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VXLAN Underlay OSPF

VXLAN requires an underlay network so that VTEPs can reach each other. There are different routing protocols to choose from, and OSPF is one of them.

OSPF is widely adopted in LANs, WANs, and data centers. Many network engineers are familiar with it. Convergence is fast, which makes OSPF suitable as the routing protocol for your VXLAN underlay.

There are some discussions about whether OSPF is suitable for very large Clos topologies. This is related to the effect of flooding, the size of the LSDB, and the speed of SPF calculations. One “issue” with OSPF is that it does a complete SPF calculation when a link changes. This isn’t much of an issue with modern hardware and smaller topologies, but it might be a scalability issue when you have very large (Clos) topologies. There are ways to mitigate this, such as using multiple areas and summarization. It’s something to be aware of when you decide on the routing protocol for your VXLAN underlay. With smaller topologies, OSPF is a great choice.

When configuring OSPF, you should always use the point-to-point network type for your interfaces. The default network type is broadcast, which means that OSPF will do a DR/BDR election. This is unnecessary because while all interfaces between the spine and leaf devices are Ethernet, they are point-to-point links. When you use the point-to-point network type, OSPF won’t create type 2 LSAs, which also reduces the size of the database.

In many VXLAN lessons, like the VXLAN MP-BGP EVPN L2 VNI lesson, I used OSPF on the underlay with /24 prefixes. I do this on purpose and to keep it simple so we can focus on the VXLAN parts. This works and is simple, but it’s not very effective. There are however two better options to configure OSPF:

  • Use a /31 on all point-to-point links.
  • Use ip unnumbered on point-to-point links.

We’ll look at these two options to see how you can configure OSPF for the VXLAN underlay, which is similar to how you might configure it in a production network. We’ll only focus on the underlay network. We won’t configure the overlay network.

Configuration

Let’s start with the physical topology:

Vxlan Underlay Ospf Physical Topology

We have two spine and four leaf switches. I’m using Cisco NX-OS 9000v version 9.3(9) on all switches. We should start by setting the correct MTU. The highest possible MTU can be different depending on your platform and OS version. On these Cisco NX-OS switches, the highest possible MTU value is 9216.

Let’s configure it on the spine switches:

SPINE1 & SPINE2
(config)# interface Ethernet 1/1-4
(config-if-range)# mtu 9216

And also on the leaf switches:

LEAF1-LEAF4
(config)# interface Ethernet 1/1-2
(config-if-range)# mtu 9216

Now, we can focus on OSPF.

/31 Prefixes

On “normal” point-to-point links, you would use a /30 prefix. This means you’ll have:

  • Network address
  • Two usable IP addresses for hosts
  • Broadcast address

A /31 prefix only has two IP addresses and can be used for point-to-point links. This will save you a lot of IP addresses. Let’s look at an example.

Let’s say we have 4 spine switches and 20 leaf switches. This means we’ll have 4 x 20 = 80 point-to-point links:

  • 80 point-to-point links x 4 IP addresses ( /30 prefixes) = 320 IP addresses required for point-to-point links.
  • 80 point-to-point links x 2 IP addresses ( /31 prefixes) = 160 IP addresses required for point-to-point links.

Our switches also require loopback interfaces. We’ll need 4 for the spine switches and 20 for the leaf switches. That’s 24 IP addresses for loopbacks.

In total, we would need:

  • /30 prefixes: 344 IP addresses
  • /31 prefixes: 184 IP addresses

We’ll save quite some IP address space by using /31 prefixes. Here’s an example of what it could look like:

Vxlan Underlay Ospf 31 Two Spine Four Leafs

I took the 192.168.1.0/24 subnet and created many /31 prefixes for the physical interfaces. Let’s configure this on the switches.

Configurations

Want to take a look for yourself? Here, you will find the startup configuration of each device.

LEAF1

hostname LEAF1

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.3001
  ip address 192.168.1.1/31
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.3002
  ip address 192.168.1.9/31
  no shutdown

interface loopback0
  ip address 3.3.3.3/32

LEAF2

hostname LEAF2

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.4001
  ip address 192.168.1.3/31
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.4002
  ip address 192.168.1.11/31
  no shutdown

interface loopback0
  ip address 4.4.4.4/32

LEAF3

hostname LEAF3

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.5001
  ip address 192.168.1.5/31
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.5002
  ip address 192.168.1.13/31
  no shutdown

interface loopback0
  ip address 5.5.5.5/32

LEAF4

hostname LEAF4

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.6001
  ip address 192.168.1.7/31
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.6002
  ip address 192.168.1.15/31
  no shutdown

