Processing Reverse Bound Traffic

Reply-message packets coming back from a server into the router are processed by the jnx_gw_data_process_ipip_packet() function in /src/sbin/jnx-gateway-data/jnx-gateway-data_packet.c.

As already described, this function is branched from jnx_gw_data_process_packet() (see Packet Processing Details).

jnx_gw_data_process_ipip_packet() handles the incoming IP-in-IP packet as follows:

• Calls jnx_gw_data_db_ipip_sub_tunnel_lookup_with_lock() to look up the tunnel in the application's IP-IP sub-tunnel database. This function is in the file jnx-gateway-data/jnx-gateway-data_utils.h.

• Removes the outer IP header from the packet

• Retrieves the egress VRF and its status

• Obtains a pointer to the inner IP header

• Calls jnx_gw_data_process_ip_packet() to process the IP layer

• Obtains the TTL value of the inner IP packet; decrements the TTL of the inner IP packet by 1

• Either calls jnx_gw_data_update_ttl_compute_inc_checksum() to compute the checksum of the inner IP packet, or appends a GRE and IP header that was already computed by the GRE tunnel. jnx_gw_data_update_ttl_compute_inc_checksum() is declared in the file jnx-gateway-data/jnx-gateway-data_utils.h.

• Sets the length of the packet to the value of ipip_sub_tunnel->ip_gre_hdr_len in the packet context structure

• Calls jbuf_copyback() to copy the IP GRE header to the beginning of the packet

• Obtains a pointer to the top of the packet data

• Modifies the data types of various fields as required to send the packet ;

• Sets the sequence number if flagged

• Computes the GRE checksum, if flagged

• Sets other fields in the header: length, TTL, and IP frag ID

• Computes the IP header checksum.

Sending the IP-IP Packet

The function sends the packet by calling the jbuf_setvrf() and the msp_data_send() functions as it did for GRE packets in Sending the Packet.

  /* Set the outgoing VRF in the PKT BUFF */
   jbuf_setvrf(pkt_ctxt->pkt_buf, pkt_ctxt->ipip_sub_tunnel->egress_vrf);

    if (msp_data_send(pkt_ctxt->dhandle, pkt_ctxt->pkt_buf,
                     MSP_MSG_TYPE_PACKET) != MSP_OK) {

        pkt_ctxt->stat_type = JNX_GW_DATA_CONG_DROP;
        return JNX_GW_DATA_DROP_PKT;
    }
  

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