Principle and configuration of MPLS

1.MPLS The background of

A packet is sent from the source to the destination host , All routers along the way must have a route to the destination address , On the WAN or LSP Your router is the destination of many routing entries , If you still look up the table and forward it in the same way as the traditional way , So the message forwarding is very slow

2.MPLS The definition of

MPLS be located TCP/IP Between the data link layer and the network layer in the protocol stack , It can provide services to all network layers , By adding additional between the data link layer and the network layer MPLS Head , be based on MPLS The header implements fast data forwarding

3.MPLS Basic concepts of （ One ）

MPLS Domain ： A series of operations MPLS The equipment of constitutes a MPLS Domain

LSR： Label switching router , It's running MPLS The routers of the protocol are label switching routers

LER： Label edge router , stay MPLS Domain edge routers , Connected at the same time ip The router of the network

4.MPLS Basic concepts of （ Two ）

Inbound LSR：LSR received ip The message will add a layer MPLS The head of

transit LSR：LSR Got it. Take it with you MPLS Header packets , After a series of treatment , A new tag will be re used and sent to the next one LSR, This action is called label replacement

Departure LSR： Departure LSR yes MPLS The last router in the network , This router is connected to ip Network devices , When receiving a packet carrier MPLS When the head of , Will be able to MPLS Peel off the head of , Because the router on the client does not recognize this MPLS The head of

5.MPLS Basic concepts of （ 3、 ... and ）

FEC： Is a set of data streams with some commonalities , These data streams are handled by the network nodes in the same way during forwarding , Generally speaking, it is divided into FEC Is based on the destination address and mask

6.MPLS Basic concepts of （ Four ）

 LSP： Label switching path , One MPLS The path that a packet passes along to its destination address is one LSP

7.MPLS Tag message of

be based on 2.5 layer , Between the data link layer and the network layer

lable：20bit, Indicates the tag to which it belongs

EXP： be used for QOS Scene ,3bit

S：1bit Used to identify MPLS Whether the label is the last layer （ At the bottom of the stack ）, If 1 It means the last , If 0 It means there is a label behind it

TTL：8bit, Time to live , and ip In the message TTL A function of the value of , Are used to prevent loops ,TTL The role of , Because in MPLS Network LSR Is not going to parse IP message , So in MPLS You need to add a... To the tag TTL To prevent loops

8. Label space

Tag space ： The label space is the scope of the label

0-15： Special labels ,0 Empty for display ,3 A hermit is empty

16-1023： For static LSP Shared tag space

1024~1048575： Used for the label range reserved by the label distribution agreement

9. Label handling

 push： Push the ,LSR received ip The message will add a layer to the message MPLS label , If the message already has a label , Then add a new layer of labels , The newly added label is closer to the data link layer , The old tag is closer to the network layer , Labels can only be pushed in by inbound LSR To complete

swap： Label switching ,LSR received MPLS The tag will use a new MPLS The label replaces the original label , Then send it to the next LSR, This can only be transferred by LSR To complete

pop： Label pop-up ,LSR received MPLS The tag will pop up the tag , Become ordinary ip The message is sent to the client router , The label ejection can only be completed by the outbound router

10.MPLS Architecture of

 

It is also composed of a control plane and a forwarding plane

The control plane has the following ：

ip Routing protocol ： Running dynamic routers , The route will be calculated according to the mechanism of the routing protocol itself , These routes will be stored in the protocol routing table

Routing information table ： Each dynamic routing protocol or dynamic routing protocol will be distributed to the local routing table

Label distribution agreement ：LDP、MP-BGP、RSVP

Label information table ： Through tag distribution protocol or static LSP The generated label will be saved to the label information table

The forwarding plane has the following ：

Forwarding information table ： The entries in the local routing table will generate the optimal path to download to the forwarding table , Routers rely on forwarding tables to forward data

Label forwarding information table ： Some tags in the tag information table will also be distributed to the tag information forwarding table ,LSR It is forwarded according to the tag forwarding information table

11.LSP Establish principles

If LSR You need to create a FEC The label of , So the router's IP The routing table must have this FEC The label of , Otherwise, it will not be established （ When the network layer protocol is IP agreement ）, The outgoing label of the local router must be equal to the incoming label of the next router

12.LSP How to build it

static state ： Manual configuration , You need to manually configure the out label and in label , And the role of the router （ Departure LSR、 transit LSR、 Departure LSR）, For small networks , When the complement changes ,LSP It doesn't change       

dynamic ： By means of LSR Configure label distribution protocol on to automatically generate labels , For large networks , When the network topology changes ,LSP Will automatically adapt

13. Tag forwarding

 FTN：FTN（FEC-to-NHLFE）： When LSR received IP Message and need to MPLS Forward with ,FTN Only in Ingress There is ,FTN Include ：Tunnel ID、FEC To NHLFE Mapping information for ,LSR Will be based on FIB In the table Tunnel ID Forward packets , If the packet's Tunnel ID Not for 0 The word "yes" means "yes" MPLS forward , If it's for 0 And it means it's common IP forward

NHLFE： Next hop tag forward table entry ,LSR To message （MPLS or IP message ） Conduct MPLS Forward with ,NHLFE stay Ingress and Transit There is ,NHLFE Include ：Tunnel ID、 Exit interface 、 Next jump 、 Tag out 、 Label operation type and other information .

ILM： Input label mapping , For guidance MPLS Forwarding of messages （MPLS or IP forward ）,ILM Only in Transit and Egress There is ,ILM Include ：Tunnel ID、 Enter the label 、 Access interface 、 Label operation type and other information .

14. Detailed forwarding process

Inbound ：LSR received IP message , The destination address of the parsing message is IP Whether the routing table exists , If it doesn't exist , Drop this packet , If there is , Then search according to the destination address FIB Corresponding entry Tunnel ID, If it is right or wrong 0, then MPLS forward , If it is 0, Then follow the normal IP forward , If it is right or wrong 0, The forwarding table will be linked to NHLFE Association . The outgoing interface is recorded inside , Tag out , Next jump , Operation type, etc

transit ：LSR received MPLS message , see ILM surface , according to ILM The corresponding Tunnel ID lookup NHLFE The output interface corresponding to the table item , Next jump , Operation type , Label, etc

Departure ：LSR received MPLS Message viewing ILM The label corresponding to the table item , Found to be pop, The label will pop up