BFD for RSVP-TE LSPs with Failure Action
This chapter describes BFD for RSVP-TE LSPs with failure action.
Topics in this chapter include:
Applicability
This chapter was initially written based on SR OS Release 15.0.R7, but the CLI in the current edition corresponds to SR OS Release 23.7.R1.
The chapter BFD for RSVP-TE and LDP LSPs is prerequisite reading.
Overview
Using the failure-action command, the operator can configure the action taken by the system if a BFD session fails for an RSVP LSP or LDP prefix list.
When failure-action failover is configured, and the LSP BFD session goes down on the currently active path, the LSP switches from the primary path to a secondary path, or from the currently active secondary path to the next best preference secondary path if the currently active path was a secondary.
When failure-action down is configured, the LSP is registered as unusable in the tunnel table manager (TTM) when BFD on the LSP goes down. A tunnel being registered as unusable in TTM is not available to the routing table manager (RTM) and all routes using that tunnel are withdrawn. SDP auto-bind will not use an LSP until it is registered as usable. Traffic cannot pass through that LSP, even when secondary paths are available for that LSP.
In either case, SNMP traps are raised when the BFD state machine for the LSP transitions.
Nokia recommends configuring the BFD control packet timer intervals long enough to deal with transient data path disruptions that may occur when the underlying transport network recovers following a failure.
LSP BFD only runs on the currently active path. It cannot determine if any non-active paths (for example, a secondary path or primary path during reversion) that the system might switch to are up and forwarding.
When BFD failure action is configured on an RSVP-TE LSP directly, the action can be failover or down. When BFD failure action is configured on an RSVP-TE LSP indirectly, through an LSP template, the only action available is down. This chapter only covers the direct configuration of a failure action.
Configuration
The following scenarios are described in this section:
Failure action failover
Topology for failure action failover shows the topology used for failure action failover. A BGP shortcut is defined in AS 65545 running between the autonomous system border routers (ASBRs) PE-5 and PE-2. That shortcut is RSVP-TE LSP lsp-1 composed of two paths, where the first path is the upper path from PE-5 via PE-1 to PE-2, and the second path is the lower path from PE-5 via PE-4 and PE-3 to PE-2.
The initial configuration includes:
-
Cards, MDAs, and ports
-
Router interfaces
-
IS-IS as IGP on all interfaces (alternatively, OSPF can be used), with traffic engineering enabled
-
MPLS and RSVP enabled on all interfaces
-
BGP configured, with RR-7 being the route reflector in AS 65545 for clients PE-2 and PE-5, and PE-6 located in AS 65546 and connected to PE-2. PE-6 advertises its prefix 192.0.2.6/32 to AS 65545.
The lsp-1 LSP is defined with primary path path-5-1-2 and secondary path path-5-4-3-2. The two paths are established when the LSP is brought up, to minimize traffic loss in case of a failure. BFD template bfdt-1 with a failure action failover is applied to lsp-1 at the LSP level.
