to the throughput results above the IMIX average packet sizes.

Measure unicast interface-to-interface and system-level throughput performance for IPv6 traffic with various extension headers and no advanced router features enabled. Pay particular attention to the throughput results above the IMIX average packet sizes.

Measure unicast interface-to-interface and system-level throughput performance for basic IPv6 traffic with advanced router features (the features targeted for the deployment such as ACLs, QoS, and so on) enabled. Pay particular attention to the throughput results above the IMIX average packet sizes.

Evaluate the CPU impact of forwarding the expected IPv6 traffic rates. Both central and linecard (where applicable based on the router design) CPU should be measured.

Measure IPv6 multicast performance in terms of both forwarding rates and replication.

This chapter is also making the point that today's routers and layer 3 switches are ready to support large-scale, high-performance IPv6 networks. They deliver line-rate forwarding of IPv6 traffic in the range of packet sizes relevant for most applications. The data presented supports this statement in the case of platforms of various designs that address the entire market spectrum. IPv6 router performance meets the high standards set by IPv4.

Copyright © 2007 Pearson Education. All rights reserved.

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