Implementing MPLS Traffic Engineering
Traditional IP routing emphasizes on forwarding traffic to the destination as fast as possible. As a result, the routing protocols find out the least-cost route according to its metric to each destination in the network and every router forwards the packet based on the destination IP address and packets are forwarded hop-by-hop. Thus, traditional IP routing does not consider the available bandwidth of the link. This can cause some links to be over-utilized compared to others and bandwidth is not efficiently utilized. Traffic Engineering (TE) is used when the problems result from inefficient mapping of traffic streams onto the network resources. Traffic engineering allows you to control the path that data packets follow and moves traffic flows from congested links to non-congested links that would not be possible by the automatically computed destination-based shortest path.
Multiprotocol Label Switching (MPLS) with its label switching capabilities, eliminates the need for an IP route look-up and creates a virtual circuit (VC) switching function, allowing enterprises the same performance on their IP-based network services as with those delivered over traditional networks such as Frame Relay or Asynchronous Transfer Mode (ATM). MPLS traffic engineering (MPLS-TE) relies on the MPLS backbone to replicate and expand upon the TE capabilities of Layer 2 ATM and Frame Relay networks.
MPLS-TE learns the topology and resources available in a network and then maps traffic flows to particular paths based on resource requirements and network resources such as bandwidth. MPLS-TE builds a unidirectional tunnel from a source to a destination in the form of a label switched path (LSP), which is then used to forward traffic. The point where the tunnel begins is called the tunnel headend or tunnel source, and the node where the tunnel ends is called the tunnel tailend or tunnel destination. A router through which the tunnel passes is called the mid-point of the tunnel.
MPLS uses extensions to a link-state based Interior Gateway Protocol (IGP), such as Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF). MPLS calculates TE tunnels at the LSP head based on required and available resources (constraint-based routing). If configured, the IGP automatically routes the traffic onto these LSPs. Typically, a packet that crosses the MPLS-TE backbone travels on a single LSP that connects the ingress point to the egress point. MPLS TE automatically establishes and maintains the LSPs across the MPLS network by using the Resource Reservation Protocol (RSVP).
Overview of MPLS-TE Features
In MPLS traffic engineering, IGP extensions flood the TE information across the network. Once the IGP distributes the link attributes and bandwidth information, the headend router calculates the best path from head to tail for the MPLS-TE tunnel. This path can also be configured explicitly. Once the path is calculated, RSVP-TE is used to set up the TE LSP (Labeled Switch Path).
To forward the traffic, you can configure autoroute, forward adjacency, or static routing. The autoroute feature announces the routes assigned by the tailend router and its downstream routes to the routing table of the headend router and the tunnel is considered as a directly connected link to the tunnel.
If forward adjacency is enabled, MPLS-TE tunnel is advertised as a link in an IGP network with the link's cost associated with it. Routers outside of the TE domain can see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.
MPLS-TE provides protection mechanism known as fast reroute to minimize packet loss during a failure. For fast reroute, you need to create back up tunnels. The autotunnel backup feature enables a router to dynamically build backup tunnels when they are needed instead of pre-configuring each backup tunnel and then assign the backup tunnel to the protected interfaces.
DiffServ Aware Traffic Engineering (DS-TE) enables you to configure multiple bandwidth constraints on an MPLS-enabled interface to support various classes of service (CoS). These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint.
The MPLS traffic engineering autotunnel mesh feature allows you to set up full mesh of TE tunnels automatically with a minimal set of MPLS traffic engineering configurations. The MPLS-TE auto bandwidth feature allows you to automatically adjusts bandwidth based on traffic patterns without traffic disruption.
The MPLS-TE interarea tunneling feature allows you to establish TE tunnels spanning multiple Interior Gateway Protocol (IGP) areas and levels, thus eliminating the requirement that headend and tailend routers should reside in a single area.
For detailed information about MPLS-TE features, see MPLS-TE Features - Details.
 Note |
MPLS-TE Nonstop Routing (NSR) is enabled by default without any user configuration and cannot be disabled. MPLS-TE NSR means the application is in hot-standby mode and standby MPLS-TE instance is ready to take over from the active instance quickly on RP failover. Note that the MPLS-TE does not do routing. If there is standby card available then the MPLS-TE instance is in a hot-standby position. The following output shows the status of MPLS-TE NSR: During any issues with the MPLS-TE, the NSR on the router gets affected which is displayed in the show redundancy output as follows: |
How MPLS-TE Works
MPLS-TE automatically establishes and maintains label switched paths (LSPs) across the backbone by using RSVP. The path that an LSP uses is determined by the LSP resource requirements and network resources, such as bandwidth. Available resources are flooded by extensions to a link state based Interior Gateway Protocol (IGP). MPLS-TE tunnels are calculated at the LSP headend router, based on a fit between the required and available resources (constraint-based routing). The IGP automatically routes the traffic to these LSPs. Typically, a packet crossing the MPLS-TE backbone travels on a single LSP that connects the ingress point to the egress point.
The following sections describe the components of MPLS-TE:
Tunnel Interfaces
From a Layer 2 standpoint, an MPLS tunnel interface represents the headend of an LSP. It is configured with a set of resource requirements, such as bandwidth and media requirements, and priority. From a Layer 3 standpoint, an LSP tunnel interface is the headend of a unidirectional virtual link to the tunnel destination.
MPLS-TE Path Calculation Module
This calculation module operates at the LSP headend. The module determines a path to use for an LSP. The path calculation uses a link-state database containing flooded topology and resource information.
RSVP with TE Extensions
RSVP operates at each LSP hop and is used to signal and maintain LSPs based on the calculated path.
MPLS-TE Link Management Module
This module operates at each LSP hop, performs link call admission on the RSVP signaling messages, and keep track on topology and resource information to be flooded.
Link-state IGP
Either Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF) can be used as IGPs. These IGPs are used to globally flood topology and resource information from the link management module.
Label Switching Forwarding
This forwarding mechanism provides routers with a Layer 2-like ability to direct traffic across multiple hops of the LSP established by RSVP signaling.
