ZebOS 7.5.1开发者指南：智能网络软件架构详解

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Zebos Arch Developer Guide 7.5.1 是针对路由工程师和其他网络专业人员的官方指南，它详细介绍了 ZebOS（Intelligent Network Software）这款智能网络软件的功能与特性。ZebOS 是 IPInfusion 公司的产品，版本发布于 2008 年 1 月，其设计目标是为用户提供一个全面而深入的理解，以便他们能够有效地进行网络架构设计、配置和优化。该文档涵盖了 ZebOS 的核心架构和开发人员需要掌握的关键概念。作为开发者指南，读者可以预期找到以下内容： 1. **ZebOS架构概述**：这部分会介绍 ZebOS 的体系结构，包括硬件抽象层（HAL）、网络处理单元（NPU）、操作系统内核、以及模块化的软件组件，如路由引擎、负载均衡器和安全服务等。 2. **接口和编程模型**：指南会说明如何与 ZebOS 进行交互，包括API接口的使用，数据包处理的原理，以及如何编写适应 ZebOS 环境的高效代码。 3. **功能特性详解**：涉及的具体功能如高级路由策略、QoS管理、流量工程、多协议支持（如IPv4/IPv6）以及网络设备虚拟化等将被详细介绍，并可能包括示例代码或配置示例。 4. **性能优化与调试**：开发者可能会学到如何分析和优化ZebOS系统的性能瓶颈，以及如何通过日志和调试工具定位并解决问题。 5. **安全性和合规性**：由于文档强调了保密协议，这部分会涵盖ZebOS的安全特性，如数据加密、访问控制和防止未授权访问的方法。 6. **许可证和法律条款**：提醒开发者在使用软件时必须遵守的许可协议，包括版权限制和非公开披露条款，确保合法合规操作。 7. **支持和联系方式**：提供IPInfusion Inc.的技术支持途径，包括电话、邮件地址等，方便用户在遇到问题时获取帮助。 Zebos Arch Developer Guide 7.5.1 是网络专业人士不可或缺的参考资料，无论是初次接触 ZebOS 的开发者还是经验丰富的网络工程师，都能从中获取宝贵的知识和实践经验。阅读和理解这个指南对于提升在ZebOS网络环境中工作的效率至关重要。

ZebOS Advanced Routing Suite

The Future of the Internet: IPv6 and IP Infusion

The Internet of today is a legacy system, far too limited to support continued, rapid growth. The original design for the

Internet Protocol (IPv4) is over 20 years old. A new addressing scheme, Internet Protocol Version 6 (IPv6) improves

Internet quality, scalability, and security. Some other benefits of IPv6 are:

• Expanded addressing. An increase in the available addresses allows many more devices to connect to the

Internet, and enable the growth of Internet applications (such as VoIP).

• Simplified header format. A new header format improves routing efficiency.

• Improved extension and option support. Implementations of header extensions improves the ways in which

routers process packets.

• Flow labeling. Related packets can be treated as streams, improving reliability.

• Improved Authentication and Privacy. Security measures are built into the IPv6 protocol.

IETF Membership

IP Infusion is a member of the IETF, and will continue its participation in this and other standards bodies. IPv6

functionality is an integral part of the ZebOS ARS, and fully supports the most recent drafts and specifications (RFCs)

from the IETF of the IPv4 and IPv6 versions of RIP, OSPF, and BGP4.

The IPv6 RFCs supported by the ZebOS Advanced Routing Suite are:

•RFC 2080 (RIPng)

•RFC 2740 (OSPF for IPv6)

•RFC 1771 and 2545 (BGP4 and Use of BGP4 Multi-protocol Extensions for IPv6 Inter-Domain Routing)

IP Infusion Product Overview

RIP

A distance-vector protocol, Routing Information Protocol (RIP) is an interior gateway protocol (IGP) that uses hop

counts as its metrics. The ZebOS ARS RIP module supports RFCs 1058 and 1723; the RIPv2 module supports more

fields in the RIP packets, and supports security authentication features.

At regular intervals of the routing update timer (a default value of 30 seconds), and at the time of change in the

topology, the RIP router sends update messages to other routers. The listening routers update their route table with the

new route, and increase the metric value of the path by one (referred to as a hop count). The router recognizes the IP

address advertising router as the next hop, then sends the routing updates to other routers. A maximum allowable hop

count is 15. If a router reaches a metric value of 16 or more (referred to as infinity), the destination is identified as

unreachable. This avoids the indefinite routing loops. The split-horizon and hold-down features are used to avoid

propagation incorrect routing information. The route becomes not valid when the route time-out timer expires; it

remains in the table until the route-flush timer expires.

OSPF

A link-state routing protocol, Open Shortest Path First (OSPF) is an interior gateway protocol (IGP) that uses the

shortest path first (SPF) Dijsktra algorithm for the Internet, and is specified in RFC 1247.

