MPLS Traffic Engineering Inter-Area and Inter-Level Tunnels

« 2023 June 29 »

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What is an MPLS TE inter-area tunnel?

MPLS Traffic Engineering tunnels can be configured across different IGP areas. An MPLS network may be deployed with a hierarchical design of the transport protocol by using different OSPF areas or IS-IS levels. As a result, functional layers can be created such as a Core Layer and an Aggregation Layer. Such a differentiation can benefit network convergence in large service provider Layer-3 VPN MPLS backbones.

MPLS TE inter-area tunnels explained

For an MPLS Traffic Engineering inter-area tunnel to work, it needs to use an explicit path which is configured on the PE routers. The explicit path contains Explicit Route Objects (ERO) which are specifically set to "Loose ERO" for the Area Border Routers (ABR). For all other devices the ERO is set to "Strict". These details are included in RSVP such as the one displayed below.

RSVP Path message Strict and Loose ERO

How to configure an MPLS TE inter-area tunnel? (OSPF)

In the following example topology a Service Provider MPLS Layer-3 VPN backbone is divided into separate functional layers. The Core Layer is configured with OSPF in area 0. The Aggregation Layer is where the Provider Edge (PE) routers are located, and it is assigned to OSPF non-backbone areas (1 and 2). Thus, Type-3 summary LSAs advertise the PE router Loopback addresses across the MPLS domain.

The separation of the OSPF network into different areas means that the dynamic path-option cannot be used on the MPLS TE tunnel. This is because the Constraint-based SPF algorithm that finds the best path for the MPLS TE LSP only works within a single IGP area.

As a result, an explicit path (ERO) needs to be configured on the PE routers, including loose hop ERO types for the ABR R4 and R6. Also, the tunnel interface requires the command tunnel mpls traffic-eng autoroute destination to transmit traffic via the MPLS TE tunnel.

MPLS Traffic Engineering inter-area tunnel with IGP OSPF in Service Provider aggregation and core layer including L3VPN in VRF Gold

Configuration:

R2 (PE) 
    R2#show run | sec ^mpls
mpls label range 200 299
mpls traffic-eng tunnels

R2#show run | sec ^vrf
vrf definition Gold
 rd 65100:1
 !
 address-family ipv4
  route-target export 65100:1
  route-target import 65100:2
 exit-address-family

R2#show run int Lo10 | sec int
interface Loopback10
 ip address 2.2.2.2 255.255.255.255

R2#show run int Gi1 | sec int 
interface GigabitEthernet1
 description ** to CE R1 **
 no ip address
 negotiation auto
 no mop enabled
 no mop sysid

R2#show run int Gi1.10 | sec int
interface GigabitEthernet1.10
 description ** to CE R1 in VRF Gold **
 encapsulation dot1Q 10
 vrf forwarding Gold
 ip address 10.0.1.1 255.255.255.252

R2#show run int Gi2 | sec int   
interface GigabitEthernet2
 description ** to R3 **
 ip address 10.1.0.2 255.255.255.252
 ip ospf network point-to-point
 negotiation auto
 mpls traffic-eng tunnels
 no mop enabled
 no mop sysid
 ip rsvp bandwidth 100 50

R2#show run int Tu10 | sec int
interface Tunnel10
 description ** MPLS TE inter-area tunnel to PE R8 **
 ip unnumbered Loopback10
 tunnel mode mpls traffic-eng
 tunnel destination 8.8.8.8
 tunnel mpls traffic-eng autoroute destination
 tunnel mpls traffic-eng priority 1 1
 tunnel mpls traffic-eng bandwidth 50
 tunnel mpls traffic-eng path-option 10 explicit name EXAMPLE-PATH

R2#show run | sec ^ip exp     
ip explicit-path name EXAMPLE-PATH enable
 index 1 next-address 3.3.3.3
 index 2 next-address loose 4.4.4.4
 index 3 next-address 5.5.5.5
 index 4 next-address loose 6.6.6.6
 index 5 next-address 7.7.7.7
 index 6 next-address 8.8.8.8

R2#show run | sec ^router
router ospf 10
 router-id 2.2.2.2
 network 2.2.2.2 0.0.0.0 area 1
 network 10.1.0.0 0.0.0.3 area 1
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng area 1
router bgp 65100
 bgp router-id 2.2.2.2
 bgp log-neighbor-changes
 neighbor 9.9.9.9 remote-as 65100
 neighbor 9.9.9.9 update-source Loopback10
 !
 address-family vpnv4
  neighbor 9.9.9.9 activate
  neighbor 9.9.9.9 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf Gold
  network 10.0.1.0 mask 255.255.255.252
  neighbor 10.0.1.2 remote-as 65001
  neighbor 10.0.1.2 activate
 exit-address-family
R8 (PE) 
    R8#show run | sec ^mpls
mpls label range 800 899
mpls traffic-eng tunnels

R8#show run | sec ^vrf
vrf definition Gold
 rd 65100:2
 !
 address-family ipv4
  route-target export 65100:2
  route-target import 65100:1
 exit-address-family

