Purpose
Primary paths are optional and when configured, limit the RSVP calculation of the complete path to the routers specified in the primary Explicit Route Object (ERO) list, which determines the physical path for the LSP. When primary paths are not configured, the ingress router determines the path to the egress router. Only one primary path is permitted per LSP, as shown in Figure 2.
Figure 2: Primary Path
Within the configuration of the primary physical path, you can specify strict or loose ERO values and parameters that affect only the primary physical path, such as bandwidth or priority. The ERO list for the primary path includes an address for each transit router. Specifying the ingress and/or egress routers is optional. For each router address, you can specify the type, which can be one of the following:
For strict addresses, you must ensure that the router immediately preceding the router you are configuring has a direct connection to that router. The address can be a loopback interface address, in which case the incoming interface is not checked.
If you are listing more than one address, specify the addresses in order, starting with the ingress router (optional) or the first transit router, and continuing sequentially along the path up to the egress router (optional) or the router immediately before the egress router. You need to specify only one address per router hop. If you specify more than one address for the same router, only the first address is used; the additional addresses are ignored and truncated.
When configuring a primary path, you can specify the bandwidth and priority values associated with that primary path.
The bandwidth value is included in the sender’s Tspec field in RSVP path setup messages. You specify the bandwidth value in bits per second, with a higher value implying a greater user traffic volume. The default bandwidth is 0 bits per second. A nonzero bandwidth requires transit routers to reserve capacity along the outbound links for the path. The RSVP reservation scheme is used to reserve this capacity. Any failure in bandwidth reservation (such as failures at RSVP policy control or admission control) might cause the LSP setup to fail.
The priority value is composed of two distinct values: a setup and a hold priority. The setup priority value is used to determine if there is enough bandwidth available at that priority level to establish the primary path. The priority level is between 0 (best) and 7 (worst).The hold priority value is used by an established primary path to retain its bandwidth reservations in the network. If insufficient link bandwidth is available during session establishment, the setup priority is compared to the hold priorities of other established sessions to determine whether some of them should be preempted to accommodate the new session. Sessions with worse hold priorities are preempted.
To configure and verify a primary path, follow these steps:
Action
To configure a primary path with an ERO list, bandwidth, and priority, follow these steps:
For example:
For example:
For example:
- [edit protocols mpls label-switched-path lsp-path-name]
- user@host# set primary primary-name bandwidth bandwidth
For example:
- [edit protocols mpls label-switched-path lsp-path-name]
- user@host# set primary primary-name priority reservation-priority setup-priority
For example:
Sample Output
The sample output below illustrates the configuration of the primary path on ingress router R1 in the network shown in Figure 2.
[edit protocols mpls]
user@R1# show
label-switched-path r1-to-r5 {
to 192.168.5.1;
primary via-r2 { # Bandwidth and priority configured at the primary path
bandwidth 35m; # level of the hierarchy
priority 6 6; # Priority setup and hold values
}
}
path via-r2 { # Primary ERO list
10.0.12.14 strict;
10.0.24.2 strict;
[...Output truncated...]
[edit protocols mpls]
user@R1# commit
commit complete
Meaning
The sample output shows a label-switched path (LSP) with bandwidth and priority applied to only one primary path. The same parameters specified one level up in the hierarchy, at the [edit protocols mpls label-switched-path lsp-path-name] hierarchy level, affect all paths.
The path, via-r2, specifies the complete strict path from the ingress to the egress routers through 10.0.12.14, 10.0.24.2, in that order. There cannot be any intermediate routers except the ones specified. However, there can be intermediate routers between 10.0.24.2 and the egress router because the egress router is not specifically listed in the path statement. To prevent intermediate routers before egress, configure the egress router as the last router, with a strict type.
For more information on configuring a primary path, see the JUNOS MPLS Applications Configuration Guide.
Primary paths must always be used in the network if they are available, therefore an LSP always moves back to the primary path after a failure, unless the configuration is adjusted. For more information on adjusting the configuration to prevent a failed primary path from reestablishing, see Preventing Use of a Path That Previously Failed.
To verify that the primary path is operational, enter the following JUNOS command-line interface (CLI) operational mode commands:
user@R1> show mpls lsp extensive ingress
Ingress LSP: 1 sessions
192.168.5.1
From: 192.168.1.1, State: Up, ActiveRoute: 0, LSPname: r1-to-r5
ActivePath: via-r2 (primary)
LoadBalance: Random
Encoding type: Packet, Switching type: Packet, GPID: IPv4
*Primary via-r2 State: Up
Priorities: 6 6
Bandwidth: 35Mbps
SmartOptimizeTimer: 180
Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 11)
10.0.12.14 S 10.0.24.2 S
Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt):
10.0.12.14 10.0.24.2
5 Apr 29 14:40:43 Selected as active path
4 Apr 29 14:40:43 Record Route: 10.0.12.14 10.0.24.2
3 Apr 29 14:40:43 Up
2 Apr 29 14:40:43 Originate Call
1 Apr 29 14:40:43 CSPF: computation result accepted
Standby via-r7 State: Dn
SmartOptimizeTimer: 180
No computed ERO.
Created: Sat Apr 29 14:40:43 2006
Total 1 displayed, Up 1, Down 0
user@R1> show rsvp interface
RSVP interface: 3 active
Active Subscr- Static Available Reserved Highwater
Interface State resv iption BW BW BW mark
fe-0/1/0.0 Up 2 100% 100Mbps 100Mbps 0bps 0bps
fe-0/1/1.0 Up 1 100% 100Mbps 100Mbps 0bps 0bps
so-0/0/3.0 Up 1 100% 155.52Mbps 155.52Mbps 0bps 0bps
Sample output 1 shows that the LSP is operational and is using the primary path (via-r2) with R2 (10.0.12.14) and R4 (10.0.24.2) as transit routers. The priority values are the same for setup and hold, 6 6. Priority 0 is the highest (best) priority and 7 is the lowest (worst) priority. The JUNOS software default for setup and hold priority is 7:0. Unless some LSPs are more important than others, preserving the default is a good practice. Configuring a setup priority that is better than the hold priority is not allowed, resulting in a failed commit in order to avoid preemption loops.