Configuring MPLS-TE
MPLS-TE requires co-ordination among several global neighbor routers. RSVP, MPLS-TE and IGP are configured on all routers and interfaces in the MPLS traffic engineering network. Explicit path and TE tunnel interfaces are configured only on the head-end routers. MPLS-TE requires some basic configuration tasks explained in this section.
-
L3VPN over MPLS TE, L2VPN over MPLS TE, IPv6 over MPLS TE, and MPLS TE over MPLS TE are currently not supported.
- In MPLS-TE fast reroute (FRR), switch over time in case of a failure is less than 50 milliseconds. However, if there are any TE tunnels that are part of the equal-cost multipath (ECMP), the switch over of the TE tunnel may exceed 50 milliseconds.
-
When the TE tunnel is in FRR active state, the tunnel statistics will be accounted over the primary TE tunnel and not over the backup TE tunnel.
Building MPLS-TE Topology
Building MPLS-TE topology, sets up the environment for creating MPLS-TE tunnels. This procedure includes the basic node and interface configuration for enabling MPLS-TE. To perform constraint-based routing, you need to enable OSPF or IS-IS as IGP extension.
Before You Begin
Before you start to build the MPLS-TE topology, the following pre-requisites are required:
-
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
-
Enable RSVP on the port interface.
Example
This example enables MPLS-TE on a node and then specifies the interface that is part of the MPLS-TE. Here, OSPF is used as the IGP extension protocol for information distribution.
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# interface hundredGigE0/0/0/3
RP/0/RP0/CPU0:router(config)# router ospf area 1
RP/0/RP0/CPU0:router(config-ospf)# area 0
RP/0/RP0/CPU0:router(config-ospf-ar)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-ospf-ar)# interface hundredGigE0/0/0/3
RP/0/RP0/CPU0:router(config-ospf-ar-if)# exit
RP/0/RP0/CPU0:router(config-ospf)# mpls traffic-eng router-id 192.168.70.1
RP/0/RP0/CPU0:router(config)# commitExample
This example enables MPLS-TE on a node and then specifies the interface that is part of the MPLS-TE. Here, IS-IS is used as the IGP extension protocol for information distribution.
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# interface hundredGigE0/0/0/3
RP/0/RP0/CPU0:router(config)# router isis 1
RP/0/RP0/CPU0:router(config-isis)# net 47.0001.0000.0000.0002.00
RP/0/RP0/CPU0:router(config-isis)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-af)# metric-style wide
RP/0/RP0/CPU0:router(config-isis-af)# mpls traffic-eng level 1
RP/0/RP0/CPU0:router(config-isis-af)# exit
RP/0/RP0/CPU0:router(config-isis)# interface hundredGigE0/0/0/3
RP/0/RP0/CPU0:router(config-isis-if)# exit
RP/0/RP0/CPU0:router(config)# commitRelated Topics
Creating an MPLS-TE Tunnel
Creating an MPLS-TE tunnel is a process of customizing the traffic engineering to fit your network topology. The MPLS-TE tunnel is created at the headend router. You need to specify the destination and path of the TE LSP.
To steer traffic through the tunnel, you can use the following ways:
-
Static Routing
-
Autoroute Announce
-
Forwarding Adjacency
From the 7.1.1 release, IS-IS autoroute announce function is enhanced to redirect traffic from a source IP address prefix to a matching IP address assigned to an MPLS-TE tunnel destination interface.
Before You Begin
The following prerequisites are required to create an MPLS-TE tunnel:
-
You must have a router ID for the neighboring router.
-
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID to the routers, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
Configuration Example
This example configures an MPLS-TE tunnel on the headend router with a destination IP address 192.168.92.125. The bandwidth for the tunnel, path-option, and forwarding parameters of the tunnel are also configured. You can use static routing, autoroute announce or forwarding adjacency to steer traffic through the tunnel.
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# interface tunnel-te 1
RP/0/RP0/CPU0:router(config-if)# destination 192.168.92.125
RP/0/RP0/CPU0:router(config-if)# ipv4 unnumbered Loopback0
RP/0/RP0/CPU0:router(config-if)# path-option 1 dynamic
RP/0/RP0/CPU0:router(config-if)# autoroute announce or forwarding adjacency
RP/0/RP0/CPU0:router(config-if)# signalled-bandwidth 100
RP/0/RP0/CPU0:router(config)# commit
Verification
Verify the configuration of MPLS-TE tunnel using the following command.
RP/0/RP0/CPU0:router# show mpls traffic-engineering tunnels brief
Signalling Summary:
LSP Tunnels Process: running
RSVP Process: running
Forwarding: enabled
Periodic reoptimization: every 3600 seconds, next in 2538 seconds
Periodic FRR Promotion: every 300 seconds, next in 38 seconds
Auto-bw enabled tunnels: 0 (disabled)
TUNNEL NAME DESTINATION STATUS STATE
tunnel-te1 192.168.92.125 up up
Displayed 1 up, 0 down, 0 recovering, 0 recovered heads Automatic Modification Of An MPLS-TE Tunnel’s Metric
If the IGP calculation on a router results in an equal cost multipath (ECMP) scenario where next-hop interfaces are a mix of MPLS-TE tunnels and physical interfaces, you may want to ensure that a TE tunnel is preferred. Consider this topology:
-
All links in the network have a metric of 5.
-
To offload a congested link between R3 and R4, an MPLS-TE tunnel is created from R3 to R2.
-
If the metric of the tunnel is also 5, traffic from R3 to R5 is load-balanced between the tunnel and the physical R3-R4 link.
To ensure that the MPLS-TE tunnel is preferred in such scenarios, configure the autoroute metric command on the tunnel interface. The modified metric is applied in the routing information base (RIB), and the tunnel is preferred over the physical path of the same metric. Sample configuration:
Router# configure
Router(config)# interface tunnel-te 1
Router(config-if)# autoroute metric relative -1
The autoroute metric command syntax is autoroute metric {absolute|relative} value
-
absolute enables the absolute metric mode, for a metric range between 1 and 2147483647.
-
relative enables the relative metric mode, for a metric range between -10 and 10, including zero.