R8#show run int Lo10 | sec int
interface Loopback10
 ip address 8.8.8.8 255.255.255.255

R8#show run int Gi1 | sec int 
interface GigabitEthernet1
 description ** to CE R10 **
 no ip address
 negotiation auto
 no mop enabled
 no mop sysid

R8#show run int Gi1.10 | sec int 
interface GigabitEthernet1.10
 description ** to CE R10 in VRF Gold **
 encapsulation dot1Q 10
 vrf forwarding Gold
 ip address 10.0.2.1 255.255.255.252

R8#show run int Gi2 | sec int
interface GigabitEthernet2
 description ** to R7 **
 ip address 10.7.0.2 255.255.255.252
 ip ospf network point-to-point
 negotiation auto
 mpls traffic-eng tunnels
 no mop enabled
 no mop sysid
 ip rsvp bandwidth 100 50
 
R8#show run int Tu10 | sec int 
interface Tunnel10
 description ** MPLS TE inter-area tunnel to PE R2 **
 ip unnumbered Loopback10
 tunnel mode mpls traffic-eng
 tunnel destination 2.2.2.2
 tunnel mpls traffic-eng autoroute destination
 tunnel mpls traffic-eng priority 1 1
 tunnel mpls traffic-eng bandwidth 50
 tunnel mpls traffic-eng path-option 10 explicit name EXAMPLE-PATH

R8#show run | sec ^ip exp
ip explicit-path name EXAMPLE-PATH enable
 index 1 next-address 7.7.7.7
 index 2 next-address loose 6.6.6.6
 index 3 next-address 5.5.5.5
 index 4 next-address loose 4.4.4.4
 index 5 next-address 3.3.3.3
 index 6 next-address 2.2.2.2

R8#show run | sec ^router
router ospf 10
 router-id 8.8.8.8
 network 8.8.8.8 0.0.0.0 area 2
 network 10.7.0.0 0.0.0.3 area 2
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng area 2
router bgp 65100
 bgp router-id 8.8.8.8
 bgp log-neighbor-changes
 neighbor 9.9.9.9 remote-as 65100
 neighbor 9.9.9.9 update-source Loopback10
 !
 address-family vpnv4
  neighbor 9.9.9.9 activate
  neighbor 9.9.9.9 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf Gold
  network 10.0.2.0 mask 255.255.255.252
  neighbor 10.0.2.2 remote-as 65002
  neighbor 10.0.2.2 activate
 exit-address-family
R4 (ABR) 
    R4#show run | sec ^mpls
mpls label range 400 499
mpls traffic-eng tunnels

R4#show run int Lo10 | sec int
interface Loopback10
 ip address 4.4.4.4 255.255.255.255

R4#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to R3 **
 ip address 10.2.0.2 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R4#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to R5 **
 ip address 10.3.0.1 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R4#show run | sec ^router
router ospf 10
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng area 0
 mpls traffic-eng area 1
 router-id 4.4.4.4
 network 4.4.4.4 0.0.0.0 area 0
 network 10.2.0.0 0.0.0.3 area 1
 network 10.3.0.0 0.0.0.3 area 0
R6 (ABR) 
    R6#show run | sec ^mpls
mpls label range 600 699
mpls traffic-eng tunnels

R6#show run int Lo10 | sec int
interface Loopback10
 ip address 6.6.6.6 255.255.255.255

R6#show run int Gi0/0 | sec int 
interface GigabitEthernet0/0
 description ** to R7 **
 ip address 10.6.0.1 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R6#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to R5 **
 ip address 10.4.0.2 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R6#show run | sec ^router
router ospf 10
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng area 0
 mpls traffic-eng area 2
 router-id 6.6.6.6
 network 6.6.6.6 0.0.0.0 area 0
 network 10.4.0.0 0.0.0.3 area 0
 network 10.6.0.0 0.0.0.3 area 2
R9 (BGP RR) 
    R9#show run int Lo10 | sec int
interface Loopback10
 ip address 9.9.9.9 255.255.255.255

R9#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to R5 **
 ip address 10.5.0.2 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45

R9#show run | sec ^router
router ospf 10
 router-id 9.9.9.9
 network 9.9.9.9 0.0.0.0 area 0
 network 10.5.0.0 0.0.0.3 area 0
router bgp 65100
 bgp router-id 9.9.9.9
 bgp log-neighbor-changes
 neighbor 2.2.2.2 remote-as 65100
 neighbor 2.2.2.2 update-source Loopback10
 neighbor 8.8.8.8 remote-as 65100
 neighbor 8.8.8.8 update-source Loopback10
 !
 address-family vpnv4
  neighbor 2.2.2.2 activate
  neighbor 2.2.2.2 send-community extended
  neighbor 2.2.2.2 route-reflector-client
  neighbor 8.8.8.8 activate
  neighbor 8.8.8.8 send-community extended
  neighbor 8.8.8.8 route-reflector-client
 exit-address-family
R3 
    R3#show run | sec ^mpls
mpls label range 300 399
mpls traffic-eng tunnels

R3#show run int Lo10 | sec int
interface Loopback10
 ip address 3.3.3.3 255.255.255.255

