Tag: traffic engineering

MPLS – Traffic Engineering (MPLS-TE) Lab

What is MPLS Traffic Engineering (MPLS-TE)?

MPLS Traffic Engineering (MPLS-TE) is a technology that enhances the capabilities of MPLS (Multiprotocol Label Switching) to enable more granular control over traffic flow within a network.

Traffic engineering refers to the practice of optimizing the flow of network traffic in a way that ensures efficient use of network resources, avoids congestion, and achieves better overall performance. In traditional IP networks, traffic generally follows the shortest path, which can lead to suboptimal usage of network capacity and congestion. MPLS-TE allows operators to move beyond shortest-path routing by explicitly setting up paths through the network that distribute traffic in a desired way.

In this lab I am going to configure a tunnel to overrule the IGP shortest path and chose a different path.

MPLS Lab Setup

Labs download

Two CML Labs are available for download here.

1 – Lab Pre MPLS-TE config (OSPF, MPLS, LDP).
2 – Lab Post MPLS-TE config (OSPF (With TE), MPLS-TE, LDP, RSVP, Tunnel).

Using Cisco’s Modeling Labs (CML) I build the following MPLS lab using OSPF and LDP neighbor relationships using virtual routers running IOSv.

3 x P routers (Router1, Router2, Router3)
2 x PE router (Router4, Router5)
2 x CE router (Router6, Router7)

Default Behaviour
The default traffic flow behaviour from PE Router4 towards PE Router5 will follow the IGP shortest path via P Router3. This path is one hop instead of traversing via Router1+Router2 being two hops away and double the cost.

MPLS-TE
With MPLS-TE we can define a different path via Router1+Router2.
There can be many reasons why we would want to do this and many ways how we can achieve this. In this Lab I am going to enable MPLS-TE and simply exclude Router3 from our path.

Device	Function	Loopback address	Subnets	Label Ranges
Router1	P Router	1.1.1.1/32	Gi0/0 10.1.2.1/24 Gi0/1 10.1.3.1/24 Gi0/3 10.1.4.1/24	100-199
Router2	P Router	2.2.2.2/32	Gi0/0 10.1.2.2/24 Gi0/1 10.2.3.2/24 Gi0/3 10.2.4.2/24	200-299
Router3	P Router	3.3.3.3/32	Gi0/0 10.3.4.3/24 Gi0/1 10.1.3.3/24 Gi0/2 10.2.3.3/24 Gi0/3 10.3.5.3/24	300-399
Router4	PE Router	4.4.4.4/32	Gi0/0 10.3.4.4/24 Gi0/1 10.4.6.4/24 Gi0/3 10.1.4.4/24	400-499
Router5	PE Router	5.5.5.5/32	Gi0/1 10.1.5.5/24 Gi0/2 10.5.7.5/24 Gi0/3 10.4.5.5/24	500-599
Router6	CE Router	6.6.6.6/32	Gi0/1 10.4.6.6/24 Gi0/0 192.168.1.1/24	–
Router7	CE Router	7.7.7.7/32	Gi0/2 10.4.6.6/24 Gi0/0 192.168.2.1/24	–

IP Addressing:
The point-to-point links are configured with the following IP addressing scheme:

“10.<Lowest Router Id>.<Highest Router Id>.<Router Id>./24.”

For example the link between Router1 and Router2 gives on Router1: 10.1.2.1/24 and on Router2: 10.1.2.2/24.

