01_02_引入MPLS标签和标签堆栈

2019年7月27日 05:13 作者：金淼淋分类：MPLS  588

Outline — Overview — What Are MPLS Labels? — What Is the MPLS Label Format? — Where Are MPLS Labels Inserted? — What Is an MPLS Label Stack? — What Are MPLS Label Operations? — Summary w.w.v.yeslab.com.cn YES LAB (+LÆMPLSbj*E? MPLS Labels YES LAB — Are 4 byte identifiers used for forwarding decisions,eh} — Identify a forwarding equivalence class (fry: (FEC) — Have local significance • Each LSR independently maps a label to an FEC in a label • Label bindings are exchanged between w.w.v.yeslab.com.cn $YES LAB 》属于某特定组的组播报文》目的甲地址匹配了某一个特定前缀的报文》根据 DCSP 字段，有相同 QOS 策略的报文 >MPLS\/PN 中，属于同一个 VPN 的报文》报文的目的甲地址属于 BGP 学习到的路由，并且该路由的下一跳地址相同 ' 垆 y 巳 ab 工 0m 工 n wwwyeslab-net$ Label Switched Path (LSP) Intf In 3 3 Label In 50 Dest 47.1 YES LAB Intf Out Intf In 3 Dest Intf out 47.1 47.3 3 Label out 50 Dest 47.1 2 lntf out Label out 40 Intf In 3 Label In 40 w 47.1.1.1 47.2 11)47.1.1.1 (LSP) , w.w.v.yeslab.com.cn MPLS Labels: Frame-Mode Frame Header Layer 2 Frame Header Layer 2 Label Shim Header IP Header Layer 3 IP Header Layer 3 w.w.v.yeslab.com.cn YES LAB Payload (From IP Network) (To Frame-Mode Core) Payload Example: MPLS Label Stac Frame Header TE Label LDP Label VPN Label IP Header YES LAB Outer Label Inner Labels — The outer label is used for switching the packet in the MPLS networlt/ ointsto the TE destination). — Inner labels are used to separate packets at egress points fpinhs to egress router and identifies VPN). wwwyeslabxom.cn www.yeslab.net Example: MPLS Label Stack Fo Frame Top Middle Bottom Header PID=ox8847 IP Header YES LAB Pay load - The PID in a Layer 2 header specifies that the payload starts with a label (labels) followed by an IP header. The bottom-of-stack bit indicates whether the label is the last label in the stack. — The receiving router uses the top label only. (0800 (GPPP+: MPLSCP, ffhdox8281*bjåR V}iA'-4ffhd0X0281 MPLS Label Operations YES LAB — An LSR can perform these functions:LsRüJPIikfjPIFJJJfjÉ: • Insert (impose or push) a label or a stack of labels on ingress edge • Swap a label with a next-hop label or a stack of labels in thecore. • Remove (pop) a label on egress edge LSR. w.w.v.yeslab.com.cn MPLS Label Operations: Frame 10.1.1.1 MPLS Domain 23 10.1.1.1 IP Lookup 10.0.0.0/8-»1abel 23 YES LAB 10.1.1.1 LAB label 23. label 25 25 10.1.1.1 LAB label 25 pop IP Lookup 10.0.O.O/8*Nexthop On ingress, a label is assigned and imposed. LSRs in the core swap labels based on the contents of the label forwarding On egress, the label is removed and a routing lookup is used to forward the packet.