# on ASBR PE-5:
configure
router Base
mpls
lsp "lsp-1"
to 192.0.2.2
path-computation-method local-cspf
bfd
bfd-template "bfdt-1"
bfd-enable
failure-action failover
exit
primary "path-5-1-2"
exit
secondary "path-5-4-3-2"
standby
exit
no shutdown
exit
The details of the LSP show the configured failure action, as follows:
*A:PE-5# show router mpls lsp "lsp-1" detail
===============================================================================
MPLS LSPs (Originating) (Detail)
===============================================================================
Legend :
+ - Inherited
===============================================================================
-------------------------------------------------------------------------------
Type : Originating
-------------------------------------------------------------------------------
LSP Name : lsp-1
LSP Type : RegularLsp LSP Tunnel ID : 1
LSP Index : 1 TTM Tunnel Id : 1
From : 192.0.2.5
To : 192.0.2.2
Adm State : Up Oper State : Up
LSP Up Time : 0d 00:08:32 LSP Down Time : 0d 00:00:00
Transitions : 1 Path Changes : 1
Retry Limit : 0 Retry Timer : 30 sec
Signaling : RSVP Resv. Style : SE
---snip---
BFD Template : bfdt-1 BFD Ping Intvl : 60
BFD Enable : True BFD Failure-action : Failover
WaitForUpTimer : 4
---snip---
Primary(a) : path-5-1-2
Up Time : 0d 00:08:32
Bandwidth : 0 Mbps
Standby : path-5-4-3-2
Up Time : 0d 00:08:32
Bandwidth : 0 Mbps
===============================================================================
With this configuration, the BFD session is running over the upper path, as follows:
*A:PE-5# show router bfd session
===============================================================================
Legend:
Session Id = Interface Name | LSP Name | Prefix | RSVP Sess Name | Service Id
wp = Working path pp = Protecting path
===============================================================================
BFD Session
===============================================================================
Session Id State Tx Pkts Rx Pkts
Rem Addr/Info/SdpId:VcId Multipl Tx Intvl Rx Intvl
Protocols Type LAG Port LAG ID
Loc Addr LAG name
-------------------------------------------------------------------------------
lsp-1::path-5-1-2 Up 305 280
192.0.2.2 5 2000 2000
rsvpLsp central N/A N/A
192.0.2.5
-------------------------------------------------------------------------------
No. of BFD sessions: 1
===============================================================================
BGP route 192.0.2.6/32 is advertised by PE-6 out of AS 65546, as follows. This route has next hop 192.0.2.2, which is the system address of PE-2.
*A:PE-5# show router bgp routes
===============================================================================
BGP Router ID:192.0.2.5 AS:65545 Local AS:65545
===============================================================================
Legend -
Status codes : u - used, s - suppressed, h - history, d - decayed, * - valid
l - leaked, x - stale, > - best, b - backup, p - purge
Origin codes : i - IGP, e - EGP, ? - incomplete
===============================================================================
BGP IPv4 Routes
===============================================================================
Flag Network LocalPref MED
Nexthop (Router) Path-Id IGP Cost
As-Path Label
-------------------------------------------------------------------------------
u*>i 192.0.2.6/32 100 None
192.0.2.2 1 20
65546 -
-------------------------------------------------------------------------------
Routes : 1
===============================================================================
To keep the core of AS 65545 BGP free, traffic is tunneled through the lsp-1 LSP, as follows:
*A:PE-5# show router route-table 192.0.2.6/32
===============================================================================
Route Table (Router: Base)
===============================================================================
Dest Prefix[Flags] Type Proto Age Pref
Next Hop[Interface Name] Metric
-------------------------------------------------------------------------------
192.0.2.6/32 Remote BGP 00h08m32s 170
192.0.2.2 (tunneled:RSVP:1) 20
-------------------------------------------------------------------------------
No. of Routes: 1
Flags: n = Number of times nexthop is repeated
B = BGP backup route available
L = LFA nexthop available
S = Sticky ECMP requested
===============================================================================
The LSP and path details can also be shown using a tools dump command, as follows. LSP lsp-1 is up, path-5-1-2 is the active path taking three hops, so the operational metric is 20, and path-5-4-3-2 is the standby path, but not active.
