[c-nsp] What MTU for Bellsouth BBG / BRAS <-> LNS l2TP tunnel?

[Brian Feeny]

I see so your trying to allow for the larger payload?  I would think 
1548 would nail it assuming
worst case l2tp/pppoE, etc.  Maybe 1550 if your using sequencing 
options.

What really interesting is to look at the entire encapsulation process 
and calculate the most
"ideal" MTU that would lead to the most efficiency (less fragmenting, 
and more efficient use of
packets/cells).

Brian


On Oct 27, 2004, at 7:49 PM, Ash Garg wrote:

> Guys, we have set to 1560 on the ATM subIF and haven't had any 
> problems with
> MTU so far.
>
> Regards,
> Ash
>
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net]On Behalf Of Jon Lewis
> Sent: Thursday, 28 October 2004 10:40 AM
> To: Brian Feeny
> Cc: cisco-nsp
> Subject: Re: [c-nsp] What MTU for Bellsouth BBG / BRAS <-> LNS l2TP
> tunnel?
>
>
> On Wed, 27 Oct 2004, Brian Feeny wrote:
>
>> So you are running MTU 4470 on the PVC over which your L2TP session is
>> built, but I am using 1500, and thats probably the difference.
>
> Yes.  The ATM interface and L2TP carrying PVCs have the default (for 
> ATM
> DS3) MTU of 4470.  I haven't tried setting it to anything else to see 
> if
> other sized would work / break things.
>
>> In the old days I use to think PPPoE was more ideal, because it could
>> terminate on the customer desktop (WinPoet, etc).  But of course DSL 
>> is
>> almost always terminated into CPE, so maybe I should look more closely
>> at PPPoA vs. PPPoE.
>
> PPPoE may have been nice back when DSL bridges were so popular, but 
> since
> pretty much all DSL CPE can do PPPoA now, may as well use that when
> possible.
>
> ----------------------------------------------------------------------
>  Jon Lewis                   |  I route
>  Senior Network Engineer     |  therefore you are
>  Atlantic Net                |
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>
---------------------------------------------
Brian Feeny, CCIE #8036, CISSP
Network Engineer
ShreveNet Inc.

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