NX-OS OSPF Routing - Directly on Ethernet Interface vs. VLAN Interface

[mbrown-revitycu]

We are encountering an issue with setting up OSPF routing on two Nexus9000 switches we recently put into service.

We have several branch locations in our network. Each has its own branch router or L3 device. These devices use OSPF to form neighbor relationships.

When we first setup the two Nexus9000 devices, we attempted to set up the OSPF routing on a VLAN interface. This interface was set up on both devices with HSRP applied.

The config was very much like this:

Nexus A

interface Vlan990
description CharterMPLS
no shutdown
no ip redirects
ip address 172.16.99.237/24
no ipv6 redirects
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 3 keygoeshere
no ip ospf passive-interface
ip router ospf 10 area 0.0.0.0
hsrp 90
priority 150
timers 1 3
ip 172.16.99.236

Nexus B

interface Vlan990
description CharterMPLS
no shutdown
no ip redirects
ip address 172.16.99.238/24
no ipv6 redirects
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 3 keygoeshere
no ip ospf passive-interface
ip router ospf 10 area 0.0.0.0
hsrp 90
priority 150
timers 1 3
ip 172.16.99.236

Ethernet interface for connection:

interface Ethernet1/6
switchport
switchport mode trunk
switchport trunk allowed vlan 990

Under this configuration the Nexus devices would not form neighbor relationships with the other devices in the network.

However, if we configured an ethernet interface directly with the OSPF info, neighboring came right up and works perfectly.

Config on the interface:

interface Ethernet1/45
description CHARTER_MPLS
no ip redirects
ip address 172.16.99.236/24
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 3 keygoeshere
no ip ospf passive-interface
ip router ospf 10 area 0.0.0.0
no shutdown

Do we have errors in our config somewhere such that setting OSPF on the VLAN interface causes the neighbor relationships to not be built?

Thanks!

[MHM Cisco World]

sorry I dont understand the connection between two NSK and other device 
can you draw topolgy 

MHM

[mbrown-revitycu]

This is the WAN topology.

Each branch has an OSPF network configured on its local router/L3 switch. This router/L3 switch connects to a Spectrum WAN router at each branch. The OSPF connection is made across the private WAN. OSPF subnet is 172.16.99.0/24, each router has an interface with an address in this subnet.

This is our basic LAN topology at each branch.

The Silverpeak SD-WAN devices at each branch uses both the local internet connection and the private WAN connection to form tunnels to Silverpeak devices at other branches.

The Silverpeak device has an interface that is in the same 172.16.99.0/24 subnet. This interface uses the interface on the router/L3 switch as next hop. OSPF is still being done by the router/L3 switch.

Hopefully this helpful.

Thanks!

[paul driver]

Hello

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@mbrown-revitycu wrote:

under this configuration the Nexus devices would not form neighbor relationships with the other devices in the network.However, if we configured an ethernet interface directly with the OSPF info, neighboring came right up and works perfectly.

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Note: When you have opsf on a SVI, the mtu needs to have parity with the L2 interface associated with the L3 interface and with any other ospf peer otherwise the adjacency WILL fail

sh run ospf
sh ip ospf interface vlan 900
sh int vlan 900 | in MTU
sh int eth1/6 | in MTU
clear ip ospf event-history adjacency
clear ip ospf neighbor *
sh ip ospf event-history adjacency | in mtu

Edited
Just noticed @Giuseppe Larosa  has suggested the same thing  <->  CHECK YOUR MTU !