OSPF sends link-state advertisements (LSAs) to all other routers within the same hierarchical area. Data on attached

interfaces, metrics used, and other variables, are included in OSPF LSAs. As OSPF routers accumulate link-state data,

they use the SPF algorithm to calculate the shortest path to each node.

An Autonomous System (AS) or Domain is defined as a group of networks with common routing infrastructure. OSPF

can work in one AS; or receive or send routes from or to different AS systems. Autonomous systems consist of areas.

An area is a group of neighboring networks or attached hosts. A router attached to multiple areas with its interfaces is

called an Area Border Router (ABR). It creates a distinct topological database: a group of LSAs received from all

routers in the same area, for each area. All the routers in the same area have an identical topological database. OSPF

routing traffic is restricted in the area because areas are unknown to each other. The routing information is distributed

between areas, area border routers, networks, and connected routers by the OSPF backbone.

All backbone OSPF area routers use the same procedures and algorithms to maintain routing information within the

backbone that any area router would. The backbone topology is invisible to all routers within an area. The individual

area topologies are invisible to the backbone. Sometimes the backbone is not a contiguous area. Virtual links function

as if they were direct links, and are configured between backbone routers that share a link to a non-backbone area.

AS border routers running OSPF learn about exterior routes through exterior gateway protocols (EGPs) such as the

Border Gateway Protocol (BGP).

During boot-up, an OSPF router initializes its routing-protocol-specific data structures and tables. When the lower-layer

protocols with which it interfaces are functional, it sends the OSPF Hello protocol packets to find neighboring routers. A

router sends Hello packets as keep-alive packets, informing other routers about its continuing functionality.

Two routers are adjacent when their link state databases are synchronized. Multi-access networks have more than two

routers. On multi-access networks, the hello protocol chooses a designated router and a designated backup-router.

The designated router generates LSAs for the entire multi-access network, and reduces network traffic and the size of

the topological database. The designated router also determines the adjacency of routers and the synchronization of

their topological databases. The data on a router's adjacencies or state changes are provided by periodic transmission

of an LSA. Failed routers are detected, and topology is changed quickly by comparison of adjacencies to link states.

Each router calculates a shortest path tree, with itself as a root, from the topological database generated from these

LSAs. This shortest path tree creates a routing table.

IP Infusion Product Overview

BGP

Border Gateway Protocol (BGP) is an exterior gateway protocol (EGP) that determines the best path in networks,

performs optimal routing between multiple autonomous systems or domains, and exchanges routing information with

other BGP systems. The RFCs 1771 (BGP4), 1654 (first BGP4 specification), and 1105, 1163, 1267 (older version of

BGP) describe BGP and BGP4.

Multiple-peer BGP routers in different autonomous systems, or administrative domains on the same physical network,

support consistent internetwork topology using inter-autonomous system routing. Multiple-peer BGP routers within the

same AS support consistent system topology using inter-autonomous system routing. BGP determines the router to

serve as the connection point for specific external autonomous system routing services. Multiple-peer BGP routers

transport traffic across an autonomous system that does not run BGP using pass-through autonomous-systems

routing. In this case, if the traffic does not originate, or is destined for an autonomous system under consideration, the

AS is used only to transport (pass-through) the traffic using another intra-autonomous system routing protocol.

BGP exchanges information about the list of autonomous system paths with other BGP systems. A connectivity

mapping between autonomous systems is created, routing loops are pruned, and other autonomous systems-level

policy decisions are taken. Each BGP router maintains a routing table of all feasible and optimal paths to other

networks and incrementally updates the routing information received from other peer BGP routers.

The BGP routing metric describes the preference of the path, and is assigned to each link by the network administrator.

The network administrator assigns this value to a link depending on path criteria such as:

•the number of autonomous systems through which the path passes

•the history of stability

•the line speed

• any delays

• cost per packet

MPLS

Multi-Protocol Label Switching (MPLS) brings the Traffic Engineering (TE) capabilities of ATM to a packet-based

network. It tags IP packets with labels that specify a route and priority. It combines the scalability and flexibility of

routing with performance and traffic management of layer 2 switching. Routing protocols such as OSPF or IS-IS define

reachability, and the binding and mapping between Forwarding Equivalence Class (FEC) and next-hop addresses.

MPLS gets routing information from OSPF or IS-IS. No changes are required to routing protocols to support MPLS,

MPLS-TE, MPLS QoS, or MPLS-BGP virtual private networks (VPNs). It works with any control protocol other than IP,

and layers on top of any link-layer protocol. At the network layer, MPLS supports IPv6, IPv4, IPX and AppleTalk. At the

link layer, MPLS supports Ethernet, Token Ring, FDDI, ATM, Frame Relay, and Point-to-Point Links. It supports most

transport media (ATM, FR, POS, Ethernet, etc.), instead of being tied to a specific Layer-2 encapsulation. Because it

uses IP for its addressing, it uses common routing/signaling protocols (OSPF, I S- IS , R SVP e t c . ) .

