PPPoe DMVPN mtu

[Mario Lessard]

Hi,

     I have a problem with all PPPoe spoker on my network with DMVPN. The problem is the stability of the tunnel DMVPN. All spoker with PPPoe I have a problem. 

When I do a ping on the spoker to the hub like this:

ping [dest IP Hub] sou [local IP tunnel] I have only 50% of success. 

In spoker log I have this message:

%DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor X.X.X.X (Tunnel2) is down: Peer Termination received

I'm pretty sure it's related with mtu setting. Only int tunnel 2 on spoker I try to play with ip mtu and ip tcp adjust-mss size. No success

But is it normal if in int dialer1 I set the mtu to 1492 and with I do a sh int dialer 1 the mtu is 1500?

I don't know what is the right recipe in this case when I have multiple spoker not all PPPoe with the hub? Do I have to create an other DMVPN just for PPPoe spoker? If yes, what is the parameter I have to do for PPPoe with DMVPN. Do I have to set the mtu on tunnel port? Both place, hub and spoker? Etc....

Because if I use GRE with VPN on a remote where PPPoe is install, I don't have a problem anymore. For the simplicity of the code and maintenance, I prefer to use DMVPN for sure. So, if it's possible to configure it it will be nice. 

Thank you

[Francesco Molino]

Hi

You are facing some issues because there first of all 40 bytes to add to the initial size (TCP payload + IP header) and another 28 bytes for GRE; You're oversizing the 1500 MTU limit

I would suggest to use the ip tcp adjust-mss command and configure like : ip tcp adjust-mss 1360 under the dialer interface

Thanks

PS: Please don't forget to rate and mark as correct answer if this solved your issue

[Mario Lessard]

Thanks for the answer,

Presently, under dialer interface the ip mtu is 1492 and the ip tcp adjust-mss 1360. I still to receive the log Peer termination received and the ping from tunnel interface ip address is 50% of success. 

Presently, under tunnel interface I remove all settings regards mtu. Everything is by default. 

Any suggestion?

Thank you

[Francesco Molino]

Hi

Usually we set a mtu of 1400 for dmvpn. And mss is mtu - 40 = 1360

You can, also test the maximum of data you can send over the tunnel by using the command:

ping src-tun-ip sou dst-tun-ip df-bit size 1360.

You can increase this number by 10 on each test to see where is the limit. 

On my customer environment, with pppoe and dmvpn, with mtu as 1400 it works fine. 

Thanks 

PS: Please don't forget to rate and mark as correct answer if this solved your issue 

[Mario Lessard]

Hi, 

   Do I have to set this mtu on the virtual port for the tunnel? On the hub and the spokers? 

Thank you

[Francesco Molino · Accepted solution]

MTU has to be set on tunnel interface for hubs and spockes.

If you want to save bits, you can even use mode transport instead of mode tunnel.

Thanks 

PS: Please don't forget to rate and mark as correct answer if this solved your issue