Verification on Router3 (P):

Router3#sh ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
4.4.4.4           0   FULL/  -        00:00:35    10.3.4.4        GigabitEthernet0/0
1.1.1.1           0   FULL/  -        00:00:38    10.1.3.1        GigabitEthernet0/1
2.2.2.2           0   FULL/  -        00:00:35    10.2.3.2        GigabitEthernet0/2
5.5.5.5           0   FULL/  -        00:00:33    10.3.5.5        GigabitEthernet0/3

Router3#sh mpls interfaces
Interface              IP            Tunnel   BGP Static Operational
GigabitEthernet0/0     Yes (ldp)     No       No  No     Yes
GigabitEthernet0/1     Yes (ldp)     No       No  No     Yes
GigabitEthernet0/2     Yes (ldp)     No       No  No     Yes
GigabitEthernet0/3     Yes (ldp)     No       No  No     Yes

Router3#sh mpls ldp neighbor
    Peer LDP Ident: 5.5.5.5:0; Local LDP Ident 3.3.3.3:0
        TCP connection: 5.5.5.5.57381 - 3.3.3.3.646
        State: Oper; Msgs sent/rcvd: 46/45; Downstream
        Up time: 00:26:54
        LDP discovery sources:
          GigabitEthernet0/3, Src IP addr: 10.3.5.5
        Addresses bound to peer LDP Ident:
          10.2.5.5        5.5.5.5         10.3.5.5
    Peer LDP Ident: 4.4.4.4:0; Local LDP Ident 3.3.3.3:0
        TCP connection: 4.4.4.4.42087 - 3.3.3.3.646
        State: Oper; Msgs sent/rcvd: 44/46; Downstream
        Up time: 00:26:54
        LDP discovery sources:
          GigabitEthernet0/0, Src IP addr: 10.3.4.4
        Addresses bound to peer LDP Ident:
          10.3.4.4        4.4.4.4         10.1.4.4
    Peer LDP Ident: 2.2.2.2:0; Local LDP Ident 3.3.3.3:0
        TCP connection: 2.2.2.2.646 - 3.3.3.3.23943
        State: Oper; Msgs sent/rcvd: 45/45; Downstream
        Up time: 00:26:51
        LDP discovery sources:
          GigabitEthernet0/2, Src IP addr: 10.2.3.2
        Addresses bound to peer LDP Ident:
          10.1.2.2        10.2.5.2        10.2.3.2        2.2.2.2
    Peer LDP Ident: 1.1.1.1:0; Local LDP Ident 3.3.3.3:0
        TCP connection: 1.1.1.1.646 - 3.3.3.3.22044
        State: Oper; Msgs sent/rcvd: 45/45; Downstream
        Up time: 00:26:51
        LDP discovery sources:
          GigabitEthernet0/1, Src IP addr: 10.1.3.1
        Addresses bound to peer LDP Ident:
          10.1.2.1        10.1.3.1        10.1.4.1        1.1.1.1

Router Configurations

P Routers: (Router1, Router2, Router3)

The P routers are configured with the standard subnetting scheme from the table above in combination with OSPF area 0 and LDP as the labelling protocol. The Label range is based on the Router number.

Router1, Router2, Router2#

#---- MPLS ranges and LDP
#---- Modify label range per router
mpls label range 100 199
mpls label protocol ldp
mpls ldp router-id Loopback0 force


#---- Interface configuration with MPLS & OSPF
interface Loopback0
 ip address 1.1.1.1 255.255.255.255
 ip ospf 1 area 0
!
interface GigabitEthernet0/0
 ip address 10.1.2.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 0
 mpls ip
!
interface GigabitEthernet0/1
 ip address 10.1.3.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 0
 mpls ip
!
interface GigabitEthernet0/3
 ip address 10.1.4.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 0
 mpls ip
!

PE Routers: (Router4, Router5)

The PE routers are configured with the standard subnetting scheme from the table above in combination with OSPF area 0 and LDP as the labelling protocol.
Each PE routers has an IBGP session to the other PE router (Router4 <-> Router5) for CE traffic.