*A:PE-5# tools dump router mpls lspinfo "lsp-1" detail
LSP "lsp-1" LspIdx 1 LspType Dynamic State LSPS_UP Flags 0x2000
AdminState Up OperState Up RowStatus Active
From N/A To 192.0.2.2
NumPaths 2 NumSdps 0 NumCBFSdps 0 NumFltrEntries 0
ActivePath lsp-1::path-5-1-2(LspId 54272)
HoldTimeRemaining 0secs ClassType 0 SoftPreemption TRUE Metric 0 OperMetric 20
LDPoRsvp Include VprnAutoBind Include IgpShortCut Include BgpShortCut Include
BgpTransTunnel Include IpShCutTtlPropLocal TRUE IpShCutTtlPropTans TRUE
RelativeMetricOffset 2147483647 MTU 8982 InUseByLdp FALSE TTMPref 7
EntropyLabel inherit OperEntropyLabel enable NegEntropyLabel disable
ClassForwarding: Disabled
BFD Enabled Template bfdt-1 PingInterval 60 FailureAction failover WaitForUp 4sec
PCE Report: Disabled PCE Control: Disabled
Path Profile:
None
Admin Tags:
None
Lsp-self-ping: Config: inherit, Oper: Disabled, TimedOutCnt: 0 OamNoRsc: 0
Path "path-5-1-2" LspId 54272 LspPathIndex 2 PathType Primary ActivePath Yes
RowStatus Active LastChange 000 00:09:36.420
AdminState Up OperState Up OperStateChange 000 00:09:36.400
TE Computed Hop List:
Hop[1] IngIp 192.0.2.5 IngLnkId 0 EgrIp 192.168.15.2 EgrLnkId 0 RtrId 192.0.2.5 Flag 0x0
Hop[2] IngIp 192.168.15.1 IngLnkId 0 EgrIp 192.168.12.1 EgrLnkId 0 RtrId 192.0.2.1 Flag 0x0
Hop[3] IngIp 192.168.12.2 IngLnkId 0 EgrIp 192.0.2.2 EgrLnkId 0 RtrId 192.0.2.2 Flag 0x0
LspPath FsmState LSP_PATH_S_UP Flags 0x0 miscFlags 0x2
RetryAttempts 0 RetryInterval 30 NextRetryIn 0secs
FailNode 0.0.0.0 FailCode noError
Class Type 0 SetupPri 7 HoldPri 0 Pref 0 HopLimit 255 BW 0Mbps
TotIgpCost 20 OperMetric 20 MTU 8982
BFD Disabled Template n/a PingInterval 60 WaitForUp 4sec
Degraded No
Oper Values:
Class Type 0 SetupPri 7 HoldPri 0 HopLimit 255 BW 0Mbps
RecordRoute RecordLabel No Adspec
No PropagateAdminGroup Exclude 0x00000000 Include 0x00000000
No FRR
Metric 20 CSPF No Least Fill Intra-area
NegotiatedEntropyLabel Disabled
PCE-Computed No PCE-Reported No PCE-Controlled No
BFD State Up InitTime 0d 00:09:36 UpTime 0d 00:09:32
OldMBBPathsCleanedUp Yes
Path "path-5-4-3-2" LspId 54274 LspPathIndex 3 PathType Standby ActivePath No
RowStatus Active LastChange 000 00:09:36.410
AdminState Up OperState Up OperStateChange 000 00:09:36.400
TE Computed Hop List:
Hop[1] IngIp 192.0.2.5 IngLnkId 0 EgrIp 192.168.45.2 EgrLnkId 0 RtrId 192.0.2.5 Flag 0x0
Hop[2] IngIp 192.168.45.1 IngLnkId 0 EgrIp 192.168.34.2 EgrLnkId 0 RtrId 192.0.2.4 Flag 0x0
Hop[3] IngIp 192.168.34.1 IngLnkId 0 EgrIp 192.168.23.2 EgrLnkId 0 RtrId 192.0.2.3 Flag 0x0
Hop[4] IngIp 192.168.23.1 IngLnkId 0 EgrIp 192.0.2.2 EgrLnkId 0 RtrId 192.0.2.2 Flag 0x0
LspPath FsmState LSP_PATH_S_UP Flags 0x0 miscFlags 0x2
RetryAttempts 0 RetryInterval 30 NextRetryIn 0secs
FailNode 0.0.0.0 FailCode noError
Class Type 0 SetupPri 7 HoldPri 0 Pref 255 HopLimit 255 BW 0Mbps
TotIgpCost 30 OperMetric 30 MTU 8982
SRLG Disabled SRLGDisjoint No
BFD Disabled Template n/a PingInterval 60 WaitForUp 4sec
Degraded No
Oper Values:
Class Type 0 SetupPri 7 HoldPri 0 HopLimit 255 BW 0Mbps
RecordRoute RecordLabel No Adspec
No PropagateAdminGroup Exclude 0x00000000 Include 0x00000000
No FRR
Metric 30 CSPF No Least Fill Intra-area
