The goal of this article will be to provide you with the required steps to build a Virtual eXtensible LAN Ethernet VPN (VXLAN EVPN) fabric using the Cisco NXOS-9000v.
The topology will be built using various protocols, so before we dive in let's look at the various protocols, some background and how they fit together.
Note: The NXOS version used throughout this guide is 7.0(3)I7(1).
VXLAN (Virtual eXtensible LAN) is a network virtualization overlay protocol that was created to address some of the challenges seen within traditional networks, such as,
Addressing VLAN scalability issues due to being limited to 4094 VLANs by adding a 24-bit segment ID and increasing the number of available IDs to 16 million.
Flexible placement of multi-tenant segments throughout the data center. Tenant workload can be placed across physical segments in the data center.
Traffic can be routed over an L3 fabric removing the requirement for STP/legacy L2 fabrics.
VXLAN works via the use of VTEP's (Virtual Tunnel Endpoint). VTEP's encapsulate the original frame (aka 'MAC-in-UDP', see Figure 1). The packet is then sent to the remote VTEP over the underlying network. The remote VTEP then removes the encapsulation headers and forwards the original frame onto its destination.
Figure 1 - VXLAN header.
VXLAN natively operates on a flood-n-learn based mechanism, in which BUM (Broadcast, Unknown Unicast, Multicast) traffic in a given VXLAN network is sent to every VTEP that has membership in that network. There are two ways to send such traffic - IP multicast or via Head-end Replication (unicast).
Flood-and-learn allows each peer VTEP to perform the following.
- End-host learning by decapsulating the packet and performing MAC learning via the inner frame.
- Peer discovery via the inner source MAC to outer source IP (source VTEP).
From this information reverse traffic can be unicasted back towards the previously learnt peer.
To minimize the extent to which flooding needs to occur, EVPN was defined by IETF as the standards-based control plane for VXLAN overlays. EVPN is an extension (i.e address family) of MP-BGP (Multi-Protocol BGP) that allows for the MAC and IP of end-hosts behind VXLAN VTEPs to be advertised and exchanged.
One key point to note, even with an EVPN control plane, VXLAN flood and learn will still be used, however greatly minimized. This is because EVPN will exchange known end-hosts, i.e. end-hosts that are populated within the destination MAC table. Only if the host is unknown will F&L be performed.
The topology we will be building will be based around 2 layers - the underlay and the overlay.
The underlay will provide connectivity (aka a fabric) between each spine and leaf. This connectivity will later be used by the overlay for BGP-EVPN and VXLAN (i.e VTEP-to-VTEP communication). The protocols we will configure within the underlay are:
- OSPF (IGP) - Provides loopback reachability between all nodes (leaf/spine).
- PIM (IP Multicast) - For VXLAN flood-and-learn.
The overlay will send encapsulated traffic over the underlay network. The protocols we will configure within the overlay are:
- VXLAN - Encapsulates/decapsulates traffic between VTEPs i.e. the dataplane.
- BGP-EVPN - Operates as the control plane to distribute end-host and VTEP reachability information.
Our topology will also be configured to use Distributed IP Anycast Gateway and ARP Suppression/
Figure 2 - Topology Overview.
There are a few limitations with the version of NXOSv-9000 we will be using. Therefore the following will not be configured within this fabric:
- Jumbo frames on the L2 links (i.e edge ports)
- PIM BiDir
Various commands are different between the NXOSv-9000 to standard NXOS. The key command to note is
show system internal l2fwder mac which should be used instead of
show mac address-table.
The first part to our topology will be to build the underlay fabric. This will be based upon the following:
- Spine and Leaf topology to provide equidistant reachability and scalability.
- An OSPF IGP to provide connectivity between loopbacks.
- IP Multicast PIM-SM to reduce the flood-and-learn traffic upon the network.
- Unnumbered interfaces (sourced from lo0). This will allow for easier (templated) configurations.
- Lo0 reachability across the fabric for BGP peering.
- Jumbo frames upon all links to reduce ethernet header overhead.
Let's begin ...
First of all we will configure each of the links within the underlay. The configuration will:
- Turn each link to Layer 3.
- Enable the link.