Router4 (PE)


# ============= MPLS
mpls label range 400 499
mpls label protocol ldp
mpls ldp router-id Loopback0 force

# ===== Interfaces 

interface Loopback0
 ip address 4.4.4.4 255.255.255.255
 ip ospf 1 area 0
!
interface GigabitEthernet0/0
 ip address 10.3.4.4 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 0
 mpls ip
!
interface GigabitEthernet0/1
 ip vrf forwarding CUST
 ip address 10.4.6.4 255.255.255.0
!
interface GigabitEthernet0/3
 ip address 10.1.4.4 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 0
 mpls ip

# ============= OSPF
router ospf 1
 router-id 4.4.4.4
!

# =========== BGP
router bgp 65000
 template peer-session IBGP
  remote-as 65000
  transport connection-mode active
  update-source Loopback0
 exit-peer-session
 !
 bgp router-id 4.4.4.4
 bgp log-neighbor-changes
 no bgp default ipv4-unicast
 neighbor 5.5.5.5 inherit peer-session IBGP
 neighbor 5.5.5.5 transport connection-mode passive
 !
 address-family ipv4
 exit-address-family
 !
 address-family vpnv4
  neighbor 5.5.5.5 activate
  neighbor 5.5.5.5 send-community extended
  neighbor 5.5.5.5 next-hop-self
 exit-address-family
 !
 address-family ipv4 vrf CUST
  neighbor 10.4.6.6 remote-as 65006
  neighbor 10.4.6.6 activate
  neighbor 10.4.6.6 as-override
 exit-address-family

Router5 (PE)


# ============= MPLS
mpls label range 500 599
mpls label protocol ldp
mpls ldp router-id Loopback0 force

# ===== Interfaces 

interface Loopback0
 ip address 5.5.5.5 255.255.255.255
 ip ospf 1 area 0
!
interface GigabitEthernet0/1
 ip address 10.2.5.5 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 0
 mpls ip
!
interface GigabitEthernet0/2
 ip vrf forwarding CUST
 ip address 10.5.7.5 255.255.255.0
!
interface GigabitEthernet0/3
 ip address 10.3.5.5 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 0
 mpls ip

# ============= OSPF
router ospf 1
 router-id 5.5.5.5
!

# =========== BGP
router bgp 65000
 template peer-session IBGP
  remote-as 65000
  transport connection-mode active
  update-source Loopback0
 exit-peer-session
 !
 bgp router-id 5.5.5.5
 bgp log-neighbor-changes
 no bgp default ipv4-unicast
 neighbor 4.4.4.4 inherit peer-session IBGP

 !
 address-family ipv4
 exit-address-family
 !
 address-family vpnv4
  neighbor 4.4.4.4 activate
  neighbor 4.4.4.4 send-community extended
  neighbor 4.4.4.4 next-hop-self
 exit-address-family
 !
 address-family ipv4 vrf CUST
  neighbor 10.5.7.7 remote-as 65006
  neighbor 10.5.7.7 activate
  neighbor 10.5.7.7 as-override
 exit-address-family

Traceroute between CE routers before TE (R6->R7)

When performing a traceroute between CE routers we see the default IGP shortest path behaviour.
R6 -> R4 -> R3 -> R5 -> R7.
After MPLS-TE we will have created the following path:
R6 -> R4 -> R1 -> R2 -> R5 -> R7.

Router6#traceroute 7.7.7.7 source 6.6.6.6
Type escape sequence to abort.
Tracing the route to 7.7.7.7
VRF info: (vrf in name/id, vrf out name/id)
  1 10.4.6.4 2 msec 3 msec 2 msec
  2 10.3.4.3 [MPLS: Labels 303/511 Exp 0] 10 msec 8 msec 7 msec
  3 10.5.7.5 [AS 65000] [MPLS: Label 511 Exp 0] 9 msec 8 msec 11 msec
  4 10.5.7.7 [AS 65000] 12 msec 12 msec *

MPLS Traffic Engineering Configuration

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MPLS – Traffic Engineering (MPLS-TE) Options

MPLS, or Multiprotocol Label Switching, is a technique that enhances the speed and efficiency of data flow across complex networks. It operates by adding short path labels to network packets, directing them through a predetermined Label-Switched Path (LSP) rather than traditional IP-based routing. These labels contain all the forwarding information, allowing routers to forward packets based on the label rather than performing complex IP lookups. By simplifying the routing decision process, MPLS can reduce latency, optimize network performance, and enable quality-of-service (QoS) features that guarantee certain levels of bandwidth and prioritize critical applications like voice and video.

