PATH is a daemon that handles the installation and deletion of Segment Routing (SR) Policies.

Starting PATH

Default configuration file for pathd is pathd.conf. The typical location of pathd.conf is /etc/frr/pathd.conf.

If the user is using integrated config, then pathd.conf need not be present and the frr.conf is read instead.

PATH supports all the common FRR daemon start options which are documented elsewhere.

PCEP Support

To build the PCC for pathd, the externall library pceplib 1.2 is required.

To build FRR with support for PCEP the following steps must be followed:

  • Checkout and build pceplib:

` $ git clone $ cd pceplib $ make $ make install $ export PCEPLIB_ROOT=$PWD `

  • Configure FRR with the extra parameters:

` --enable-pcep LDFLAGS="-L${PCEPLIB_ROOT}/install/lib" CPPFLAGS="-I${PCEPLIB_ROOT}/install/include" `

To start pathd with pcep support the extra parameter -M pathd_pcep should be passed to the pathd daemon.

Pathd Configuration


debug pathd pcep basic
  segment-list SL1
   index 10 mpls label 16010
   index 20 mpls label 16030
  policy color 1 endpoint
   name default
   binding-sid 4000
   candidate-path preference 100 name CP1 explicit segment-list SL1
   candidate-path preference 200 name CP2 dynamic
    affinity include-any 0x000000FF
    bandwidth 100000
    metric bound msd 16 required
    metric te 10
    objective-function mcp required
   pce-config GROUP1
    tcp-md5-auth secret
    timer keep-alive 30
   pce PCE1
    config GROUP1
    address ip
   pce PCE2
    config GROUP1
    address ip
    peer PCE1 precedence 10
    peer PCE2 precedence 20

Configuration Commands


Configure segment routing.


Configure segment routing traffic engineering.

segment-list NAME

Delete or start a segment list definition.

index INDEX mpls label LABEL [nai node ADDRESS]

Delete or specify a segment in a segment list definition.

policy color COLOR endpoint ENDPOINT

Delete or start a policy definition.

name NAME

Specify the policy name.

binding-sid LABEL

Specify the policy SID.

candidate-path preference PREFERENCE name NAME explicit segment-list SEGMENT-LIST-NAME

Delete or define an explicit candidate path.

candidate-path preference PREFERENCE name NAME dynamic

Delete or start a dynamic candidate path definition.

affinity {exclude-any|include-any|include-all} BITPATTERN

Delete or specify an affinity constraint for a dynamic candidate path.

bandwidth BANDWIDTH [required]

Delete or specify a bandwidth constraint for a dynamic candidate path.

metric [bound] METRIC VALUE [required]

Delete or specify a metric constraint for a dynamic candidate path.

The possible metrics are:
  • igp: IGP metric
  • te: TE metric
  • hc: Hop Counts
  • abc: Aggregate bandwidth consumption
  • mll: Load of the most loaded link
  • igp: Cumulative IGP cost
  • cte: Cumulative TE cost
  • igp: P2MP IGP metric
  • pte: P2MP TE metric
  • phc: P2MP hop count metric
  • msd: Segment-ID (SID) Depth
  • pd: Path Delay metric
  • pdv: Path Delay Variation metric
  • pl: Path Loss metric
  • ppd: P2MP Path Delay metric
  • pdv: P2MP Path Delay variation metric
  • ppl: P2MP Path Loss metric
  • nap: Number of adaptations on a path
  • nlp: Number of layers on a path
  • dc: Domain Count metric
  • bnc: Border Node Count metric
objective-function OBJFUN1 [required]

Delete or specify a PCEP objective function constraint for a dynamic candidate path.

The possible functions are:
  • mcp: Minimum Cost Path [RFC5541]
  • mlp: Minimum Load Path [RFC5541]
  • mbp: Maximum residual Bandwidth Path [RFC5541]
  • mbc: Minimize aggregate Bandwidth Consumption [RFC5541]
  • mll: Minimize the Load of the most loaded Link [RFC5541]
  • mcc: Minimize the Cumulative Cost of a set of paths [RFC5541]
  • spt: Shortest Path Tree [RFC8306]
  • mct: Minimum Cost Tree [RFC8306]
  • mplp: Minimum Packet Loss Path [RFC8233]
  • mup: Maximum Under-Utilized Path [RFC8233]
  • mrup: Maximum Reserved Under-Utilized Path [RFC8233]
  • mtd: Minimize the number of Transit Domains [RFC8685]
  • mbn: Minimize the number of Border Nodes [RFC8685]
  • mctd: Minimize the number of Common Transit Domains [RFC8685]
  • msl: Minimize the number of Shared Links [RFC8800]
  • mss: Minimize the number of Shared SRLGs [RFC8800]
  • msn: Minimize the number of Shared Nodes [RFC8800]
debug pathd pcep [basic|path|message|pceplib]