R3#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to PE R2 **
 ip address 10.1.0.1 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R3#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to ABR R4 **
 ip address 10.2.0.1 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R3#show run | sec ^router
router ospf 10
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng area 1
 router-id 3.3.3.3
 network 3.3.3.3 0.0.0.0 area 1
 network 10.1.0.0 0.0.0.3 area 1
 network 10.2.0.0 0.0.0.3 area 1
R5 
    R5#show run | sec ^mpls
mpls label range 500 599
mpls traffic-eng tunnels

R5#show run int Lo10 | sec int
interface Loopback10
 ip address 5.5.5.5 255.255.255.255

R5#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to ABR R4 **
 ip address 10.3.0.2 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R5#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to ABR R6 **
 ip address 10.4.0.1 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R5#show run int Gi0/2 | sec int
interface GigabitEthernet0/2
 description ** to BGP RR R9 **
 ip address 10.5.0.1 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45

R5#show run | sec ^router
router ospf 10
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng area 0
 router-id 5.5.5.5
 network 5.5.5.5 0.0.0.0 area 0
 network 10.3.0.0 0.0.0.3 area 0
 network 10.4.0.0 0.0.0.3 area 0
 network 10.5.0.0 0.0.0.3 area 0
R7 
    R7#show run | sec ^mpls
mpls label range 700 799
mpls traffic-eng tunnels

R7#show run int Lo10 | sec int
interface Loopback10
 ip address 7.7.7.7 255.255.255.255

R7#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to PE R8 **
 ip address 10.7.0.1 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R7#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to ABR R6 **
 ip address 10.6.0.2 255.255.255.252
 ip ospf network point-to-point
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 ip rsvp bandwidth 100 50

R7#show run | sec ^router
router ospf 10
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng area 2
 router-id 7.7.7.7
 network 7.7.7.7 0.0.0.0 area 2
 network 10.6.0.0 0.0.0.3 area 2
 network 10.7.0.0 0.0.0.3 area 2
R1 (CE) 
    R1#show run | sec ^vrf
vrf definition Gold
 rd 1:1
 !
 address-family ipv4
 exit-address-family

R1#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to Host1 **
 no ip address
 duplex auto
 speed auto
 media-type rj45

R1#show run int Gi0/0.1 | sec int
interface GigabitEthernet0/0.1
 description ** to Host1 in VRF Gold (VLAN 1) **
 encapsulation dot1Q 1 native
 vrf forwarding Gold
 ip address 192.168.1.2 255.255.255.0

R1#show run int Gi0/1 | sec int   
interface GigabitEthernet0/1
 description ** to PE R2 **
 no ip address
 duplex auto
 speed auto
 media-type rj45
 
R1#show run int Gi0/1.10 | sec int
interface GigabitEthernet0/1.10
 description ** to PE R2 in VRF Gold **
 encapsulation dot1Q 10
 vrf forwarding Gold
 ip address 10.0.1.2 255.255.255.252

R1#show run | sec ^router
router bgp 65001
 bgp router-id 1.1.1.1
 bgp log-neighbor-changes
 !
 address-family ipv4 vrf Gold
  network 192.168.1.0
  neighbor 10.0.1.1 remote-as 65100
  neighbor 10.0.1.1 activate
 exit-address-family
R10 (CE) 
    R10#show run | sec ^vrf
vrf definition Gold
 rd 1:1
 !
 address-family ipv4
 exit-address-family

R10#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to Host2 **
 no ip address
 duplex auto
 speed auto
 media-type rj45

R10#show run int Gi0/0.1 | sec int
interface GigabitEthernet0/0.1
 description ** to Host2 in VRF Gold (VLAN 1) **
 encapsulation dot1Q 1 native
 vrf forwarding Gold
 ip address 192.168.2.2 255.255.255.0

R10#show run int Gi0/1 | sec int   
interface GigabitEthernet0/1
 description ** to PE R8 **
 no ip address
 duplex auto
 speed auto
 media-type rj45

R10#show run int Gi0/1.10 | sec int
interface GigabitEthernet0/1.10
 description ** to PE R8 in VRF Gold **
 encapsulation dot1Q 10
 vrf forwarding Gold
 ip address 10.0.2.2 255.255.255.252

R10#show run | sec ^router
router bgp 65002
 bgp router-id 10.10.10.10
 bgp log-neighbor-changes
 !
 address-family ipv4 vrf Gold
  network 192.168.2.0
  neighbor 10.0.2.1 remote-as 65100
  neighbor 10.0.2.1 activate
 exit-address-family
Host1 
    Host1#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to CE R1 **
 ip address 192.168.1.1 255.255.255.0
 duplex auto
 speed auto
 media-type rj45

Host1#show run | sec ^ip route
ip route 0.0.0.0 0.0.0.0 192.168.1.2

R2#show mpls traffic-eng tunnels brief 
Signalling Summary:
    LSP Tunnels Process:            running
    Passive LSP Listener:           running
    RSVP Process:                   running
    Forwarding:                     enabled
    auto-tunnel:
        p2p    Disabled (0), id-range:62336-64335