interface loopback0
  ip address 6.6.6.6/32

SPINE1

hostname SPINE1

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.1001
  ip address 192.168.1.0/31
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.1002
  ip address 192.168.1.2/31
  no shutdown

interface Ethernet1/3
  no switchport
  mac-address 0050.c253.1003
  ip address 192.168.1.4/31
  no shutdown

interface Ethernet1/4
  no switchport
  mac-address 0050.c253.1004
  ip address 192.168.1.6/31
  no shutdown

interface loopback0
  ip address 1.1.1.1/32

SPINE2

hostname SPINE2

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.2001
  ip address 192.168.1.8/31
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.2002
  ip address 192.168.1.10/31
  no shutdown

interface Ethernet1/3
  no switchport
  mac-address 0050.c253.2003
  ip address 192.168.1.12/31
  no shutdown

interface Ethernet1/4
  no switchport
  mac-address 0050.c253.2004
  ip address 192.168.1.14/31
  no shutdown

interface loopback0
  ip address 2.2.2.2/32
Configuring /31 IP addresses on interfaces is tedious and prone to errors. It’s a good idea to use network automation for this.

Now, let’s configure OSPF. We’ll enable the feature on all devices:

LEAF1-LEAF4, SPINE1 & SPINE2
(config)# feature ospf

Now, we can start the OSPF process and set the router ID:

SPINE1(config)# router ospf UNDERLAY
SPINE1(config-router)# router-id 1.1.1.1
SPINE2(config)# router ospf UNDERLAY
SPINE2(config-router)# router-id 2.2.2.2
LEAF1(config)# router ospf UNDERLAY
LEAF1(config-router)# router-id 3.3.3.3
LEAF2(config)# router ospf UNDERLAY
LEAF2(config-router)# router-id 4.4.4.4
LEAF3(config)# router ospf UNDERLAY
LEAF3(config-router)# router-id 5.5.5.5
LEAF4(config)# router ospf UNDERLAY
LEAF4(config-router)# router-id 6.6.6.6

We’ll use a named process and call it UNDERLAY. Now, let’s enable OSPF on the loopback interfaces:

LEAF1-LEAF4, SPINE1 & SPINE2
(config)# interface Loopback 0
(config-if)# ip router ospf UNDERLAY area 0.0.0.0

We’ll have to make sure we use the point-to-point network type on the physical interfaces. We’ll do this on the leaf switches:

LEAF1-LEAF4
(config)# interface Ethernet 1/1-2
(config-if-range)# ip ospf network point-to-point
(config-if-range)# ip router ospf UNDERLAY area 0.0.0.0

And the spine switches:

SPINE1 & SPINE2
(config)# interface Ethernet 1/1-4
(config-if-range)# ip ospf network point-to-point
(config-if-range)# ip router ospf UNDERLAY area 0.0.0.0

That completes the configuration.

Verification

Let’s check the OSPF process:

SPINE1# show ip ospf

 Routing Process UNDERLAY with ID 1.1.1.1 VRF default
 Routing Process Instance Number 1
 Stateful High Availability enabled
 Graceful-restart is configured
   Grace period: 60 state: Inactive 
   Last graceful restart exit status: None
 Supports only single TOS(TOS0) routes
 Supports opaque LSA
 Administrative distance 110
 Reference Bandwidth is 40000 Mbps
 SPF throttling delay time of 200.000 msecs,
   SPF throttling hold time of 1000.000 msecs, 
   SPF throttling maximum wait time of 5000.000 msecs
 LSA throttling start time of 0.000 msecs,
   LSA throttling hold interval of 5000.000 msecs, 
   LSA throttling maximum wait time of 5000.000 msecs
 Minimum LSA arrival 1000.000 msec
 LSA group pacing timer 10 secs
 Maximum paths to destination 8
 Number of external LSAs 0, checksum sum 0
 Number of opaque AS LSAs 0, checksum sum 0
 Number of areas is 1, 1 normal, 0 stub, 0 nssa
 Number of active areas is 1, 1 normal, 0 stub, 0 nssa
 Install discard route for summarized external routes.
 Install discard route for summarized internal routes.
 Number of new LSAs originated : 4
 Number of new LSAs received : 47
 RFC1583: Disabled, IOS Compatibility: Disabled
   Area BACKBONE(0.0.0.0) 
        Area has existed for 03:14:26
        Interfaces in this area: 5 Active interfaces: 5
        Passive interfaces: 0  Loopback interfaces: 1
        No authentication available
        SPF calculation has run 12 times
         Last SPF ran for 0.000440s
        Area ranges are
        Number of LSAs: 6, checksum sum 0x20dd9