- Enable jumbo frames.
interface Ethernet1/1-X no switchport mtu 9216 no shutdown
The validation will be to check that each of the interfaces shows as connected.
nx-osv9000-1# show int status -------------------------------------------------------------------------------- Port Name Status Vlan Duplex Speed Type -------------------------------------------------------------------------------- mgmt0 OOB Management connected routed full 1000 -- Eth1/1 to nx-osv9000-3 connected routed full 1000 10g Eth1/2 to nx-osv9000-4 connected routed full 1000 10g Eth1/3 to nx-osv9000-5 connected routed full 1000 10g Eth1/4 to nx-osv9000-6 connected routed full 1000 10g
Next we configure OSPF as the IGP for connectivity between loopbacks. This will be based upon a single OSPF area, also each OSPF interface will be configured as a Point-to-Point network type in order to reduce the amount of LSA's required on the network, and also within the LSDB. Details of the loopback addresses are shown below:
Figure 3 - OSPF Underlay.
feature ospf router ospf OSPF_UNDERLAY_NET log-adjacency-changes interface Ethernet1/1-4 medium p2p ip unnumbered loopback0 ip router ospf OSPF_UNDERLAY_NET area 0.0.0.0 interface loopback0 description Loopback ip address 192.168.0.X/32 ip router ospf OSPF_UNDERLAY_NET area 0.0.0.0
feature ospf router ospf OSPF_UNDERLAY_NET log-adjacency-changes interface Ethernet1/1-2 medium p2p ip unnumbered loopback0 ip router ospf OSPF_UNDERLAY_NET area 0.0.0.0 interface loopback0 description Loopback ip address 192.168.0.X/32 ip router ospf OSPF_UNDERLAY_NET area 0.0.0.0
The validation is pretty straight forward. We check the OSPF neighbor states, the RIB for the OSPF learned routes and perform a quick ping to confirm Lo0 connectivity.
nx-osv9000-1# show ip ospf neighbors OSPF Process ID OSPF_UNDERLAY_NET VRF default Total number of neighbors: 4 Neighbor ID Pri State Up Time Address Interface 192.168.0.3 1 FULL/ - 00:35:35 192.168.0.3 Eth1/1 192.168.0.4 1 FULL/ - 00:35:36 192.168.0.4 Eth1/2 192.168.0.5 1 FULL/ - 00:35:36 192.168.0.5 Eth1/3 192.168.0.6 1 FULL/ - 00:35:35 192.168.0.6 Eth1/4 nx-osv9000-1# show ip route ospf-OSPF_UNDERLAY_NET IP Route Table for VRF "default" '*' denotes best ucast next-hop '**' denotes best mcast next-hop '[x/y]' denotes [preference/metric] '%<string>' in via output denotes VRF <string> 192.168.0.2/32, ubest/mbest: 4/0 *via 192.168.0.3, Eth1/1, [110/81], 00:33:29, ospf-OSPF_UNDERLAY_NET, intra *via 192.168.0.4, Eth1/2, [110/81], 00:33:29, ospf-OSPF_UNDERLAY_NET, intra *via 192.168.0.5, Eth1/3, [110/81], 00:33:29, ospf-OSPF_UNDERLAY_NET, intra *via 192.168.0.6, Eth1/4, [110/81], 00:33:29, ospf-OSPF_UNDERLAY_NET, intra 192.168.0.3/32, ubest/mbest: 1/0 *via 192.168.0.3, Eth1/1, [110/41], 00:35:20, ospf-OSPF_UNDERLAY_NET, intra via 192.168.0.3, Eth1/1, [250/0], 00:35:09, am 192.168.0.4/32, ubest/mbest: 1/0 *via 192.168.0.4, Eth1/2, [110/41], 00:35:21, ospf-OSPF_UNDERLAY_NET, intra via 192.168.0.4, Eth1/2, [250/0], 00:35:07, am 192.168.0.5/32, ubest/mbest: 1/0 *via 192.168.0.5, Eth1/3, [110/41], 00:35:21, ospf-OSPF_UNDERLAY_NET, intra via 192.168.0.5, Eth1/3, [250/0], 00:35:11, am 192.168.0.6/32, ubest/mbest: 1/0 *via 192.168.0.6, Eth1/4, [110/41], 00:35:18, ospf-OSPF_UNDERLAY_NET, intra via 192.168.0.6, Eth1/4, [250/0], 00:35:18, am nx-osv9000-1# ping 192.168.0.5 interval 1 count 2 PING 192.168.0.5 (192.168.0.5): 56 data bytes 64 bytes from 192.168.0.5: icmp_seq=0 ttl=254 time=3.09 ms 64 bytes from 192.168.0.5: icmp_seq=1 ttl=254 time=3.029 ms
PIM is configured for the VXLAN Flood and Learn mechanism. Our multicast configuration will be based upon the following:
- PIM Sparse-Mode.
