05-17-2024 09:11 AM
Hello experts
I have a problem with an MPLS adjacency.
I have an ASR900 connected to a 10Gb C9300, MPLS and OSPF are enabled in this interface, adjacencies are created and everything works.
When the C9300 is restarted, the MPLS and OSPF adjacencies are not recreated, they are only created if I enter ASR900 and delete and re-enter the MPLS IP command.
Can you tell me why?
05-17-2024 09:22 AM
Hello,
So when your 9300 comes up your OSPF Adjacencies do NOT come up? You need to fix that problem first as the MPLS rides over the routing protocols to for adjacencies. Make sure your loopbacks are also advertised into OSPF as that's what MPLS uses for neighbors unless otherwise configured. Based on the synopsis it seems as if the configuration isnt saved before rebooting.
Can you provide the running config of both devices?
-David
05-17-2024 09:29 AM - edited 05-19-2024 01:40 AM
I think the opsf is UP but the mpls not re-established after SW reboot.
This ldp-igp sync
MHM
05-17-2024 10:30 AM
The ospf process does not go up because there is no mpls adjacency.
The loopback was inserted into the ospf process, as I said, before the reboot of the c9300 all ospf and mpls worked.
After the reboot nothing goes up anymore.
05-17-2024 10:47 AM
Do
Show ip ospf neighbor
Show ip ospf interface breif
Are you see neighbor? Are the interface are UP DR/BDR/DOTHER?
MHM
05-18-2024 05:39 PM
Also share
Show ip ospf mpls ldp interface <ospf interface>
MHM
05-17-2024 12:35 PM
MPLS is independent of OSPF so the fact the adjacency does not come up is not a problem with MPLS its a problem with OSPF.
05-18-2024 08:57 PM - edited 05-18-2024 09:15 PM
Hi @vin.marco ,
Do you use the MPLS LDP IGP synchronization feature by any chance ("mpls ldp sync" under the ospf process)?
If so, could please provide the output for the following command for both devices:
show mpls ldp igp sync
Regards,
05-19-2024 11:44 PM
Thanks all for support, below the output first the C9300 reload:
OSPF:
interface TenGigabitEthernet0/1/7
description Link to TEST
mtu 9198
ip address 10.86.186.253 255.255.255.252
ip ospf network point-to-point
ip ospf 1000 area 0
cdp enable
mpls ip
bfd template RID
!
interface Loopback86
description Loopback vrf Global
ip address 10.86.1.23 255.255.255.255
end
ASR900#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.86.1.105 0 FULL/ - 00:00:34 10.86.186.254 TenGigabitEthernet0/1/7
ASR900#sh ip ospf interface l86
Loopback86 is up, line protocol is up
Internet Address 10.86.1.23/32, Interface ID 25, Area 0
Attached via Network Statement
Process ID 1000, Router ID 10.86.1.23, Network Type LOOPBACK, Cost: 1
Topology-MTID Cost Disabled Shutdown Topology Name
0 1 no no Base
Loopback interface is treated as a stub Host
RMC4DFDI12002#sh ip ospf interface t0/1/7
TenGigabitEthernet0/1/7 is up, line protocol is up
Internet Address 10.86.186.253/30, Interface ID 23, Area 0
Attached via Interface Enable
Process ID 1000, Router ID 10.86.1.23, Network Type POINT_TO_POINT, Cost: 1
Topology-MTID Cost Disabled Shutdown Topology Name
0 1 no no Base
Enabled by interface config, including secondary ip addresses
Transmit Delay is 1 sec, State POINT_TO_POINT, BFD enabled
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:05
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Can be protected by per-prefix Loop-Free FastReroute
Can be used for per-prefix Loop-Free FastReroute repair paths
Not Protected by per-prefix TI-LFA
Index 1/9/9, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 20
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.86.1.105
Suppress hello for 0 neighbor(s)
MPLS
ASR900#sh mpls ldp neighbor
Peer LDP Ident: 10.86.1.105:0; Local LDP Ident 10.86.1.23:0
TCP connection: 10.86.1.105.38041 - 10.86.1.23.646
State: Oper; Msgs sent/rcvd: 4682/4896; Downstream
Up time: 2d17h
LDP discovery sources:
TenGigabitEthernet0/1/7, Src IP addr: 10.86.186.254
Targeted Hello 10.86.1.23 -> 10.86.1.105, active, passive
Addresses bound to peer LDP Ident:
10.86.1.105 10.86.187.85 10.86.186.254
ASR900#sh ip ospf mpls ldp interface tenGigabitEthernet 0/1/7
TenGigabitEthernet0/1/7
Process ID 1000, Area 0
LDP is not configured through LDP autoconfig
LDP-IGP Synchronization : Required
Holddown timer is not configured
Interface is up
ASR900#
RMC4DFDI12002#sh mpls ldp igp sync
TenGigabitEthernet0/1/7:
LDP configured; LDP-IGP Synchronization enabled.
