[cisco-nas] ATM/L2TP/PPP MTU question

[Anastassios Chatzithomaoglou]

If i leave it on the default (4470 from our side, 8000+ from telco's side) will there be 
any problem?

What are the possibilites of such a HUGE packet? Are there any disadvantages?

Dennis Peng wrote:
> Tassos Chatzithomaoglou [achatz at forthnet.gr] wrote:
> 
>>Here is the network diagram:
>>
>>          DSL         ATM              ATM         ATM       ETH
>>ADSL CPE ----- DSLAM ----- ATM SWITCH ----- BBRAS ----- LNS ----- INTERNET
>>    |-------------- PPPoE/A------------------||----L2TP---|
>>    |----------------------- PPP -------------------------|
>>
>>What is the recommended MTU setting for the ip/atm connection between 
>>BBRAS/LNS (default for ATM is 4470), if we have to :
>>
>>1. Do not change anything on user's side
>>2. Do not load BBRAS/LNS with extra fragmentation/reassembly
>>
>>Should i make it 1540 (1500 + 40 bytes of IP, UDP and L2TP headers) ?
> 
> 
> Yes, 1540 should do it if you are going Cisco to Cisco. If you are
> going inter-vendor, it depends on the L2TP header options the other
> vendor may use (eg. data sequencing would add additional
> overhead). You may want to increase to 1550 to be safe.
> 
> Dennis
> 
> 
>>-- 
>>***********************************
>>   Chatzithomaoglou Anastasios
>>Network Design & Operations Center
>>          FORTHnet S.A.
>>      <achatz at forthnet.gr>
>>***********************************
>>
>>_______________________________________________
>>cisco-nas mailing list
>>cisco-nas at puck.nether.net
>>http://puck.nether.net/mailman/listinfo/cisco-nas
> 
> 

-- 
***********************************
    Chatzithomaoglou Anastasios
Network Design & Operations Center
           FORTHnet S.A.
       <achatz at forthnet.gr>
***********************************