Note |
Since the relative metric is not saved in the IGP database, the advertised metric of the MPLS-TE tunnel remains 5, and doesn't affect SPF calculation outcomes on other nodes. |
Related Topics
Configuring Fast Reroute
Fast reroute (FRR) provides link protection to LSPs enabling the traffic carried by LSPs that encounter a failed link to be rerouted around the failure. The reroute decision is controlled locally by the router connected to the failed link. The headend router on the tunnel is notified of the link failure through IGP or through RSVP. When it is notified of a link failure, the headend router attempts to establish a new LSP that bypasses the failure. This provides a path to reestablish links that fail, providing protection to data transfer. The path of the backup tunnel can be an IP explicit path, a dynamically calculated path, or a semi-dynamic path. For detailed conceptual information on fast reroute, see MPLS-TE Features - Details
Before You Begin
The following prerequisites are required to create an MPLS-TE tunnel:
-
You must have a router ID for the neighboring router.
-
Stable router ID is required at either end of the link to ensure that the link is successful. If you do not assign a router ID to the routers, the system defaults to the global router ID. Default router IDs are subject to change, which can result in an unstable link.
Configuration Example
This example configures fast reroute on an MPLS-TE tunnel. Here, tunnel-te 2 is configured as the back-up tunnel. You can use the protected-by command to configure path protection for an explicit path that is protected by another path.
RP/0/RP0/CPU0:router # configure
RP/0/RP0/CPU0:router(config)# interface tunnel-te 1
RP/0/RP0/CPU0:router(config-if)# fast-reroute
RP/0/RP0/CPU0:router(config-if)# exit
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# interface HundredGigabitEthernet0/0/0/3
RP/0/RP0/CPU0:router(config-mpls-te-if)# backup-path tunnel-te 2
RP/0/RP0/CPU0:router(config)# interface tunnel-te 2
RP/0/RP0/CPU0:router(config-if)# backup-bw global-pool 5000
RP/0/RP0/CPU0:router(config-if)# ipv4 unnumbered Loopback0
RP/0/RP0/CPU0:router(config-if)# destination 192.168.92.125
RP/0/RP0/CPU0:router(config-if)# path-option l explicit name backup-path protected by 10
RP/0/RP0/CPU0:router(config-if)# path-option l0 dynamic
RP/0/RP0/CPU0:router(config)# commit
Verification
Use the show mpls traffic-eng fast-reroute database command to verify the fast reroute configuration.
RP/0/RP0/CPU0:router# show mpls traffic-eng fast-reroute database
Tunnel head FRR information:
Tunnel Out intf/label FRR intf/label Status
---------- ---------------- ---------------- -------
tt4000 HundredGigabitEthernet 0/0/0/3:34 tt1000:34 Ready
tt4001 HundredGigabitEthernet 0/0/0/3:35 tt1001:35 Ready
tt4002 HundredGigabitEthernet 0/0/0/3:36 tt1001:36 Ready
Related Topics
Configuring Auto-Tunnel Backup
The MPLS Traffic Engineering Auto-Tunnel Backup feature enables a router to dynamically build backup tunnels on the interfaces that are configured with MPLS TE tunnels instead of building MPLS-TE tunnels statically.
The MPLS-TE Auto-Tunnel Backup feature has these benefits:
-
Backup tunnels are built automatically, eliminating the need for users to pre-configure each backup tunnel and then assign the backup tunnel to the protected interface.
-
Protection is expanded—FRR does not protect IP traffic that is not using the TE tunnel or Label Distribution Protocol (LDP) labels that are not using the TE tunnel.
The TE attribute-set template that specifies a set of TE tunnel attributes, is locally configured at the headend of auto-tunnels. The control plane triggers the automatic provisioning of a corresponding TE tunnel, whose characteristics are specified in the respective attribute-set.
Configuration Example
This example configures Auto-Tunnel backup on an interface and specifies the attribute-set template for the auto tunnels. In this example, unused backup tunnels are removed every 20 minutes using a timer and also the range of tunnel interface numbers are specified.
RP/0/RP0/CPU0:router # configure
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# interface HundredGigabitEthernet0/0/0/3
RP/0/RP0/CPU0:router(config-mpls-te-if)# auto-tunnel backup
RP/0/RP0/CPU0:router(config-mpls-te-if-auto-backup)# attribute-set ab
RP/0/RP0/CPU0:router(config-mpls-te)# auto-tunnel backup timers removal unused 20
RP/0/RP0/CPU0:router(config-mpls-te)# auto-tunnel backup tunnel-id min 6000 max 6500
RP/0/RP0/CPU0:router(config)# commit
Verification
RP/0/RP0/CPU0:router# show mpls traffic-eng tunnels brief
TUNNEL NAME DESTINATION STATUS STATE
tunnel-te0 200.0.0.3 up up
tunnel-te1 200.0.0.3 up up
tunnel-te2 200.0.0.3 up up
tunnel-te50 200.0.0.3 up up
*tunnel-te60 200.0.0.3 up up
*tunnel-te70 200.0.0.3 up up
*tunnel-te80 200.0.0.3 up up Related Topics
Configuring Next Hop Backup Tunnel
The backup tunnels that bypass only a single link of the LSP path are referred as Next Hop (NHOP) backup tunnels because they terminate at the LSP's next hop beyond the point of failure. They protect LSPs, if a link along their path fails, by rerouting the LSP traffic to the next hop, thus bypassing the failed link.
Configuration Example
This example configures next hop backup tunnel on an interface and specifies the attribute-set template for the auto tunnels. In this example, unused backup tunnels are removed every 20 minutes using a timer and also the range of tunnel interface numbers are specified.
RP/0/RP0/CPU0:router # configure
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# interface HundredGigabitEthernet0/0/0/3
RP/0/RP0/CPU0:router(config-mpls-te-if)# auto-tunnel backup nhop-only
RP/0/RP0/CPU0:router(config-mpls-te-if-auto-backup)# attribute-set ab
RP/0/RP0/CPU0:router(config-mpls-te)# auto-tunnel backup timers removal unused 20
RP/0/RP0/CPU0:router(config-mpls-te)# auto-tunnel backup tunnel-id min 6000 max 6500
RP/0/RP0/CPU0:router(config)# commit
Related Topics
Configuring SRLG Node Protection
Shared Risk Link Groups (SRLG) in MPLS traffic engineering refer to situations in which links in a network share common resources. These links have a shared risk, and that is when one link fails, other links in the group might fail too.