- Anycast RP to provide RP (Rendezvous Point) redundancy.
- Each Spine configured as an RP (Rendezvous Point).
Figure 4 - Underlay Multicast PIM.
feature pim ip pim rp-address 18.104.22.168 group-list 22.214.171.124/4 ip pim ssm range 126.96.36.199/8 ip pim anycast-rp 188.8.131.52 192.168.0.1 ip pim anycast-rp 184.108.40.206 192.168.0.2 interface loopback1 ip address 220.127.116.11/32 ip router ospf OSPF_UNDERLAY_NET area 0.0.0.0 ip pim sparse-mode interface loopback0 ip pim sparse-mode int Ethernet1/1-4 ip pim sparse-mode
feature pim ip pim rp-address 18.104.22.168 group-list 22.214.171.124/4 ip pim ssm range 126.96.36.199/8 interface loopback0 ip pim sparse-mode interface Ethernet1/1 ip pim sparse-mode interface Ethernet1/2 ip pim sparse-mode
To validate we check that PIM is successfully enabled on the interfaces and that the Anycast RP is operational.
nx-osv9000-1# show ip pim interface brief PIM Interface Status for VRF "default" Interface IP Address PIM DR Address Neighbor Border Count Interface Ethernet1/1 192.168.0.1 192.168.0.3 1 no Ethernet1/2 192.168.0.1 192.168.0.4 1 no Ethernet1/3 192.168.0.1 192.168.0.5 1 no Ethernet1/4 192.168.0.1 192.168.0.6 1 no loopback0 192.168.0.1 192.168.0.1 0 no loopback1 188.8.131.52 184.108.40.206 0 no nx-osv9000-1# show ip pim rp PIM RP Status Information for VRF "default" BSR disabled Auto-RP disabled BSR RP Candidate policy: None BSR RP policy: None Auto-RP Announce policy: None Auto-RP Discovery policy: None Anycast-RP 220.127.116.11 members: 192.168.0.1* 192.168.0.2 RP: 18.104.22.168*, (0), uptime: 01:56:56 priority: 255, RP-source: (local), group ranges: 22.214.171.124/4
For more information about PIM, see https://www.packetflow.co.uk/what-is-pim-protocol-independent-multicast
Network Virtual Endpoint (NVE)
The NVE (Network Virtual Endpoint) is a logical interface where the encapsulation and de-encapsulation occurs.
We will configure a single NVE upon each leaf only. In addition, the NVE will use a source address of Lo0.
interface nve1 no shutdown host-reachability protocol bgp source-interface loopback0
nx-osv9000-3# show interface nve 1 nve1 is up admin state is up, Hardware: NVE MTU 9216 bytes Encapsulation VXLAN Auto-mdix is turned off RX ucast: 0 pkts, 0 bytes - mcast: 0 pkts, 0 bytes TX ucast: 0 pkts, 0 bytes - mcast: 0 pkts, 0 bytes
As previously mentioned EVPN will be used as the control plane for the VXLAN data plane; distributing the address information of our end-hosts (IP, MAC) so that the VXLAN flood-and-learn behaviour can be reduced.
The BGP-EVPN control plane will be based on the following:
- iBGP based adjacencies.
- Each spine acting as a BGP route reflector.