    Periodic reoptimization:        every 3600 seconds, next in 2059 seconds
    Periodic FRR Promotion:         Not Running
    Periodic auto-bw collection:    every 300 seconds, next in 259 seconds
    SR tunnel max label push:       13 primary path labels (13 repair path labels)

P2P TUNNELS/LSPs:
TUNNEL NAME                      DESTINATION      UP IF     DOWN IF   STATE/PROT
** MPLS TE inter-area tunnel...  8.8.8.8          -         Gi2       up/up       « MPLS TE tunnel is up
** MPLS TE inter-area tunnel...  2.2.2.2          Gi2       -         up/up
Displayed 1 (of 1) heads, 0 (of 0) midpoints, 1 (of 1) tails

P2MP TUNNELS:
Displayed 0 (of 0) P2MP heads
          
P2MP SUB-LSPS:
Displayed 0 P2MP sub-LSPs:
          0 (of 0) heads, 0 (of 0) midpoints, 0 (of 0) tails
		  




Host1#ping 192.168.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 48/51/53 ms            « Host1 (Site 1) can reach Host2 (Site 2)





Host1#trace 192.168.2.1 probe 1
Type escape sequence to abort.
Tracing the route to 192.168.2.1
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.1.2 1 msec
  2 10.0.1.1 40 msec
  3 10.1.0.1 [MPLS: Labels 301/802 Exp 0] 49 msec                     « MPLS label stack is used
  4 10.2.0.2 [MPLS: Labels 401/802 Exp 0] 49 msec
  5 10.3.0.2 [MPLS: Labels 501/802 Exp 0] 51 msec
  6 10.4.0.2 [MPLS: Labels 601/802 Exp 0] 49 msec
  7 10.6.0.2 [MPLS: Labels 701/802 Exp 0] 50 msec
  8 10.0.2.1 [MPLS: Label 802 Exp 0] 29 msec                          « PE router R8 assigns VPN Service Label
  9 10.0.2.2 51 msec
 10 192.168.2.1 50 msec
 






R2#show ip bgp vpnv4 rd 65100:2 192.168.2.0    
BGP routing table entry for 65100:2:192.168.2.0/24, version 5         « MP-BGP VPNv4 prefix from Site 2
Paths: (1 available, best #1, no table)
  Not advertised to any peer
  Refresh Epoch 1
  65002
    8.8.8.8 (via default) from 9.9.9.9 (9.9.9.9)                      « PE router R8 advertises this prefix
      Origin IGP, metric 0, localpref 100, valid, internal, best
      Extended Community: RT:65100:2
      Originator: 8.8.8.8, Cluster list: 9.9.9.9
      mpls labels in/out nolabel/802                                  « PE R8 assigns VPN Service Label 802
      rx pathid: 0, tx pathid: 0x0
      Updated on Apr 25 2024 17:19:21 UTC
	  
	  
	  
	  
	  


Host2#trace 192.168.1.1 probe 1
Type escape sequence to abort.
Tracing the route to 192.168.1.1
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.2.2 2 msec
  2 10.0.2.1 33 msec
  3 10.7.0.1 [MPLS: Labels 700/202 Exp 0] 50 msec
  4 10.6.0.1 [MPLS: Labels 600/202 Exp 0] 50 msec
  5 10.4.0.1 [MPLS: Labels 500/202 Exp 0] 53 msec
  6 10.3.0.1 [MPLS: Labels 400/202 Exp 0] 50 msec
  7 10.2.0.1 [MPLS: Labels 300/202 Exp 0] 51 msec
  8 10.0.1.1 [MPLS: Label 202 Exp 0] 28 msec
  9 10.0.1.2 50 msec
 10 192.168.1.1 51 msec

As visible, the two sites can connect using the MPLS VPN label stack. The following output displays the MPLS transport network IGP routing table on PE R2. Note that the IGP OSPF domain is divided into different areas, and for this reason OSPF inter-area routes are advertised.

R2#show ip route ospf | beg Ga
Gateway of last resort is not set

      3.0.0.0/32 is subnetted, 1 subnets
O        3.3.3.3 [110/2] via 10.1.0.1, 00:37:47, GigabitEthernet2
      4.0.0.0/32 is subnetted, 1 subnets
O IA     4.4.4.4 [110/3] via 10.1.0.1, 00:37:47, GigabitEthernet2          « inter-area Type-3 summary LSA
      5.0.0.0/32 is subnetted, 1 subnets
O IA     5.5.5.5 [110/4] via 10.1.0.1, 00:37:47, GigabitEthernet2
      6.0.0.0/32 is subnetted, 1 subnets
O IA     6.6.6.6 [110/5] via 10.1.0.1, 00:37:47, GigabitEthernet2
      7.0.0.0/32 is subnetted, 1 subnets
O IA     7.7.7.7 [110/6] via 10.1.0.1, 00:37:47, GigabitEthernet2
      9.0.0.0/32 is subnetted, 1 subnets
O IA     9.9.9.9 [110/5] via 10.1.0.1, 00:37:47, GigabitEthernet2
      10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
O        10.2.0.0/30 [110/2] via 10.1.0.1, 00:37:47, GigabitEthernet2
O IA     10.3.0.0/30 [110/3] via 10.1.0.1, 00:37:47, GigabitEthernet2
O IA     10.4.0.0/30 [110/4] via 10.1.0.1, 00:37:47, GigabitEthernet2
O IA     10.5.0.0/30 [110/4] via 10.1.0.1, 00:37:47, GigabitEthernet2
O IA     10.6.0.0/30 [110/5] via 10.1.0.1, 00:37:47, GigabitEthernet2
O IA     10.7.0.0/30 [110/6] via 10.1.0.1, 00:37:47, GigabitEthernet2