In an MPLS (RFC 3031, 3032) network, incoming packets are assigned a label by a label edge router (LER). Packets

are forwarded along a label switch path (LSP) where each label switch router (LSR) makes forwarding decisions

depending on the contents of the label. At each hop, the LSR strips off the existing label, and assigns a new label that

tells the next hop how to forward the packet.

Label Switch Paths (LSPs) are configured by network operators to guarantee a certain level of performance, to route

around network congestion, or to create IP tunnels for network-based virtual private networks. An LSP can be

established that crosses multiple Layer-2 transports, such as ATM, Frame Relay or Ethernet. This creates end-to-end

circuits, with specific performance characteristics, across any type of transport medium, and eliminates the need for

overlay networks or Layer-2-only control mechanisms. MPLS evolved from earlier technologies, such as Cisco's Tag

Switching, IBM's ARIS, and Toshiba's Cell-Switched Router.

IP Infusion Product Overview

RSVP-TE and LDP

RSVP-TE extends Resource Reservation Protocol (RSVP), and CR-LDP extends Label Distribution Protocol (LDP), to

support label distribution and explicit routing. Traffic Engineering (TE) selects paths chosen by data traffic to balance

the traffic load on the various links, routers, and switches in the network. Traffic engineering is important in networks

with multiple parallel or alternate paths.

The label assigned to a packet represents the Forwarding Equivalence Class (FEC) to which that packet is assigned.

An FEC is a set of packets that are forwarded in the same manner (for example, over the same path with the same

forwarding treatment). An LSP is provisioned using Label Distribution Protocols (LDPs, RFC 3036) such as RSVP-TE

or CR-LDP. Either of these protocols establishes a path through an MPLS network, and reserves necessary resources

to meet pre-defined service requirements for the data path. The LDP specification lets an LSR distribute labels to its

LDP peers; and enables LSR peers to find each other, and establish communication. CR-LDP and RSVP-TE are

signaling mechanisms used to support traffic engineering across an MPLS backbone.

MPLS-TE and MPLS VPN

MPLS-TE makes use of the following concepts:

•Constrained shortest path first (CSPF) algorithm, a modified version of the well-known SPF algorithm, is used in

path calculation.

•RSVP-TE extension or CR-LDP is used to establish the forwarding state along the path, and to reserve resources

along the path.

•Link-state routing protocols with an extension (OSPF with Opaque LSAs or TE, IS-IS with Link State Packets TLV

[type, length, value]) keep track of topology change propagation

Because MPLS allows the creation of virtual circuits or tunnels across an IP network, providers use MPLS to provision

VPN services. There are multiple proposals for using MPLS to provision IP-based VPNs. MPLS-BGP/VPN enables

MPLS-VPNs (RFC 2547) via extensions to Border Gateway Protocol (BGP); BGP propagates VPN-IPv4 data using the

BGP multi-protocol extensions (MP-BGP) for handling these extended addresses. MP-BGP propagates reachability

data (VPN-IPv4 addresses) among Edge Label Switch Routers (Provider Edge router). The reachability data for a

given VPN are propagated only to other members of that VPN. The BGP multi-protocol extensions identify the valid

recipients for VPN routing data. All members of the VPN learn routes from other members. MP-BGP is implemented

using either IPV6 BGP4+, IPv4 multicast (MBGP), or MPLS VPN/BGP (BGP-AD for AutoDiscovery). MPLS can also be

used to create IP-VPNs, based on the idea of maintaining separate routing tables for various VPNs, and does not

involve BGP.

RSVP-TE

Resource Reservation Protocol (RSVP) is an independent protocol that establishes a level of service quality for a data

stream or path through a network. Host machines use RSVP to request specific service quality from a network for

particular data streams. Routers along these data streams use RSVP to deliver quality of service requests to all nodes

in a path or data stream, to establish the level of service, and to maintain the quality of service.

This protocol is a signaling protocol that supports explicit routing capability. To do this, a simple EXPLICIT_ROUTE

object is incorporated into RSVP PATH messages. The object encapsulates a sequence of hops which constitutes the

explicitly routed path. Using this object, the paths taken by the label-switched RSVP-MPLS flows can be predetermined

without conventional IP routing. The explicitly routed path can be administratively specified or computed based on

CSPF and policy requirements, and the current state of the network.

One useful application of explicit routing is Traffic Engineering (TE). Using explicitly routed LSPs, an ingress node can

control the path through which traffic flows from itself, through the MPLS network, to the egress node. Explicit routing is

therefore useful for the optimization of network resources and an increase in the quality of traffic-oriented performance.

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