MPLS is widely used in service provider networks, supporting technologies like VPNs (Virtual Private Networks) and traffic engineering. In a typical MPLS setup, labels are assigned and stripped at the network’s edge, so the core network can process packets quickly without IP overhead. Additionally, MPLS is adaptable to various network protocols and media, enabling seamless interoperability across different types of infrastructure. By allowing network operators to manage traffic dynamically and reroute around congestion or failures, MPLS ensures greater reliability and robustness, making it a preferred choice for large-scale enterprise and ISP networks.

MPLS Traffic Engineering (MPLS-TE) is a technology that enhances the capabilities of MPLS to enable more granular control over traffic flow within a network. This is achieved by manipulating traffic paths to optimize resource usage, avoid congestion, and meet specific service requirements, like bandwidth guarantees or low latency. Here are key methods by which MPLS-TE can manipulate paths and traffic flow:

MPLS-TE Traffic manipulation options

Explicit Routing with Constraint-Based Routing (CBR)

Constraint-based routing allows MPLS-TE to create Label-Switched Paths (LSPs) that follow a specific path through the network, rather than relying on traditional routing protocols.
Explicit path setup enables network operators to define exact paths based on link attributes, resource availability, or even administrative preferences, avoiding congested or unreliable links.
Constraints can include bandwidth, latency, maximum hop count, and available resources.

! Define an explicit path list for the TE tunnel
Router(config)# ip explicit-path name Path_R1_R3
Router(config-ip-expl-path)# next-address 10.1.1.2  ! IP of Router2
Router(config-ip-expl-path)# next-address 10.1.2.2  ! IP of Router3

! Configure the TE Tunnel
Router(config)# interface Tunnel1
Router(config-if)# ip unnumbered Loopback0
Router(config-if)# tunnel mode mpls traffic-eng
Router(config-if)# tunnel destination 10.1.3.3     ! Destination (Router3)
Router(config-if)# tunnel mpls traffic-eng path-option 1 explicit name Path_R1_R3
Router(config-if)# tunnel mpls traffic-eng bandwidth 1000   ! Set bandwidth constraint
Router(config-if)# no shutdown

Traffic Engineering Database (TED)

The TED collects information on the state of the network, such as available bandwidth, link utilization, and link properties.
MPLS-TE uses the TED to make dynamic routing decisions based on real-time information, thus selecting paths that avoid congested areas and optimize resource use.

! Enable traffic engineering on OSPF
Router(config)# router ospf 1
Router(config-router)# mpls traffic-eng router-id Loopback0
Router(config-router)# mpls traffic-eng area 0

! Ensure interfaces participate in TE
Router(config)# interface GigabitEthernet0/1
Router(config-if)# ip router ospf 1 area 0
Router(config-if)# mpls traffic-eng tunnels

Resource Reservation with RSVP-TE

RSVP-TE (Resource Reservation Protocol with TE extensions) is used to signal and reserve resources along the selected path.
This protocol sets up traffic-engineered LSPs (TE LSPs) and reserves the necessary bandwidth to meet quality-of-service (QoS) requirements.
With RSVP-TE, MPLS-TE can ensure certain traffic flows (like voice or video) get dedicated resources, reducing packet loss and jitter.

! Enable RSVP globally
Router(config)# mpls traffic-eng tunnels
Router(config)# ip rsvp signaling hello

! Enable RSVP on each interface used by the MPLS-TE tunnel
Router(config)# interface GigabitEthernet0/1
Router(config-if)# ip rsvp bandwidth 10000 1000  ! Interface bandwidth in kbps, reserved bandwidth

! Configure an MPLS-TE tunnel with RSVP
Router(config)# interface Tunnel2
Router(config-if)# ip unnumbered Loopback0
Router(config-if)# tunnel mode mpls traffic-eng
Router(config-if)# tunnel destination 10.1.3.3
Router(config-if)# tunnel mpls traffic-eng bandwidth 2000
Router(config-if)# tunnel mpls traffic-eng path-option 1 dynamic
Router(config-if)# no shutdown

Fast Reroute (FRR)

Fast Reroute enables rapid path switching in case of a link or node failure, ensuring minimal disruption.
FRR pre-establishes backup LSPs so that traffic can be diverted almost instantaneously in case of an issue on the primary path, enhancing reliability and service continuity.