NegotiatedEntropyLabel Disabled
PCE-Computed No PCE-Reported No PCE-Controlled No
BFD State N/A
OldMBBPathsCleanedUp Yes
Total Ingress LSP Count : 1
Bringing down the link between PE-1 and PE-2 results in the secondary path, path-5-4-3-2 of LSP lsp-1, becoming active, and the BFD session is re-established on that path, as follows:
*A:PE-5# show router bfd session
===============================================================================
Legend:
Session Id = Interface Name | LSP Name | Prefix | RSVP Sess Name | Service Id
wp = Working path pp = Protecting path
===============================================================================
BFD Session
===============================================================================
Session Id State Tx Pkts Rx Pkts
Rem Addr/Info/SdpId:VcId Multipl Tx Intvl Rx Intvl
Protocols Type LAG Port LAG ID
Loc Addr LAG name
-------------------------------------------------------------------------------
lsp-1::path-5-4-3-2 Up 2 6
192.0.2.2 5 2000 2000
rsvpLsp central N/A N/A
192.0.2.5
-------------------------------------------------------------------------------
No. of BFD sessions: 1
===============================================================================
BFD sessions changing state are logged in the trap log, as follows:
83 2023/08/11 06:19:01.580 UTC WARNING: MPLS #2012 Base VR 1:
"LSP path lsp-1::path-5-1-2 is operationally disabled ('shutdown') because resvTear"
84 2023/08/11 06:19:01.580 UTC MINOR: MPLS #2027 Base VR 1:
"LSP lsp-1 active path lsp-1::path-5-1-2 has changed to active path lsp-1::path-5-4-3-2"
85 2023/08/11 06:19:01.580 UTC MINOR: BFD #2004 Base 192.0.2.2
"The protocol (RSVP LSP) using BFD session on node 192.0.2.2 has been cleared"
86 2023/08/11 06:19:01.581 UTC MINOR: BFD #2003 Base 192.0.2.2
"The lspHead BFD Session with Local Discriminator 1 on 192.0.2.2 has been deleted"
87 2023/08/11 06:19:01.581 UTC MINOR: BFD #2004 Base 192.0.2.2
"The protocol (RSVP LSP) using BFD session on node 192.0.2.2 has been added"
88 2023/08/11 06:19:06.562 UTC MINOR: BFD #2002 Base 192.0.2.2
"The lspHead BFD session with Local Discriminator 2 on 192.0.2.2 is up (Tunnel Id 1, Path LSP ID 54274)"
The tools dump command shows that lsp-1 is still up, and path-5-4-3-2 is active with four hops, so the LSP operational metric is 30, as follows:
*A:PE-5# tools dump router mpls lspinfo "lsp-1" detail
LSP "lsp-1" LspIdx 1 LspType Dynamic State LSPS_UP Flags 0x2000
AdminState Up OperState Up RowStatus Active
From N/A To 192.0.2.2
NumPaths 2 NumSdps 0 NumCBFSdps 0 NumFltrEntries 0
ActivePath lsp-1::path-5-4-3-2(LspId 54274)
HoldTimeRemaining 0secs ClassType 0 SoftPreemption TRUE Metric 0 OperMetric 30
LDPoRsvp Include VprnAutoBind Include IgpShortCut Include BgpShortCut Include
BgpTransTunnel Include IpShCutTtlPropLocal TRUE IpShCutTtlPropTans TRUE
RelativeMetricOffset 2147483647 MTU 8982 InUseByLdp FALSE TTMPref 7
EntropyLabel inherit OperEntropyLabel enable NegEntropyLabel disable
ClassForwarding: Disabled
BFD Enabled Template bfdt-1 PingInterval 60 FailureAction failover WaitForUp 4sec
PCE Report: Disabled PCE Control: Disabled
Path Profile:
None
Admin Tags:
None
