Adjusting the Path of a CR-LSP
Pre-configuration Tasks
CSPF uses the TEDB and constraints to calculate appropriate paths and establishes CR-LSPs through the signaling protocol. MPLS TE provides many methods to affect CSPF computation to adjust the CR-LSP path.
- Configure a dynamic MPLS TE tunnel. For details, see Configuring a Dynamic MPLS TE Tunnel.
- Configure a dynamic DS-TE tunnel. For details, see Configuring a Dynamic DS-TE Tunnel.
Configuration Procedure
The following configurations are optional and can be performed in any sequence.
- Configuring Tie-Breaking of CSPF
- Configuring Metrics for Path Calculation
- Configuring CR-LSP Hop Limit
- Configuring Route Pinning
- Configuring Administrative Group and Affinity Property
- Configuring SRLG
- Associating CR-LSP Establishment with the Overload Setting
- Configuring Failed Link Timer
- Configuring Flooding Threshold
- Verifying the Configuration of Adjusting the Path of a CR-LSP
Configuring Tie-Breaking of CSPF
Context
You can configure the CSPF tie-breaking function to select a path from multiple paths with the same weight value.
Perform the following configurations on the ingress node of an MPLS TE tunnel.
Procedure
- Run system-view
The system view is displayed.
- Run mpls
The MPLS view is displayed.
- Run mpls te tie-breaking { least-fill | most-fill | random }
CR-LSP tie-breaking policy for the LSR is configured.
Tie-breaking policies are classified as follows:
least-fill: the route with the smallest ratio of the occupied available bandwidth to the maximum reservable bandwidth is selected.
most-fill: the route with the largest ratio of the occupied available bandwidth to the maximum reservable bandwidth is selected.
random: selects a route randomly.
The default tie-breaking policy is random.
The maximum reservable bandwidth is the bandwidth configured by the command mpls te bandwidth max-reservable-bandwidth bw-value.
- Run quit
Return to the system view.
- Run interface tunnel interface-number
The tunnel interface view of the MPLS TE tunnel is displayed.
- Run mpls te tie-breaking { least-fill | most-fill | random }
The CR-LSP tie-breaking policy for current tunnel is configured.
The parameters have the same functions as those used in step 3.
- Run mpls te commit
The current tunnel configuration is committed.
The tunnel preferentially takes the tie-breaking policy configured in its tunnel interface view. If the tie-breaking policy is not configured in the tunnel interface view, the configuration in the MPLS view is used.
Configuring Metrics for Path Calculation
Procedure
- Specifying the metric type used by the tunnel
Perform the following configurations on the ingress node of an MPLS TE tunnel.
- (Optional) Configuring the TE metric value of the path
If the metric type of a specified tunnel is TE, you can modify the TE metric value of the path on the outbound interface of the ingress and the transit node by performing the following configurations.
- Run mpls te metric value
The TE metric value of the path is configured.
By default, the path uses the IGP metric value as the TE metric value.
If the IGP is OSPF and the current device is a stub router, the mpls te metric command does not take effect.
- Run mpls te metric value
Configuring CR-LSP Hop Limit
Context
Similar to the administrative group and the affinity property, the hop limit is a condition for CR-LSP path selection and is used to specify the number of hops along a CR-LSP to be set up.
Perform the following configurations on the ingress node of an MPLS TE tunnel.
Procedure
- Run system-view
The system view is displayed.
- Run interface tunnel interface-number
The tunnel interface view of the MPLS TE tunnel is displayed.
- Run mpls te hop-limit hop-limit-value [ best-effort | secondary ]
The number of hops along the CR-LSP is set. The hop-limit-value is an integer ranging from 1 to 32.
- Run mpls te commit
The current tunnel configuration is committed.
Configuring Route Pinning
Context
By configuring the route pinning function, you can use the path that is originally selected, rather than another eligible path, to set up a CR-LSP.
Perform the following configurations on the ingress node of an MPLS TE tunnel.
If route pinning is enabled, the MPLS TE re-optimization cannot be used at the same time.
Procedure
- Run system-view
The system view is displayed.
- Run interface tunnel interface-number
The tunnel interface view of the MPLS TE tunnel is displayed.
- Run mpls te route-pinning
Route pinning is enabled.
By default, route pinning is disabled.
- Run mpls te commit
The current tunnel configuration is committed.
