routing(7)						 Miscellaneous Information Manual						routing(7)

NAME

       routing - system support for local network packet routing

DESCRIPTION

       The network facilities for HP-UX provide general packet routing support.  Routing table maintenance is handled by application processes.

       A  routing  table consists of a set of data structures used by the network facilities to select the appropriate remote host or gateway when
       transmitting packets.  The table contains a single entry for each route to a specific network or host, as displayed by the command with the
       or options (see netstat(1)).  Routes that are not valid are not displayed.

	      _______________________________________________________________
	      # netstat -r
	      Routing tables
	      Destination     Gateway	      Flags  Refs  Use Interface Pmtu
	      hpindwr.cup.hp.com
			      localhost       UH	1   39 lo0	 4608
	      localhost       localhost       UH	0   68 lo0	 4608
	      147.253.56.195  localhost       UH	0    0 lo0	 4608
	      147.253.144.66  localhost       UH	0    0 lo0	 4608
	      default	      hpinsmh.cup.hp.com
					      UG	1   21 lan0	 1500
	      15.13.136       hpindwr.cup.hp.com
					      U 	1   92 lan0	 1500
	      147.253.56      147.253.56.195  U 	0    7 lan2	 1500
	      147.253.144.64  147.253.144.66  U 	0    7 lan1	 1500
	      _______________________________________________________________
	      # netstat -rn
	      Routing tables
	      Destination     Gateway	      Flags  Refs  Use Interface Pmtu
	      15.13.136.66    127.0.0.1       UH	1   39 lo0	 4608
	      127.0.0.1       127.0.0.1       UH	0   68 lo0	 4608
	      147.253.56.195  127.0.0.1       UH	0    0 lo0	 4608
	      147.253.144.66  127.0.0.1       UH	0    0 lo0	 4608
	      default	      15.13.136.11    UG	2   30 lan0	 1500
	      15.13.136.0     15.13.136.66    U 	1  113 lan0	 1500
	      147.253.56.0    147.253.56.195  U 	0    7 lan2	 1500
	      147.253.144.64  147.253.144.66  U 	0    7 lan1	 1500
	      _______________________________________________________________
	      # netstat -rv
	      Routing tables
	      Dest/Netmask    Gateway	      Flags  Refs  Use Interface Pmtu
	      hpindwr.cup.hp.com/0xffffffff
			      localhost       UH	1   39 lo0	 4608
	      localhost/0xffffffff
			      localhost       UH	0   68 lo0	 4608
	      147.253.56.195/0xffffffff
			      localhost       UH	0    0 lo0	 4608
	      147.253.144.66/0xffffffff
			      localhost       UH	0    0 lo0	 4608
	      default/0x00000000
			      hpinsmh.cup.hp.com
					      UG	2   31 lan0	 1500
	      15.13.136/0xfffff800
			      hpindwr.cup.hp.com
					      U 	1  129 lan0	 1500
	      147.253.56/0xfffffe00
			      147.253.56.195  U 	0    7 lan2	 1500
	      147.253.144.64/0xfffffff0
			      147.253.144.66  U 	0    7 lan1	 1500
	      _______________________________________________________________
	      # netstat -rnv
	      Routing tables
	      Dest/Netmask    Gateway	      Flags  Refs  Use Interface Pmtu
	      15.13.136.66/255.255.255.255
			      127.0.0.1       UH	1   39 lo0	 4608
	      127.0.0.1/255.255.255.255
			      127.0.0.1       UH	0   68 lo0	 4608
	      147.253.56.195/255.255.255.255
			      127.0.0.1       UH	0    0 lo0	 4608
	      147.253.144.66/255.255.255.255
			      127.0.0.1       UH	0    0 lo0	 4608
	      default/0.0.0.0 15.13.136.11    UG	3   40 lan0	 1500
	      15.13.136.0/255.255.248.0
			      15.13.136.66    U 	1  153 lan0	 1500
	      147.253.56.0/255.255.254.0
			      147.253.56.195  U 	0    8 lan2	 1500
	      147.253.144.64/255.255.255.240
			      147.253.144.66  U 	0    8 lan1	 1500
	      _______________________________________________________________

