Route

The Route.exe command allows you to print and modify the routing table. The routing table determines which IP interface a connection request or a datagram occurs on. The IP Helper library offers several functions for manipulating the routing table. All of the functions related to routing are available on Windows 98, Windows 2000, and Windows NT 4 Service Pack 4 (or later).

First, let's discuss the capabilities of the Route.exe command. Its most basic function is to print the routing table. A route consists of a destination address, a netmask, a gateway, a local IP interface, and a metric. You also have the ability to add and delete a route. To add a route, you must specify all the parameters we just described. To delete a route, you must specify only the destination address. In this section, we'll look at the IP Helper functions that print the routing table. Then we'll discuss adding and deleting a route.

Getting the Routing Table

The most basic action that Route.exe performs is printing the table. This is accomplished with the GetIpForwardTable function, which is defined as

 DWORD GetIpForwardTable ( PMIB_IPFORWARDTABLE pIpForwardTable, PULONG pdwSize, BOOL bOrder ); 

The first parameter, pIpForwardTable, contains the routing table information upon return. When you call the function, this parameter should point to a buffer of sufficient size. If you call the function with pIpForwardTable equal to NULL (or if the buffer size is insufficient to begin with), the pdwSize parameter returns the length of the buffer needed for the call to complete successfully. The last parameter, bOrder, indicates whether the results should be sorted upon return. The default sorting order is

1. Destination address
2. Protocol that generated the route
3. Multipath routing policy
4. Next-hop address

The routing information is returned in the form of the MIB_IPFORWARDTABLE structure, which is defined as

 typedef struct _MIB_IPFORWARDTABLE { DWORD dwNumEntries; MIB_IPFORWARDROW table[ANY_SIZE]; } MIB_IPFORWARDTABLE, *PMIB_IPFORWARDTABLE; 

This structure is a wrapper for an array of MIB_IPFORWARDROW structures. The dwNumEntries field indicates the number of these structures present in the array. The MIB_IPFORWARDROW structure is defined below.

 typedef struct _MIB_IPFORWARDROW { DWORD dwForwardDest; DWORD dwForwardMask; DWORD dwForwardPolicy; DWORD dwForwardNextHop; DWORD dwForwardIfIndex; DWORD dwForwardType; DWORD dwForwardProto; DWORD dwForwardAge; DWORD dwForwardNextHopAS; DWORD dwForwardMetric1; DWORD dwForwardMetric2; DWORD dwForwardMetric3; DWORD dwForwardMetric4; DWORD dwForwardMetric5; } MIB_IPFORWARDROW, *PMIB_IPFORWARDROW; 

The fields of this structure are defined as follows:

• dwForwardDest Is the IP address of the destination host.
• dwForwardMask Is the subnet mask for the destination host.
• dwForwardPolicy Specifies a set of conditions that would cause the selection of a multipath route. Usually these conditions are in the form of IP Type of Service (TOS). For more information about TOS, see Chapter 9 and the IP_TOS option. For more information on multipath routing, see RFC 1354.
• dwForwardNextHop Is the IP address for the next hop in the route.
• dwForwardIfIndex Indicates the index of the interface for this route.
• dwForwardType Indicates the route type as defined in RFC 1354. Table B-4 lists the possible values and meanings for this field.
• dwForwardProto Is the protocol that generated the route. Table B-5 lists the possible values for this field. The values for IPX protocols are defined in Routprot.h, while the IP entries are included in Iprtrmib.h.
• dwForwardAge Indicates the age of the route in seconds.
• dwForwardNextHopAS Is the autonomous system number of the next hop.
• dwForwardMetric1 Is a routing protocol-specific metric value. For more information, see RFC 1354. The field contains the route metric value that you normally see when executing the Route.exe print command. For this and the following four fields, if the entry is unused, the value is MIB_IPROUTE_METRIC_UNUSED (-1).
• dwForwardMetric2 Is a routing protocol-specific metric value. For more information, see RFC 1354.
• dwForwardMetric3 Is a routing protocol-specific metric value. For more information, see RFC 1354.
• dwForwardMetric4 Is a routing protocol-specific metric value. For more information, see RFC 1354.
• dwForwardMetric5 Is a routing protocol-specific metric value. For more information, see RFC 1354.

