Purpose
This case study presents a Multiprotocol Label Switching (MPLS) network topology and CSPF failure scenario designed to demonstrate techniques and commands that are particularly useful when addressing CSPF problems in your network. The focus of the study is the incorrect association of user-provided constraints, specifically administrative groups (also known as link coloring).
When calculating a path, the CSPF algorithm factors in user–provided constraints. The ingress router determines the physical path for each LSP by applying a CSPF algorithm to the information in the traffic engineering database. CSPF is a shortest-path-first (SPF) algorithm that has been modified to take into account constraints when calculating the shortest path across the network. Links that do not comply with the restrictions are removed from the tree and cannot be factored into the resulting SPF calculations.
CSPF integrates topology link-state information that is learned from interior gateway protocol (IGP) traffic engineering extensions and is maintained in the traffic engineering database. The information stored in the traffic engineering database includes attributes associated with the state of network resources.
The network topology shown in Figure 4 illustrates a network in which the LSP is constrained by administrative group coloring (also known as link coloring), and CSPF tracing is configured on the ingress router RI. In this example, the LSP is forced to transit R5 in accordance with the restrictions imposed.
Figure 4: CSPF Topology with Administrative Group Coloring
The network shown in Figure 4 is an MPLS router-only network with SONET interfaces. For more details about the MPLS network topology, see Configuring CSPF Tracing.
The MPLS network shown in Figure 4 is configured with administrative group coloring as follows:
To check that the network is configured correctly and the LSP is established, follow these steps:
Check that the LSP shown in Figure 4 is established and traversing the path from R1 to R6 through the red links.
To verify that the LSP is established, enter the following JUNOS command-line interface (CLI) operational mode command:
user@R1> show mpls lsp extensive | no-more
Ingress LSP: 1 sessions
10.0.0.6
From: 10.0.0.1, State: Up, ActiveRoute: 1, LSPname: R1-to-R6
ActivePath: (primary)
LoadBalance: Random
Metric: 100
Encoding type: Packet, Switching type: Packet, GPID: IPv4
*Primary State: Up
Include: red Exclude: blue
Computed ERO
(S [L] denotes strict [loose] hops): (CSPF metric: 20)
10.1.15.2 S 10.1.56.2 S
Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt):
10.1.15.2 10.1.56.2
6 May 11 19:31:42 Selected as active path
5 May 11 19:31:42 Record Route: 10.1.15.2 10.1.56.2
4 May 11 19:31:42 Up
3 May 11 19:31:42 Originate Call
2 May 11 19:31:42 CSPF: computation result accepted
1 May 11 19:31:12 CSPF failed: no route toward 10.0.0.6[5 times]
Created: Wed May 11 19:29:17 2005
Total 1 displayed, Up 1, Down 0
[...Output truncated...]
[edit protocols mpls] user@R5# run show mpls lsp Ingress LSP: 0 sessions Total 0 displayed, Up 0, Down 0 Egress LSP: 0 sessions Total 0 displayed, Up 0, Down 0 Transit LSP: 2 sessions To From State Rt Style Labelin Labelout LSPname 10.0.0.1 10.0.0.6 Up 1 1 FF 100352 3 R6-to-R1 10.0.0.6 10.0.0.1 Up 1 1 FF 100384 3 R1-to-R6 Total 2 displayed, Up 2, Down 0
Sample Output 1 from ingress router R1 shows that LSP R1-to-R6 is successfully established as indicated by the Explicit Route Object (ERO) 10.1.15.2 S 10.1.56.2 S, the log message CSPF: computation result accepted, and State: Up. Also, the LSP is routing packets correctly over the red links, avoiding the blue links or the links without any coloring. See Step 3 in Configuring CSPF Tracing for information on the steps CSPF takes to select a path.
Sample Output 2 from transit router R5 shows that LSP R1-to-R6 is transiting R5 as expected.