       The following columns are of particular interest:

	      The destination Internet address: host name, network name, or
				  The  keyword	indicates a wildcard route, used as a last resort if no route is specified for a particular remote
				  host or network.  See

	      The netmask and the destination Internet address together define
				  a range of IP addresses that may be reached by the route's gateway.  A host route by default has  a  netmask	of
				  all 1's.  A default route by default has a netmask of all 0's.  The netmask is also used in selecting a route to
				  forward an IP packet.  See the subsection.

	      The gateway to use to get to the destination:
				  a remote gateway or the local host.  See

	      The type of route:

				       The route is "up" or available (see
					      ifconfig(1M)).
				       The route uses a remote host as a gateway;
					      otherwise, the local host is shown as the gateway (see route(1M)).
				       The destination is a host;
					      otherwise, the destination is a network (see route(1M)).

	      The interface connections:

				       The local loopback after system boot.

				       The interface cards installed on the local host after the
							   command is executed at boot time (see ifconfig(1M)).

       The values of the count and destination type fields in the command determine the presence of the and flags in  the  display  and  thus  the
       route type, as shown in the following table.

	      Count   Destination Type	 Flags		Route Type
	      -------------------------------------------------------------
	       =0	  network	 U	 Route	  to   a   network
						 directly from	the  local
						 host
	       >0	  network	 UG	 Route	  to   a   network
						 through  a  remote   host
						 gateway
	       =0	    host	 UH	 Route	to  a  remote host
						 directly from	the  local
						 host
	       >0	    host	 UGH	 Route	to  a  remote host
						 through  a  remote   host
						 gateway
	       =0	  default	 U	 Wildcard  route  directly
						 from the local host
	       >0	  default	 UG	 Wildcard route through  a
						 remote host gateway
	      -------------------------------------------------------------

   Subnets
       The network facilities support variable-length subnetting.  An Internet address is made up of a portion, and a portion of an address in the
       form:

       Subnet addresses are defined as a portion of the network's Internet address.  This scheme provides for:

	 o  Network addresses that identify physically distinct networks.
	 o  Subnet addresses that identify physically distinct subnetworks of the same network.

       A network manager can subdivide the Internet address of the local network into subnets using the host number space.  This  facility  allows
       several physical networks to share a single Internet address.

       To  allow  for  this, three Internet classes are defined, each accommodating a different amount of network and host addresses.  The address
       classes are defined by the most significant bit of the binary form of the address.

       The following table lists the number of networks, nodes, and the address ranges for each address class:

				    Nodes per
	       Class	 Networks    Network	       Address Range
	      --------------------------------------------------------------
		 A	      127    16777215	  0.0.0.1 - 127.225.225.254
		 B	    16383	65535	128.0.0.1 - 191.255.255.254
		 C	  2097151	  255	192.0.0.1 - 223.244.244.243
	      Reserved	       --	   --	224.0.0.0 - 255.255.255.255
	      --------------------------------------------------------------

       The first 8 bits of a Class A network has network space for only 127, while accommodating the largest number of nodes  possible	among  the
       classes defined.  A single class B network has the network address limitation of 16 bits, and 16 bits to define the nodes.

       For example, a Class C address space is as follows:

	      ______________________________________
	      Indicates 		 Class C
	      Class C			 subnet
	      networks			 portion
		 |			    |
		---			   ---
		10000000.00000110.00000001.11100001
		--------------------------    -----
			    |			|
		     Network Address	       Host
			= 192.6.1	     Address
					       = 1
	      ______________________________________

       A subnet for a given host is specified with the command (see ifconfig(1M)), using the parameter with a 32-bit subnet mask.

