Thursday, May 14, 2026

Complete MPLS Inter-AS VPN Lab Part 4 | MP-BGP VPNv4, VRF & Route Reflector Configuration

Complete MPLS Inter-AS VPN Lab Part 4 | Intra-AS MPLS VPN Configuration

Complete MPLS Inter-AS VPN Lab Part 4

Welcome to Part 4 of the MPLS Inter-AS VPN Lab Series.

In this section we will configure a complete Intra-AS MPLS VPN infrastructure using:

VRFs
VPNv4 MP-BGP
Route Reflectors
PE-CE BGP
Route Targets
Route Distinguishers

The primary goal is to establish end-to-end MPLS VPN communication between:

1. MPLS VPN Architecture Overview
2. Configure MPLS VPN in US Site
3. Configure MPLS VPN in UK Site
4. Configure Route Reflectors
5. Configure MP-iBGP Between RRs
6. Verification Commands
7. MPLS VPN Mathematics
8. Troubleshooting
9. Best Practices
10. Related Articles

1. MPLS VPN Architecture Overview

An MPLS VPN allows multiple customers to use the same provider backbone while maintaining traffic separation.

The separation is achieved using:

VRFs
Route Distinguishers
Route Targets
VPNv4 routes

MPLS VPN Formula

$$ VPNv4 = RD + IPv4\\ Prefix $$

Example:

$$ 100:1 + 10.9.9.0/24 $$

This creates a globally unique VPNv4 route.

💡 Important MPLS VPN Components

VRF = Virtual Routing and Forwarding
RD = Route Distinguisher
RT = Route Target
PE = Provider Edge Router
CE = Customer Edge Router
RR = Route Reflector

2. Configure Intra-AS MPLS VPN in AS 100 US Site

We first configure the US MPLS VPN infrastructure connecting:

Configure PE Router R1

Code Example

vrf definition Cust-A

R1

router bgp 100
 neighbor 3.3.3.3 remote-as 100
 neighbor 3.3.3.3 update-source lo0
!

address-family vpnv4
 neighbor 3.3.3.3 activate
!

vrf definition Cust-A
 rd 100:1

 address-family ipv4
  route-target both 100:1
!

interface E0/2
 vrf forwarding Cust-A
 ip address 192.168.10.1 255.255.255.0
 no shut
!

router bgp 100

 address-family ipv4 vrf Cust-A
  neighbor 192.168.10.9 remote-as 65009

Configure PE Router R2

R2

router bgp 100
 neighbor 3.3.3.3 remote-as 100
 neighbor 3.3.3.3 update-source lo0
!

address-family vpnv4
 neighbor 3.3.3.3 activate
!

vrf definition Cust-A
 rd 100:1

 address-family ipv4
  route-target both 100:1
!

interface E0/2
 vrf forwarding Cust-A
 ip address 192.168.20.2 255.255.255.0
 no shut
!

router bgp 100

 address-family ipv4 vrf Cust-A
  neighbor 192.168.20.10 remote-as 65010

Configure Route Reflector R3

R3

router bgp 100

 neighbor IBGP peer-group
 neighbor IBGP remote-as 100
 neighbor IBGP update-source lo0

 neighbor 1.1.1.1 peer-group IBGP
 neighbor 2.2.2.2 peer-group IBGP
!

address-family vpnv4
 neighbor IBGP route-reflector-client

 neighbor 1.1.1.1 activate
 neighbor 2.2.2.2 activate

Configure Customer Edge Router R9

R9

router bgp 65009
 neighbor 192.168.10.1 remote-as 100

 network 10.9.9.0 mask 255.255.255.0

Configure Customer Edge Router R10

R10

router bgp 65010
 neighbor 192.168.20.2 remote-as 100

 network 10.10.10.0 mask 255.255.255.0

Why Route Reflectors Are Needed

Without Route Reflectors:

$$ Number\\ of\\ iBGP\\ Sessions = \frac{n(n-1)}{2} $$

This creates scalability problems.

Route Reflectors reduce the number of required BGP peerings.

Route Reflector Scaling Formula

$$ Full\\ Mesh = \frac{n(n-1)}{2} $$

3. Configure Intra-AS MPLS VPN in AS 100 UK Site

Now we configure the UK MPLS VPN infrastructure connecting:

Configure PE Router R5

R5

router bgp 100
 neighbor 7.7.7.7 remote-as 100
 neighbor 7.7.7.7 update-source lo0
!

address-family vpnv4
 neighbor 7.7.7.7 activate
!

vrf definition Cust-A
 rd 100:1

 address-family ipv4
  route-target both 100:1
!

interface E0/2
 vrf forwarding Cust-A
 ip address 192.168.50.5 255.255.255.0
 no shut
!

router bgp 100

 address-family ipv4 vrf Cust-A
  neighbor 192.168.50.11 remote-as 65011

Configure PE Router R6

R6

router bgp 100
 neighbor 7.7.7.7 remote-as 100
 neighbor 7.7.7.7 update-source lo0
!

address-family vpnv4
 neighbor 7.7.7.7 activate
!

vrf definition Cust-A
 rd 100:1

 address-family ipv4
  route-target both 100:1
!

