Cisco EVN (Easy Virtual Network)

Yes to all of your config questions. I can ping across the trunk, but no neighborship. It is GNS3 with csr1000v (free trial) routers. The vrf config is good. It behaves as expected from the ISP router to the Bluex and Redx routers.

I did turn on ospf debugging and I see the hello going out, but nothing comes back.

Hello Don.

I’m not sure how else I can be of help. It looks to me to be a glitch within the GNS3 engine. If everything else is functioning, it is very strange. I will have @ReneMolenaar take a look and see if he has any suggestions.

Thanks!

Laz

Hi Rene,

I would like to understand why vrf Green gets all connected and ospf routes replicated from Red and Blue, however when you check vrf Blue route table, for example, only the connected route from Red (replicated from Green) is there, but not the ospf route:

ISP1#show ip route vrf Green (snippet only showing routes copied from vrf Blue & Red)

C   +    192.168.1.0/24 is directly connected, GigabitEthernet1
L        192.168.1.254/32 is directly connected, GigabitEthernet1
      192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks
C   +    192.168.2.0/24 is directly connected, GigabitEthernet2
L        192.168.2.254/32 is directly connected, GigabitEthernet2
O   + 192.168.3.0/24 
           [110/2] via 192.168.56.6 (Blue), 01:26:38, GigabitEthernet3.10
O   + 192.168.4.0/24 
           [110/2] via 192.168.56.6 (Red), 01:19:37, GigabitEthernet3.20
ISP1#show ip route vrf Blue (snippet only showing routes copied from Green/Red)


C   +    5.5.5.0/24 is directly connected, Loopback0  (copied from Green)
L        5.5.5.5/32 is directly connected, Loopback0
      192.168.2.0/32 is subnetted, 1 subnets
L   +    192.168.2.254 is directly connected, GigabitEthernet2 (copied from Green but originally a Red route)

I was also expecting to see this, since that is an originally ospf route in vrf Red that got copied to Green and since all Green routes are replicated to Blue, still don’t get why this one doesn’t make it.

O   + 192.168.4.0/24 
           [110/2] via 192.168.56.6 (Red), 01:19:37, GigabitEthernet3.20

Hi Mercedes,

Good question, I can’t think of any technical reason why those routes don’t show up but I think they did it on purpose. EVN is one of those “automatically” solutions (unlike VRF lite) and I think they do it so you don’t accidentally share routes from VRF X > Y > Z unintentionally.

If you look at vrf Blue on ISP1, it doesn’t have the entire 192.168.2.0/254 network from VRF Red but only 192.168.2.254 (its own IP address).

Rene

Hi not a big deal since all the configs work for me and I can lab this, but I am using the
c7200-adventerprisek9-mz.152-4.S3.image not a XE router and everything seems to work fine for me. Am I not running a “true” EVN? Thanks for any help you can give me!

Hi Kevin,

If the commands are supported and it works then it’s all good. I didn’t know the 7200 also supported this.

Rene

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Dear Rene, in your video explaining EVN, What kind of SSH/Telnet client are you using? The blue lined background caught my eyes lol

Oh and thanks for the easy and clear explanation of the topic, choosing red and blue client is really smart.

Hello Fady

Based on other answers that Rene has given, I believe he uses SecureCRT. The colours and backgrounds can be configured accordingly.

I hope this has been helpful!

Laz

Hello!
Can you please let me know the difference between:

ip vrf forwarding and vrf forwarding under interface configuration.

Hello Johnson

The vrf forwarding command can only be used under the interface configuration. You may be referring to the ip vrf forwarding command which can also be implemented in global configuration mode.

Cisco explains the difference like so:

In earlier Cisco IOS releases, you created a VRF to be applied only to an IPv4 address family (single-protocol VRF) by entering the ip vrf command. To activate the single-protocol VRF on an interface, you entered the ip vrf forwarding (interface configuration) command.

You can now define multiple address families under the same VRF or configure separate VRFs for each IPv4 or IPv6 address family by entering the vrf definition command. To activate the multiprotocol VRF on an interface, you enter the vrf forwarding command. A given VRF, identified by its name and a set of policies, can apply to both an IPv4 VPN and an IPv6 VPN at the same time. This VRF can be activated on a given interface, even though the routing and forwarding tables are different for the IPv4 and IPv6 protocols.

This has been taken from the following Cisco documentation:

I hope this has been helpful!

Laz

1 Like

In the VRF Lite lesson, a VRF was created with the ip vrf command, but in this lesson it’s vrf definition. What’s the difference between these?

Hello Jeremy

By using the ip vrf command, we are creating a single protocol VRF, namely using IPv4. The vrf definition command creates a VRF with multiprotocol support. So such a VRF can function using IPv4 and IPv6. Notice in this lesson that there is the added command address-family ipv4 which is required to specify the participating protocols, whereas under the ip vrf command, IP is already specified.

Essentially, both configurations are the same, from the moment that only IPv4 is being used.

I hope this has been helpful!

Laz

1 Like

My question is about a particular situation. What if we have another router in the middle, and we do not want any of its interfaces in any particular vrf but we do want his links to be used as VNET TRUNKS. Is there a way to accomplish such a task ?

I have tried to stick a router in the middle and have created two VRF’s on this router also enabled both interfaces connecting two neighboring routers as VNET TRUNKS.

These two remaining routers have the same vrf’s configured with the same VNET TAGS and enabled on some interfaces and if they were directly connected to each other they would have formed a VNET TRUNK no problem.

Than I have configured super simple OSPF to encompass all of the interfaces on the router in the middle and specific OSPF on both routers connecting to that middle one :slight_smile:

Unfortunately neighborships are not being formed and I am wandering what could I do to solve this. I did not really find any solution in Cisco’s docs for now, so decided to ask here. Sorry for the trouble …

Regards,
Kamil

Hello Kamil

The EVN configuration should indeed work with three routers in the core network. Take a look at this Cisco documentation especially Figure 3 within it:


When you create such a topology, keep the following in mind:

  1. You must create a VRF definition of RED and BLUE in all three ISP routers and include the VNET tags appropriately
  2. Employ the vnet trunk command on all intervening interfaces within the core network including the two interfaces connecting to ISP1 and ISP2, that is, the ISP routers connected to the customer equipment.
  3. Configure OSPF on all three ISP routers such that the included networks in OSPF are those of the core interfaces (those not connecting to end equipment) and are included in both the RED and BLUE OSPF configuration.

If you can get OSPF to function between ISP1 and ISP2 in the original topology (without the third router) then you should be able to get the neighborhood relation up and running between ISP1 and the intervening router, and the intervening router and ISP 2.

I hope this has been helpful!

Laz

Hello Lazaros :slight_smile:

Thank you a lot for this nice reply, I think that I have already tried doing it in a similar way my friend although I am going to give it another bash tonight after I finish with revising BGP :slight_smile:

Kind Regards,
Kamil

Hello Kamil

Great, and thanks for the reply. Let us know your results when you make your second attempt.

Laz

Hello Laz,

Does EVN supports ipv6 ?

Thanks,
Sachin

Hello Sachin

According to Cisco, IPv6 is not supported on an EVN trunk, except on vnet global. This is a predefined EVN which refers to the global routing contect and corresponds to the default RIB. For more information about EVN and it’s support or IPv6, take a look at this documentation:

I hope this has been helpful!

Laz

Hi Laz,
evn is still usefull ?

Thanks ,
Heriberto

Hello Heriberto

EVN is still useful especially when running multiple isolated networks end-to-end over the same L3 infrastructure. Many of the benefits of this technology can be found at the following Cisco documentation.

I hope this has been helpful!

Laz