R2#show ip route 8.8.8.8
Routing entry for 8.8.8.8/32
  Known via "static", distance 1, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via Tunnel10                 « PE R2 learns PE R8 Loopback IP through MPLS TE tunnel via directly connected static route
      Route metric is 0, traffic share count is 1

On the PE router R2 it is visible that the Loopback IP address 8.8.8.8/32 (PE R8) is not displayed among the prefixes learnt via OSPF in the RIB. This is due to the command tunnel mpls traffic-eng autoroute destination issued under the MPLS TE tunnel interface on PE R2 and the explicit path configuration. The same is true on PE R8, where the Loopback IP of PE R2 points to the MPLS TE tunnel as the next-hop.

As an addition to the current OSPF configuration, inter-area prefixes can be filtered to optimize the routing table in each non-backbone area. This is possible because the PE routers only need the single Loopback IP address of the BGP Route Reflector R9 to receive the VPNv4 prefix of each site. All other OSPF prefixes are not necessary on the PE routers in area 1 and area 2. Thus, the following configuration can be applied on the ABR routers R4 and R6.

R4>enable
R4#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R4(config)#
R4(config)#ip prefix-list PL-PERMIT-BGP-RR permit 9.9.9.9/32 
R4(config)#
R4(config)#router ospf 10
R4(config-router)#area 1 filter-list prefix PL-PERMIT-BGP-RR in
R4(config-router)#
R4(config-router)#exit
R4(config)#exit
R4#


-------------------------------------------------------------------


R6>enable
R6#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R6(config)#
R6(config)#ip prefix-list PL-PERMIT-BGP-RR permit 9.9.9.9/32 
R6(config)#
R6(config)#router ospf 10
R6(config-router)#area 2 filter-list prefix PL-PERMIT-BGP-RR in
R6(config-router)#
R6(config-router)#exit
R6(config)#exit
R6#

After the filter-list is applied on each ABR, the following output is visible on the PE routers. Notice that the routing table on the PE routers is now considerably smaller. Also, note that the PE Loopback IP address is still not displayed in the RIB because it is used as the MPLS TE tunnel next-hop via the explicit path LSP.

R2#show ip route ospf | beg Ga
Gateway of last resort is not set

      3.0.0.0/32 is subnetted, 1 subnets
O        3.3.3.3 [110/2] via 10.1.0.1, 01:03:38, GigabitEthernet2
      9.0.0.0/32 is subnetted, 1 subnets
O IA     9.9.9.9 [110/5] via 10.1.0.1, 00:10:41, GigabitEthernet2       « Loopback IP of BGP RR
      10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O        10.2.0.0/30 [110/2] via 10.1.0.1, 01:03:38, GigabitEthernet2




R2#show ip route 8.8.8.8      
Routing entry for 8.8.8.8/32
  Known via "static", distance 1, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via Tunnel10
      Route metric is 0, traffic share count is 1




R8#show ip route ospf | beg Ga
Gateway of last resort is not set

      7.0.0.0/32 is subnetted, 1 subnets
O        7.7.7.7 [110/2] via 10.7.0.1, 01:03:41, GigabitEthernet2
      9.0.0.0/32 is subnetted, 1 subnets
O IA     9.9.9.9 [110/5] via 10.7.0.1, 00:07:28, GigabitEthernet2
      10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O        10.6.0.0/30 [110/2] via 10.7.0.1, 01:03:41, GigabitEthernet2




R8#show ip route 2.2.2.2
Routing entry for 2.2.2.2/32
  Known via "static", distance 1, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via Tunnel10
      Route metric is 0, traffic share count is 1




Host1#trace 192.168.2.1 probe 1
Type escape sequence to abort.
Tracing the route to 192.168.2.1
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.1.2 1 msec
  2 10.0.1.1 23 msec
  3 10.1.0.1 [MPLS: Labels 303/804 Exp 0] 50 msec
  4 10.2.0.2 [MPLS: Labels 407/804 Exp 0] 50 msec
  5 10.3.0.2 [MPLS: Labels 502/804 Exp 0] 50 msec
  6 10.4.0.2 [MPLS: Labels 603/804 Exp 0] 50 msec
  7 10.6.0.2 [MPLS: Labels 704/804 Exp 0] 49 msec
  8 10.0.2.1 [MPLS: Label 804 Exp 0] 28 msec
  9 10.0.2.2 50 msec
 10 192.168.2.1 52 msec

How to configure an MPLS TE inter-level tunnel? (IS-IS)

In the following example scenario, IS-IS is configured as the IGP for an MPLS L3VPN backbone network. An IS-IS Level-2 area is used for the Core Layer, and IS-IS Level-1 areas are assigned to the Aggregation Layer. This means that R4 and R6 are IS-IS Level-1/Level-2 routers and advertise only a single default route into ther respective Level-1 areas.

