May 2025
Intermediate to advanced
920 pages
13h 33m
Chinese
Content preview from SDN时代中的MPLS
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第 14 章 TE 带宽预留 TE 带宽预订
本作品已使用人工智能进行翻译。欢迎您提供反馈和意见：translation-feedback@oreilly.com
带宽预留是一个重要工具，您可以用它来完成以下工作：
-
避免 ISP 主干网等流量较大的网络出现链路拥塞。
-
确保最关键的应用程序有可用的带宽资源。
本章将介绍执行带宽预留所需的控制平面。迄今为止，能够在网络中实际预留带宽的协议只有 RSVP-TE。大多数转发平面细节，特别是某些流量与某些 LSP 的细粒度映射，是每个平台所特有的，超出了本书的讨论范围。
备注
本书不涉及 DiffServ-TE。DiffServ-TE 并未广泛部署。
第 13 章讨论的流量工程 (TE) 链路约束非常简单，用单个数字表示。本章将介绍更复杂的 TE 用例，包括复合 TE 链路属性（如带宽）。
TE 静态带宽限制
下一个 TE 链路特性是带宽。带宽有点特殊。它不再是单一属性，而是一组属性，可在 IGP 的链路状态数据库、流量工程 数据库 (TED) 和 RSVP-TE 报文中找到。
TE 带宽属性
让我们来看看构成 TE 带宽的不同属性。
最大带宽（4 个字节）
这是物理接口带宽（如 10GE 接口为 1.25 GByte/s）。通常情况下，该参数继承自接口带宽，但也可以手动设置。此参数不用于 TE 计算，纯属信息性参数。
最大可预留带宽（4 个八位字节）
这是允许 RSVP-TE 预留的带宽。它可以大于最大带宽（如果允许 RSVP-TE 超额订阅）、等于最大带宽（如果 RSVP-TE 占用了所有接口带宽）或小于最大带宽（如果不允许 RSVP-TE 占用全部接口带宽）。通常，该参数是手动配置的。如果没有明确配置，Junos 的默认值是全部接口带宽，而 IOS XR 的默认值是零。
每个优先级的未预留带宽（8 x 4 个八位字节）
这是一组八个计数器，用于跟踪每个 RSVP-TE 优先级的可用带宽（优先级将在本章后面讨论）。虽然前两个参数比较稳定（启动 IGP 后，会持续公布相同的值），但未预留带宽是动态变化的。每次建立新的带宽预留 LSP，或拆除现有的带宽预留 LSP，或改变其带宽预留时，都会调整该参数的值，并通过 IGP 泛洪。实际上，当带宽变化不大时，典型的 IGP 实现会设置一些阈值来抑制泛洪。
综上所述，IGP 使用 40 个八位位组（4 + 4 + 32）以及正常的 TLV 标头来分发带宽信息。所有带宽值的单位都是字节/秒（而不是比特/秒）。带宽是随着 OSPF 和 IS-IS 中最初的 TE 扩展引入的。
默认 TE 接口带宽
说完这一小段理论，让我们进入实验室。首先，Junos 和 IOS XR 的默认行为完全不同。如前所述，在没有任何显式 RSVP-TE 带宽配置的情况下，Junos 允许 RSVP-TE 使用全部接口带宽，而 IOS XR 不允许 RSVP-TE 预留任何带宽。
例 14-1. 在 PE1 上使用默认带宽的 RSVP 接口状态（Junos）
juniper@PE1> show rsvp interface RSVP interface: 2 active Active Subscr- Static Available Reserved Highwater Interface St resv iption BW BW BW mark ge-2/0/2.0 Up 8 100% 1000Mbps 1000Mbps 0bps 0bps ge-2/0/3.0 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.