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Re: 为什么bgp不能触发建立LSP?

Label-binding information can be distributed using the LDP or by piggybacking the label-binding information on top of modified routing protocols.

Link-state routing protocols such as OSPF flood routing information among a set of routers that are not necessarily adjacent, whereas label-binding information is distributed only among adjacent routers. This makes link-state routing protocols unsuitable for distributing label-binding information. However, extensions to routing protocols such as PIM and BGP can be used to distribute label-binding information. This makes the distribution of label-binding information consistent with the distribution of routing information and avoids a rare condition wherein an MPLS node
might receive label-binding information and not have proper routing information. It also simplifies overall system operation because it obviates the need for a separate protocol such as LDP to distribute label-binding information.

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Re: 为什么bgp不能触发建立LSP?

你的意思是说 lable只能在直连的设备间发送,使用bgp可能造成有标签,没路由。是吧。

This makes link-state routing protocols unsuitable for distributing label-binding information。这句话有问题吧,实际应用中就有用ospf 或isis 的

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Re: 为什么bgp不能触发建立LSP?

意思是说OSPF在FLOOD路由信息时,有可能是不需要建立adjacent的,然而,标记信息是在adjacent的路由器上分发的。所以不可以直接用OSPF等链路协议直接分发label,也因此需要LDP这个协议来分发标记。而向PIM和扩展BGP自己是可以分发标记信息的。由于BGP发label-binding info和routing info是相同的方式,因此可以避免在某些极端环境下MPLS节点收到LABEL但是没有路由的情况。而且可以使事情变得更简单,因为仅需1种协议即可干2间事情。

因此BGP不会触发LDP建立LSP,因为 BGP本身就可以完成LDP的功能。

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