OcNOS SP : Segment Routing Guide : Segment Routing Configuration : Seamless BFD On Qumran2
Seamless BFD On Qumran2
Overview
Seamless Bidirectional Forwarding Detection (S-BFD) is an extension or enhancement of Bidirectional Forwarding Detection (BFD). This protocol is primarily used in IP-based networks to monitor and detect faults quickly between systems. S-BFD is designed to provide a seamless and rapid fault detection mechanism while minimizing the impact on network resources. It is a simplified mechanism for using BFD with a large proportion of negotiation aspects eliminated. BFD provides a smooth and continuous operational experience for applications in a network.
Feature Characteristics
S-BFD consists of an initiator (a network node hosts an S-BFD Initiator) and a responder (a network node hosts an S-BFD Reflector). In network traffic, S-BFD detects a link failure, and the traffic immediately switches to a backup path. The traffic returns to the primary once the link is up or the corresponding path becomes active.
S-BFD works on the following concepts:
Initiator: A network node hosting an S-BFDInitiator.
Responder: A network node hosting an S-BFDReflector.
S-BFD Initiator: In a network, an S-BFD session performs a continuity test by sending S-BFD packets to a remote entity.
BFD Discriminator: A BFD Discriminator is allocated for an SBFDInitiator.
SBFD Reflector: In a network node, S-BFD session gathers incoming S-BFD control packets from local entities and generates responses to S-BFD control packets.
For more information, see the Seamless BFD for SR-TE in the OcNOS Segment Routing Config Guide document.
Benefits
The following are the benefits of using S-BFD on Q2:
Quick provisioning: S-BFD can be deployed in any network with less time and effort, ensuring the configured environment is rapid and efficient.
Improved control: S-BFD continuously monitors the network, predicts the network blocks, and diverts the network traffic to back up path.
Flexibility for network nodes: S-BFD easily adapts to network functionalities, ensuring efficient traffic distribution and minimizing congestion.
Initiating path monitoring: Path monitoring in a network involves regular monitoring and checking the communication path between two network endpoints.
S-BFD provides quick convergence time is 50 milliseconds.
Prerequisites
The following prerequisites are mandatory before installing S-BFD:
Configure ISIS.
Configure Segment Routing policy.
Configuration
S-BFD is supported only on Qumran2 platforms. The topology below describes active routers PE1,P3,P4, PE2 and as a backup PE1,P2, PE2 with lowest preference.
For more information on the S-BFD configurations, see the Seamless BFD for SR-TE Configuration in the OcNOS Segment Routing Config Guide.
Topology
In a network, a node can be either the initiator or the reflector, the initiator sends an S-BFD packet for the detection to the reflector. The reflector reflects the received S-BFD packet. As soon as the S-BFD packet is received from the initiator, it checks that the S-BFD discriminator in the packet is the same. If it doesn't match the packet is discarded. If it matches, the reflector reflects the packet.
The following topology illustrates the S-BFD process.
S-BFD on Qumran2
For this topology to work, ensure that these following conditions are met
 
Note:  
1. Ensure that prefix SIDs are unique globally.
2. Use L1 or L2 routers throughout your SR domain.
3. Redistribution from L1 to L2 and vice-versa is not supported for Segment Routing.
 
Validation
PE2-7048#show bfd session
 
BFD process for VRF: (DEFAULT VRF)
=====================================================================================
Sess-Idx Remote-Disc Lower-Layer Sess-Type Sess-State UP-Time Interface Down-Reason Remote-Addr
1281 45.45.45.45 MPLS LSP Single-Hop Up 00:01:15 po1.10 NA 45.45.45.45/32
 
Number of Sessions: 1
 
 
PE2-7048#show segment-routing policy detail
 
Policy-Name: 1    Color 1      End-point 45.45.45.45      Tunnel-ID: 1
  Admin-Status: UP    Oper-Status: UP for 00:01:13
  State Transition Count: 1
  CSPF Retry Limit: 100    CSPF Retry Interval: 10
  S-BFD is enabled.
  Binding SID :
  BSID: 25600
  Alloc mode: Dynamic
  Oper State: Programmed
 
  CP ID: 1, Active
    Preference: 300    Path Type: Explicit    CP Origin: Local
    CP state: Valid
    Segment List:
    Total no. of segments: 2
    Segment0[LABEL]: Label :16042
    Segment1[LABEL]: Label :16045
    Out-if: po1.10       Out-label-stack: 3/16045
    Backup ftn_ix: 6        (calculated based on s-bfd)
    Attributes:
    Configured:
    Explicit segment-list Name: 48-42
    Last Recorded Error: Next-hop resolution failed for SID-LIST, 00:02:15 ago
 
  CP ID: 2, S-BFD backup
    Preference: 100    Path Type: Explicit    CP Origin: Local
    CP state: Valid
    Segment List:
    Total no. of segments: 2
    Segment0[LABEL]: Label :16043
    Segment1[LABEL]: Label :16045
    Out-if: xe0          Out-label-stack: 3/16045
    Attributes:
    Configured:
    Explicit segment-list Name: 48-43
    Last Recorded Error: Next-hop resolution failed for SID-LIST, 00:02:15 ago
For more information, see the Seamless BFD for SR-TE Validation in the OcNOS Segment Routing Config Guide document.
Implementation Examples
To achieve minimal traffic convergence time and a quick switch over to backup if there is any link failure in the primary path.
1. Configure the S-BFD Segment Routing policy NAME where the data enters the traffic on a network and decides which path to flow.
2. Configure the S-BFD discriminator A.B.C.D at the outgoing or existing data from the network traffic.
3. S-BFD starts monitoring the segment routing policy path, once it is mapped to S-BFD.
Troubleshooting
1. Check if the discriminator is learnt at initiator.
2. Check if the learnt discriminator is the same as the segment routing policy end-point address.
3. Check if the segment routing policy is mapped to S-BFD is operationally up.
Abbreviations
 
Acronym
Description
S-BFD
Seamless Bidirectional Forwarding Detection
SR
Segment Routing
SID
Segment Identifiers
ISIS
Intermediate System to Intermediate System
Q2
Qumran
Glossary
The following provides definitions for key terms used throughout this document.
 
ISIS
ISIS protocol provides the solution for connecting and managing virtual networks within a data center or network infrastructure
SR
Segment Routing is a method where the sender of a packet can partially or completely specify a route in a network through which a packet is sent
SID
A segment routing mapping server allocates Segment Identifiers (SIDs) for prefixes and ranges in an ISIS segment routing domain
Ingress
Flow of data traffic into a network
Egress
Outgoing or exiting data traffic from a network