NDIS Filter Clarification on Header-Data split on send path

NTDEV
1

Good day all.

I just want more clarification on the NDIS Header split on send and receive.

The first thing I have noticed is that the header split rules apply to receive Path and that one NET_BUFFER_LIST pointing to one NET_BUFFER also pointing to one MDL.

Some of the header split rules on the Receive

  1. Do not split Non-IP frames(0x0800) and such protocols may include (ARP 0x0806, PPPOE 0x8863/64) etc.
  2. You can split in the middle of a header provided that the number of bytes in the first mdl is equal to the lookahead size.

upper layer protocols in this context are TCP, UDP and ICMP

  1. You can split IP Frames at the beginning of the tcp,udp,icmp header or at the tcp,udp payload (other rules for upper layer protocols).

As far as I understand it, this header split rules that are mentioned above (rule 1,2 and 3) are only applicable to the receive path. Now I would to verify If I

understood correctly, that on the sending side rules on header split

On the Send side

  1. You can have NET_BUFFER_LIST with a chain of NET_BUFFERS and each NET_BUFFER may have a chain of MDLs
  2. You should not split the packet in the middle of the header (eg ethernet, Ip and TCP), meaning you can only split at the end of the header.

Now I am writing a code that doesn't require copying buffers, I receive an IP (0x0800) packet from one adapter (let's call it adapter 1), but want to translate it to PPPOE, and then send

it to the other adapter (let's call it adapter 2).

The translation I will create a PPPOE packet (Ethernet Header (14 bytes) + PPPOE Header (6 bytes) and PPP header (2 bytes)) in the first MDL). The second MDL will point at the start of the IP header received from adapter 1. The first MDL points to the second MDL to make a chain.

Now I want to know the receive path header split rules will be enforced on the send path side (e.g. do not split non-IP frame meaning do not split PPPOE). I want to know if my algorithm and thinking is correct and that I am not violating any NDIS rules.Good day all.

I just want more clarification on the NDIS Header split on send and receive.

The first thing I have noticed is that the header split rules apply to receive Path and that one NET_BUFFER_LIST pointing to one NET_BUFFER also pointing to one MDL.

Some of the header split rules on the Receive

  1. Do not split Non-IP frames(0x0800) and such protocols may include (ARP 0x0806, PPPOE 0x8863/64) etc.
  2. You can split in the middle of a header provided that the number of bytes in the first mdl is equal to the lookahead size.

upper layer protocols in this context are TCP, UDP and ICMP

  1. You can split IP Frames at the beginning of the tcp,udp,icmp header or at the tcp,udp payload (other rules for upper layer protocols).

As far as I understand it, this header split rules that are mentioned above (rule 1,2 and 3) are only applicable to the receive path. Now I would to verify If I

understood correctly, that on the sending side rules on header split

On the Send side

  1. You can have NET_BUFFER_LIST with a chain of NET_BUFFERS and each NET_BUFFER may have a chain of MDLs
  2. You should not split the packet in the middle of the header (eg ethernet, Ip and TCP), meaning you can only split at the end of the header.

Now I am writing a code that doesn't require copying buffers, I receive an IP (0x0800) packet from one adapter (let's call it adapter 1), but want to translate it to PPPOE, and then send

it to the other adapter (let's call it adapter 2).

The translation I will create a PPPOE packet (Ethernet Header (14 bytes) + PPPOE Header (6 bytes) and PPP header (2 bytes)) in the first MDL). The second MDL will point at the start of the IP header received from adapter 1. The first MDL points to the second MDL to make a chain.

Now I want to know the receive path header split rules will be enforced on the send path side (e.g. do not split non-IP frame meaning do not split PPPOE). I want to know if my algorithm and thinking is correct and that I am not violating any NDIS rules.