Campus Switching and Routing

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Occasional Contributor II

ArubaOS-Switch Tunneled-node MTU

Hi Airheads,

 

I'm trying to use Tunneled-node on a Aruba 3810M creating a tunnel back to an 7010 controller. I was able to get that working after i found out you required 6.5 or higher on the controller!! Anyhow, it is working now, however I've found requiring 1584 MTU on the path of the tunnel quite restricting, is there anyway to lower the MTU in the tunnel how the APs do so it is not required to increase the MTU through the network??

 

Richard

Re: ArubaOS-Switch Tunneled-node MTU

Hi,

1584 MTU is a requirement as far as I can see. I would imagine it's purpose it to ensure that Ethernet packets encapsulated in the tunnel do not get fragmented.
Cheers
James

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Contributor II

Re: ArubaOS-Switch Tunneled-node MTU

Following the ASE template (https://ase.arubanetworks.com/solutions/id/134), I see the following commands:

 

jumbo max-frame-size 1584
jumbo ip-mtu 1584

 

However, upon entering the 2nd command, I get this error:

 

"IP-MTU size must be 18 bytes lesser than max-frame-size."

 

So, is the correct version:

 

1)

jumbo max-frame-size 1602
jumbo ip-mtu 1584

 

...OR...

 

2)

jumbo max-frame-size 1584
jumbo ip-mtu 1566

 

EDIT (additional question):

 

I'm also trying to understand the reason for 1584 bytes. Here's how I add it up in a worst case scenario where both the outer and inner Ethernet frames include a 4 byte 802.1Q tag:

 

Ethernet + .1Q (outer): 22 bytes

IP (outer) + GRE: 24 bytes

Ethernet + .1Q (inner): 22 bytes

IP (inner) + payload: 1500 bytes

 

Total outer frame size: 1568 bytes

Total outer IP size: 1546

 

So where does 1584 come from?

Tim Haynie, ACMX #508, ACDX #384, ACCP, CWSP, CWAP, CWDP, CCNP R/S, CCNP Wireless, CCNA Security, CCDA
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