[cisco-bba] ppp-max-payload - PPPOE Clients rfc4638

Christoph Loibl cl at sil.at
Fri Apr 6 09:00:20 EDT 2007

Hi Bba-Group!

I resently stumbled over the pretty new BRAS feature introduced on  
the Cisco


Does anyone know about CPE devices that do support the sending of  
such PPP-Max-Payload tags?

The feature made it to 12.2.31-SB(2-3) release of the router software  
images (Is it planned to extend the support to other releases?). The  
basic functionality as far as I understand is that PPPOE clients may  
send an additional TAG within their PPPoE PADI packets to allow the  
BRAS to negotiate a MRU larger than 1500. As long as the connection  
between the BRAS-DSLAM-CPE supports that larger frames. This should  
allow the initiating CPE to send "large" (1500 IP MTU) IP packets  
through the pppoe session (which normally has an overhead of 8 byte  
thus reducing the ip mtu to 1492).

The configuration on the BRAS is pretty simple:

bba-group pppoe TEST
  virtual-template 1
  tag ppp-max-payload minimum 1400 maximum 1700

But who knows CPEs that support the "Dialer" side of this ppp-max- 
payload tag (actually sending that tag - to allow the bras to  
negotiate this feature)?



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Ing Christoph Loibl <cl at sil.at>                Senior Network Engineer
CL8-RIPE                          http://www.sil.at, http://pix.tix.at

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