Lsp-self-ping: Config: inherit, Oper: Disabled, TimedOutCnt: 0 OamNoRsc: 0
Path "path-5-1-2" LspId 54276 LspPathIndex 2 PathType Primary ActivePath No
RowStatus Active LastChange 000 00:11:04.410
AdminState Up OperState Down OperStateChange 000 00:01:01.470
LspPath FsmState LSP_PATH_S_DOWN Flags 0x0 miscFlags 0x2
RetryAttempts 2 RetryInterval 30 NextRetryIn 17secs
FailNode 192.0.2.5 FailCode noCspfRouteToDestination
Class Type 0 SetupPri 7 HoldPri 0 Pref 0 HopLimit 255 BW 0Mbps
TotIgpCost 0 OperMetric 16777215 MTU 0
BFD Disabled Template n/a PingInterval 60 WaitForUp 4sec
Degraded No
OldMBBPathsCleanedUp Yes
Path "path-5-4-3-2" LspId 54274 LspPathIndex 3 PathType Standby ActivePath Yes
RowStatus Active LastChange 000 00:11:04.400
AdminState Up OperState Up OperStateChange 000 00:11:04.390
TE Computed Hop List:
Hop[1] IngIp 192.0.2.5 IngLnkId 0 EgrIp 192.168.45.2 EgrLnkId 0 RtrId 192.0.2.5 Flag 0x0
Hop[2] IngIp 192.168.45.1 IngLnkId 0 EgrIp 192.168.34.2 EgrLnkId 0 RtrId 192.0.2.4 Flag 0x0
Hop[3] IngIp 192.168.34.1 IngLnkId 0 EgrIp 192.168.23.2 EgrLnkId 0 RtrId 192.0.2.3 Flag 0x0
Hop[4] IngIp 192.168.23.1 IngLnkId 0 EgrIp 192.0.2.2 EgrLnkId 0 RtrId 192.0.2.2 Flag 0x0
LspPath FsmState LSP_PATH_S_UP Flags 0x0 miscFlags 0x2
RetryAttempts 0 RetryInterval 30 NextRetryIn 0secs
FailNode 0.0.0.0 FailCode noError
Class Type 0 SetupPri 7 HoldPri 0 Pref 255 HopLimit 255 BW 0Mbps
TotIgpCost 30 OperMetric 30 MTU 8982
SRLG Disabled SRLGDisjoint No
BFD Disabled Template n/a PingInterval 60 WaitForUp 4sec
Degraded No
Oper Values:
Class Type 0 SetupPri 7 HoldPri 0 HopLimit 255 BW 0Mbps
RecordRoute RecordLabel No Adspec
No PropagateAdminGroup Exclude 0x00000000 Include 0x00000000
No FRR
Metric 30 CSPF No Least Fill Intra-area
NegotiatedEntropyLabel Disabled
PCE-Computed No PCE-Reported No PCE-Controlled No
BFD State Up InitTime 0d 00:01:01 UpTime 0d 00:00:56
OldMBBPathsCleanedUp Yes
Total Ingress LSP Count : 1The secondary path, path-5-4-3-2, becoming active does not result in a change of the BGP next-hop. Traffic continues to flow from PE-5 to PE-6 via LSP lsp-1, but now via the lower path. The BFD failure action failover combined with standby secondary paths can help detect failures faster, with minimal traffic loss, which is especially useful in larger domains, or when the LSP passes through multiple domains.
Failure action down
Topology for failure action down shows the topology used for failure action down. BGP shortcuts are defined in AS 65545 running between the ASBRs PE-5, PE-2, and PE-3. A first shortcut is offered through an RSVP-TE LSP called lsp-2, with a single path from PE-5 via PE-1 to PE-2; the second shortcut is offered through another RSVP-TE LSP called lsp-3, with a single path from PE-5 via PE-4 to PE-3. When LSP lsp-2 fails and the failure gets detected by BFD, LSP lsp-2 is unavailable in the TTM and traffic starts using lsp-3, implying a change of the BGP next hop; this scenario being an edge prefix-independent convergence (PIC) scenario. See the "BGP Fast Reroute" chapter in the 7450 ESS, 7750 SR, and 7950 XRS Unicast Routing Protocols Advanced Configuration Guide for Classic CLI for more information about edge PIC.