Figure 5 - EVPN BGP Overlay.
nv overlay evpn feature bgp feature fabric forwarding feature interface-vlan feature vn-segment-vlan-based feature nv overlay router bgp 64520 log-neighbor-changes address-family ipv4 unicast address-family l2vpn evpn retain route-target all template peer VXLAN_LEAF remote-as 64520 update-source loopback0 address-family ipv4 unicast send-community extended route-reflector-client soft-reconfiguration inbound address-family l2vpn evpn send-community send-community extended route-reflector-client neighbor 192.168.0.3 inherit peer VXLAN_LEAF neighbor 192.168.0.4 inherit peer VXLAN_LEAF neighbor 192.168.0.5 inherit peer VXLAN_LEAF neighbor 192.168.0.6 inherit peer VXLAN_LEAF
nv overlay evpn feature bgp feature fabric forwarding feature interface-vlan feature vn-segment-vlan-based feature nv overlay router bgp 64520 log-neighbor-changes address-family ipv4 unicast address-family l2vpn evpn template peer VXLAN_SPINE remote-as 64520 update-source loopback0 address-family ipv4 unicast send-community extended soft-reconfiguration inbound address-family l2vpn evpn send-community send-community extended neighbor 192.168.0.1 inherit peer VXLAN_SPINE neighbor 192.168.0.2 inherit peer VXLAN_SPINE
For the verification, we first ensure that the address family is enabled. Then we check that the BGP adjacencies are established. If this was not the case then the state would be shown (in other words the state is only shown when the peering is not fully established).
nx-osv9000-3# show ip bgp neighbors 192.168.0.1 | inc "Address family L2VPN EVPN" Address family L2VPN EVPN: advertised received
nx-osv9000-3# show bgp l2vpn evpn summary BGP summary information for VRF default, address family L2VPN EVPN BGP router identifier 192.168.0.3, local AS number 64520 BGP table version is 24, L2VPN EVPN config peers 2, capable peers 2 5 network entries and 10 paths using 1424 bytes of memory BGP attribute entries [10/1600], BGP AS path entries [0/0] BGP community entries [0/0], BGP cluster list entries [6/24] Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 192.168.0.1 4 1 58 55 24 0 0 00:46:30 3 192.168.0.2 4 1 58 55 24 0 0 00:46:10 3
Now that we have our underlay running, and an EVPN control plane functional we will add some small enhancements to our topology.
Distributed IP Anycast Gateway
The distributed IP anycast gateway is a feature that allows you to configure the default gateway of a subnet across multiple ToR's using the same IP and MAC address. This solves the issue of traffic tromboning, seen in traditional networks by ensuring the end-host's default gateway is at its closest point. This, in turn, provides optimal traffic forwarding within the fabric.
To configure this feature the anycast gateway MAC is defined and the feature added to the relevant SVI interface. Like so:
fabric forwarding anycast-gateway-mac 0000.0010.0999 interface vlan <vlan_id> fabric forwarding mode anycast-gateway
To validate we will checking the fabric forwarding mode. Like so:
nx-osv9000-3# show fabric forwarding internal topo-info | grep Anycast Forward Mode : Anycast Gateway
ARP suppression is a feature that reduces the flooding of ARP request broadcasts upon the network. ARP suppression is enabled on a per VNI basis. Once enabled, VTEPs maintain an ARP suppression cache table for known IP hosts and their associated MAC addresses in the VNI segment. 
At the point an end-host sends an ARP request, the local VTEP intercepts the ARP request and checks its ARP suppression cache for the IP. At this point, one of 2 things will happen:
- Hit - If there is a match within the cache - the local VTEP sends an ARP response on behalf of the remote end host.
- Miss - If the local VTEP doesn't have the ARP-resolved IP address in its ARP suppression table, it floods the ARP request to the other VTEPs in the VNI.
The configuration is pretty straightforward, we enable the tcam region and then add the
suppress-arp command to each VNI that we want to suppress ARP upon. Like so:
hardware access-list tcam region arp-ether 256 interface nve1 ! member vni <vni> suppress-arp
Note: You may find when configuring the tcam region that you receive an error much like this:
Warning: Please configure TCAM region for Ingress ARP-Ether ACL for ARP suppression to work.
