A Path Computation Element Protocol (PCEP) session is a TCP session between a PCC and a PCE with protocol messages. The PCEP functions are verified based on the PCC functions. The configuration and verification show that the request is accepted and path computation is provided based on PCReq message from the client. The passive reporting enables a router to report a tunnel instead of delegating it to a PCE. The PCE is aware of the tunnel even though it cannot modify the tunnel.

PCEP functions are useful when a network has both router-controlled and PCE delegated tunnels. The PCE is aware of both the tunnels and can make an accurate decision on path computation.

For redundancy it may be required to deploy redundant PCE servers. A PCC uses precedence to select stateful PCEs for delegating LSPs. Precedence can take any value between 0 and 255. The default precedence value is 255. When there are multiple stateful PCEs with active PCEP session, PCC chooses the PCE with the lowest precedence value. In case where primary PCE server session goes down, PCC router re-delegates all tunnels to next available PCE server. You can use the following CLIs in the case of redundant PCEs:

R2(config)#mpls traffic-eng pcc peer 77.77.77.77 source 22.22.22.22 precedence 255 
R2(config)#mpls traffic-eng pcc peer 88.88.88.88  source 22.22.22.22 precedence 100 
!
end

In the above example PCE server with IP address 88.88.88.88 is the primary PCE server since it has lower precedence value.

Perform the following task to configure dynamic PCC globally

enable
configure terminal
mpls traffic-eng tunnels
mpls traffic-eng pcc peer 10.0.0.1    ----(10.0.0.1 is the PCE server address)
mpls traffic-eng pcc report-all
end

Note	mpls traffic-eng pcc report-all is not mandatory for PCE/PCC basic operational delegated tunnels. It is required to report locally calculated LSPs to the PCE server.

Perform the following task to configure dynamic PCC on an interface

interface Tunnel1
 ip unnumbered Loopback0
 tunnel mode mpls traffic-eng
 tunnel destination 7.7.7.7
 tunnel mpls traffic-eng autoroute announce
 tunnel mpls traffic-eng priority 5 5
 tunnel mpls traffic-eng bandwidth 200
 tunnel mpls traffic-eng path-option 10 dynamic pce segment-routing
end

To enable Dynamic PCC with verbatim path option, use the following CLI under the SR-TE tunnel interface:

R1#
interface Tunnel2
ip unnumbered Loopback11
tunnel mode mpls traffic-eng
tunnel destination 66.66.66.66
tunnel mpls traffic-eng autoroute destination
tunnel mpls traffic-eng path-option 1 dynamic segment-routing pce verbatim

The following sample output is from the show pce client peer detail command.

Device# show pce client peer detail
 
PCC's peer database:
--------------------

Peer address: 1.1.1.1
  State up
  Capabilities: Stateful, Update, Segment-Routing
  PCEP has been up for: 23:44:58
  PCEP session ID: local 1, remote: 0
  Sending KA every 30 seconds
  Minimum acceptable KA interval: 20 seconds
  Peer timeout after 120 seconds
  Statistics:
    Keepalive messages: rx    2798 tx    2112
    Request messages:   rx       0 tx      32
    Reply messages:     rx      32 tx       0
    Error messages:     rx       0 tx       0
    Open messages:      rx       1 tx       1
    Report messages:    rx       0 tx      57
    Update messages:    rx      72 tx       0

The following sample output is from the show mpls traffic-eng tunnels tunnel 1 command which shows the LSP details.

