+/*
+ * Copyright (c) 2009 Nicira Networks.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+#include "packets.h"
+#include <netinet/in.h>
+#include "ofpbuf.h"
+
+/* Fills 'b' with an 802.2 SNAP packet with Ethernet source address 'eth_src',
+ * the Nicira OUI as SNAP organization and 'snap_type' as SNAP type. The text
+ * string in 'tag' is enclosed as the packet payload.
+ *
+ * This function is used by Open vSwitch to compose packets in cases where
+ * context is important but content doesn't (or shouldn't) matter. For this
+ * purpose, 'snap_type' should be a random number and 'tag' should be an
+ * English phrase that explains the purpose of the packet. (The English phrase
+ * gives hapless admins running Wireshark the opportunity to figure out what's
+ * going on.) */
+void
+compose_benign_packet(struct ofpbuf *b, const char *tag, uint16_t snap_type,
+ const uint8_t eth_src[ETH_ADDR_LEN])
+{
+ struct eth_header *eth;
+ struct llc_snap_header *llc_snap;
+
+ /* Compose basic packet structure. (We need the payload size to stick into
+ * the 802.2 header.) */
+ ofpbuf_clear(b);
+ eth = ofpbuf_put_zeros(b, ETH_HEADER_LEN);
+ llc_snap = ofpbuf_put_zeros(b, LLC_SNAP_HEADER_LEN);
+ ofpbuf_put(b, tag, strlen(tag) + 1); /* Includes null byte. */
+ ofpbuf_put(b, eth_src, ETH_ADDR_LEN);
+
+ /* Compose 802.2 header. */
+ memcpy(eth->eth_dst, eth_addr_broadcast, ETH_ADDR_LEN);
+ memcpy(eth->eth_src, eth_src, ETH_ADDR_LEN);
+ eth->eth_type = htons(b->size - ETH_HEADER_LEN);
+
+ /* Compose LLC, SNAP headers. */
+ llc_snap->llc.llc_dsap = LLC_DSAP_SNAP;
+ llc_snap->llc.llc_ssap = LLC_SSAP_SNAP;
+ llc_snap->llc.llc_cntl = LLC_CNTL_SNAP;
+ memcpy(llc_snap->snap.snap_org, "\x00\x23\x20", 3);
+ llc_snap->snap.snap_type = htons(snap_type);
+}