       The default masks for the three classes of Internet addresses are as follows:

	      Class A: 255.0.0.0
	      Class B: 255.255.0.0
	      Class C: 255.255.255.0

       An example Class C network number is 192.34.17.0.  The last field specifies the host number.  Thus, all hosts with the prefix 192.34.17 are
       recognized as being on the same logical and physical network.

       If subnets are not in use, the default mask used is 255.255.255.0.

       If subnets are used and the 8-bit host field is partitioned into 3 bits of subnet and 5 bits of host as in the above example, then the sub-
       net mask would be 255.255.255.192.

       If  a  host  has  multiple interfaces, then it can belong to different subnets.	Unlike past releases, the subnets can have different sizes
       even if they may have the same network address.	This is accomplished by using a different netmask on each of  the  host  interfaces.   For
       example,  the  and interface shown in the tables above are connected to two distinct subnets of the same network, 147.253.  The subnet that
       belongs to can have at most 14 hosts, because its netmask is 255.255.255.240.

       Note:  The host portion of those IP addresses in the subnet cannot be all 1's or all 0's, therefore this subnet can support only 14  hosts,
	      not 16.

       The subnet that belongs to can have up to 510 hosts, because its netmask is 255.255.254.0.

   Supernets
       A supernet is a collection of smaller networks.	Supernetting is a technique of using the netmask to aggregate a collection of smaller net-
       works into a supernet.  This technique is particularly useful for class C networks.  A Class C network can only have 254 hosts.	 This  can
       be  too	restrictive for some companies.  For these companies, a netmask that only contains a portion of the network part can be applied to
       the hosts in these class C networks to form a supernet.	This supernet netmask should be applied to those interfaces that  connect  to  the
       supernet  using the ifconfig command (see ifconfig(1M)).  For example, a host can configure its interface to connect to a class C supernet,
       for example, 192.6, by configuring an IP address of 192.6.1.1 and a netmask of 255.255.0.0 to its interface.

   Routing Algorithm
       The routing table entries are of three types:

	 o  Entries for a specific host.
	 o  Entries for all hosts on a specific network.
	 o  Wildcard entries for any destination not matched by entries of the first two types.

       To select a route for forwarding an IP packet, the network facilities select the complete set of "matching" routing table entries from  the
       routing table.  A routing table entry is considered a match, if the result of the bit-wise AND operation between the netmask in the routing
       entry and the IP packet's destination address equals the destination address in the routing entry.

       The network facilities then select from the set the routing entries that have the longest netmask.  The length of a netmask is  defined	as
       the  number  of contiguous 1 bits starting from the leftmost bit position in the 32-bit netmask field.  In other words, the network facili-
       ties select the routing entry that specifies the narrowest range of IP addresses.  For example, the host route entry that  has  a  destina-
       tion/netmask  pair  of  (147.253.56.1,  0xFFFFFFFF),  is  more specific than the network route entry that has a destination/netmask pair of
       (147.253.56.0, 0xFFFFFE00); therefore, the network facilities select the host route entry.  The default route by  default  has  a  destina-
       tion/netmask  pair  of  (0,0).  Therefore, the default route matches all destinations but it is also the least specific.  The default route
       will be selected only if there is not a more specific route.

       There may still be multiple routing entries remaining.  In that case, the IP packet is routed over the first entry displayed by Such multi-
       ple routes include:

	      o  Two or more routes to a host via different gateways.
	      o  Two or more routes to a network via different gateways.

       A  superuser  can  change  entries in the table by using the command (see route(1M), or by information received in Internet Control Message
       Protocol (ICMP) redirect messages.

       If there are more than one default gateways for a particular net or subnet, each will be used in turn to effect the  even  distribution	of
       datagrams to the different gateways.

WARNINGS

       Reciprocal  commands  must be executed on the local host and the destination host, as well as all intermediate hosts, if routing is to suc-
       ceed in the cases of virtual circuit connections or bidirectional datagram transfers.

AUTHOR

       was developed by the University of California, Berkeley.

FILES

SEE ALSO

       netstat(1), ifconfig(1M), route(1M), route(7P).

																	routing(7)