If so you can edit one of the other regions to make space:
hardware access-list tcam region vpc-convergence 0
To validate we can check the arp suppression cache, after issuing some pings from our end hosts. Within this table, we will check for the entries learnt, shown under the
nx-osv9000-3# show ip arp suppression-cache detail Flags: + - Adjacencies synced via CFSoE L - Local Adjacency R - Remote Adjacency L2 - Learnt over L2 interface PS - Added via L2RIB, Peer Sync RO - Dervied from L2RIB Peer Sync Entry Ip Address Age Mac Address Vlan Physical-ifindex Flags Remote Vtep Addrs 10.10.1.1 00:00:57 fa16.3e94.17d1 10 Ethernet1/3 L 10.10.1.2 02:02:38 fa16.3e0f.521e 10 (null) R 192.168.0.5
L2 Bridging/L3 Routing
With the EVPN VXLAN fabric built, we can now turn our attention to the configuration required to perform L2 bridging (L2VNI) and L3 routing (L3VNI) from our end hosts.
For the VNI numbers and for further clarity on how our topology will look once configured, see below:
Figure 6 - L2VNI/L3VNI's.
Once configured, the traffic flows (intra-VNI and inter-VNI), will look like the below:
Figure 7 - L2VNI/L3VNI Traffic Flows.
L2 bridging aka the bridging of traffic (L2 frames) between end-hosts on the same VNI will be achieved via the L2VNI.
Leafs (NXOS-3 + NXOS-5)
fabric forwarding anycast-gateway-mac 0000.0011.1234 vlan 10 vn-segment 100010 interface Vlan10 no shutdown ip address 10.10.1.254/24 fabric forwarding mode anycast-gateway interface nve1 ! member vni 100010 suppress-arp mcast-group 126.96.36.199 evpn vni 100010 l2 rd auto route-target import auto route-target export auto
Leafs (NXOS-4 and NXOS-6)
fabric forwarding anycast-gateway-mac 0000.0011.1234 vlan 20 vn-segment 100020 interface Vlan20 no shutdown ip address 10.20.1.254/24 fabric forwarding mode anycast-gateway interface nve1 ! member vni 100020 suppress-arp mcast-group 188.8.131.52 evpn vni 100020 l2 rd auto route-target import auto route-target export auto
To validate we can view the EVPN routes learnt against one of the L2VNI's. Once done we can check connectivity.
nx-osv9000-3# show bgp l2vpn evpn vni-id 100010 BGP routing table information for VRF default, address family L2VPN EVPN BGP table version is 5644, Local Router ID is 192.168.0.3 Status: s-suppressed, x-deleted, S-stale, d-dampened, h-history, *-valid, >-best Path type: i-internal, e-external, c-confed, l-local, a-aggregate, r-redist, I-injected Origin codes: i - IGP, e - EGP, ? - incomplete, | - multipath, & - backup Network Next Hop Metric LocPrf Weight Path Route Distinguisher: 192.168.0.3:32777 (L2VNI 100010) *>i::::[fa16.3e0f.521e]::[0.0.0.0]/216 192.168.0.5 100 0 i *>l::::[fa16.3e94.17d1]::[0.0.0.0]/216 192.168.0.3 100 32768 i *>i::::[fa16.3e0f.521e]::[10.10.1.2]/272 192.168.0.5 100 0 i *>l::::[fa16.3e94.17d1]::[10.10.1.1]/272 192.168.0.3 100 32768 i
cisco@server-1:~$ sudo mtr --report 10.10.1.2 Start: Wed Jan 16 22:23:41 2019 HOST: server-1 Loss% Snt Last Avg Best Wrst StDev 1.|-- 10.10.1.2 0.0% 10 27.0 18.0 13.7 27.0 4.0
In order to forward traffic between VNIs, we will configure an L3VNI. Traffic will be routed to the L3 VNI within the leaf when destined for another VNI. The packet will then be sent (bridged) over the L3 VNI to the remote node, where the traffic will again be routed to the destination VNI. In other words, the traffic is routed, bridged and then routed.
Below shows an example of a capture packet from one of the leaf to spine uplinks. As you can see the packet is sent over the L3VNI (VNI 100999).