The initial configuration includes:
-
Cards, MDAs, and ports
-
Router interfaces
-
IS-IS as IGP on all interfaces (alternatively, OSPF can be used), with traffic engineering enabled
-
MPLS and RSVP-TE enabled on all interfaces
-
BGP configured, with RR-7 being the route reflector for clients PE-2, PE-3, and PE-5 in AS 65545, and PE-6 located in AS 65546 and connected to PE-2 and PE-3. PE-6 exports prefix 192.0.2.6/32 to PE-2 and PE-3.
The LSPs from Topology for failure action down are configured with a single path, as follows. The paths referred to from these LSPs are fully strict paths, using interface IP addresses. Both lsp-2 and lsp-3 have BFD enabled with failure action down.
# on PE-5
configure
router Base
mpls
path "path-5-1-2"
hop 10 192.168.15.1 strict
hop 20 192.168.12.2 strict
no shutdown
exit
path "path-5-4-3"
hop 10 192.168.45.1 strict
hop 20 192.168.34.1 strict
no shutdown
exit
lsp "lsp-2"
to 192.0.2.2
path-computation-method local-cspf
bfd
bfd-template "bfdt-1"
bfd-enable
failure-action down
exit
primary "path-5-1-2"
exit
no shutdown
exit
lsp "lsp-3"
to 192.0.2.3
path-computation-method local-cspf
bfd
bfd-template "bfdt-1"
bfd-enable
failure-action down
exit
primary "path-5-4-3"
exit
no shutdown
exit
no shutdown
exit
The details of the LSP show the configured failure action, as follows:
*A:PE-5# show router mpls lsp "lsp-2" detail
===============================================================================
MPLS LSPs (Originating) (Detail)
===============================================================================
Legend :
+ - Inherited
===============================================================================
-------------------------------------------------------------------------------
Type : Originating
-------------------------------------------------------------------------------
LSP Name : lsp-2
LSP Type : RegularLsp LSP Tunnel ID : 2
LSP Index : 2 TTM Tunnel Id : 2
From : 192.0.2.5
To : 192.0.2.2
Adm State : Up Oper State : Up
LSP Up Time : 0d 00:08:57 LSP Down Time : 0d 00:00:00
Transitions : 1 Path Changes : 1
Retry Limit : 0 Retry Timer : 30 sec
Signaling : RSVP Resv. Style : SE
Hop Limit : 255 Negotiated MTU : 8982
Adaptive : Enabled ClassType : 0
FastReroute : Disabled Oper FR : Disabled
PathCompMethod : local-cspf ADSPEC : Disabled
FallbkPathComp : not-applicable
Metric : N/A Metric Type : igp
Load Bal Wt : N/A ClassForwarding : Disabled
Include Grps : Exclude Grps :
None None
Least Fill : Disabled Soft Preemption : Enabled
BFD Template : bfdt-1 BFD Ping Intvl : 60
BFD Enable : True BFD Failure-action : Down
WaitForUpTimer : 4
Revert Timer : Disabled Next Revert In : N/A
Entropy Label : Enabled+ Oper Entropy Label : Enabled
Negotiated EL : Disabled
Auto BW : Disabled
LdpOverRsvp : Enabled
VprnAutoBind : Enabled
IGP Shortcut : Enabled BGP Shortcut : Enabled
IGP LFA : Disabled IGP Rel Metric : Disabled
AllowSrOverSrte : Disabled
BGPTransTun : Enabled
Oper Metric : 20
Prop Adm Grp : Disabled
PCE Report : Disabled+
PCE Control : Disabled
Path Profile : None
Admin Tags : None
Lsp Self Ping : Disabled+ Self Ping Timeouts : 0
SelfPingOAMFail*: 0
Primary(a) : path-5-1-2
Up Time : 0d 00:08:57
Bandwidth : 0 Mbps
===============================================================================
* indicates that the corresponding row element may have been truncated.