To create an inter-level MPLS TE tunnel between the PE router R2 and PE R8 an explicit path (ERO) is configured with the IS-IS L1/L2 routers being loose ERO hops. This solution works without the need to redistribute routes from the Level-2 IS-IS area into the Level-1 area, or in other words no IS-IS route leaking is configured.

MPLS TE inter-level tunnel configuration with IS-IS including Layer-3 VPN

Configuration:

R2 (PE) 
    R2#show run | sec ^mpls
mpls label range 200 299
mpls traffic-eng tunnels

R2#show run | sec ^vrf 
vrf definition Gold
 rd 65100:1
 !
 address-family ipv4
  route-target export 65100:1
  route-target import 65100:2
 exit-address-family

R2#show run int Lo10 | sec int 
interface Loopback10
 ip address 2.2.2.2 255.255.255.255

R2#show run int Gi1 | sec int 
interface GigabitEthernet1
 description ** to CE R1 **
 no ip address
 negotiation auto
 no mop enabled
 no mop sysid

R2#show run int Gi1.10 | sec int
interface GigabitEthernet1.10
 description ** to CE R1 in VRF Gold **
 encapsulation dot1Q 10
 vrf forwarding Gold
 ip address 10.0.1.1 255.255.255.252

R2#show run int Gi2 | sec int   
interface GigabitEthernet2
 description ** to R3 **
 ip address 10.1.0.2 255.255.255.252
 ip router isis 
 negotiation auto
 mpls traffic-eng tunnels
 no mop enabled
 no mop sysid
 isis circuit-type level-1
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R2#show run int Tu10 | sec int
interface Tunnel10
 description ** MPLS TE inter-level tunnel to PE R8 **
 ip unnumbered Loopback10
 tunnel mode mpls traffic-eng
 tunnel destination 8.8.8.8
 tunnel mpls traffic-eng autoroute destination
 tunnel mpls traffic-eng priority 1 1
 tunnel mpls traffic-eng bandwidth 50
 tunnel mpls traffic-eng path-option 10 explicit name EXAMPLE-PATH

R2#show run | sec ^ip exp
ip explicit-path name EXAMPLE-PATH enable
 index 1 next-address 3.3.3.3
 index 2 next-address loose 4.4.4.4
 index 3 next-address 5.5.5.5
 index 4 next-address loose 6.6.6.6
 index 5 next-address 7.7.7.7
 index 6 next-address 8.8.8.8

R2#show run | sec ^router
router isis
 net 49.0010.0000.0000.0002.00
 is-type level-1
 advertise passive-only
 metric-style wide
 log-adjacency-changes
 passive-interface Loopback10
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng level-1
router bgp 65100
 bgp router-id 2.2.2.2
 bgp log-neighbor-changes
 neighbor 9.9.9.9 remote-as 65100
 neighbor 9.9.9.9 update-source Loopback10
 !
 address-family vpnv4
  neighbor 9.9.9.9 activate
  neighbor 9.9.9.9 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf Gold
  network 10.0.1.0 mask 255.255.255.252
  neighbor 10.0.1.2 remote-as 65001
  neighbor 10.0.1.2 activate
 exit-address-family
R8 (PE) 
    R8#show run | sec ^mpls
mpls label range 800 899
mpls traffic-eng tunnels

R8#show run | sec ^vrf 
vrf definition Gold
 rd 65100:2
 !
 address-family ipv4
  route-target export 65100:2
  route-target import 65100:1
 exit-address-family

R8#show run int Lo10 | sec int
interface Loopback10
 ip address 8.8.8.8 255.255.255.255

R8#show run int Gi1 | sec int 
interface GigabitEthernet1
 description ** to CE R10 **
 no ip address
 negotiation auto
 no mop enabled
 no mop sysid

R8#show run int Gi1.10 | sec int
interface GigabitEthernet1.10
 description ** to CE R10 in VRF Gold **
 encapsulation dot1Q 10
 vrf forwarding Gold
 ip address 10.0.2.1 255.255.255.252

R8#show run int Gi2 | sec int   
interface GigabitEthernet2
 description ** to R7 **
 ip address 10.7.0.2 255.255.255.252
 ip router isis 
 negotiation auto
 mpls traffic-eng tunnels
 no mop enabled
 no mop sysid
 isis circuit-type level-1
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R8#show run int Tu10 | sec int
interface Tunnel10
 description ** MPLS TE inter-level tunnel to PE R2 **
 ip unnumbered Loopback10
 tunnel mode mpls traffic-eng
 tunnel destination 2.2.2.2
 tunnel mpls traffic-eng autoroute destination
 tunnel mpls traffic-eng priority 1 1
 tunnel mpls traffic-eng bandwidth 50
 tunnel mpls traffic-eng path-option 10 explicit name EXAMPLE-PATH

