Application viewpoint: Router Protocol experience summary

With the development of China's routing technology, we have also promoted the improvement of the router protocol. Here we mainly introduce the experience of the Router Protocol. In the design of the IP network, the fault cannot be restored within less than 1 s. However, applications such as VoIP and IPTV require rapid Fault Detection and recovery. As a draft IETF standard, Bidirectional Forwarding Detection (BFD) provides a method for detecting the forwarding capability of links or systems to improve fault detection and recovery speeds.

Technically, BFD establishes a session on two routers to monitor two-way forwarding routes between the two routers and serve the upper-layer Router Protocol. BFD does not discover the mechanism, but is notified of WHO to establish a session with by the upper-layer protocol of the service, after a session is established, if the peer BFD control packet is not received within the detection time, it is deemed that a fault has occurred, and the upper-layer protocol of the service is notified, and the upper-layer protocol is processed accordingly.

BFD is a simple "Hello" protocol. It periodically sends detection packets through session channels established between systems, if a system does not receive the peer detection packet for a long enough time, it is deemed that a part of the two-way channel to the adjacent system has a fault. Although the BFD Router Protocol is relatively simple, it is a very new technology, so how to test it is the focus of current routing equipment vendors. An enterprise uses IXIA to test the topology of the BFD protocol. IXIA supports single-hop and multi-hop Session tests. In addition, it has the following features:

1) one port can simulate multiple BFD routers, multiple interfaces, and multiple Sessions.

2) supports Asynchronous mode and Demand mode verification, and Echo function.

3) the BFD protocol can be applied separately to implement Function Testing and Session capacity testing.

(4) BFD protocol can also be used with BGP4, BGP4 +, OSPFv2/v3, ISISv4/v6, VPN and PIM-SMv4/v6 vro protocols.

Graceful Restart (perfect Restart) is a mechanism designed to minimize the impact of Router Protocol Restart. It aims to minimize route Jitter Caused by router Restart, reduces the waste of route computing resources and network bandwidth resources. Various router protocols such as OSPF, BGP, ISIS and MPLS protocol RSVP-TE and LDP protocols both need to support the GR function for Non-Stop Forwarding ).

The core of the GR mechanism is that when the Router Protocol of a device is restarted, GR Helper can be notified to maintain a stable relationship between its neighbors and routes within a certain period of time. After the routing protocol is restarted, GR Helper synchronizes the routing information to restore the routing information of the device to the status before the restart. During the Protocol restart process, the network routing and forwarding remain highly stable, and the packet forwarding path remains unchanged. The entire system can continuously forward IP packets. This process is called Perfect restart. Figure 4 shows the specific communication process between GR Restarer and GR Helper. IXIA supports the GR features of vro and MPLS protocols. See table 2. The test of the GR feature is relatively simple. You need to support the GR feature of the corresponding protocol to verify whether the GR feature of the tested device is valid. Figure 4 is also a typical test environment.

In principle, QoS evaluates the service capability of packets transmitted over the network. As the services provided by the network are diverse, QoS evaluation can be based on different aspects. QoS is usually used to evaluate the support service capability for core requirements such as latency, latency jitter, and packet loss rate during data packet transmission. There are four types of QoS:

1) 802.1 p VLAN priority: it is located in the second-layer packet header. It is suitable for scenarios where no layer-3 header needs to be analyzed and QoS needs to be ensured in the second-layer environment.

2) IP priority: the TOS field in the IP Header has eight bits. The first three bits indicate the IP priority. The value range is 0 ~ 7.

3) ToS priority: the TOS field in the IP Header has eight bits, 3rd ~ 6. These four bits indicate the ToS priority. The value range is 0 ~ 15.

4) DSCP priority: four types of traffic are defined:

Expedited Forwarding, EF) class. Make sure to forward the Assured Forwarding, AF) class. There are four sub-categories. Each sub-category is divided into three discard priorities, which can be subdivided into AF service levels. The QoS level of the AF class is lower than that of the EF class. Class Selector, CS) compatible with the IP priority ). From the IP ToS field, there are 8 categories. Best Effort to forward the Best Effort, BE) class. It is a special type in CS and has no guarantee. After the AF class is exceeded, it can BE downgraded to BE class, and the existing IP network traffic is also default to this class.

The QoS priority remarking function uses the ACL for stream recognition and re-specifies the priority for matched packets. QoS testing is a traditional test item, and all the testing instruments have good support. However, QoS re-labeling testing is relatively complicated, because in terms of the testing principle, the performance test must track specific fields. However, because QoS is "remarked", the specific fields tracked are changed. Currently, only the multi-field tracking feature provided by IXIA can support the QoS re-marking feature, and can be combined with the control layer test of the routing switch device. Taking Figure 5 as an example, a QoS priority can be "remarked" by The tested device as multiple other priorities. The traditional method of "packet capture" analysis is powerless.

The multi-field tracking feature of IXIA is flexible. In addition to testing the QoS re-labeling feature, it can also be used for VLAN leakage, tests on important features such as PBB/PBT forwarding performance of Carrier-class Ethernet. At present, multiple device manufacturers and evaluation institutions use this feature to evaluate the QoS remarking performance of devices and PBB/PBT forwarding performance. IXIA's leading route exchange test solution can fully meet and exceed customers' expectations for simulation of various complex network environments, and provide real environment and traffic simulation for Route exchange devices, with the transition from traditional routing testing to the latest routing method, as users demand high performance, high density and high scalability, IXIA's latest Optixia test platform and IxNetwork route exchange test software can fully meet and exceed the diversified testing requirements of users.