OSPF is up and running. We can also check each interface:

SPINE1# show ip ospf interface Ethernet 1/1
 Ethernet1/1 is up, line protocol is up
    IP address 192.168.1.0/31
    Process ID UNDERLAY VRF default, area 0.0.0.0
    Enabled by interface configuration
    State P2P, Network type P2P, cost 40
    Index 2, Transmit delay 1 sec
    1 Neighbors, flooding to 1, adjacent with 1
    Timer intervals: Hello 10, Dead 40, Wait 40, Retransmit 5
      Hello timer due in 00:00:05
    No authentication
    Number of opaque link LSAs: 0, checksum sum 0
    Interface ospf state change count: 3

This tells us that OSPF is enabled on the interface and that the network type is point-to-point. Let’s check the neighbor adjacencies:

SPINE1# show ip ospf neighbors
 OSPF Process ID UNDERLAY VRF default
 Total number of neighbors: 4
 Neighbor ID     Pri State            Up Time  Address         Interface
 3.3.3.3           1 FULL/ -          00:12:45 192.168.1.1     Eth1/1 
 4.4.4.4           1 FULL/ -          00:06:57 192.168.1.3     Eth1/2 
 5.5.5.5           1 FULL/ -          00:06:56 192.168.1.5     Eth1/3 
 6.6.6.6           1 FULL/ -          00:06:55 192.168.1.7     Eth1/4
SPINE2# show ip ospf neighbors
 OSPF Process ID UNDERLAY VRF default
 Total number of neighbors: 4
 Neighbor ID     Pri State            Up Time  Address         Interface
 3.3.3.3           1 FULL/ -          00:08:30 192.168.1.9     Eth1/1 
 4.4.4.4           1 FULL/ -          00:14:15 192.168.1.11    Eth1/2 
 5.5.5.5           1 FULL/ -          00:14:15 192.168.1.13    Eth1/3 
 6.6.6.6           1 FULL/ -          00:14:14 192.168.1.15    Eth1/4

Each spine switch has four neighbor adjacencies, so that’s looking good. Let’s take a look at some routes:

SPINE1# show ip route ospf
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%' in via output denotes VRF 

2.2.2.2/32, ubest/mbest: 4/0
    *via 192.168.1.1, Eth1/1, [110/81], 00:08:52, ospf-UNDERLAY, intra
    *via 192.168.1.3, Eth1/2, [110/81], 00:09:03, ospf-UNDERLAY, intra
    *via 192.168.1.5, Eth1/3, [110/81], 00:08:59, ospf-UNDERLAY, intra
    *via 192.168.1.7, Eth1/4, [110/81], 00:08:59, ospf-UNDERLAY, intra
3.3.3.3/32, ubest/mbest: 1/0
    *via 192.168.1.1, Eth1/1, [110/41], 00:14:47, ospf-UNDERLAY, intra
4.4.4.4/32, ubest/mbest: 1/0
    *via 192.168.1.3, Eth1/2, [110/41], 00:09:03, ospf-UNDERLAY, intra
5.5.5.5/32, ubest/mbest: 1/0
    *via 192.168.1.5, Eth1/3, [110/41], 00:08:59, ospf-UNDERLAY, intra
6.6.6.6/32, ubest/mbest: 1/0
    *via 192.168.1.7, Eth1/4, [110/41], 00:08:59, ospf-UNDERLAY, intra
192.168.1.8/31, ubest/mbest: 1/0
    *via 192.168.1.1, Eth1/1, [110/80], 00:13:14, ospf-UNDERLAY, intra
192.168.1.10/31, ubest/mbest: 1/0
    *via 192.168.1.3, Eth1/2, [110/80], 00:09:03, ospf-UNDERLAY, intra
192.168.1.12/31, ubest/mbest: 1/0
    *via 192.168.1.5, Eth1/3, [110/80], 00:08:59, ospf-UNDERLAY, intra
192.168.1.14/31, ubest/mbest: 1/0
    *via 192.168.1.7, Eth1/4, [110/80], 00:08:59, ospf-UNDERLAY, intra

SPINE1 knows how to reach all loopback interfaces. We see the same thing on SPINE2:

SPINE2# show ip route ospf
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%' in via output denotes VRF 