OSPF and IS-IS flood the SRLG value information (including other TE link attributes such as bandwidth availability and affinity) using a sub-type length value (sub-TLV), so that all routers in the network have the SRLG information for each link.
MPLS-TE SRLG feature enhances backup tunnel path selection by avoiding using links that are in the same SRLG as the interfaces it is protecting while creating backup tunnels.
Configuration Example
This example creates a backup tunnel and excludes the protected node IP address from the explicit path.
RP/0/RP0/CPU0:router # configure
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# interface HundredGigabitEthernet0/0/0/3
RP/0/RP0/CPU0:router(config-mpls-te-if)# backup-path tunnl-te 2
RP/0/RP0/CPU0:router(config-mpls-te-if)# exit
RP/0/RP0/CPU0:router(config)# interface tunnel-te 2
RP/0/RP0/CPU0:router(config-if)# ipv4 unnumbered Loopback0
RP/0/RP0/CPU0:router(config-if)# path-option 1 explicit name backup-srlg
RP/0/RP0/CPU0:router(config-if)# destination 192.168.92.125
RP/0/RP0/CPU0:router(config-if)# exit
RP/0/RP0/CPU0:router(config)# explicit-path name backup-srlg-nodep
RP/0/RP0/CPU0:router(config-if)# index 1 exclude-address 192.168.91.1
RP/0/RP0/CPU0:router(config-if)# index 2 exclude-srlg 192.168.92.2
RP/0/RP0/CPU0:router(config)# commit
Related Topics
Configuring Flexible Name-Based Tunnel Constraints
MPLS-TE Flexible Name-based Tunnel Constraints provides a simplified and more flexible means of configuring link attributes and path affinities to compute paths for the MPLS-TE tunnels.
In traditional TE, links are configured with attribute-flags that are flooded with TE link-state parameters using Interior Gateway Protocols (IGPs), such as Open Shortest Path First (OSPF).
MPLS-TE Flexible Name-based Tunnel Constraints lets you assign, or map, up to 32 color names for affinity and attribute-flag attributes instead of 32-bit hexadecimal numbers. After mappings are defined, the attributes can be referred to by the corresponding color name.
Configuration Example
This example shows assigning a how to associate a tunnel with affinity constraints.
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# affinity-map red 1
RP/0/RP0/CPU0:router(config-mpls-te)# interface HundredGigabitEthernet0/0/0/3
RP/0/RP0/CPU0:router(config-mpls-te-if)# attribute-names red
RP/0/RP0/CPU0:router(config)# interface tunnel-te 2
RP/0/RP0/CPU0:router(config-if)# affinity include red
RP/0/RP0/CPU0:router(config)# commit
Configuring Automatic Bandwidth
Automatic bandwidth allows you to dynamically adjust bandwidth reservation based on measured traffic. MPLS-TE automatic bandwidth monitors the traffic rate on a tunnel interface and resizes the bandwidth on the tunnel interface to align it closely with the traffic in the tunnel. MPLS-TE automatic bandwidth is configured on individual Label Switched Paths (LSPs) at every headend router.
The following table specifies the parameters that can be configured as part of automatic bandwidth configuration.
|
Bandwidth Parameters |
Description |
|---|---|
|
Application frequency |
Configures how often the tunnel bandwidths changed for each tunnel. The default value is 24 hours. |
|
Bandwidth limit |
Configures the minimum and maximum automatic bandwidth to set on a tunnel. |
|
Bandwidth collection frequency |
Enables bandwidth collection without adjusting the automatic bandwidth. The default value is 5 minutes. |
|
Overflow threshold |
Configures tunnel overflow detection. |
|
Adjustment threshold |
Configures the tunnel-bandwidth change threshold to trigger an adjustment. |
Configuration Example
This example enables automatic bandwidth on MPLS-TE tunnel interface and configure the following automatic bandwidth variables.
-
Application frequency
-
Bandwidth limit
-
Adjustment threshold
-
Overflow detection
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# interface tunnel-te 1
RP/0/RP0/CPU0:router(config-if)# auto-bw
RP/0/RP0/CPU0:router(config-if-tunte-autobw)# application 1000
RP/0/RP0/CPU0:router(config-if-tunte-autobw)# bw-limit min 30 max 1000
RP/0/RP0/CPU0:router(config-if-tunte-autobw)# adjustment-threshold 50 min 800
RP/0/RP0/CPU0:router(config-if-tunte-autobw)# overflow threshold 100 limit 1
RP/0/RP0/CPU0:router(config)# commit
Verification
Verify the automatic bandwidth configuration using the show mpls traffic-eng tunnels auto-bw brief command.
RP/0/RP0/CPU0:router# show mpls traffic-eng tunnels auto-bw brief
Tunnel LSP Last appl Requested Signalled Highest Application
Name ID BW(kbps) BW(kbps) BW(kbps) BW(kbps) Time Left
-------------- ------ ---------- ---------- ---------- ---------- --------------
tunnel-te1 5 500 300 420 1h 10mRelated Topics
Configuring Autoroute Announce
The segment routing tunnel can be advertised into an Interior Gateway Protocol (IGP) as a next hop by configuring the autoroute announce statement on the source router. The IGP then installs routes in the Routing Information Base (RIB) for shortest paths that involve the tunnel destination. Autoroute announcement of IPv4 prefixes can be carried through either OSPF or IS-IS. Autoroute announcement of IPv6 prefixes can be carried only through IS-IS. IPv6 forwarding over tunnel needs additional parameter in tunnel configuration.
Restrictions
The Autoroute Announce feature is supported with the following restrictions:
-
A maximum on 128 tunnels can be announced.
-
Tunnels in ECMP may not be path diverse.
Note |
Configuring Segment Routing and Autoroute Destination together is not supported. If autoroute functionality is required in an Segment Routing network, we recommend you to configure Autoroute Announce. |
Configuration
To specify that the Interior Gateway Protocol (IGP) should use the tunnel (if the tunnel is up) in its enhanced shortest path first (SPF) calculation, use the autoroute announce command in interface configuration mode.