Check that the administrative group coloring is correct and the relevant interfaces are associated with each administrative group correctly
To check the administrative group configuration, enter the following JUNOS CLI operational mode commands, or issue the show command at the [edit protocols mpls] hierarchy level, as shown in the example below:
- user@host> show configuration protocols mpls
- user@host> show mpls interface
- user@host> show ted database extensive nodeID
[edit protocols mpls]
user@R1# show
traceoptions {
file cspf;
flag cspf;
flag cspf-node;
flag cspf-link;
}
admin-groups {
blue 4;
red 8;
}
label-switched-path R1-to-R6 {
to 10.0.0.6;
metric 100;
admin-group {
include red;
exclude blue;
}
}
interface so-0/0/0.0;
interface so-0/0/1.0 {
admin-group red;
}
interface so-0/0/2.0 {
admin-group blue;
}
interface fxp0.0 {
disable;
}
[edit protocols mpls]
user@R3# show
admin-groups {
blue 4;
}
interface fxp0.0 {
disable;
}
interface so-0/0/0.0;
interface so-0/0/1.0;
interface so-0/0/2.0 {
interface so-0/0/3.0 {
admin-group blue;
}
[edit protocols mpls]
user@R5# show
admin-groups {
red 8;
}
interface fxp0.0 {
disable;
}
interface so-0/0/0.0 {
admin-group red;
}
interface so-0/0/1.0;
interface so-0/0/2.0;
[edit protocols mpls]
user@R6# show
admin-groups {
blue 4;
red 8;
}
label-switched-path R6-to-R1 {
to 10.0.0.1;
}
interface so-0/0/0.0 {
admin-group red;
}
interface so-0/0/1.0;
interface so-0/0/2.0;
interface so-0/0/3.0 {
admin-group blue;
}
useruser@R1> show mpls interface show mpls interface Interface State Administrative groups so-0/0/0.0 Up <none> so-0/0/1.0 Up red so-0/0/2.0 Up blue user@R1> show mpls interface Interface State Administrative groups so-0/0/0.0 Up <none> so-0/0/1.0 Up red so-0/0/2.0 Up blue user@R3> show mpls interface Interface State Administrative groups so-0/0/0.0 Up <none> so-0/0/1.0 Up <none> so-0/0/2.0 Up <none> so-0/0/3.0 Up blue user@R5> show mpls interface Interface State Administrative groups so-0/0/0.0 Up red so-0/0/1.0 Up <none> so-0/0/2.0 Up <none> user@R6> show mpls interface Interface State Administrative groups so-0/0/0.0 Up red so-0/0/1.0 Up <none> so-0/0/2.0 Up <none> so-0/0/3.0 Up blue
user@R1> show ted database extensive R1
TED database: 6 ISIS nodes 6 INET nodes
NodeID: R1.00(10.0.0.1)
Type: Rtr, Age: 665 secs, LinkIn: 3, LinkOut: 3
Protocol: IS-IS(2)
To: R2.00(10.0.0.2), Local: 10.1.12.1, Remote: 10.1.12.2
Color: 0 <none>
Metric: 10
Static BW: 155.52Mbps
Reservable BW: 155.52Mbps
Available BW [priority] bps:
[0] 155.52Mbps [1] 155.52Mbps [2] 155.52Mbps [3] 155.52Mbps
[4] 155.52Mbps [5] 155.52Mbps [6] 155.52Mbps [7] 155.52Mbps
Interface Switching Capability Descriptor(1):
Switching type: Packet
Encoding type: Packet
Maximum LSP BW [priority] bps:
[0] 155.52Mbps [1] 155.52Mbps [2] 155.52Mbps [3] 155.52Mbps
[4] 155.52Mbps [5] 155.52Mbps [6] 155.52Mbps [7] 155.52Mbps
To: R5.00(10.0.0.5), Local: 10.1.15.1, Remote: 10.1.15.2
Color: 0x100 red
Metric: 10
Static BW: 155.52Mbps
Reservable BW: 155.52Mbps
Available BW [priority] bps:
[0] 155.52Mbps [1] 155.52Mbps [2] 155.52Mbps [3] 155.52Mbps
[4] 155.52Mbps [5] 155.52Mbps [6] 155.52Mbps [7] 155.52Mbps
Interface Switching Capability Descriptor(1):
Switching type: Packet
Encoding type: Packet
Maximum LSP BW [priority] bps:
[0] 155.52Mbps [1] 155.52Mbps [2] 155.52Mbps [3] 155.52Mbps
[4] 155.52Mbps [5] 155.52Mbps [6] 155.52Mbps [7] 155.52Mbps
To: R3.00(10.0.0.3), Local: 10.1.13.1, Remote: 10.1.13.2
Color: 0x10 blue
Metric: 10
Static BW: 155.52Mbps
Reservable BW: 155.52Mbps
Available BW [priority] bps:
[0] 155.52Mbps [1] 155.52Mbps [2] 155.52Mbps [3] 155.52Mbps
[4] 155.52Mbps [5] 155.52Mbps [6] 155.52Mbps [7] 155.52Mbps
Interface Switching Capability Descriptor(1):
Switching type: Packet
Encoding type: Packet
Maximum LSP BW [priority] bps:
[0] 155.52Mbps [1] 155.52Mbps [2] 155.52Mbps [3] 155.52Mbps
[4] 155.52Mbps [5] 155.52Mbps [6] 155.52Mbps [7] 155.52Mbps
Sample Output 1 shows that administrative group coloring is correctly configured on all relevant routers. Administrative groups redand blue are configured at the [edit protocols mpls] hierarchy level, and relevant interfaces are associated with each administrative group correctly.
R3 is configured with blue coloring and the include and exclude statements are included in the configuration of R1 to ensure that LSP R1-to-R6 always transits R5. The inclusion of red coloring is not strictly necessary. To force the LSP to transit R5,you could color the links on R2 and R3 blue and then exclude the blue links. Red coloring is included in this example to demonstrate the fact that the CSPF algorithm excludes links that do not have a color configured, when the include statement is configured at the [edit protocols mpls] hierarchy level.
In addition, ingress router R1 has CSPF tracing configured in preparation for gathering information when the CSPF algorithm fails later in this example.
Sample Output 2 shows that the correct interfaces are associated with the red and blue administration groups on R1, R3, R5, and R6.
Sample Output 3 confirms that link coloring is correctly reported in the traffic engineering database for R1. Not shown is the traffic engineering database output for the remaining routers, which is similar to the R1 output, and correct.
