BSDROUTINGPARMS statement

Restriction: The BSDROUTINGPARMS statement applies only to IPv4 interfaces defined with the LINK statement.

Use the BSDROUTINGPARMS statement to define the characteristics of every physical link defined at the host. This includes links used for static routing.

For more information about subnet masking, see z/OS Communications Server: IP Configuration Guide.

When not using OMPROUTE, define links in BSDROUTINGPARMS. Otherwise, the values for MTU and subnet mask for links are filled in from BEGINROUTES statements, if any. These assumed definitions might not provide good performance or function.

If using OMPROUTE, it is not necessary to define the BSDROUTINGPARMS statement because the parameters are overridden by OMPROUTE. However, if the Ignore_Undefined_Interfaces option is defined in OMPROUTE such that a default interface definition is not generated for a corresponding link, BSDROUTINGPARMS might need to be defined to specify interface characteristics for that link. If OMPROUTE does not have the equivalent parameters coded for a corresponding link, it provides defaults that might not provide good performance or function.

Parameters

TRUE

Specifies that the maximum packet size for the interface is always used regardless of whether the destination is one or more hops away.

FALSE

Specifies that the default maximum packet size of 576 is used (rather than the packet size of the interface) when sending to networks that are not locally attached.

link_name

The name of the link as defined in a LINK statement.

Requirements:

• Each link must be defined once in the BSDROUTINGPARMS statement.
• To be used, a link must be defined at the time the BSDROUTINGPARMS statement is processed. If the corresponding link name is not defined in the HOME list, the link has no HOME address and is rendered as unusable until a HOME address is assigned.

mtu

The maximum packet size for this interface. The DEFAULTSIZE keyword can be used to designate the default of 576. The minimum value is 1, and the maximum value is 65 535.

See Figure 1 for more information about the largest MTU value supported by each link type.

The MTU value specified on BSDROUTINGPARMS statement is also used for applications that use the setsockopt() IP_MULTICAST_IF option to specify the route for multicast datagrams.

Tip: See z/OS Communications Server: IP Configuration Guide, section Maximum transmission unit considerations, for additional information about how TCP/IP uses the MTU to determine the largest size frame to send.

cost_metric

Specifies the interface-level metric associated with the cost of use for the link. If using OMPROUTE, the value of cost_metric is overridden with a corresponding interface parameter value that might be coded or set (Cost0= on OSPF_INTERFACE or In_Metric= on RIP_INTERFACE). The default is 0.

subnet_mask

A bit mask (expressed in dotted decimal form), having bits in the network or host portions, that define the link-level subnet mask associated with the link and acts as a default for a route-level subnet mask to be used for routes dynamically created over this link.

Requirement: The bits must be contiguous from left to right.

The subnet_mask is related to the HOME IP address of the link. If the subnet_mask equals 0 to indicate that the network is not subnetted, the default is the network class mask, which is based on an IP address class. By definition, the network class masks are:

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

A subnet mask is used in calculation of a subnet, network, or supernet route. A subnet route is used to represent multiple hosts in a subnet, a network route is used to represent multiple subnet routes (or multiple hosts if the network is not subnetted), and a supernet route is used to represent multiple network routes in a supernet. For Classless Inter-Domain Routing (CIDR) support, variable-length subnet masks can be used. Variable-length subnet masks can be used in a single network; that is, multiple subnets having the same network number can have different subnet masks. Fixed-length subnet masks are used in a single network with multiple subnets having the same network number and subnet mask. A subnet mask that is less than the network class mask is considered to be a supernet mask. A supernet mask can be defined such that multiple networks can be represented by a single supernet.

Restriction: The host mask of 255.255.255.255 cannot be used for the interface-level subnet mask; however, an implicit host route based on its home IP address is dynamically created internally for this link.

dest_addr

Destination address applies to point-to-point links only. A nonzero destination address applies to nonbroadcast-capable and nonmulticast-capable point-to-point links. If 0 is coded, a directed broadcast or multicast address is used; otherwise, insert the address of the host on the other end of the link. For VIPA links, this field should be 0.

See Figure 1 for more descriptions about devices and links.

Steps for modifying

To modify the BSDROUTINGPARMS statement for a link, use a VARY TCPIP,,OBEYFILE command with a data set which defines a new BSDROUTINGPARMS statement for a link with the same link_name. The new BSDROUTINGPARMS statement is a complete replacement for the original BSDROUTINGPARMS statement. If you have changed the link's IP address, or the order of the HOME list entries, along with the BSDROUTINGPARMS changes, remember to include the new HOME list statement in the same VARY TCPIP,,OBEYFILE command data set as the new BSDROUTINGPARMS statement.

For more information about the VARY TCPIP commands, see z/OS Communications Server: IP System Administrator's Commands .

Usage notes

• For rules on defining virtual IP addresses for VIPA links, see HOME statement.
• The maximum transmission unit (MTU) and metric of any other links with a destination address in the same subnet are updated to ensure that all entries in the same subnet have the same routing values. Except for these links and the LOOPBACK link, all links get default BSD values if not specified.
• If no HOME address exists for a LINK or if a HOME address is changed by way of a later VARY TCPIP,,OBEYFILE command, processing of the HOME statement verifies whether subnet_mask value on the BSDROUTINGPARMS statement is within the valid ranges.
• When an incorrect BSDROUTINGPARMS entry is encountered, all entries following that entry on that BSDROUTINGPARMS statement are ignored. Subsequent BSDROUTINGPARMS statements are processed.
• BSDROUTINGPARMS statements can only be coded for LINK names that exist in the HOME list when the statement is processed. Thus, LINKs from IPCONFIG DYNAMICXCF and the VIPADYNAMIC block should not be included in BSDROUTINGPARMS statements of the initial PROFILE.TCPIP. However, the data set used on a VARY TCPIP,,OBEYFILE command can contain BSDROUTINGPARMS statements with LINKs from IPCONFIG DYNAMICXCF and the VIPADYNAMIC block.
• The BSDROUTINGPARMS parameter values are displayed with the Netstat DEvlinks/-d commands. If the BSDROUTINGPARMS statement is not defined, the values of the displayed parameters are either the defaults from the BEGINROUTES statement, or are from the OMPROUTE configuration statements.

Related topics

• BEGINROUTES statement
• DEVICE and LINK - VIRTUAL devices statement
• HOME statement
• IPCONFIG statement