Configuring Administrative Group and Affinity Property
Context
The configuration of the administrative group affects only LSPs to be set up; the configuration of the affinity property affects established LSPs by recalculating the paths.
Perform the following configurations on the ingress node of an MPLS TE tunnel.
Procedure
- Run system-view
The system view is displayed.
- Run interface interface-type interface-number
The interface view of the MPLS-TE-enabled interface is displayed.
- Run mpls te link administrative group value
The administrative group of the MPLS TE link is configured.
The modification of administrative group takes effect only on LSPs that are established after modification.
- Run quit
Return to the system view.
- Run interface tunnel interface-number
The tunnel interface view of the MPLS TE tunnel is displayed.
- Run mpls te affinity property properties [ mask mask-value ] [ secondary | best-effort ]
The affinity for the tunnel is configured.
By default, the values of administrative group, affinity property, and mask are all 0x0.
After the modified affinity property is committed, the established LSP in this tunnel may be affected and the system recalculates the path for the TE tunnel.
- Run mpls te commit
The current tunnel configuration is committed.
Configuring SRLG
Context
In the networking scenario where the hot standby CR-LSP is set up or TE FRR is enabled, configure the SRLG attribute on the outbound interface of the ingress node of the MPLS TE tunnel or the PLR and the other member links of the SRLG to which the outbound interface belongs.
Configuring SRLG includes:
Perform the following configurations according to actual networking.
Procedure
- Configuring SRLG for the
link
Perform the following configurations on the links which are in the same SRLG.
- Configuring SRLG path calculation
mode for the tunnel
Perform the following configurations on the ingress node of the hot-standby tunnel or the TE FRR tunnel.
- Run mpls te srlg path-calculation [ strict | preferred ]
The SRLG path calculation mode is configured.
If you specify the strict keyword, CSPF avoids the following links when calculating the bypass CR-LSP or backup CR-LSP:- Link with the same SRLG attributes as SRLG attributes of the primary CR-LSP
- All links along the primary CR-LSP regardless of whether the links are configured with SRLG attributes
If you specify the strict keyword, CSPF always considers the SRLG as a constraint when calculating the path for the bypass CR-LSP or the backup CR-LSP.
If you specify the preferred keyword, CSPF tries to calculate the path which avoids the links in the same SRLG as protected interfaces; if the calculation fails, CSPF does not consider the SRLG as a constraint.
- Run mpls te srlg path-calculation [ strict | preferred ]
- Delete the member interfaces
of all SRLGs.
Perform the following configurations to delete member interfaces of all SRLGs from a node of the MPLS TE tunnel.
- Run undo mpls te srlg all-config
The member interfaces of all SRLGs are deleted from the MPLS TE node.
The undo mpls te srlg all-config does not delete an SRLG-based path calculation mode configured in the mpls te srlg path-calculation command in the MPLS view.
- Run undo mpls te srlg all-config
Associating CR-LSP Establishment with the Overload Setting
Context
When the node is transmitting a large number of services and its system resources are exhausted, the node marks itself overloaded.
When the node is transmitting a large number of services and its CPU is overburdened, an administrator can run the set-overload command to mark the node overloaded.
If there are overloaded nodes on an MPLS TE network, associate CR-LSP establishment with the IS-IS overload setting to ensure that CR-LSPs are established over paths excluding overloaded nodes. This configuration prevents overloaded nodes from being further burdened and improves CR-LSP reliability.
Perform the following configurations on the ingress node of an MPLS TE tunnel.
Procedure
- Run system-view
The system view is displayed.
- Run mpls
The MPLS view is displayed.
- Run mpls te path-selection overload
CR-LSP establishment is associated with the IS-IS overload setting. This association allows CSPF to calculate paths excluding overloaded IS-IS nodes.
Before the association is configured, the mpls te record-route command must be run to enable the route and label record.
Traffic travels through an existing CR-LSP before a new CR-LSP is established. After the new CR-LSP is established, traffic switches to the new CR-LSP and the original CR-LSP is deleted. This traffic switchover is performed based on the Make-Before-Break mechanism. Traffic is not dropped during the switchover.
The mpls te path-selection overload command has the following influences on the CR-LSP establishment:CSPF recalculates paths excluding overloaded nodes for established CR-LSPs.
CSPF calculates paths excluding overloaded nodes for new CR-LSPs.
This command does not take effect on bypass tunnels.
