PPPoE Host-Uniq limited to 32 chars

[lluke]

Hi All,
while investigating some issues with my PPPoE connection it seems that I've to configure the Host-Uniq tag to a specific value.

The value I should provide is

1ced6f301223aaaaaaaa04000000aaaaaaaa4621426f78202020aaaaaaaa

which seems to be incompatible with Asus WRT Merlin (tested on 386.5_2) since it is 61 chars length and the system has an hard limit to 32 characters.

As per the RFC 2516 the Host-Uniq can be of any value and length

   0x0103 Host-Uniq

      This TAG is used by a Host to uniquely associate an Access
      Concentrator response (PADO or PADS) to a particular Host request
      (PADI or PADR).  The TAG_VALUE is binary data of any value and
      length that the Host chooses.  It is not interpreted by the Access
      Concentrator.  The Host MAY include a Host-Uniq TAG in a PADI or
      PADR.  If the Access Concentrator receives this TAG, it MUST
      include the TAG unmodified in the associated PADO or PADS
      response.

Trying to force a longer value through APIs I'm getting the following error from the logs

httpd: nvram_check fail: nvram wan_pppoe_hostuniq over length (60 > 32)

Is there any reason for this limitation? Is there any possibility to get rid of it or is it possible to fix this behavior in a future release of the firmware?

 

[RMerlin]

Variables cannot be set to allow "any length" due to internal buffer limitations within the firmware, so Asus decided on a specific max length probably based on the specific case that brought them to implement this feature.

I could try increasing the max size to 256, but I would first need to ensure that any section of code that manipulates this variable is able to deal with a longer length, which is not guaranteed. I.e., it's not as trivial as just changing the value in two locations (webui and libshared).

 

[lluke]

Variables cannot be set to allow "any length" due to internal buffer limitations within the firmware, so Asus decided on a specific max length probably based on the specific case that brought them to implement this feature.

I could try increasing the max size to 256, but I would first need to ensure that any section of code that manipulates this variable is able to deal with a longer length, which is not guaranteed. I.e., it's not as trivial as just changing the value in two locations (webui and libshared).

Got it, thanks a lot for the response @RMerlin.
256 will definitely be great, but also only 64 would cover my scenario that I hope is not so common among users.

I'll stay tuned to see if you would manage to work on this.

Thanks again for the support

 

[RMerlin]

It should be safe to increase the max length. I will also forward the request upstream.