Sync status: sync achieved; peer reachable.
Sync delay time: 0 seconds (0 seconds left)
IGP holddown time: infinite.
Peer LDP Ident: 10.86.1.105:0
IGP enabled: OSPF 1000
Configuration
mpls ldp nsr
mpls ldp graceful-restart
mpls ldp session protection
mpls ldp label
mpls ldp router-id Loopback86 force
!
router ospf 1000
router-id 10.86.1.23
nsr
nsf ietf
fast-reroute per-prefix enable area 0 prefix-priority high
fast-reroute per-prefix enable prefix-priority high
fast-reroute keep-all-paths
redistribute static
network 10.86.1.23 0.0.0.0 area 0
network 10.86.186.8 0.0.0.3 area 0
network 10.86.186.16 0.0.0.3 area 0
network 10.86.186.24 0.0.0.3 area 0
network 10.86.186.28 0.0.0.3 area 0
network 10.86.186.60 0.0.0.3 area 0
network 10.86.248.23 0.0.0.0 area 0
bfd all-interfaces
mpls ldp sync
!
today i tried the reload C9300 but i had no problems
05-20-2024 12:03 AM
As I and @Harold Ritter suspect
there is sync
you use LO as MPLS router-id and MPLS ldp need reachability of router-id to work, and so it need ospf which is not work since you run sync.
so fast solution is use static route for LO user as MPLS LDP router-id and this make MPLS work and follow by OSPF
try this way
MHM
05-20-2024 12:11 AM
in fact I configured a static route only for the LO and everything went back up, but what I don't understand is why it happens.
05-20-2024 12:19 AM
It like egg or chicken
The ospf depends on mpls to be up
The mpls depend of ospf to advertise LO to be UP
And this loop end in both not work.
So as workaround we use static route for LO use as mpls ldp router-id to make mpls up then ospg automatically follow mpls and be up too.
Goodluck
MHM
05-20-2024 09:14 AM
Indeed' holdtime can solution' I already try this in lab today' but the max metric is stop me.
I need to know the effect of max metric on both ospf and ldp.
Update you soon
Thanks
MHM
05-20-2024 09:21 AM - edited 05-20-2024 09:22 AM
Hi @MHM Cisco World ,
Configuring "mpls ldp igp sync holddown" definitely solves this issue.
I had a large service provider customer that run into this issue a long time ago. They had an aggregate static route configured on the edge devices and had "mpls ldp igp sync holddown" set to its default value (infinite). This caused an outage in their network. They set the "mpls ldp igp sync holddown" short value and the issue was fixed.
Regards,
05-20-2024 09:31 AM
Hi Mr @Harold Ritter I know holdtime but I need to confirm that LO is learn when the one side send it with max metric
so that why I postponed my suggestion BUT, since I have little time NOW I run lab and confirm that the LO that MPLS LDP use as router-ID is advertise by OSPF after holdtime is end, and the Peer can use it if there is no other path to this LO
I make holdtime 30 ms (it small I know)
the R1 advertise the 1.1.1.1 to R2, LO 1.1.1.1 is MPLS LDP router-id and you can see it metric is MAX still R2 use it since it dont have anyother path to LO.
HOPE this solve your issue
MHM
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