R2511-HP MSR Router Series MPLS Configuration Guide(V5)

Figure 21 VC label calculation

As shown in Figure 21, PEs calculates VC labels for a VC as follows (take the VC between CE 1 and CE

12 as an example):

• PE 1 calculates the VC label it assigns to the VC:

PE 1 compares the ID (12) of the peer CE (CE 12) with the label blocks assigned by PE 1. If a label

block meets LO<=CE ID<LO+LR, PE 1 assigns a label from the label block. In this example, label

block 2 (1055/5/10) meets LO<=CE ID<LO+LR (5<=12<5+10). PE 1 assigns a label to the VC

from label block 2. The assigned label value = LB+CE ID-LO, namely 1062 (1055+12-5).

• PE 1 calculates the VC label that PE 2 assigns to the VC:

PE 1 compares the ID (1) of the local CE (CE 1) with the label blocks assigned by PE 2. A label

block that meets LO<=CE ID<LO+LR is used by PE 2 to assign a label value to the VC. In this

example, label block (3000/0/15) meets LO<=CE ID<LO+LR (0<=1<0+15). PE 2 assigns a label

value to the VC from the label block. The assigned label value = LB+CE ID-LO, namely 3001

(3000+1-0).

• PE 2 performs the same calculations and gets the same results: the VC label that PE 2 assigns to the

VC is 3001 and that PE 1 assigns to the VC is 1062.

A PE adds the VC label assigned by the peer PE into a Layer 2 packet from a local CE. For example,

when PE 1 forwards packets from CE 1 to CE 2, it adds VC label 3001.

Figure 22 Label distribution in Kompella mode

VPN 1

CE 1

CE 2

PE 1 PE 2

VPN 1 VPN 1

Label block 1: 1000/0/5

Label block 2: 1055/5/10

CE 12

Label block for CE 2: 2000/0/15

Label block for CE 12: 3000/0/15

VC connected CE 1 and CE 2:

local VC label: 1002

remote VC label: 2001

VC connected CE 1 and CE 12:

local VC label: 1062

remote VC label: 3001

VC connected CE 1 and CE 2:

local VC label: 2001

remote VC label: 1002

VC connected CE 1 and CE 12:

local VC label: 3001

remote VC label: 1062

Label block allocated Label block allocated

VC labels calculated