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# interface tunnel-te 10
RP/0/RP0/CPU0:router(config-if)# autoroute announce [include-ipv6]
RP/0/RP0/CPU0:router(config-if)# commitVerification
Verify the route using the following commands:
RP/0/RP0/CPU0:router# Show route
Mon Aug 8 00:31:29.406 UTC
Codes: C - connected, S - static, R - RIP, B - BGP, (>) - Diversion path
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - ISIS, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, su - IS-IS summary null, * - candidate default
U - per-user static route, o - ODR, L - local, G - DAGR, l - LISP
A - access/subscriber, a - Application route
M - mobile route, r - RPL, (!) - FRR Backup path
Gateway of last resort is not set
i L1 9.1.0.0/24 [115/30] via 9.9.9.9, 2d19h, tunnel-te3195
[115/30] via 9.9.9.9, 2d19h, tunnel-te3196
[115/30] via 9.9.9.9, 2d19h, tunnel-te3197
[115/30] via 9.9.9.9, 2d19h, tunnel-te3198
[115/30] via 9.9.9.9, 2d19h, tunnel-te3199
[115/30] via 9.9.9.9, 2d19h, tunnel-te3200
[115/30] via 9.9.9.9, 2d19h, tunnel-te3201
[115/30] via 9.9.9.9, 2d19h, tunnel-te3202
i L1 9.9.9.9/32 [115/30] via 9.9.9.9, 2d22h, tunnel-te3195
[115/30] via 9.9.9.9, 2d22h, tunnel-te3196
[115/30] via 9.9.9.9, 2d22h, tunnel-te3197
[115/30] via 9.9.9.9, 2d22h, tunnel-te3198
[115/30] via 9.9.9.9, 2d22h, tunnel-te3199
[115/30] via 9.9.9.9, 2d22h, tunnel-te3200
[115/30] via 9.9.9.9, 2d22h, tunnel-te3201
[115/30] via 9.9.9.9, 2d22h, tunnel-te3202RP/0/RP0/CPU0:router# show route ipv6
Tue Apr 26 04:02:07.968 UTC
Codes: C - connected, S - static, R - RIP, B - BGP, (>) - Diversion path
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - ISIS, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, su - IS-IS summary null, * - candidate default
U - per-user static route, o - ODR, L - local, G - DAGR, l - LISP
A - access/subscriber, a - Application route
M - mobile route, r - RPL, (!) - FRR Backup path
Gateway of last resort is not set
L ::ffff:127.0.0.0/104
[0/0] via ::, 00:17:36
C 2002::/64 is directly connected,
00:39:01, TenGigE0/0/0/2
L 2002::1/128 is directly connected,
00:39:01, TenGigE0/0/0/2
i L1 2003::/64
[115/20] via ::, 00:02:32, tunnel-te992
[115/20] via ::, 00:02:32, tunnel-te993
[115/20] via ::, 00:02:32, tunnel-te994
[115/20] via ::, 00:02:32, tunnel-te995
[115/20] via ::, 00:02:32, tunnel-te996
[115/20] via ::, 00:02:32, tunnel-te997
[115/20] via ::, 00:02:32, tunnel-te998
[115/20] via ::, 00:02:32, tunnel-te999
C 2006::/64 is directly connected,
00:39:01, TenGigE0/0/0/6
L 2006::1/128 is directly connected,
00:39:01, TenGigE0/0/0/6
i L1 2007::/64
[115/20] via ::, 00:02:32, tunnel-te992
[115/20] via ::, 00:02:32, tunnel-te993
[115/20] via ::, 00:02:32, tunnel-te994
[115/20] via ::, 00:02:32, tunnel-te995
[115/20] via ::, 00:02:32, tunnel-te996
[115/20] via ::, 00:02:32, tunnel-te997
[115/20] via ::, 00:02:32, tunnel-te998
[115/20] via ::, 00:02:32, tunnel-te999
show cef ipv6 2007::5 hardware egress location 0/0/CPU0
Sun May 1 03:18:55.151 UTC 2007::/64, version 50, internal 0x1000001 0x0 (ptr 0x895e819c) [1], 0x0 (0x894d3678), 0x0 (0x0) Updated May 1 03:13:49.066 Prefix Len 64, traffic index 0, precedence n/a, priority 2
via ::/128, tunnel-te1, 2 dependencies, weight 0, class 0 [flags 0x0]
path-idx 0 NHID 0x0 [0x8b5ea420 0x0]
next hop ::/128
local adjacency
via ::/128, tunnel-te2, 2 dependencies, weight 0, class 0 [flags 0x0]
path-idx 1 NHID 0x0 [0x8b5ea5e0 0x0]
next hop ::/128
local adjacency
LEAF - HAL pd context :
sub-type : IPV6, ecd_marked:0, has_collapsed_ldi:0 collapse_bwalk_required:0, ecdv2_marked:0 HW Walk:
LEAF:
Handle: 0xaabbccdd type: 1 FEC handle: 0x8999fb18
LWLDI:
PI:0x894d3678 PD:0x894d36b8 rev:214 p-rev:212 ldi type:3
FEC hdl: 0x8999fb18 fec index: 0x0(0) num paths:2, bkup: 0
SHLDI:
PI:0x893658e8 PD:0x89365968 rev:212 p-rev:0 flag:0x0
FEC hdl: 0x8999fb18 fec index: 0x20000002(2) num paths: 2 bkup paths: 2
Path:0 fec index: 0x20004000(16384) DSP:0x440 Dest fec index: 0x2000101c(4124)
Path:1 fec index: 0x20004002(16386) DSP:0x440 Dest fec index: 0x2000101c(4124)
Path:2 fec index: 0x20004001(16385) DSP:0x440 Dest fec index: 0x2000101c(4124)
Path:3 fec index: 0x20004003(16387) DSP:0x440 Dest fec index: 0x2000101c(4124)
V6TE NH HAL PD context :
pdptr 0x8b5ea488, flags :1, index:0
TE-NH:
Flag: PHP HW Tun_O_Tun frr_active_chg te_protect_chg , PD(0x880d1640), Push: 0, Swap: 0, Link: 0
ifhandle:0x800001c llabel:24001 FEC hdl: 0x896d4eb8 fec index: 0x20001022(4130), SRTE fec hdl:(nil)
V6TE NH HAL PD context :
pdptr 0x8b5ea648, flags :1, index:0
TE-NH:
Flag: PHP HW , PD(0x880d12d0), Push: 0, Swap: 0, Link: 0x8b34d518
ifhandle:0x8000024 llabel:24000 FEC hdl: 0x896d4238 fec index: 0x2000101c(4124), SRTE fec hdl:(nil)
Configuring Auto-Tunnel Mesh
The MPLS-TE auto-tunnel mesh (auto-mesh) feature allows you to set up full mesh of TE Point-to-Point (P2P) tunnels automatically with a minimal set of MPLS traffic engineering configurations. You can configure one or more mesh-groups and each mesh-group requires a destination-list (IPv4 prefix-list) listing destinations, which are used as destinations for creating tunnels for that mesh-group.
