Building the (Inner) VPN Label
The close characterization identifies the approachable interface out which the departure PE should advanced the
unlabeled packet. This close label, alleged the VPN label, charge be allocated for anniversary avenue added to
each chump VRF. More specifically, a chump CE will acquaint routes to the PE, with the PE
storing those routes in that customer’s VRF. In adjustment to adapt to advanced packets to those
customer subnets, the PE needs to admeasure a new bounded label, accessory the characterization with the prefix
(and the route’s next-hop IP abode and approachable interface), and abundance that advice in the
LFIB.
Figure 19-19 shows PE2’s routes for 10.3.3.0/24 in both VRF-A and VRF-B and the resulting
LFIB entries. The amount shows the after-effects of PE2’s action of allocating a bounded characterization for anniversary of
the two routes and again additionally announcement those labels application BGP. (Note that the LFIB is not a per-
VRF table; the LFIB is the one and alone LFIB for PE2.)
Figure 19-19 Creating the VPN Characterization LFIB Access on the Departure PE
NOTE As was the case with the archetype apparent in Amount 19-13, the capacity at Accomplish 3 and 4
will alter hardly in practice, as a aftereffect of the PHP feature, which is explained about Figure
19-23 at the end of this chapter.
CE-A2
CE-B2
PE2
In Label
3333
4444
Next-Hop
192.168.37.7
192.168.38.8
Out Int.
S0/1/0
S0/1/1
LFIB
Action
pop
pop
NLRI
1:111:10.3.3.0/24
2:222:10.3.3.0/24
Label
3333
4444
Next-Hop
3.3.3.3
3.3.3.3
BGP Table
RT
1:100
2:200
Source
RIP
Next-Hop
192.168.37.7
Out Int.
S0/1/0
VRF-A Routing Table
Prefix
10.3.3.0/24
Source
RIP
Next-Hop
192.168.38.8
Out Int.
S0/1/1
VRF-B Routing Table
Prefix
10.3.3.0/24
4
1 3
2
S0/1/0 —VRF-A
S0/1/1 —VRF-B
Subnet
10.3.3.0/24
Subnet
10.3.3.0/24
IBGP to PE1
The accomplish apparent in the amount are as follows:
1. After abacus a avenue for 10.3.3.0/24 to VRF-A, PE2 allocates a bounded characterization (3333) to associate
with the route. PE2 again food the bounded characterization and agnate abutting hop and outgoing
interface from VRF-A’s avenue for 10.3.3.0/24 into the LIB (not shown) and LFIB.
2. PE2 repeats the argumentation in Footfall 1 for anniversary avenue in anniversary VRF, including the avenue in VRF-B
shown at Footfall 2. After acquirements a avenue for 10.3.3.0/24 in VRF-B, PE2 allocates a different
label amount (4444), assembly that route’s next-hop IP abode and approachable interface with the
new label, and adds the advice to a new LFIB entry.
3. PE2 adds the bounded labels to the BGP table access for the routes, respectively, when
redistributing routes into BGP.
4. PE2 uses IBGP to acquaint the routes to PE1, with the BGP Update including the VPN label.
As a aftereffect of the aboriginal two accomplish in the figure, if PE3 receives a labeled packet and analyzes a label
value of 3333, PE2 would be able to advanced the packet accurately to CE-A2. Similarly, PE2 could
correctly advanced a accustomed labeled packet with characterization 4444 to CE-B2.
NOTE Accomplish 3 and 4 in Amount 19-19 do annihilation to aid PE2 to advanced packets; these steps
were included to be referenced at an accessible footfall after in this section.