interface E0/2
 vrf forwarding Cust-A
 ip address 192.168.60.6 255.255.255.0
 no shut
!

router bgp 100

 address-family ipv4 vrf Cust-A
  neighbor 192.168.60.12 remote-as 65012

Configure Route Reflector R7

R7

router bgp 100

 neighbor IBGP peer-group
 neighbor IBGP remote-as 100
 neighbor IBGP update-source lo0

 neighbor 5.5.5.5 peer-group IBGP
 neighbor 6.6.6.6 peer-group IBGP
!

address-family vpnv4
 neighbor IBGP route-reflector-client

 neighbor 5.5.5.5 activate
 neighbor 6.6.6.6 activate

Configure Customer Edge Router R11

R11

router bgp 65011
 neighbor 192.168.50.5 remote-as 100

 network 10.11.11.0 mask 255.255.255.0

Configure Customer Edge Router R12

R12

router bgp 65012
 neighbor 192.168.60.6 remote-as 100

 network 10.12.12.0 mask 255.255.255.0

Route Target Import Formula

$$ Import\\ RT = Export\\ RT $$

Routes are imported only when Route Targets match.

4. Configure Route Reflector Relationship

Route Reflectors reduce iBGP scaling complexity.

R3 and R7 act as local Route Reflectors.

VPNv4 Reflection Formula

$$ RR \rightarrow Reflect\\ VPNv4\\ Routes $$

5. Configure MP-iBGP Between Route Reflectors

Configure R3

R3

router bgp 100

 neighbor 7.7.7.7 remote-as 100
 neighbor 7.7.7.7 update-source lo0
!

address-family vpnv4
 neighbor 7.7.7.7 activate
 neighbor 7.7.7.7 route-reflector-client

Configure R7

R7

router bgp 100

 neighbor 3.3.3.3 remote-as 100
 neighbor 3.3.3.3 update-source lo0
!

address-family vpnv4
 neighbor 3.3.3.3 activate
 neighbor 3.3.3.3 route-reflector-client

Understanding VPNv4 MP-BGP

Standard IPv4 BGP cannot transport VPN information.

MP-BGP extends BGP using:

VPNv4 address family
Route Targets
MPLS labels

This allows multiple customer VPNs to coexist in the same provider backbone.

MP-BGP Formula

$$ MP\text{-}BGP = IPv4 + VPN\\ Metadata + Label $$

6. Verification Commands

Command	Purpose
show bgp vpnv4 unicast all	Verify VPNv4 routes
show ip vrf	Verify VRFs
show ip route vrf Cust-A	Verify VRF routes
show bgp vpnv4 summary	Verify MP-BGP neighbors
ping	Verify reachability
traceroute	Verify forwarding path

Sample VPNv4 Output

R1#show bgp vpnv4 unicast all

Route Distinguisher: 100:1
*>i10.10.10.0/24
*>i10.11.11.0/24
*>i10.12.12.0/24

Expected Ping Verification

R9#ping 10.12.12.1

!!!!!
Success rate is 100 percent

🎯 Verification Goals

All PE routers must learn VPNv4 routes
Route Reflectors must reflect routes correctly
VRF routing tables must contain remote customer routes
R9 to R12 communication must succeed

7. MPLS VPN Mathematics

VPNv4 Prefix Formula

$$ VPNv4 = RD + IPv4\\ Prefix $$

Label Stack Formula

$$ Transport\\ Label + VPN\\ Label $$

Route Reflection Scaling Formula

$$ n^2 \rightarrow Centralized\\ Reflection $$

VRF Isolation Formula

$$ Separate\\ VRF = Separate\\ Routing\\ Table $$

RT Matching Formula

$$ Import\\ RT = Export\\ RT $$

8. Troubleshooting MPLS VPN

Problem	Cause	Solution
No VPNv4 routes	Neighbor not activated	Activate VPNv4 AF
No VRF routes	RT mismatch	Verify RT values
No CE connectivity	BGP neighbor down	Verify PE-CE peering
No route reflection	Missing RR client	Configure route-reflector-client
Ping failure	No MPLS labels	Verify MPLS forwarding

9. Best Practices

Use Loopbacks for MP-BGP sessions
Use Route Reflectors for scalability
Maintain consistent Route Targets
Use descriptive VRF names
Verify MPLS before enabling VPNv4
Separate customer traffic using VRFs
Document Route Distinguishers carefully

💡 Key Takeaways

VRFs isolate customer routing tables
Route Distinguishers create unique VPNv4 routes
Route Targets control route import/export
MP-BGP exchanges VPNv4 routes
Route Reflectors improve scalability
MPLS labels transport VPN traffic

Final Conclusion

In Part 4 we successfully configured a complete Intra-AS MPLS VPN environment using VRFs, MP-BGP VPNv4 and Route Reflectors.

We established:

PE-CE BGP connectivity
VPNv4 route exchange
Route Reflector infrastructure
VRF-based customer separation
End-to-end MPLS VPN communication

The MPLS provider backbone can now securely transport multiple customer VPNs while maintaining traffic isolation and scalability.

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Thursday, May 14, 2026