You can configure MPLS-TE auto-mesh type attribute-sets (templates) and associate them to mesh-groups. Label Switching Routers (LSRs) can create tunnels using the tunnel properties defined in this attribute-set.
Auto-Tunnel mesh configuration minimizes the initial configuration of the network. You can configure tunnel properties template and mesh-groups or destination-lists on TE LSRs that further creates full mesh of TE tunnels between those LSRs. It eliminates the need to reconfigure each existing TE LSR in order to establish a full mesh of TE tunnels whenever a new TE LSR is added in the network.
Configuration Example
This example configures an auto-tunnel mesh group and specifies the attributes for the tunnels in the mesh-group.
RP/0/RP0/CPU0:router # configure
RP/0/RP0/CPU0:router(config)# mpls traffic-eng
RP/0/RP0/CPU0:router(config-mpls-te)# auto-tunnel mesh
RP/0/RP0/CPU0:router(config-mpls-te-auto-mesh)# tunnel-id min 1000 max 2000
RP/0/RP0/CPU0:router(config-mpls-te-auto-mesh)# group 10
RP/0/RP0/CPU0:router(config-mpls-te-auto-mesh-group)# attribute-set 10
RP/0/RP0/CPU0:router(config-mpls-te-auto-mesh-group)# destination-list dl-65
RP/0/RP0/CPU0:router(config-mpls-te)# attribute-set auto-mesh 10
RP/0/RP0/CPU0:router(config-mpls-te-attribute-set)# autoroute announce
RP/0/RP0/CPU0:router(config-mpls-te-attribute-set)# auto-bw collect-bw-only
RP/0/RP0/CPU0:router(config)# commit
Verification
Verify the auto-tunnel mesh configuration using the show mpls traffic-eng auto-tunnel mesh command.
RP/0/RP0/CPU0:router# show mpls traffic-eng auto-tunnel mesh
Auto-tunnel Mesh Global Configuration:
Unused removal timeout: 1h 0m 0s
Configured tunnel number range: 1000-2000
Auto-tunnel Mesh Groups Summary:
Mesh Groups count: 1
Mesh Groups Destinations count: 3
Mesh Groups Tunnels count:
3 created, 3 up, 0 down, 0 FRR enabled
Mesh Group: 10 (3 Destinations)
Status: Enabled
Attribute-set: 10
Destination-list: dl-65 (Not a prefix-list)
Recreate timer: Not running
Destination Tunnel ID State Unused timer
---------------- ----------- ------- ------------
192.168.0.2 1000 up Not running
192.168.0.3 1001 up Not running
192.168.0.4 1002 up Not running
Displayed 3 tunnels, 3 up, 0 down, 0 FRR enabled
Auto-mesh Cumulative Counters:
Last cleared: Wed Oct 3 12:56:37 2015 (02:39:07 ago)
Total
Created: 3
Connected: 0
Removed (unused): 0
Removed (in use): 0
Range exceeded: 0Configuring an MPLS Traffic Engineering Interarea Tunneling
The MPLS TE Interarea Tunneling feature allows you to establish MPLS TE tunnels that span multiple Interior Gateway Protocol (IGP) areas and levels. This feature removes the restriction that required the tunnel headend and tailend routers both to be in the same area. The IGP can be either Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF).To configure an inter-area tunnel, you specify on the headend router a loosely routed explicit path for the tunnel label switched path (LSP) that identifies each area border router (ABR) the LSP should traverse using the next-address loose command. The headend router and the ABRs along the specified explicit path expand the loose hops, each computing the path segment to the next ABR or tunnel destination.
Configuration Example
This example configures an IPv4 explicit path with ABR configured as loose address on the headend router.
Router# configure
Router(config)# explicit-path name interarea1
Router(config-expl-path)# index1 next-address loose ipv4 unicast 172.16.255.129
Router(config-expl-path)# index 2 next-address loose ipv4 unicast 172.16.255.131
Router(config)# interface tunnel-te1
Router(config-if)# ipv4 unnumbered Loopback0
Router(config-if)# destination 172.16.255.2
Router(config-if)# path-option 10 explicit name interarea1
Router(config)# commit
Configure Autoroute Tunnel as Designated Path
|
Feature Name |
Release Information |
Feature Description |
|---|---|---|
|
Configure Autoroute Tunnel as Designated Path |
Release 7.6.2 |
We now provide you the flexibility to simplify the path selection for a traffic class and split traffic among multiple TE tunnels. To split traffic, you can specify an autoroute tunnel to forward traffic to a particular tunnel destination address without considering the IS-IS metric for traffic path selection. IS-IS metric provides the shortest IGP path to a destination based only on link costs along the path. However, you may want to specify a tunnel interface to carry traffic regardless of IGP cost to meet your specific organizational requirements. Earlier, MPLS-TE considered either the Forwarding Adjacency (FA) or Autoroute (AA) tunnel for forwarding traffic based only on the IS-IS metric. The feature introduces the mpls traffic-eng tunnel restricted command. |
MPLS-TE builds a unidirectional tunnel from a source to a destination using label switched path (LSP) to forward traffic.