Enable or disable debugging for the pcep module:

  • basic: Enable basic PCEP logging
  • path: Log the path structures
  • message: Log the PCEP messages
  • pceplib: Enable pceplib logging

Configure PCEP support.

pce-config NAME

Define a shared PCE configuration that can be used in multiple PCE declarations.

pce NAME

Define or delete a PCE definition.

config WORD

Select a shared configuration. If not defined, the default configuration will be used.

address <ip A.B.C.D | ipv6 X:X::X:X> [port (1024-65535)]

Define the address and port of the PCE.

If not specified, the port is the standard PCEP port 4189.

This should be specified in the PCC peer definition.

source-address [ip A.B.C.D | ipv6 X:X::X:X] [port PORT]

Define the address and/or port of the PCC as seen by the PCE. This can be used in a configuration group or a PCC peer declaration.

If not specified, the source address will be the router identifier selected by zebra, and the port will be the standard PCEP port 4189.

This can be specified in either the PCC peer definition or in a configuration group.

tcp-md5-auth WORD

Enable TCP MD5 security with the given secret.

This can be specified in either the PCC peer definition or in a configuration group.


Specify if a PCE only support segment routing draft 7, this flag will limit the PCC behavior to this draft.

This can be specified in either the PCC peer definition or in a configuration group.


Specify if PCE-initiated LSP should be allowed for this PCE.

This can be specified in either the PCC peer definition or in a configuration group.

timer [keep-alive (1-63)] [min-peer-keep-alive (1-255)] [max-peer-keep-alive (1-255)] [dead-timer (4-255)] [min-peer-dead-timer (4-255)] [max-peer-dead-timer (4-255)] [pcep-request (1-120)] [session-timeout-interval (1-120)] [delegation-timeout (1-60)]

Specify the PCEP timers.

This can be specified in either the PCC peer definition or in a configuration group.


Disable or start the definition of a PCC.

msd (1-32)

Specify the maximum SID depth in a PCC definition.

peer WORD [precedence (1-255)]

Specify a peer and its precedence in a PCC definition.

Introspection Commands

show sr-te policy [detail]

Display the segment routing policies.

router# show sr-te policy

 Endpoint  Color  Name     BSID  Status
 ------------------------------------------   1      default  4000  Active
router# show sr-te policy detail

Endpoint:  Color: 1  Name: LOW_DELAY  BSID: 4000  Status: Active
    Preference: 100  Name: cand1  Type: explicit  Segment-List: sl1  Protocol-Origin: Local
  * Preference: 200  Name: cand1  Type: dynamic  Segment-List: 32453452  Protocol-Origin: PCEP

The asterisk (*) marks the best, e.g. active, candidate path. Note that for segment-lists which are retrieved via PCEP a random number based name is generated.

show sr-te pcep counters

Display the counters from pceplib.

show sr-te pcep pce-config [NAME]

Display a shared configuration. if no name is specified, the default configuration will be displayed.

show sr-te pcep pcc

Display PCC information.

show sr-te pcep session [NAME]

Display the information of a PCEP session, if not name is specified all the sessions will be displayed.

Utility Commands

clear sr-te pcep session [NAME]

Reset the pcep session by disconnecting from the PCE and performing the normal reconnection process. No configuration is changed.

Usage with BGP route-maps

It is possible to steer traffic ‘into’ a segment routing policy for routes learned through BGP using route-maps:

route-map SET_SR_POLICY permit 10
 set sr-te color 1
router bgp 1
 bgp router-id
 neighbor remote-as 1
 neighbor update-source lo
 address-family ipv4 unicast
  neighbor next-hop-self
  neighbor route-map SET_SR_POLICY in
  redistribute static

In this case, the SR Policy with color 1 and endpoint is selected.

Sample configuration

! Default pathd configuration sample
password frr
log stdout

  segment-list test1
   index 10 mpls label 123
   index 20 mpls label 456
  segment-list test2
   index 10 mpls label 321
   index 20 mpls label 654
  policy color 1 endpoint
   name one
   binding-sid 100
   candidate-path preference 100 name test1 explicit segment-list test1
   candidate-path preference 200 name test2 explicit segment-list test2
  policy color 2 endpoint
   name two
   binding-sid 101
   candidate-path preference 100 name def explicit segment-list test2
   candidate-path preference 200 name dyn dynamic
    bandwidth 12345
    metric bound abc 16 required
    metric te 10
   pcc-peer PCE1
    address ip
    peer PCE1