Multiple BGP paths are available out of PE-5 to reach PE-6, as follows. The path via PE-2 is the currently active path, the path via PE-3 is the backup path.
*A:PE-5# show router route-table protocol bgp alternative
===============================================================================
Route Table (Router: Base)
===============================================================================
Dest Prefix[Flags] Type Proto Age Pref
Next Hop[Interface Name] Metric
Alt-NextHop Alt-
Metric
-------------------------------------------------------------------------------
192.0.2.6/32 Remote BGP 00h02m24s 170
192.0.2.2 (tunneled:RSVP:2) 20
192.0.2.6/32 (Backup) Remote BGP 00h02m24s 170
192.0.2.3 (tunneled:RSVP:3) 20
-------------------------------------------------------------------------------
No. of Routes: 2
Flags: n = Number of times nexthop is repeated
Backup = BGP backup route
LFA = Loop-Free Alternate nexthop
S = Sticky ECMP requested
===============================================================================
The first of the following BFD sessions is running over the active path:
*A:PE-5# show router bfd session
===============================================================================
Legend:
Session Id = Interface Name | LSP Name | Prefix | RSVP Sess Name | Service Id
wp = Working path pp = Protecting path
===============================================================================
BFD Session
===============================================================================
Session Id State Tx Pkts Rx Pkts
Rem Addr/Info/SdpId:VcId Multipl Tx Intvl Rx Intvl
Protocols Type LAG Port LAG ID
Loc Addr LAG name
-------------------------------------------------------------------------------
lsp-2::path-5-1-2 Up 136 127
192.0.2.2 5 2000 2000
rsvpLsp central N/A N/A
192.0.2.5
lsp-3::path-5-4-3 Up 137 127
192.0.2.3 5 2000 2000
rsvpLsp central N/A N/A
192.0.2.5
-------------------------------------------------------------------------------
No. of BFD sessions: 2
===============================================================================
The BFD session running over the active path of the lsp-2 LSP is also indicated in the output of the following tools command:
*A:PE-5# tools dump router mpls lspinfo "lsp-2" detail
LSP "lsp-2" LspIdx 2 LspType Dynamic State LSPS_UP Flags 0x2000
AdminState Up OperState Up RowStatus Active
From N/A To 192.0.2.2
NumPaths 1 NumSdps 0 NumCBFSdps 0 NumFltrEntries 0
ActivePath lsp-2::path-5-1-2(LspId 36352)
HoldTimeRemaining 0secs ClassType 0 SoftPreemption TRUE Metric 0 OperMetric 20
LDPoRsvp Include VprnAutoBind Include IgpShortCut Include BgpShortCut Include
BgpTransTunnel Include IpShCutTtlPropLocal TRUE IpShCutTtlPropTans TRUE
RelativeMetricOffset 2147483647 MTU 8982 InUseByLdp FALSE TTMPref 7
EntropyLabel inherit OperEntropyLabel enable NegEntropyLabel disable
ClassForwarding: Disabled
BFD Enabled Template bfdt-1 PingInterval 60 FailureAction down WaitForUp 4sec
PCE Report: Disabled PCE Control: Disabled
Path Profile:
None
Admin Tags:
None
Lsp-self-ping: Config: inherit, Oper: Disabled, TimedOutCnt: 0 OamNoRsc: 0
Path "path-5-1-2" LspId 36352 LspPathIndex 2 PathType Primary ActivePath Yes
RowStatus Active LastChange 000 00:09:52.960
AdminState Up OperState Up OperStateChange 000 00:09:52.950
TE Computed Hop List:
Hop[1] IngIp 192.0.2.5 IngLnkId 0 EgrIp 192.168.15.2 EgrLnkId 0 RtrId 192.0.2.5 Flag 0x0
Hop[2] IngIp 192.168.15.1 IngLnkId 0 EgrIp 192.168.12.1 EgrLnkId 0 RtrId 192.0.2.1 Flag 0x0
Hop[3] IngIp 192.168.12.2 IngLnkId 0 EgrIp 192.0.2.2 EgrLnkId 0 RtrId 192.0.2.2 Flag 0x0