Figure 8 - ICMP Packet between VNIs over L3VNI
vlan 999 vn-segment 100999 vrf context TENANT1 vni 100999 rd auto address-family ipv4 unicast route-target both auto route-target both auto evpn interface Vlan999 no shutdown vrf member TENANT1 ip forward interface nve1 ! member vni 100999 associate-vrf
Leafs (NXOS-3 + NXOS-5)
router bgp 64520 vrf TENANT1 log-neighbor-changes address-family ipv4 unicast network 10.10.1.0/24 advertise l2vpn evpn
Leafs (NXOS-4 + NXOS-6)
router bgp 64520 vrf TENANT1 log-neighbor-changes address-family ipv4 unicast network 10.20.1.0/24 advertise l2vpn evpn
To validate we can view the EVPN routes learnt against the L3VNI. Once done we can check connectivity.
nx-osv9000-3# show bgp l2vpn evpn vni-id 100999 BGP routing table information for VRF default, address family L2VPN EVPN BGP table version is 5644, Local Router ID is 192.168.0.3 Status: s-suppressed, x-deleted, S-stale, d-dampened, h-history, *-valid, >-best Path type: i-internal, e-external, c-confed, l-local, a-aggregate, r-redist, I-injected Origin codes: i - IGP, e - EGP, ? - incomplete, | - multipath, & - backup Network Next Hop Metric LocPrf Weight Path Route Distinguisher: 192.168.0.3:3 (L3VNI 100999) *>i::::[fa16.3e0f.521e]::[10.10.1.2]/272 192.168.0.5 100 0 i *>i::::[fa16.3e34.693a]::[10.20.1.2]/272 192.168.0.6 100 0 i *>i::::[fa16.3ec5.7233]::[10.20.1.1]/272 192.168.0.4 100 0 i * i::::[10.10.1.0]:[0.0.0.0]/224 192.168.0.5 100 0 i *>l 192.168.0.3 100 32768 i * i::::[10.20.1.0]:[0.0.0.0]/224 192.168.0.6 100 0 i *>i 192.168.0.4 100 0 i
cisco@server-1:~$ sudo mtr --report 10.20.1.1 Start: Wed Jan 16 22:28:20 2019 HOST: server-1 Loss% Snt Last Avg Best Wrst StDev 1.|-- 10.10.1.254 0.0% 10 4.7 4.6 3.5 5.7 0.6 2.|-- 10.20.1.254 0.0% 10 22.6 14.3 11.4 22.6 3.6 3.|-- 10.20.1.1 0.0% 10 17.4 19.0 15.6 27.1 3.1
Phew! We made it. As you can see there is a lot to configure, with many layers and protocols to take into account. I hope you enjoyed this tutorial, you can find all the final configurations, plus VIRL topology file at:
If you are interested in learning more about EVPN I would highly recommend the heading over to ipspace.net and checking out their range of networking courses.
"[ VXLAN ]: Are VXLANs Really the Future of Data Center Networks ...." 1 Dec. 2017, https://www.serro.com/vxlan-vxlan-really-future-data-center-networks/. Accessed 4 Jan. 2019. ↩︎
"Cisco Programmable Fabric with VXLAN BGP EVPN Configuration ...." 18 Jul. 2018, https://www.cisco.com/c/en/us/td/docs/switches/datacenter/pf/configuration/guide/b-pf-configuration/Introducing-Cisco-Programmable-Fabric-VXLAN-EVPN.html. Accessed 11 Jan. 2019. ↩︎
"Deploy a VXLAN Network with an MP-BGP EVPN Control Plane - Cisco." https://www.cisco.com/c/en/us/products/collateral/switches/nexus-7000-series-switches/white-paper-c11-735015.pdf. Accessed 4 Jan. 2019. ↩︎
"EVPN MPLS with ARP suppression - Cisco Community." 1 Sep. 2017, https://community.cisco.com/t5/xr-os-and-platforms/evpn-mpls-with-arp-suppression/td-p/3179016. Accessed 14 Jan. 2019. ↩︎
"EVPN MPLS with ARP suppression - Cisco Community." 1 Sep. 2017, https://community.cisco.com/t5/xr-os-and-platforms/evpn-mpls-with-arp-suppression/td-p/3179016. Accessed 14 Jan. 2019. ↩︎