[ale] PPP Perfromance

[Geoffrey]

James P. Kinney III wrote:
> On Thu, 2003-10-30 at 21:52, Ryan wrote:
> 
>>I thought MRU and MTU were things that ppp negotiates automatically when
>>bringing the link up. Is there any benefit to forcibly setting them? Or
>>are they required to give ppp an idea of what to say during that
>>negotiation?
>>
> 
> I'm 99% certain that mtu and mru are NOT "negotiated" during setup of a
> PPP link.

You can most definitely set both mtu and mru via pppd options, but 
negotiation is an option.  There are default values, but you can set 
them.  See 'man pppd:'

mru n  Set the MRU [Maximum Receive Unit] value to n. Pppd
               will ask the peer to send packets of no more than n
               bytes.  The minimum MRU value is 128.  The  default
               MRU  value  is 1500.  A value of 296 is recommended
               for slow links (40 bytes for TCP/IP  header  +  256
               bytes of data).  (Note that for IPv6 MRU must be at
               least 1280)
 

        mtu n  Set the MTU [Maximum Transmit  Unit]  value  to  n.
               Unless  the  peer  requests a smaller value via MRU
               negotiation, pppd will request that the kernel net-
               working  code  send  data packets of no more than n
               bytes through the  PPP  network  interface.   (Note
               that for IPv6 MTU must be at least 1280)

As for negotiation see:

default-mru
               Disable  MRU  [Maximum  Receive  Unit] negotiation.
               With this option, pppd will  use  the  default  MRU
               value  of  1500  bytes  for  both  the transmit and
               receive direction.

I do not see a corresponding option for mtu though.

-- 
Until later, Geoffrey	esoteric at 3times25.net

Building secure systems inspite of Microsoft