02_01_发现LDP邻居-Work Blog

Label Assignment and Distribution
YES LAB
Discovering LDP Neighbors
YES LAB
w.w.v.yeslab.com.cn MPLS LDP
YES LAB
有了标签，转发是很简单的事，但是如何生成标签，在 MPLS 中有多种办法
来生成和分发标签。在 MPLS 中，其中一种就是 LDP (Label Distribution
Protocol) ，是一个动态的生成标签的协议。
其实 LDP 与 IP 中的动态路山协议十分相像，都具备如下的几大要素：
报文（或者叫消息）
· 邻居的自动发现和维护机制
一套算法，用来根据搜集到的信息计算最终结果。
只不过前者计算的结果是标签，后者是路山。
' 垆 y 巳 ab 工 0m 工 n wwwyeslab-net Outline
YES LAB
— Overview
— Establishing an LDP Adjacent Session
— What Are LDP Hello Messages?
— Negotiating Label Space
— Discovering LDP Neighbors
— Negotiating LDP Sessions
— Discovering Nonadjacent Neighbors
— Summary
w.w.v.yeslab.com.cn LDP Neighbor Discovery
Hello@iWiåC1+UZ646
UDP: Hello
1.0.0.2:1064
UDP: Hello
UDP: Hell
MPLS A
1.0.0.1
_0.2:646
UDP; Hello
1.0.0.1:1051
1.0.0.1:646)
1.0.0.4:1033 • 224_0.0.2:
UDP: Hello
1.0.0.4:1034 224.0.0.2:646
UDP: Hello
1.004:1035 2240.0.2:
YES LAB
MPLS B
1.0.0.2
1.0.0.3
MPLS D
1.0.0.4
• An LDP session is established from the router with the higher IP address.
w.w.v.yeslab.com.cn $LDP 会话的建立和维护邻居发现；通过互发 h 刨 0 报文（ UDP / prot ： 646 刀 p ： 224 ． 0 ． 0 ． 2 ）建立 TCP 连接：由地址大的一方主动发起。 (TCP/port:646) 会话初始化：由 Master 发出初始化消息，并携带协商参数。由 ve 检查参数能否接受，如果能则发送初始化消息，并携带协商参数。并随后发送 keep 訕 ve 消息。 master 检查参数能否接受，如果能则发送 keepalive\i±j 息。相互收到 keep 訕 ve 消息，会话建立。期间收到任何差错消息，均关闭会话，断开 TCP 连接对等人首先交换初始化消息。 Peers first exchange initialization messages. YES LAB M M M 会 The session is ready to exchange label mappings after receiving the first keepalive. 话准备好在收到第一个保持活动后交换标签映射。 " M' y 巳 ab 工日 m 工 n www-yeslab-net$ LDP Discovery of Nonadjacent
Neighbors
YES LAB
— LDP neighbor discovery of nonadjacent neighbors differs
from normal discovery only in the addressing of hello
• Hello packets use unicast IP addresses instead of
multicast add resses.
— When a neighbor is discovered, the mechanism to
establish a session is the same.
w.w.v.yeslab.com.cn Targeted LDP Session Applica
YES LAB
- MPLS Fast Reroute (FRR)
(FRR)
— MPLS Nonstop Forwarding(NSF) (NSF)
— MPLS LDP Session Protection MPLS LDp±iÉfRåP
w.w.v.yeslab.com.cn Summary
YES LAB
— UDP multicast is used to discover adjacent LDP neighbors, while TCP is used
to establish a session.
— LDP hello messages contain an identifier field that uniquely
identifies the neighbor and the label space. LDP helloii'j
— Per-platform label space requiresonlyone LDP session.
+LDP4?ifi0
w.w.v.yeslab.com.cn Summary(cont.)
YES LAB
— An LDP session is initiated in TCP from the higher IP address router.dE$Q
— LDP session negotiation is a three-step process: establishing the TCP session,
exchanging initialization messages, and exchanging initial keepalive
messages.
— Nonadjacent neighbordiscoveryisaccomplished by usingunicast
IP addresses instead of multicast.
w.w.v.yeslab.com.cn