Device# show mpls traffic-eng tunnels tunnel 1

Name: d1_t1                        (Tunnel1) Destination: 7.7.7.7
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected
    path option 10, (SEGMENT-ROUTING) (PCE) type dynamic (Basis for Setup, path weight 0)

  Config Parameters:
    Bandwidth: 200      kbps (Global)  Priority: 5  5   Affinity: 0x0/0xFFFF
    Metric Type: TE (default)
    Path Selection:
     Protection: any (default)
    Path-selection Tiebreaker:
      Global: not set   Tunnel Specific: not set   Effective: min-fill (default)
    Hop Limit: disabled
    Cost Limit: disabled
    Path-invalidation timeout: 10000 msec (default), Action: Tear
    AutoRoute: enabled  LockDown: disabled Loadshare: 200 [10000000] bw-based
    auto-bw: disabled
    Fault-OAM: disabled, Wrap-Protection: disabled, Wrap-Capable: No
  Active Path Option Parameters:
    State: dynamic path option 10 is active
    BandwidthOverride: disabled  LockDown: disabled  Verbatim: disabled

  PCEP Info:
    Delegation state: Working: yes   Protect: no
    Current Path Info:
      Request status: processed
      Created via PCRep message from PCE server: 1.1.1.1
    Reported paths:
      Tunnel Name: csr551_t2001
       LSPs:
        LSP[0]:
         source 2.2.2.2, destination 7.7.7.7, tunnel ID 1, LSP ID 5
         State: Admin up, Operation active
         Setup type: SR
         Bandwidth: signaled 0
         LSP object:
           PLSP-ID 0x807D1, flags: D:0 S:0 R:0 A:1 O:2
         Reported path:
           Metric type: TE, Accumulated Metric 0

  History:
    Tunnel:
      Time since created: 34 minutes, 3 seconds
      Time since path change: 1 minutes, 44 seconds
      Number of LSP IDs (Tun_Instances) used: 5
    Current LSP: [ID: 5]
      Uptime: 1 minutes, 44 seconds
    Prior LSP: [ID: 3]
      ID: path option unknown
      Removal Trigger: path verification failed
  Tun_Instance: 5
  Segment-Routing Path Info (isis  level-1)
    Segment0[Node]: 3.3.3.3, Label: 20270
    Segment1[Node]: 6.6.6.6, Label: 20120
    Segment2[Node]: 7.7.7.7, Label: 20210

The following sample output is from the show pce client lsp detail command.

Device# show pce client lsp detail 

PCC's tunnel database:
----------------------
Tunnel Name: d1_t1
 LSPs:
  LSP[0]:
   source 2.2.2.2, destination 7.7.7.7, tunnel ID 1, LSP ID 5
   State: Admin up, Operation active
   Setup type: SR
   Bandwidth: signaled 0
   LSP object:
     PLSP-ID 0x807D1, flags: D:0 S:0 R:0 A:1 O:2
   Reported path:
     Metric type: TE, Accumulated Metric 0

The following sample output is from the show pce lsp detail command which shows the tunnel is delegated.

Device# show pce lsp detail 

Thu Jul  7 10:24:30.836 EDT

PCE's tunnel database: 
----------------------
PCC 102.103.2.1: 

Tunnel Name: d1_t1
 LSPs:
  LSP[0]:
   source 2.2.2.2, destination 7.7.7.7, tunnel ID 1, LSP ID 5
   State: Admin up, Operation active
   Binding SID: 0
   PCEP information: 
     plsp-id 526289, flags: D:1 S:0 R:0 A:1 O:2
   Reported path: 
     Metric type: TE, Accumulated Metric 0
      SID[0]: Node, Label 20270, Address 3.3.3.3
      SID[1]: Node, Label 20120, Address 6.6.6.6
      SID[2]: Node, Label 20210, Address 7.7.7.7
   Computed path: 
     Metric type: TE, Accumulated Metric 30
      SID[0]: Node, Label 20270, Address 3.3.3.3
      SID[1]: Node, Label 20120, Address 6.6.6.6
      SID[2]: Node, Label 20210, Address 7.7.7.7
   Recorded path: 
     None

The following sample output is from the show pce client lsp detail command for reported tunnel.

Device# show pce client lsp detail 

PCC's tunnel database:
----------------------
Tunnel Name: d1_t2
 LSPs:
  LSP[0]:
   source 2.2.2.2, destination 7.7.7.7, tunnel ID 2, LSP ID 1
   State: Admin up, Operation active
   Setup type: SR
   Bandwidth: signaled 0
   LSP object:
     PLSP-ID 0x807D2, flags: D:0 S:0 R:0 A:1 O:2
   Reported path:
     Metric type: TE, Accumulated Metric 30

The following sample output is from the show pce lsp detail command which shows the tunnel is not delegated.