R8#show run | sec ^ip exp
ip explicit-path name EXAMPLE-PATH enable
 index 1 next-address 7.7.7.7
 index 2 next-address loose 6.6.6.6
 index 3 next-address 5.5.5.5
 index 4 next-address loose 4.4.4.4
 index 5 next-address 3.3.3.3
 index 6 next-address 2.2.2.2

R8#show run | sec ^router
router isis
 net 49.0020.0000.0000.0008.00
 is-type level-1
 advertise passive-only
 metric-style wide
 log-adjacency-changes
 passive-interface Loopback10
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng level-1
router bgp 65100
 bgp router-id 8.8.8.8
 bgp log-neighbor-changes
 neighbor 9.9.9.9 remote-as 65100
 neighbor 9.9.9.9 update-source Loopback10
 !
 address-family vpnv4
  neighbor 9.9.9.9 activate
  neighbor 9.9.9.9 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf Gold
  network 10.0.2.0 mask 255.255.255.252
  neighbor 10.0.2.2 remote-as 65002
  neighbor 10.0.2.2 activate
 exit-address-family
R4 (L1/L2) 
    R4#show run | sec ^mpls
mpls label range 400 499
mpls traffic-eng tunnels

R4#show run int Lo10 | sec int
interface Loopback10
 ip address 4.4.4.4 255.255.255.255

R4#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to R3 **
 ip address 10.2.0.2 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-1
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R4#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to R5 **
 ip address 10.3.0.1 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-2-only
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R4#show run | sec ^router
router isis
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng level-1
 mpls traffic-eng level-2
 net 49.0010.0000.0000.0004.00
 advertise passive-only
 metric-style wide
 log-adjacency-changes
 passive-interface Loopback10
R6 (L1/L2) 
    R6#show run | sec ^mpls
mpls label range 600 699
mpls traffic-eng tunnels

R6#show run int Lo10 | sec int
interface Loopback10
 ip address 6.6.6.6 255.255.255.255

R6#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to R7 **
 ip address 10.6.0.1 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-1
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R6#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to R5 **
 ip address 10.4.0.2 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-2-only
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R6#show run | sec ^router
router isis
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng level-1
 mpls traffic-eng level-2
 net 49.0020.0000.0000.0006.00
 advertise passive-only
 metric-style wide
 log-adjacency-changes
 passive-interface Loopback10
R9 (BGP RR) 
    R9#show run int Lo10 | sec int
interface Loopback10
 ip address 9.9.9.9 255.255.255.255

R9#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to R5 **
 ip address 10.5.0.2 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 isis circuit-type level-2-only
 isis network point-to-point 

R9#show run | sec ^router
router isis
 net 49.0005.0000.0000.0009.00
 is-type level-2-only
 advertise passive-only
 metric-style wide
 log-adjacency-changes
 passive-interface Loopback10
router bgp 65100
 bgp router-id 9.9.9.9
 bgp log-neighbor-changes
 neighbor 2.2.2.2 remote-as 65100
 neighbor 2.2.2.2 update-source Loopback10
 neighbor 8.8.8.8 remote-as 65100
 neighbor 8.8.8.8 update-source Loopback10
 !
 address-family vpnv4
  neighbor 2.2.2.2 activate
  neighbor 2.2.2.2 send-community extended
  neighbor 2.2.2.2 route-reflector-client
  neighbor 8.8.8.8 activate
  neighbor 8.8.8.8 send-community extended
  neighbor 8.8.8.8 route-reflector-client
 exit-address-family
R3 
    R3#show run | sec ^mpls
mpls label range 300 399
mpls traffic-eng tunnels

R3#show run int Lo10 | sec int
interface Loopback10
 ip address 3.3.3.3 255.255.255.255

R3#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to PE R2 **
 ip address 10.1.0.1 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-1
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R3#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to ABR R4 **
 ip address 10.2.0.1 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-1
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R3#show run | sec ^router
router isis
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng level-1
 net 49.0010.0000.0000.0003.00
 is-type level-1
 advertise passive-only
 metric-style wide
 log-adjacency-changes
 passive-interface Loopback10
R5 
    R5#show run | sec ^mpls
mpls label range 500 599
mpls traffic-eng tunnels

R5#show run int Lo10 | sec int
interface Loopback10
 ip address 5.5.5.5 255.255.255.255

R5#show run int Gi0/0 | sec int
interface GigabitEthernet0/0
 description ** to ABR R4 **
 ip address 10.3.0.2 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-2-only
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R5#show run int Gi0/1 | sec int
interface GigabitEthernet0/1
 description ** to ABR R6 **
 ip address 10.4.0.1 255.255.255.252
 ip router isis 
 duplex auto
 speed auto
 media-type rj45
 mpls traffic-eng tunnels
 isis circuit-type level-2-only
 isis network point-to-point 
 ip rsvp bandwidth 100 50