! Configure fast reroute on the tunnel interface
Router(config)# interface Tunnel2
Router(config-if)# mpls traffic-eng fast-reroute
Router(config-if)# tunnel mpls traffic-eng path-option 1 dynamic
Router(config-if)# no shutdown

Load Balancing and Path Diversity

MPLS-TE supports load balancing by distributing traffic across multiple LSPs. This is particularly useful for high-traffic routes that need more bandwidth than a single path can provide.
Path diversity ensures that critical data can be split across multiple paths, reducing the risk of a single point of failure and improving network redundancy.

Router(config)# interface Tunnel3
Router(config-if)# ip unnumbered Loopback0
Router(config-if)# tunnel mode mpls traffic-eng
Router(config-if)# tunnel destination 10.1.3.3
Router(config-if)# tunnel mpls traffic-eng path-option 1 dynamic
Router(config-if)# tunnel mpls traffic-eng path-option 2 explicit name Path_R1_R3
Router(config-if)# no shutdown

Bandwidth Guarantees and Traffic Prioritization

MPLS-TE can allocate bandwidth to specific traffic flows, ensuring certain types of traffic, like real-time or high-priority data, meet their QoS requirements.
Differentiated services (DiffServ) can be implemented within MPLS-TE, allowing traffic prioritization at the LSP level and ensuring high-priority traffic gets preferential treatment.

! Set bandwidth requirement for TE tunnel
Router(config)# interface Tunnel4
Router(config-if)# tunnel mode mpls traffic-eng
Router(config-if)# tunnel destination 10.1.3.3
Router(config-if)# tunnel mpls traffic-eng bandwidth 5000   ! 5000 kbps reserved
Router(config-if)# no shutdown

Administrative Policies and Affinity-Based Routing

Administrative policies (affinity or coloring) can be used to prefer or avoid certain links based on the type of traffic.
Affinity or link coloring allows paths to be marked for certain traffic types (e.g., customer A’s traffic can only use certain links), enabling more precise traffic segregation and adherence to SLA requirements.

! Define affinity on an interface (e.g., marking it with color 0x10)
Router(config)# interface GigabitEthernet0/2
Router(config-if)# mpls traffic-eng administrative-weight 0x10

! Set affinity for the tunnel
Router(config)# interface Tunnel5
Router(config-if)# tunnel mode mpls traffic-eng
Router(config-if)# tunnel destination 10.1.3.3
Router(config-if)# tunnel mpls traffic-eng path-option 1 dynamic
Router(config-if)# tunnel mpls traffic-eng attribute-flags affinity 0x10
Router(config-if)# no shutdown

Dynamic Path Computation with Path Computation Element (PCE)

The Path Computation Element (PCE) is a centralized network component that dynamically computes paths for MPLS-TE LSPs based on network-wide data.
PCE enhances scalability and efficiency in large networks by providing real-time, optimized path computation and reducing computational strain on routers.

! Enable PCEP on the router
Router(config)# pce
Router(config-pce)# address ipv4 10.1.4.4
Router(config-pce)# source Loopback0
Router(config-pce)# no shutdown

! Configure the tunnel to use PCE for path computation
Router(config)# interface Tunnel6
Router(config-if)# tunnel mode mpls traffic-eng
Router(config-if)# tunnel destination 10.1.3.3
Router(config-if)# tunnel mpls traffic-eng path-option 1 dynamic pce
Router(config-if)# no shutdown

These examples demonstrate basic configurations for MPLS-TE features. Advanced setups may require customizations based on network architecture, device capabilities, and specific application needs.