To forward the traffic through MPLS tunneling, you can use autoroute, forwarding adjacency, or static routing:
-
Autoroute (AA) functionality allows to insert the MPLS TE tunnel in the Shortest Path First (SPF) tree for the tunnel to transport all the traffic from the headend to all destinations behind the tail-end. AA is only known to the tunnel headend router.
-
Forwarding Adjacency (FA) allows the MPLS-TE tunnel to be advertised as a link in an IGP network with the cost of the link associated with it. Routers outside of the TE domain can see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.
-
Static routing allows you to inject static IP traffic into a tunnel as the output interface for the routing decision.
Prior to this release, by default, MPLS-TE considers FA or AA tunnels to forward traffic based on the IS-IS metric. The lower metric is always used to forward traffic. There was no mechanism to forward traffic to a specific tunnel interface.
For certain prefixes to achieve many benefits such as security and service-level agreements, there might be a need to forward traffic to a specific tunnel interface that has a matching destination address.
With this feature, you can exclusively use AA tunnels to forward traffic to their tunnel destination address irrespective of IS-IS metric. Traffic steering is performed based on the prefixes and not metrics. Traffic to other prefixes defaults to the forwarding-adjacency (FA) tunnels.
To enable this feature, use the mpls traffic-eng tunnel restricted command.
Also, you may require more than one AA tunnel to a particular remote PE and use ECMP to forward traffic across AA tunnels. You can configure a loopback interface with one primary address and multiple secondary addresses on the remote PE, using one IP for the FA tunnel destination, and others for the AA tunnels destinations. Multiple IP addresses are advertised in the MPLS TE domain using the typed length value (TLV) 132 in IS-IS. A TLV-encoded data stream contains code related to the record type, the record length of the value, and value. TLV 132 represents the IP addresses of the transmitting interface.
Feature Behavior
When MPLS-TE tunnel restricted is configured, the following is the behavior:
-
A complete set of candidate paths is available for selection on a per-prefix basis during RIB update as the first hop computation includes all the AA tunnels terminating on a node up to a limit of 64 and the lowest cost forwarding-adjacency or native paths terminating on the node or inherited from the parent nodes in the first hops set for the node.
-
During per-prefix computation, AA tunnel first hops are used for traffic sent to their tunnel destination address even if FA tunnel or native first hops have a better metric. AA tunnel first-hops are not used for any other prefixes.
-
ECMP is used when multiple AA tunnel first hops have the same destination address and metric.
-
During per-prefix computation, AA tunnel first hops are used for traffic sent to their tunnel destination address, and for all other destinations on the tunnel tail node or behind it, even if a native path has a better metric.
Adding mpls traffic-eng tunnel preferred configuration has no effect when the tunnel restricted is already configured.
-
If there’s no AA tunnel or if the tunnel is down, then native paths are used for all other destinations on the tunnel tail node or behind it.
The route metric for a prefix reflects the chosen first-hop, not necessarily the lowest cost SPF distance to the node.
Restrictions for Configure Autoroute Tunnel as Designated Path
-
The total number of interface addresses to the number that can be contained in 255 bytes is 63 for IPv4 and 15 for IPv6.
-
When this feature is enabled, a maximum of 64 tunnels can terminate on the tail node.
Configure Autoroute Tunnel as Designated Path
Let's understand how to configure the feature using the following topology:
Consider the topology where PE1 has three MPLS tunnels connecting to PE2.
-
Tunnel-t31: Forwarding adjacency (FA) is configured to the primary address of Loopback 0 on PE2 (10.1.1.103).
-
Tunnel- t32: Autoroute announce (AA) is configured to a secondary address of Loopback 0 on PE2 (10.1.2.103).
-
Tunnel-t33: Autoroute announce (AA) is configured to a secondary address of Loopback 0 on PE2 (10.1.3.103).
This feature is not enabled by default. When this feature is not enabled, traffic is load balanced over all AA tunnels towards the same remote PE provided the tunnel metric is the same:
Router# show routes
i L2 10.1.1.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
i L2 10.1.2.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
i L2 10.1.3.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
i L2 10.2.0.103/32 [115/40] via 10.1.2.103, 00:00:30, tunnel-t32
[115/40] via 10.1.3.103, 00:00:30, tunnel-t33
10.2.0.104/32 [115/50] via 10.1.2.103, 00:00:30, tunnel-t32
[115/50] via 10.1.3.103, 00:00:30, tunnel-t33
Configuration Example
You can configure the feature using the mpls traffic-eng tunnel restricted command.
RP/0/RSP0/CPU0:ios# configure
RP/0/RSP0/CPU0:ios(config)# router isis 1
RP/0/RSP0/CPU0:ios(config-isis)# address-family ipv4 unicast
RP/0/RSP0/CPU0:ios(config-isis-af# mpls traffic-eng tunnel restricted
Running Configuration
The following example shows the AA tunnel metric running configuration:
router isis 1
address-family ipv4 unicast
mpls traffic-eng tunnel restricted
!
!
end
Verification
When you enable the feature, traffic towards a particular prefix is sent only over the tunnel that has that IP address as destination.
Router# show route
i L2 10.1.1.103/32 [115/40] via 10.1.1.103, 00:00:04, tunnel-t31
i L2 10.1.2.103/32 [115/40] via 10.1.2.103, 00:00:04, tunnel-t32
i L2 10.1.3.103/32 [115/40] via 10.1.3.103, 00:00:04, tunnel-t33
i L2 10.2.0.103/32 [115/40] via 10.1.1.103, 00:00:04, tunnel-t31
i L2 10.2.0.104/32 [115/50] via 10.1.1.103, 00:00:04, tunnel-t31
When multiple restricted AA tunnels are created towards the same destination IP address, router load balances traffic across all those tunnels:
Router# show route
i L2 10.1.1.103/32 [115/40] via 10.1.1.101, 00:00:08, GigabitEthernet0/0/0/2
[115/40] via 10.1.3.101, 00:00:08, GigabitEthernet0/0/0/3
i L2 10.1.2.103/32 [115/40] via 10.1.2.103, 00:00:08, tunnel-t32
[115/40] via 10.1.2.103, 00:00:30, tunnel-t34
i L2 10.1.3.103/32 [115/40] via 10.1.3.103, 00:00:08, tunnel-t33
i L2 10.2.0.103/32 [115/40] via 10.1.1.101, 00:00:08, GigabitEthernet0/0/0/2
[115/40] via 10.1.3.101, 00:00:08, GigabitEthernet0/0/0/3
i L2 10.2.0.104/32 [115/50] via 10.1.1.101, 00:00:08, GigabitEthernet0/0/0/2
[115/50] via 10.1.3.101, 00:00:08, GigabitEthernet0/0/0/3
MPLS-TE Features - Details
MPLS TE Fast Reroute Link and Node Protection
Fast Reroute (FRR) is a mechanism for protecting MPLS TE LSPs from link and node failures by locally repairing the LSPs at the point of failure, allowing data to continue to flow on them while their headend routers try to establish new end-to-end LSPs to replace them. FRR locally repairs the protected LSPs by rerouting them over backup tunnels that bypass failed links or node.