LspPath FsmState LSP_PATH_S_UP Flags 0x0 miscFlags 0x2
RetryAttempts 0 RetryInterval 30 NextRetryIn 0secs
FailNode 0.0.0.0 FailCode noError
Class Type 0 SetupPri 7 HoldPri 0 Pref 0 HopLimit 255 BW 0Mbps
TotIgpCost 20 OperMetric 20 MTU 8982
BFD Disabled Template n/a PingInterval 60 WaitForUp 4sec
Degraded No
Oper Values:
Class Type 0 SetupPri 7 HoldPri 0 HopLimit 255 BW 0Mbps
RecordRoute RecordLabel No Adspec
No PropagateAdminGroup Exclude 0x00000000 Include 0x00000000
No FRR
Metric 20 CSPF No Least Fill Intra-area
NegotiatedEntropyLabel Disabled
PCE-Computed No PCE-Reported No PCE-Controlled No
BFD State Up InitTime 0d 00:09:53 UpTime 0d 00:09:48
OldMBBPathsCleanedUp Yes
Total Ingress LSP Count : 1
Emulating a path failure by bringing down port 1/1/c2/1 on PE-2 brings the primary path in the lsp-2 LSP down, as follows:
*A:PE-5# show router mpls lsp "lsp-2" path
===============================================================================
MPLS LSP lsp-2 Path
===============================================================================
-------------------------------------------------------------------------------
LSP Name : lsp-2
From : 192.0.2.5
To : 192.0.2.2
Adm State : Up Oper State : Down
-------------------------------------------------------------------------------
Path Name Next Hop Type Out I/F Adm Opr
-------------------------------------------------------------------------------
path-5-1-2
n/a Primary n/a Up Dwn
===============================================================================
The only remaining BFD session is now the BFD session for the lsp-3 LSP with next hop 192.0.2.3, as follows:
*A:PE-5# show router bfd session
===============================================================================
Legend:
Session Id = Interface Name | LSP Name | Prefix | RSVP Sess Name | Service Id
wp = Working path pp = Protecting path
===============================================================================
BFD Session
===============================================================================
Session Id State Tx Pkts Rx Pkts
Rem Addr/Info/SdpId:VcId Multipl Tx Intvl Rx Intvl
Protocols Type LAG Port LAG ID
Loc Addr LAG name
-------------------------------------------------------------------------------
lsp-3::path-5-4-3 Up 213 197
192.0.2.3 5 2000 2000
rsvpLsp central N/A N/A
192.0.2.5
-------------------------------------------------------------------------------
No. of BFD sessions: 1
===============================================================================BGP traffic is diverted into lsp-3, and the BGP next hop is 192.0.2.3, as follows:
*A:PE-5# show router route-table protocol bgp alternative
===============================================================================
Route Table (Router: Base)
===============================================================================
Dest Prefix[Flags] Type Proto Age Pref
Next Hop[Interface Name] Metric
Alt-NextHop Alt-
Metric
-------------------------------------------------------------------------------
192.0.2.6/32 Remote BGP 00h01m50s 170
192.0.2.3 (tunneled:RSVP:3) 20
-------------------------------------------------------------------------------
No. of Routes: 1
Flags: n = Number of times nexthop is repeated
Backup = BGP backup route
LFA = Loop-Free Alternate nexthop
S = Sticky ECMP requested
===============================================================================Conclusion
The BFD failure action failover or down can help detect failures faster with minimal traffic loss on switchover, which is especially useful in larger domains or when the LSP passes through multiple domains.