|Protocol type:||Transport layer protocol.|
Each AX.25 frame is encapsulated in one IP datagram. Normally no AX.25 frame will exceed 330 bytes, so fragmentation at the IP layer should not be necessary. However, experiments with larger AX.25 frame sizes may require the use of standard IP fragmentation and reassembly procedures. When an AX.25 frame is encapsulated within an IP packet, HDLC framing elements (flags and zero-stuffing) are omitted, as the IP datagram adequately delimits the beginning and end of each AX.25 frame. The 16-bit CRC-CCITT frame check sequence (normally generated by the HDLC transmission hardware) is included. In all other respects, AX.25 frames are encapsulated unaltered.
[RFC 1226] Internet Protocol Encapsulation of AX.25 Frames.