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MPLS
多协议标签交换将虚电路转发嫁接到数据报互联网上：边缘路由器将每个到达的分组分类到一个转发等价类，并附加一个短的固定长度标签，该标签携带在链路层与网络层之间的垫片首部中；内部路由器通过精确匹配的标签交换进行转发，而从不读取 IP 地址；控制平面仍是普通的 IP 路由，因此标签遵循相同的路径，除非显式路由另有选择；该技术的持久应用包括在无法进行 IP 查找的设备上进行转发、沿预计算路径的流量工程，以及通过堆叠第二个标签来区分客户的虚拟专用网。
1. The Shim
The Shim
2. Bindings and Classes
Bindings and Classes
3. Same Routes, Cheaper Forwarding
Same Routes, Cheaper Forwarding
4. Explicit Routes and Private Networks
Explicit Routes and Private Networks
5. What the label replaces
Inside an MPLS domain, what does a label-switching router examine when forwarding a packet?
6. Where the shim sits
Where is an MPLS label carried in a packet?
7. Equivalence classes
MPLS forwarding tables are indexed by class rather than by address. What exactly is a forwarding equivalence class?
8. Engineering the path
An operator wants certain traffic to use an underutilized long path instead of the congested shortest one. How does MPLS make that possible?
9. The VPN stack
Two customers of one provider both number their sites with the same private address range. How does the provider's MPLS backbone keep them apart?
10. Why not for speed
What became of MPLS's original promise of faster forwarding than IP?
11. The classifier
At an MPLS domain's edge, which router performs the full IP lookup and pushes the first label onto a packet?
12. The shim width
An MPLS label shim header is how many bits long?
13. The swap
An interior label-switching router rewrites the incoming label to the outgoing label, an operation called what?
14. Outer and inner
In an MPLS VPN, the label that names the customer is the inner label, while the label that tunnels the packet across the backbone is the what?