Use Symmetric BFD Configurations Between Both Devices in a Bidirectional LSP Scenario
In a bidirectional LSP scenario, when BFD configurations are asymmetric between both devices, the LDP LSP goes Down. As a result, services carried on the LDP LSP are interrupted.
Scenario
On the network shown in Figure 1-4, LSPs exist from Router A to Router B and from Router B to Router A. BFD for peer IP is configured on Router A, and BFD for TE LSP is configured on Router B. An LDP LSP with the same peer IP address exists on RouterA. If the TE LSP fails, services carried on the LDP LSP are interrupted.
Configuration Requirements
The consistent BFD type (BFD for TE LSP) must be configured on both devices.
Misconfiguration Risks
Risk description:
If the TE LSP on Router B fails, the status of the BFD session detecting the LDP LSP goes Down. As a result, services carried on the LDP LSP are interrupted.
Identification method:
Check whether BFD configurations are symmetric between both devices.
The following information indicates that BFD configurations on both devices are asymmetric. BFD for peer IP is configured on Router A, whereas BFD for TE LSP is configured on Router B.
# Run the display current-configuration configuration bfd command in any view of Router A.
<HUAWEI> display current-configuration configuration bfd#
bfd ieclsptowac bind peer-ip 100.1.1.1
discriminator local 101
discriminator remote 302
min-tx-interval 50
min-rx-interval 50
commit
#
# Run the display current-configuration configuration bfd command in any view of Router B.
<HUAWEI> display current-configuration configuration bfd#
bfd ieclsptowac bind mpls-te interface Tunnel0/0/1 te-lsp
discriminator local 302
discriminator remote 101
min-tx-interval 50
min-rx-interval 50
commit
#
Check the status of the BFD session detecting the peer IP address on Router A.
# Run the display bfd session all command in any view of Router A. Check that the BFD session's status is Down.
<HUAWEI> display bfd session all----------------------------------------------------------------------- Local Remote PeerIpAddr State Type InterfaceName ----------------------------------------------------------------------- 5 6 100.1.1.1 Down S_IP_PEER - ----------------------------------------------------------------------- Total UP/DOWN Session Number : 0/1# Run the display mpls lsp include ip-address mask-len verbose command in any view of Router B. Check that the status of the BFD session detecting the LDP LSP is Down.
<HUAWEI> display mpls lsp include 100.1.1.1 32 verbose ------------------------------------------------------------------------------- LSP Information: LDP LSP ------------------------------------------------------------------------------- No : 1 VrfIndex : Fec : 100.1.1.1/32 Nexthop : 100.2.1.1 In-Label : NULL Out-Label : 153468 In-Interface : ---------- Out-Interface : GigabitEthernet1/0/0 LspIndex : 191839 Token : 0x2001476 FrrToken : 0x0 LsrType : Ingress Outgoing token : 0x0 Label Operation : PUSH Mpls-Mtu : 9000 TimeStamp : 144908sec Bfd-State : DownBGPKey : ------
Recovery measures:
Configure BFD for peer IP on the device where BFD for TE LSP is configured to allow BFD to go Up through negotiation, and then delete the BFD configuration.
