Configuring SRLG
Context
A shared risk link group (SRLG) is a set of links which are likely to fail concurrently because they share a physical resource (for example, an optical fiber). In an SRLG, if one link fails, the other links in the SRLG also fail.
An SRLG enhances CR-LSP reliability on an MPLS TE network with CR-LSP hot standby or TE FRR enabled. Two or more links are at the same risk level if they share physical resources. For example, sub-interfaces share risks with their interface. These sub-interfaces will go Down if the interface goes Down. If the links of a primary tunnel and a backup or bypass tunnel are in the same SRLG, the links of the backup or bypass tunnel share risks with the links of the primary tunnel. The backup or bypass tunnel will go Down if the primary tunnel goes Down. After SRLG is configured, CSPF must calculate a bypass CR-LSP or a hot-standby CR-LSP according to the SRLG attribute. The link that the primary path uses and the link that the bypass CR-LSP or hot-standby CR-LSP uses cannot be in the same SRLG.
The configuration of SRLG takes effect only on the new CR-LSP, without affecting the existing CR-LSPs.
On a TE FRR-enabled network, modifying the SRLG configuration may result in an FRR bypass tunnel protection failure. To prevent this problem, the upgrade mpls te bypass command is used to forcibly upgrade FRR protection and repair bypass tunnel protection.
Perform the following configurations according to actual networking.
Procedure
- 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 bypass tunnel.
- Run mpls te srlg path-calculation [ preferred | strict ]
The SRLG path calculation mode is configured.
If strict is specified, CSPF always considers SRLG attribute as a constraint when calculating paths for the hot-standby CR-LSP or the bypass CR-LSP.
If preferred is specified, CSPF considers SRLG as a constraint to calculate paths for the hot-standby CR-LSP or the bypass CR-LSP for the first time. If the calculation fails, CSPF tries to calculate again without considering SRLG.
By default, when calculating a path, CSPF does not check whether the primary CR-LSP and a hot-standby CR-LSP or a bypass CR-LSP are in the same SRLG.
- Run mpls te srlg path-calculation [ preferred | strict ]
- Configuring SRLG for the link
Perform the following configurations on the links which are in the same SRLG.
- On an Ethernet interface, run undo portswitch
The interface is switched to Layer 3 mode.
By default, an Ethernet interface works in Layer 2 mode.
The mode switching function takes effect when the interface only has attribute configurations (for example, shutdown and description configurations). Alternatively, if configuration information supported by both Layer 2 and Layer 3 interfaces exists (for example, mode lacp and lacp system-id configurations), no configuration that is not supported after the working mode of the interface is switched can exist. If unsupported configurations exist on the interface, delete the configurations first and then run the undo portswitch command.
If many Ethernet interfaces need to be switched to Layer 3 mode, run the undo portswitch batch interface-type { interface-number1 [ to interface-number2 ] } &<1-10> command in the system view to switch these interfaces to Layer 3 mode in batches.
- Run mpls te srlg srlg-number
The link on which the interface resides joins the SRLG.
On a network with hot standby or TE FRR, the SRLG attribute needs to be configured for the outbound interface of the ingress on a tunnel and other members of the SRLG. A link joins an SRLG after the SRLG attribute is configured on an outbound interface of the link.
By default, an interface is not added to any SRLG.
To delete the SRLG attribute from all interfaces on a device, run the undo mpls te srlg all-config command in the MPLS view.
- On an Ethernet interface, run undo portswitch