1.1.1.1/32, ubest/mbest: 4/0
    *via 192.168.1.9, Eth1/1, [110/81], 00:09:12, ospf-UNDERLAY, intra
    *via 192.168.1.11, Eth1/2, [110/81], 00:09:23, ospf-UNDERLAY, intra
    *via 192.168.1.13, Eth1/3, [110/81], 00:09:19, ospf-UNDERLAY, intra
    *via 192.168.1.15, Eth1/4, [110/81], 00:09:19, ospf-UNDERLAY, intra
3.3.3.3/32, ubest/mbest: 1/0
    *via 192.168.1.9, Eth1/1, [110/41], 00:09:12, ospf-UNDERLAY, intra
4.4.4.4/32, ubest/mbest: 1/0
    *via 192.168.1.11, Eth1/2, [110/41], 00:14:52, ospf-UNDERLAY, intra
5.5.5.5/32, ubest/mbest: 1/0
    *via 192.168.1.13, Eth1/3, [110/41], 00:14:51, ospf-UNDERLAY, intra
6.6.6.6/32, ubest/mbest: 1/0
    *via 192.168.1.15, Eth1/4, [110/41], 00:14:51, ospf-UNDERLAY, intra
192.168.1.0/31, ubest/mbest: 1/0
    *via 192.168.1.9, Eth1/1, [110/80], 00:09:12, ospf-UNDERLAY, intra
192.168.1.2/31, ubest/mbest: 1/0
    *via 192.168.1.11, Eth1/2, [110/80], 00:14:52, ospf-UNDERLAY, intra
192.168.1.4/31, ubest/mbest: 1/0
    *via 192.168.1.13, Eth1/3, [110/80], 00:14:51, ospf-UNDERLAY, intra
192.168.1.6/31, ubest/mbest: 1/0
    *via 192.168.1.15, Eth1/4, [110/80], 00:14:51, ospf-UNDERLAY, intra

This is looking good. The spine switches know about all the loopback interfaces in our topology and have all required neighbor adjacencies. Let’s check one of the leaf switches:

LEAF1# show ip route ospf
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%' in via output denotes VRF 

1.1.1.1/32, ubest/mbest: 1/0
    *via 192.168.1.0, Eth1/1, [110/41], 00:08:16, ospf-UNDERLAY, intra
2.2.2.2/32, ubest/mbest: 1/0
    *via 192.168.1.8, Eth1/2, [110/41], 00:07:22, ospf-UNDERLAY, intra
4.4.4.4/32, ubest/mbest: 2/0
    *via 192.168.1.0, Eth1/1, [110/81], 00:07:32, ospf-UNDERLAY, intra
    *via 192.168.1.8, Eth1/2, [110/81], 00:07:22, ospf-UNDERLAY, intra
5.5.5.5/32, ubest/mbest: 2/0
    *via 192.168.1.0, Eth1/1, [110/81], 00:08:15, ospf-UNDERLAY, intra
    *via 192.168.1.8, Eth1/2, [110/81], 00:07:20, ospf-UNDERLAY, intra
6.6.6.6/32, ubest/mbest: 2/0
    *via 192.168.1.0, Eth1/1, [110/81], 00:07:25, ospf-UNDERLAY, intra
    *via 192.168.1.8, Eth1/2, [110/81], 00:07:22, ospf-UNDERLAY, intra

LEAF1 knows how to reach the different loopback interfaces of the other leaf switches. The other leaf switches would show a similar output.

Configurations

Want to take a look for yourself? Here, you will find the final configuration of each device.

LEAF1

hostname LEAF1

feature ospf

interface Ethernet1/1
  no switchport
  mtu 9216
  mac-address 0050.c253.3001
  ip address 192.168.1.1/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/2
  no switchport
  mtu 9216
  mac-address 0050.c253.3002
  ip address 192.168.1.9/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/3
  switchport access vlan 10

interface loopback0
  ip address 3.3.3.3/32
  ip router ospf UNDERLAY area 0.0.0.0

router ospf UNDERLAY
  router-id 3.3.3.3

LEAF2

hostname LEAF2

feature ospf

interface Ethernet1/1
  no switchport
  mtu 9216
  mac-address 0050.c253.4001
  ip address 192.168.1.3/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/2
  no switchport
  mtu 9216
  mac-address 0050.c253.4002
  ip address 192.168.1.11/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/3
  switchport access vlan 10

interface loopback0
  ip address 4.4.4.4/32
  ip router ospf UNDERLAY area 0.0.0.0

router ospf UNDERLAY
  router-id 4.4.4.4

LEAF3

hostname LEAF3

feature ospf

interface Ethernet1/1
  no switchport
  mtu 9216
  mac-address 0050.c253.5001
  ip address 192.168.1.5/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/2
  no switchport
  mtu 9216
  mac-address 0050.c253.5002
  ip address 192.168.1.13/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/3
  switchport access vlan 10