If the ingress or egress is marked overloaded, the mpls te path-selection overload command does not take effect. The established CR-LSPs associated with the ingress or egress will not be reestablished and new CR-LSPs associated with the ingress or egress will also not be established.
Configuring Failed Link Timer
Context
CSPF uses a locally-maintained traffic-engineering database (TEDB) to calculate the shortest path to the destination address. Then, the signaling protocol applies for and reserves resources for the path. In the case of a link on a network is faulty, if the routing protocol fails to notify CSPF of updating the TEDB in time, this may cause the path calculated by CSPF to contain the faulty link.
As a result, the control packets, such as RSVP Path messages, of a signaling protocol are discarded on the faulty link. Then, the signaling protocol returns an error message to the upstream node. Receiving the link error message on the upstream node triggers CSPF to recalculate a path. The path recalculated by CSPF and returned to the signaling protocol still contains the faulty link because the TEDB is not updated. The control packets of the signaling protocol are still discarded and the signaling protocol returns an error message to trigger CSPF to recalculate a path. The procedure repeats until the TEDB is updated.
To avoid the preceding situation, when the signaling protocol returns an error message to notify CSPF of a link failure, CSPF sets the status of the faulty link to INACTIVE and enables a failed link timer. Then, CSPF does not use the faulty link in path calculation until CSPF receives a TEDB update event or the failed link timer expires.
Before the failed link timer expires, if a TEDB update event is received, CSPF deletes the failed link timer.
Perform the following configurations on the ingress node of an MPLS TE tunnel.
Procedure
- Run system-view
The system view is displayed.
- Run mpls
The MPLS view is displayed.
- Run mpls te cspf timer failed-link interval
The failed link timer is configured.
By default, the failed link timer is set to 10 seconds.
The failed link timer is a local configuration. If the failed link timers of nodes are set to different values, a failed link that is in ACTIVE state on one node may be in INACTIVE state on other nodes.
Configuring Flooding Threshold
Context
The bandwidth flooding threshold indicates the ratio of the link bandwidth occupied or released by a TE tunnel to the link bandwidth remained in the TEDB.
If the link bandwidth changes little, bandwidth flooding wastes network resources. For example, if link bandwidth is 100 Mbit/s and 100 TE tunnels (with bandwidth as 1 Mbit/s) are created along this link, bandwidth flooding need be performed for 100 times.
If the flooding threshold is set to 10%, bandwidth flooding is not performed when tunnel 1 to tunnel 9 are created. When tunnel 10 is created, the bandwidth of tunnel 1 to tunnel 10 (10 Mbit/s in total) is flooded. Similarly, bandwidth flooding is not performed when tunnel 11 to tunnel 18 are created. When tunnel 19 is created, the bandwidth of tunnel 11 to tunnel 19 is flooded. Therefore, configuring bandwidth flooding threshold can reduce the times of bandwidth flooding and hence ensure the efficient use of network resources.
By default, on a link, IGP flood information about this link and CSPF updates the TEDB accordingly if one of the following conditions is met:
The ratio of the bandwidth reserved for an MPLS TE tunnel to the bandwidth remained in the TEDB is equal to or higher than 10%.
The ratio of the bandwidth released by an MPLS TE tunnel to the bandwidth remained in the TEDB is equal to or higher than 10%.
Perform the following configurations on the ingress or transit node of an MPSL TE tunnel.
Verifying the Configuration of Adjusting the Path of a CR-LSP
Procedure
- Run the display mpls te tunnel verbose command to check information about the MPLS TE tunnel.
- Run the display mpls te srlg { srlg-number | all } command to check the SRLG configuration and interfaces in the SRLG.
- Run the display mpls te link-administration srlg-information [ interface interface-type interface-number ] command to check the SRLG that interfaces belong to.
- Run the display mpls te tunnel c-hop [ tunnel-name ] [ lsp-id ingress-lsr-id session-id lsp-id ] command to check path computation results of tunnels.
- Run the display default-parameter mpls te cspf command to check default CSPF settings.
- Configuring Tie-Breaking of CSPF
- Configuring Metrics for Path Calculation
- Configuring CR-LSP Hop Limit
- Configuring Route Pinning
- Configuring Administrative Group and Affinity Property
- Configuring SRLG
- Associating CR-LSP Establishment with the Overload Setting
- Configuring Failed Link Timer
- Configuring Flooding Threshold
- Verifying the Configuration of Adjusting the Path of a CR-LSP