Device# show pce lsp detail 

Thu Jul  7 10:29:48.754 EDT

PCE's tunnel database: 
----------------------
PCC 10.0.0.1: 

Tunnel Name: d1_t2
 LSPs:
  LSP[0]:
   source 2.2.2.2, destination 7.7.7.7, tunnel ID 2, LSP ID 1
   State: Admin up, Operation active
   Binding SID: 0
   PCEP information: 
     plsp-id 526290, flags: D:0 S:0 R:0 A:1 O:2
   Reported path: 
     Metric type: TE, Accumulated Metric 30
      SID[0]: Adj, Label 74, Address: local 172.16.0.1 remote 172.16.0.2
      SID[1]: Adj, Label 63, Address: local 173.17.0.1 remote 173.17.0.2
      SID[2]: Adj, Label 67, Address: local 174.18.0.1 remote 174.18.0.2
      SID[3]: Node, Label unknownAddress 7.7.7.7
   Computed path: 
     None
   Recorded path: 
     None

To verify proper operation with verbatim path option, use the following command:

R1#sh mpl tr tun tun 2
Name: R1_t2                               (Tunnel2) Destination: 66.66.66.66
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected
    path option 1, (SEGMENT-ROUTING) (PCE) type dynamic (verbatim) (Basis for Setup)
 
  Config Parameters:
    Bandwidth: 0        kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
    Metric Type: TE (interface)
    Path Selection:
     Protection: any (default)
    Path-selection Tiebreaker:
      Global: not set   Tunnel Specific: not set   Effective: min-fill (default)
    Hop Limit: disabled [ignore: Verbatim Path Option]
    Cost Limit: disabled
    Path-invalidation timeout: 10000 msec (default), Action: Tear
    AutoRoute: disabled LockDown: disabled Loadshare: 0 [0] bw-based
    AutoRoute destination: enabled 
    auto-bw: disabled
    Fault-OAM: disabled, Wrap-Protection: disabled, Wrap-Capable: No
  Active Path Option Parameters:
    State: dynamic path option 1 is active
    BandwidthOverride: disabled  LockDown: disabled  Verbatim: enabled 
          
  PCEP Info:
    Delegation state: Working: yes   Protect: no
    Delegation peer: 77.77.77.77
    Working Path Info:
      Request status: processed
      Created via PCRep message from PCE server: 77.77.77.77
      PCE metric: 4, type: TE
    Reported paths:
      Tunnel Name: Tunnel2_w
       LSPs:
        LSP[0]:
         source 11.11.11.11, destination 66.66.66.66, tunnel ID 2, LSP ID 1
         State: Admin up, Operation active
         Binding SID: 17
         Setup type: SR
         Bandwidth: requested 0, used 0
         LSP object:
           PLSP-ID 0x80002, flags: D:0 S:0 R:0 A:1 O:2
         ERO:
           SID[0]: Adj, Label 24, NAI: local 12.12.12.1 remote 12.12.12.2
           SID[1]: Adj, Label 26, NAI: local 25.25.25.2 remote 25.25.25.5
           SID[2]: Adj, Label 22, NAI: local 56.56.56.5 remote 56.56.56.6
         
  History:
    Tunnel:
      Time since created: 39 days, 19 hours, 9 minutes
      Time since path change: 1 minutes, 3 seconds
      Number of LSP IDs (Tun_Instances) used: 1
    Current LSP: [ID: 1]
      Uptime: 1 minutes, 3 seconds
  Tun_Instance: 1
  Segment-Routing Path Info (IGP information is not used)
    Segment0[Link]: 12.12.12.1 - 12.12.12.2, Label: 24
    Segment1[Link]: 25.25.25.2 - 25.25.25.5, Label: 26
    Segment2[Link]: 56.56.56.5 - 56.56.56.6, Label: 22
!
end