"(Before MPLS switches allowing larger packets were mainstream and 
affordable)" 

Where ? care to share ?

Gino A. Villarini
[EMAIL PROTECTED]
Aeronet Wireless Broadband Corp.
tel  787.273.4143   fax   787.273.4145

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Tom DeReggi
Sent: Tuesday, August 01, 2006 4:23 PM
To: WISPA General List
Subject: Re: [WISPA] frame size and fps - Mikrotik large packets

Jeff,

Thanks for the clarifications from your engineer.

The only comment I disagree with is....

>> The proper VLAN aware drivers show 1500 MTU for both the underlying 
>> interface
>> and the VLAN interface but it treats VLAN packets with caution, so as not

>> to
>> truncate or drop them because of their longer size.

>If that's true, then it isn't a "proper VLAN aware driver."  The MTU should

>be
>set correctly and not just show 1500 and use something else.

My statement was just bringing up that the MTU is for the size of the packet

before VLAN tags were added, and VLAN header bits are added on top of the 
existing full size packets. The reason for this is that we guarantee to 
deliver 1500 MTU to the consumer, and we want the setting to show what the 
customer expects to get. If we tag it with VLAN for our own use, we must be 
able to pass the higher size packet, and strip the VLAN off before 
delivering down to the client on the other end.

Opinions on this depend on what the provider is trying to do with the 
router. The needs as a customer premise router is different than the needs 
of a ISP transport provider router.  The way StarOS does it, to shring the 
MTU, is appropriate for Customer premise routers, and it would make sense 
under that circumstance for the MTU setting to reflect the new MTU size that

the customer would see.  But in our application as a transport provider, our

cell site routers want to appear transparent, to any application the 
consumer may want to use. Its standard that Ethernet is limited to 1500 MTU,

and the Consumer should have not problem working around that, and when they 
want to lower their own MTU. However, as a provider, we never have a need to

lower an MTU, as lowering an MTU would compromise the service delivered to 
the consumerthat would expect to receive 1500 MTU capabilty.  The problem is

not all ethernet devices pass IPSEC higher MTU. Its why it ended up not 
being a preferred method for tunneling across our network or other's 
network, without compromising delivery of 1500 MTU to subscribers.  Thus the

reason we switched to CIPE tunneling as our standard tunneling method.  And 
major reason for selecting Linux based routers.

I'd like to add, that I believe ImageStream supports CIPE tunneling. One of 
the disadvantages of Mikrotik and StarOS, is that they do NOT support CIPE 
tunneling. It was one of the reasons we built our own routers 5 years ago. 
(Before MPLS switches allowing larger packets were mainstream and 
affordable).

Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband


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