[c-nsp] Multihomed OTV on CSR Lab - Mac Address Issue

[Richard Clayton]

Hi Guys

I think I have the reason for the behavior in my lab.  I have the 'silent
host' issue which happens in labs but generally doesn't happen in live
networks.  For my host devices I used Cisco routers with an IP address on a
single interface, all these devices were doing is a ping and and ARP to a
single IP address.  In a production network these hosts would be
workstations and servers and would be a lot more chatty, generating
broadcast traffic.  When I drop the CSR1 site 1 WAN overlay the remote
Cisco host does not generate any new broadcast traffic, new broadcast
traffic would flood from the CSR1 site 2 across the overlay and eventually
into the 'customer' layer 2 at site 1.

So in summary, in a production network the hosts would generate enough
broadcast traffic to keep failover connectivity issues to a minimum.  In a
lab with silent hosts, you will have to wait 5 minutes for the 'customer'
layer 2 mac address table to age out before connectivity is restored.  For
info I used Cisco routers as end hosts because they were easy, quick and
lightweight to spin up.

I still don't fully understand why the OTV host doesn't generate a TCN as
documented so if anyone could get an answer on that it would be great.

For now I am happy to design OTV into my customer solution.

Thanks

Rick

On 26 January 2018 at 15:23, Richard Clayton <sledge121 at gmail.com> wrote:

> Hi Guys
>
> I have configured Multihomed OTV in a virtual lab on EVE-NG using Cisco
> CSR's.  The lab is 2 x CSR at one site both connected to layer2 switch and
> a single CSR at a remote site.
> Everything works good apart from one thing.  At the dual router site, when
> I drop the OTV WAN/Overlay interface on the active CSR R1, the remote mac
> appears in the R2 bridge-domain (as it should) but the 'customer' layer 2
> switch mac address table still show the mac address as facing the R1 LAN.
> After 5 minutes the mac table times out and traffic is then restored over
> the R2 path.
> Is there any way R2 can update the customer L2 switch when the remote mac
> moves over to it to make the failover quicker?
> I did read a Cisco article that said if spanning tree is enabled on the
> OTV router, it will send out a TCN which will update the L2, I have
> spanning tree enabled on the OTV routers but when I drop the OTV
> WAN/Overlay interface, it does not send out a TCN, I had wireshark running.
>
> Thanks
> Rick
>
>
> --
> If you try to reinvent the wheel you will end up with something non-round
> and should expect an uncomfortable ride. The wheel has no copyright.
> Richard Clayton - 17/11/2014.
>



-- 
If you try to reinvent the wheel you will end up with something non-round
and should expect an uncomfortable ride. The wheel has no copyright.
Richard Clayton - 17/11/2014.