R5#show run | sec ^router
router isis
 mpls traffic-eng router-id Loopback10
 mpls traffic-eng level-2
 net 49.0005.0000.0000.0005.00
 is-type level-2-only
 advertise passive-only
 metric-style wide
 log-adjacency-changes
 passive-interface Loopback10

R2#show mpls traffic-eng tunnels brief
Signalling Summary:
    LSP Tunnels Process:            running
    Passive LSP Listener:           running
    RSVP Process:                   running
    Forwarding:                     enabled
    auto-tunnel:
        p2p    Disabled (0), id-range:62336-64335

    Periodic reoptimization:        every 3600 seconds, next in 1017 seconds
    Periodic FRR Promotion:         Not Running
    Periodic auto-bw collection:    every 300 seconds, next in 117 seconds
    SR tunnel max label push:       13 primary path labels (13 repair path labels)

P2P TUNNELS/LSPs:
TUNNEL NAME                      DESTINATION      UP IF     DOWN IF   STATE/PROT
** MPLS TE inter-level tunne...  8.8.8.8          -         Gi2       up/up                  « MPLS TE tunnel is up
** MPLS TE inter-level tunne...  2.2.2.2          Gi2       -         up/up
Displayed 1 (of 1) heads, 0 (of 0) midpoints, 1 (of 1) tails

P2MP TUNNELS:
Displayed 0 (of 0) P2MP heads
          
P2MP SUB-LSPS:
Displayed 0 P2MP sub-LSPs:
          0 (of 0) heads, 0 (of 0) midpoints, 0 (of 0) tails
		  





R2#show ip route isis | beg Ga
Gateway of last resort is 10.1.0.1 to network 0.0.0.0

i*L1  0.0.0.0/0 [115/20] via 10.1.0.1, 00:54:13, GigabitEthernet2               « Only default route received from IS-IS L1/L2 router
      3.0.0.0/32 is subnetted, 1 subnets
i L1     3.3.3.3 [115/10] via 10.1.0.1, 00:59:13, GigabitEthernet2
      4.0.0.0/32 is subnetted, 1 subnets
i L1     4.4.4.4 [115/20] via 10.1.0.1, 00:56:24, GigabitEthernet2






R8#show ip route isis | beg Ga
Gateway of last resort is 10.7.0.1 to network 0.0.0.0

i*L1  0.0.0.0/0 [115/20] via 10.7.0.1, 00:54:28, GigabitEthernet2
      6.0.0.0/32 is subnetted, 1 subnets
i L1     6.6.6.6 [115/20] via 10.7.0.1, 00:55:41, GigabitEthernet2
      7.0.0.0/32 is subnetted, 1 subnets
i L1     7.7.7.7 [115/10] via 10.7.0.1, 00:59:08, GigabitEthernet2






R5#show ip route isis | beg Ga                    « IS-IS Level-2 (backbone) routers receive all the routes
Gateway of last resort is not set

      2.0.0.0/32 is subnetted, 1 subnets
i L2     2.2.2.2 [115/30] via 10.3.0.1, 00:54:45, GigabitEthernet0/0
      3.0.0.0/32 is subnetted, 1 subnets
i L2     3.3.3.3 [115/20] via 10.3.0.1, 00:54:45, GigabitEthernet0/0
      4.0.0.0/32 is subnetted, 1 subnets
i L2     4.4.4.4 [115/10] via 10.3.0.1, 00:54:45, GigabitEthernet0/0
      6.0.0.0/32 is subnetted, 1 subnets
i L2     6.6.6.6 [115/10] via 10.4.0.2, 00:54:45, GigabitEthernet0/1
      7.0.0.0/32 is subnetted, 1 subnets
i L2     7.7.7.7 [115/20] via 10.4.0.2, 00:54:45, GigabitEthernet0/1
      8.0.0.0/32 is subnetted, 1 subnets
i L2     8.8.8.8 [115/30] via 10.4.0.2, 00:54:45, GigabitEthernet0/1
      9.0.0.0/32 is subnetted, 1 subnets
i L2     9.9.9.9 [115/10] via 10.5.0.2, 00:53:14, GigabitEthernet0/2






Host1#trace 192.168.2.1 probe 1
Type escape sequence to abort.
Tracing the route to 192.168.2.1
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.1.2 1 msec
  2 10.0.1.1 23 msec
  3 10.1.0.1 [MPLS: Labels 300/802 Exp 0] 49 msec     « MPLS label stack used to reach from Host1 (Site 1) to Host2 (Site 2)
  4 10.2.0.2 [MPLS: Labels 400/802 Exp 0] 50 msec
  5 10.3.0.2 [MPLS: Labels 500/802 Exp 0] 50 msec
  6 10.4.0.2 [MPLS: Labels 600/802 Exp 0] 50 msec
  7 10.6.0.2 [MPLS: Labels 701/802 Exp 0] 51 msec
  8 10.0.2.1 [MPLS: Label 802 Exp 0] 30 msec          « VPN Service Label assigned by PE R8
  9 10.0.2.2 58 msec
 10 192.168.2.1 53 msec