md5 authentication seems to work.

bird.conf

@@ -33,7 +33,7 @@ protocol rip MyRIP_test {
 	passwords { password "ahoj" from 0 to 10;
 		password "nazdar" from 10;
 	}
-	authentication plaintext;
+	authentication md5;
 }
 
 protocol device {

proto/rip/auth.c

@@ -56,7 +56,7 @@ rip_incoming_authentication( struct proto *p, struct rip_block_auth *block, stru
       struct password_item *head;
       struct rip_md5_tail *tail;
 
-      if (block->packetlen != PACKETLEN(num) + 20) {
+      if (block->packetlen != PACKETLEN(num)) {
 	log( L_ERR "packetlen in md5 does not match computed value\n" );
 	return 1;
       }
@@ -145,7 +145,7 @@ rip_outgoing_authentication( struct proto *p, struct rip_block_auth *block, stru
       MD5Init(&ctxt);
       MD5Update(&ctxt, (char *) packet, block->packetlen );
       MD5Final((char *) (&tail->md5), &ctxt);
-      return block->packetlen;
+      return PACKETLEN(num) + block->authlen;
     }
   default:
     bug( "Uknown authtype in outgoing authentication?\n" );

proto/rip/rip.c

@@ -352,7 +352,7 @@ rip_process_packet( struct proto *p, struct rip_packet *packet, int num, ip_addr
 	    struct rip_block *block = &packet->block[i];
 	    if (block->family == 0xffff) {
 	      if (i)
-		BAD( "Authentication header is not the first" );
+		continue;	/* md5 tail has this family */
 	      if (rip_incoming_authentication(p, (void *) block, packet, num))
 		BAD( "Authentication failed" );
 	      authenticated = 1;

proto/rip/rip.h

@@ -28,7 +28,7 @@ struct rip_connection {
   int done;
 };
 
-struct rip_packet_heading {
+struct rip_packet_heading {		/* 4 bytes */
   u8 command;
 #define RIPCMD_REQUEST          1       /* want info */
 #define RIPCMD_RESPONSE         2       /* responding to request */