interface loopback0
  ip address 5.5.5.5/32
  ip router ospf UNDERLAY area 0.0.0.0

router ospf UNDERLAY
  router-id 5.5.5.5

LEAF4

hostname LEAF4

feature ospf

interface Ethernet1/1
  no switchport
  mtu 9216
  mac-address 0050.c253.6001
  ip address 192.168.1.7/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/2
  no switchport
  mtu 9216
  mac-address 0050.c253.6002
  ip address 192.168.1.15/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/3
  switchport access vlan 10

interface loopback0
  ip address 6.6.6.6/32
  ip router ospf UNDERLAY area 0.0.0.0

router ospf UNDERLAY
  router-id 6.6.6.6

SPINE1

hostname SPINE1

feature ospf

interface Ethernet1/1
  no switchport
  mtu 9216
  mac-address 0050.c253.1001
  ip address 192.168.1.0/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/2
  no switchport
  mtu 9216
  mac-address 0050.c253.1002
  ip address 192.168.1.2/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/3
  no switchport
  mtu 9216
  mac-address 0050.c253.1003
  ip address 192.168.1.4/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/4
  no switchport
  mtu 9216
  mac-address 0050.c253.1004
  ip address 192.168.1.6/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface loopback0
  ip address 1.1.1.1/32
  ip router ospf UNDERLAY area 0.0.0.0

router ospf UNDERLAY
  router-id 1.1.1.1

SPINE2

hostname SPINE2

feature ospf

interface Ethernet1/1
  no switchport
  mtu 9216
  mac-address 0050.c253.2001
  ip address 192.168.1.8/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/2
  no switchport
  mtu 9216
  mac-address 0050.c253.2002
  ip address 192.168.1.10/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/3
  no switchport
  mtu 9216
  mac-address 0050.c253.2003
  ip address 192.168.1.12/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface Ethernet1/4
  no switchport
  mtu 9216
  mac-address 0050.c253.2004
  ip address 192.168.1.14/31
  ip ospf network point-to-point
  ip router ospf UNDERLAY area 0.0.0.0
  no shutdown

interface loopback0
  ip address 2.2.2.2/32
  ip router ospf UNDERLAY area 0.0.0.0

router ospf UNDERLAY
  router-id 2.2.2.2

Unnumbered Interfaces

Let’s look at our second example. Instead of configuring IP addresses on the physical links, we can “borrow” the IP address from a loopback interface and use this for the OSPF neighbor adjacency. This saves us a lot of required IP addresses. Let’s look at an example.

Imagine we have 4 spine switches and 20 leaf switches, that’s 24 devices in total.

We’ll only need 24 IP addresses for the loopback interfaces and that’s it. That’s a big improvement over using /30 or /31 prefixes.

Let’s see how to configure this. Here is the topology:

Vxlan Underlay Ospf Ip Unnumbered Two Spine Four Leafs

We use the same topology as before, but this time, we only have IP addresses configured on the loopback interfaces.

Only a single unnumbered link between two devices (for example SPINE1 and LEAF1) is supported. If you have multiple physical links between two devices, you’ll need to configure a L3 port-channel and use that interface unnumbered.

Configurations

Want to take a look for yourself? Here, you will find the startup configuration of each device.

LEAF1

hostname LEAF1

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.3001
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.3002
  no shutdown

interface loopback0
  ip address 3.3.3.3/32

LEAF2

hostname LEAF2

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.4001
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.4002
  no shutdown

interface loopback0
  ip address 4.4.4.4/32

LEAF3

hostname LEAF3

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.5001
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.5002
  no shutdown

interface loopback0
  ip address 5.5.5.5/32

LEAF4

hostname LEAF4

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.6001
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.6002
  no shutdown

interface loopback0
  ip address 6.6.6.6/32

SPINE1

hostname SPINE1

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.1001
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.1002
  no shutdown

interface Ethernet1/3
  no switchport
  mac-address 0050.c253.1003
  no shutdown

interface Ethernet1/4
  no switchport
  mac-address 0050.c253.1004
  no shutdown

interface loopback0
  ip address 1.1.1.1/32

SPINE2

hostname SPINE2

interface Ethernet1/1
  no switchport
  mac-address 0050.c253.2001
  no shutdown

interface Ethernet1/2
  no switchport
  mac-address 0050.c253.2002
  no shutdown

interface Ethernet1/3
  no switchport
  mac-address 0050.c253.2003
  no shutdown

interface Ethernet1/4
  no switchport
  mac-address 0050.c253.2004
  no shutdown

interface loopback0
  ip address 2.2.2.2/32

Let’s configure OSPF. We’ll enable the feature first:

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