Note |
If FRR is greater than 50ms, it might lead to a loss of traffic. |
Backup tunnels that bypass only a single link of the LSP’s path provide link protection. They protect LSPs if a link along their path fails by rerouting the LSP’s traffic to the next hop (bypassing the failed link). These tunnels are referred to as next-hop (NHOP) backup tunnels because they terminate at the LSP’s next hop beyond the point of failure.
FRR provides node protection for LSPs. Backup tunnels that bypass next-hop nodes along LSP paths are called next-next-hop (NNHOP) backup tunnels because they terminate at the node following the next-hop node of the LSP paths, bypassing the next-hop node. They protect LSPs if a node along their path fails by enabling the node upstream of the failure to reroute the LSPs and their traffic around the failed node to the next-next hop. NNHOP backup tunnels also provide protection from link failures, because they bypass the failed link and the node.
NCS5000 Series Routers do not support node protection.
MPLS-TE Forwarding Adjacency
MPLS TE forwarding adjacency allows you to handle a TE label-switched path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network that is based on the Shortest Path First (SPF) algorithm. Both Intermediate System-to-Intermediate System (IS-IS) and Open Shortest Path First (OSPF) are supported as the IGP. A forwarding adjacency can be created between routers regardless of their location in the network. The routers can be located multiple hops from each other.
As a result, a TE tunnel is advertised as a link in an IGP network with the tunnel's cost associated with it. Routers outside of the TE domain see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network. TE tunnel interfaces are advertised in the IGP network just like any other links. Routers can then use these advertisements in their IGPs to compute the SPF even if they are not the headend of any TE tunnels.
Automatic Bandwidth
Automatic bandwidth allows you to dynamically adjust bandwidth reservation based on measured traffic. MPLS-TE automatic bandwidth is configured on individual Label Switched Paths (LSPs) at every headend router. MPLS-TE automatic bandwidth monitors the traffic rate on a tunnel interface and resizes the bandwidth on the tunnel interface to align it closely with the traffic in the tunnel.
- Monitors periodic polling of the tunnel output rate
- Resizes the tunnel bandwidth by adjusting the highest rate observed during a given period.
For every traffic-engineered tunnel that is configured for an automatic bandwidth, the average output rate is sampled, based on various configurable parameters. Then, the tunnel bandwidth is readjusted automatically based on either the largest average output rate that was noticed during a certain interval, or a configured maximum bandwidth value.
While re-optimizing the LSP with the new bandwidth, a new path request is generated. If the new bandwidth is not available, the last good LSP remains used. This way, the network experiences no traffic interruptions. If minimum or maximum bandwidth values are configured for a tunnel, the bandwidth, which the automatic bandwidth signals, stays within these values.
The output rate on a tunnel is collected at regular intervals that are configured by using the application command in MPLS-TE auto bandwidth interface configuration mode. When the application period timer expires, and when the difference between the measured and the current bandwidth exceeds the adjustment threshold, the tunnel is re-optimized. Then, the bandwidth samples are cleared to record the new largest output rate at the next interval. If a tunnel is shut down, and is later brought again, the adjusted bandwidth is lost, and the tunnel is brought back with the initially configured bandwidth. When the tunnel is brought back, the application period is reset.
MPLS Traffic Engineering Interarea Tunneling
The MPLS-TE interarea tunneling feature allows you to establish TE tunnels spanning multiple Interior Gateway Protocol (IGP) areas and levels, thus eliminating the requirement that headend and tailend routers reside in a single area.
Interarea support allows the configuration of a TE LSP that spans multiple areas, where its headend and tailend label switched routers (LSRs) reside in different IGP areas. Customers running multiple IGP area backbones (primarily for scalability reasons) requires Multiarea and Interarea TE . This lets you limit the amount of flooded information, reduces the SPF duration, and lessens the impact of a link or node failure within an area, particularly with large WAN backbones split in multiple areas.
The following figure shows a typical interarea TE network using OSPF.
The following figure shows a typical interlevel (IS-IS) TE Network.
As shown in the Interlevel (IS-IS) TE Network Diagram, R2, R3, R7, and R4 maintain two databases for routing and TE information. For example, R3 has TE topology information related to R2, flooded through Level-1 IS-IS LSPs plus the TE topology information related to R4, R9, and R7, flooded as Level 2 IS-IS Link State PDUs (LSPs) (plus, its own IS-IS LSP).
Loose hop optimization allows the re-optimization of tunnels spanning multiple areas and solves the problem which occurs when an MPLS-TE LSP traverses hops that are not in the LSP's headend's OSPF area and IS-IS level. Interarea MPLS-TE allows you to configure an interarea traffic engineering (TE) label switched path (LSP) by specifying a loose source route of ABRs along the path. Then it is the responsibility of the ABR (having a complete view of both areas) to find a path obeying the TE LSP constraints within the next area to reach the next hop ABR (as specified on the headend router). The same operation is performed by the last ABR connected to the tailend area to reach the tailend LSR.
- You must specify the router ID of the ABR node (as opposed to a link address on the ABR).
- When multiarea is deployed in a network that contains subareas, you must enable MPLS-TE in the subarea for TE to find a path when loose hop is specified.
- You must specify the reachable explicit path for the interarea tunnel.
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