Table B-4. Possible route types for a routing table entry

Forward Type	Description
MIB_IPROUTE_TYPE_INDIRECT	Next hop is not the final destination (remote route)
MIB_IPROUTE_TYPE_DIRECT	Next hop is the final destination (local route)
MIB_IPROUTE_TYPE_INVALID	Route is invalid
MIB_IPROUTE_TYPE_OTHER	Other route

Table B-5. Routing protocol identifiers

Protocol Identifier	Description
MIB_IPPROTO_OTHER	Protocol not listed
MIB_IPPROTO_LOCAL	Route generated by the stack
MIB_IPPROTO_NETMGMT	Route added by Route.exe utility or SNMP
MIB_IPPROTO_ICMP	Route from ICMP redirects
MIB_IPPROTO_EGP	Exterior Gateway Protocol
MIB_IPPROTO_GGP	Gateway Gateway Protocol
MIB_IPPROTO_HELLO	HELLO routing protocol
MIB_IPPROTO_RIP	Routing Information Protocol
MIB_IPPROTO_IS_IS	IP Intermediate System to Intermediate System Protocol
MIB_IPPROTO_ES_IS	IP End System to Intermediate System Protocol
MIB_IPPROTO_CISCO	IP Cisco protocol
MIB_IPPROTO_BBN	BBN protocol
MIB_IPPROTO_OSPF	Open Shortest Path First routing protocol
MIB_IPPROTO_BGP	Border Gateway Protocol
MIB_IPPROTO_NT_AUTOSTATIC	Routes that were originally added by a routing protocol but are not static
MIB_IPPROTO_NT_STATIC	Routes added by the routing user interface or the Routemon.exe utility
MIB_IPPROTO_STATIC_NON_DOD	Identical to PROTO_IP_NT_STATIC except that these routes will not cause Dial on Demand (DOD)
IPX_PROTOCOL_RIP	Routing Information Protocol for IPX
IPX_PROTOCOL_SAP	Service Advertisement Protocol
IPX_PROTOCOL_NLSP	Netware Link Services Protocol

Adding a Route

The next function of the route command is adding a route. Remember that to add a route, the destination IP, netmask, gateway, local IP interface, and metric must be specified. When adding a route, you should verify that the given local IP interface is valid. In addition, when adding a route you will need to refer to the local IP interface on which the route is based by its internal index value. You can obtain this information by calling the GetIpAddrTable function, which is defined as

 DWORD GetIpAddrTable ( PMIB_IPADDRTABLE pIpAddrTable, PULONG pdwSize, BOOL bOrder ); 

The first parameter, pIpAddrTable, is a buffer of sufficient size that will return an MIB_IPADDRTABLE structure. The pdwSize parameter is the size of the buffer passed as the first parameter. The last parameter, bOrder, specifies whether to return the local IP interfaces by ascending IP addresses. To find out the required buffer size, you can pass NULL for pIpAddrTable. Upon return, pdwSize will indicate the required buffer size. The MIB_IPADDRTABLE structure is defined as

 typedef struct _MIB_IPADDRTABLE { DWORD dwNumEntries MIB_IPADDRROW table[ANY_SIZE]; } MIB_IPADDRTABLE, *PMIB_IPADDRTABLE; 

This structure is a wrapper for an array of MIB_IPADDRROW structures. The dwNumEntries field indicates how many MIB_IPADDRROW entries are present in the table field array. The MIB_IPADDRROW structure is defined as

 typedef struct _MIB_IPADDRROW { DWORD dwAddr; DWORD dwIndex; DWORD dwMask; DWORD dwBCastAddr; DWORD dwReasmSize; unsigned short unused1; unsigned short unused2; } MIB_IPADDRROW, *PMIB_IPADDRROW; 

The fields of this structure are defined as follows:

• dwAddr Is the IP address for a given interface.
• dwIndex Is the index of the interface associated with the IP address.
• dwMask Is the subnet mask for the IP address.
• dwBCastAddr Is the broadcast address.
• dwReasmSize Is the maximum reassembly size for datagrams received.
• unused1 and unused2 Are not currently used.

Using this function, you can verify that the local IP interface for the given route is valid. The function for adding the route to the routing table is SetIpForwardEntry, which is defined as

 DWORD SetIpForwardEntry ( PMIB_IPFORWARDROW pRoute ); 

The only parameter is pRoute, which is a pointer to an MIB_IPFORWARDROW structure. This structure defines the elements needed to establish a new route. We have already discussed this structure and its member fields. To add a route, the values must be specified for the fields dwForwardIfIndex, dwForwardDest, dwForwardMask, dwForwardNextHop, and dwForwardPolicy.

Deleting a Route

The last action for the route utility is deleting a route, which is the easiest command to implement. When invoking the route command to delete a route, you must specify the destination address to delete. Then you can search for the MIB_IPFORWARDROW structure returned from GetIpForwardTable that corresponds to the destination address. The MIB_IPFORWARDROW structure can then be passed to the DeleteIpForwardEntry function to remove the given entry. This function is defined as

 DWORD DeleteIpForwardEntry ( PMIB_IPFORWARDROW pRoute ); 

Alternatively, you can specify the fields of pRoute yourself. The fields that are required to remove a route are dwForwardIfIndex, dwForwardDest, dwForwardMask, dwForwardNextHop, and dwForwardPolicy.