PATH

PATH is a daemon that handles the installation and deletion of Segment Routing (SR) Policies. Based on MPLS (This means that your OS of choice must support MPLS), SR add a stack of MPLS labels to ingress packets so these packets are egress through the desired path.

The SR policies and Segment Lists can be configured either locally by means of vtysh or centralized based on a SDN controller (ODL, Cisco, …) communicating using the PCEP protocol (RFC 5440).

Configuration

Explicit Segment Lists

This is the simplest way of configuration, no remote PCE is necessary. In order to create a config that match the graphics used in this documentation, we will create a segment list (SL) called SL1 with an element for each hop and that element will be assigned a MPLS label. Then the SL1 will be used in the policy example1, please note also the preference as in the case of multiple segment list it will be used with the criteria of bigger number more preference. Let see now the final configuration that match the graphics shown above.

segment-routing
 traffic-eng
  segment-list SL1
   index 10  mpls label 16001
   index 20  mpls label 16002
  !
  policy color 1 endpoint 192.0.2.4
   name example1
   binding-sid 1111
   candidate-path preference 100 name CP1 explicit segment-list SL1

Explicit Segment Lists and Traffic Engineering Database (TED)

Sometimes is difficult to know the values of MPLS labels (adjacency changes,…). Based on the support of IS-IS or OSPF we can activate TED support what will allow pathd to resolve MPLS based in different types of segments (:rfc: draft-ietf-spring-segment-routing-policy-07). The supported types are Type C (prefix and local interface), Type E (prefix and algorithm), Type F (a pair of IP’s). So the configuration would change to this

segment-routing
 traffic-eng
  mpls-te on
  mpls-te import ospfv2
  segment-list SL1
   index 10  nai prefix 10.1.2.1/32 iface 1
   index 20  nai adjacency 10.1.20.1 10.1.20.2
  !
  policy color 1 endpoint 192.0.2.4
   name example1
   binding-sid 1111
   candidate-path preference 100 name CP1 explicit segment-list SL1

In this case no MPLS are provided but the pathd TED support will resolve the configuration provided to corresponding MPLS labels.

Note

Please note the mpls-te configuration added that activate the TED support and points to ospfv2 so the ospfv2 (Traffic Engineering) daemon must be also running and configure to export TED information.

Note

It would be the same for isis (Traffic Engineering) but in the moment of writting it’s not fully tested.

Dynamic Segment Lists

One of the useful options to configure is the creation of policies with the dynamic option. In this case based on a given endpoint the SL will be ,first calculated, and then sended by means of PCEP protocol by the configured PCE.

traffic-eng
 !
 pcep
  !
  pce PCE1
   address ip 192.0.2.10
  !
  pcc
   peer PCE1 precedence 10
 !
 policy color 1 endpoint 192.0.2.4
  name example
  binding-sid 1111
  candidate-path preference 100 name CP2 dynamic

Note

Please note the configuration for the remote pce which allows pathd to connect to the given PCE and act as a PCC (PCEP Client)

Note

If the TED support feature is active, the data obtained from PCE will be validated, so in a SL from PCEP/PCE the IP and MPLS will be checked against local TED obtained and built from the igp configured in that case.

Pce Initiated

We can step forward in the use of our controller not only by asking to calculate paths to an endpoint but also to create the whole policies in the controller and obtain those by means of the PCEP protocol.

traffic-eng
 !
 pcep
  !
  pce PCE1
   address ip 192.0.2.10
   pce-initiated
  !
  pce PCE2
   address ip 192.0.2.9
   pce-initiated
  !
  pcc
   peer PCE1 precedence 10
   peer PCE2 precedence 20
 !

Note

Now there is no locally created policies in the config as they will be obtain from the configured pce. Please check command show sr-te policy in vtysh to see the obtained policies.

Note

Another interesting command is show mpls table to check the installed mpls configuration based in those obtained policies.

Note

SR Policies could be a mix of local, remote obtained from PCE and delegated to a PCE (but while testing Pce Initiated with Cisco PCE, happens that controller sends PCE initiated delete commands to delete the locally created configuration related to that PCE).

Starting

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

A pceplib is included in the frr source tree and build by default.

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

An example of command line with pcep module could be this

pathd -u root -g root -f pathd.conf -z /tmp/zebra-demo1.sock --vty_socket=/var/run/demo1.vty -i /tmp/pathd-demo1.pid -M frr/modules/pathd_pcep.so --log file:/tmp/kk.txt

Pathd Configuration

Example:

debug pathd pcep basic
segment-routing
 traffic-eng
  mpls-te on
  mpls-te import ospfv2
  segment-list SL1
   index 10 mpls label 16010
   index 20 mpls label 16030
  !
  segment-list SL2
   index 10  nai prefix 10.1.2.1/32 iface 1
   index 20  nai adjacency 10.1.20.1 10.1.20.2
   index 30  nai prefix 10.10.10.5/32 algorithm 0
   index 40  mpls label 18001
  !
  policy color 1 endpoint 192.0.2.1
   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
  !
  pcep
   pce-config GROUP1
    source-address 192.0.2.1
    tcp-md5-auth secret
    timer keep-alive 30
   !
   pce PCE1
    config GROUP1
    address ip 192.0.2.10
   !
   pce PCE2
    config GROUP1
    address ip 192.0.2.9
   !
   pcc
    peer PCE1 precedence 10
    peer PCE2 precedence 20
   !
  !
 !
!

Configuration Commands

segment-routing: Configure segment routing.

traffic-eng: Configure segment routing traffic engineering.

mpls-te <on|off>: Activate/Deactivate use of internal Traffic Engineering Database

mpls-te import <ospfv2|ospfv3|isis>: Load data from the selected igp

segment-list NAME: Delete or start a segment list definition.

index INDEX mpls label LABEL

index INDEX nai adjacency A.B.C.D A.B.C.D

index INDEX nai prefix A.B.C.D/M algorithm <0|1>

index INDEX nai prefix A.B.C.D/M iface (0-65535): 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] [computed]

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

pcep: 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.