Modifying the ISNO options with SMIT

You can change the ISNO options with SMIT.

Enter the following at the command line:

# smitty tcpip

Select the Futher Configuration option.
Select the Network Interfaces option.
Select the Network Interface Selection.
Select the Change/Show Characteristics of a Network Interface.
Select the interface with your cursor. For example, en0

Then, you will see the following screen:

Change / Show a Standard Ethernet Interface

Type or select values in entry fields.
Press Enter AFTER making all desired changes.

                                                     [Entry Fields]
  Network Interface Name                              en0
  INTERNET ADDRESS (dotted decimal)                  [192.0.0.1]
  Network MASK (hexadecimal or dotted decimal)       [255.255.255.0]
  Current STATE                                       up                          +
  Use Address Resolution Protocol (ARP)?              yes                         +
  BROADCAST ADDRESS (dotted decimal)                 []
  Interface Specific Network Options
    ('NULL' will unset the option)
    rfc1323                                          []
    tcp_mssdflt                                      []
    tcp_nodelay                                      []
    tcp_recvspace                                    []
    tcp_sendspace                                    []


F1=Help                       F2=Refresh                    F3=Cancel                     F4=List
Esc+5=Reset                   Esc+6=Command                 Esc+7=Edit                    Esc+8=Image
Esc+9=Shell                   Esc+0=Exit                    Enter=Do

Notice that the ISNO system defaults do not display, even thought they are set internally. For this example, override the default value for tcp_sendspace and lower it down to 65536.

Bring the interface back up with smitty tcpip and select Minimum Configuration and Startup. Then select en0, and take the default values that were set when the interface was first setup.

If you use the ifconfig command to show the ISNO options, you can see that the value of the tcp_sendspace attribute is now set to 65536. The following is an example:

# ifconfig en0
en0: flags=5e080863,c0<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT,CHECKSUM_OFFLOAD,PSEG,CHAIN>
          inet 192.0.0.1 netmask 0xffffff00 broadcast 192.0.0.255
          tcp_sendspace 65536 tcp_recvspace 65536

The lsattr command output also shows that the system default has been overridden for this attribute:

# lsattr -E -l en0
alias4                      IPv4 Alias including Subnet Mask           True
alias6                      IPv6 Alias including Prefix Length         True
arp           on            Address Resolution Protocol (ARP)          True
authority                   Authorized Users                           True
broadcast                   Broadcast Address                          True
mtu           1500          Maximum IP Packet Size for This Device     True
netaddr       192.0.0.1     Internet Address                           True
netaddr6                    IPv6 Internet Address                      True
netmask       255.255.255.0 Subnet Mask                                True
prefixlen                   Prefix Length for IPv6 Internet Address    True
remmtu        576           Maximum IP Packet Size for REMOTE Networks True
rfc1323                     Enable/Disable TCP RFC 1323 Window Scaling True
security      none          Security Level                             True
state         up            Current Interface Status                   True
tcp_mssdflt                 Set TCP Maximum Segment Size               True
tcp_nodelay                 Enable/Disable TCP_NODELAY Option          True
tcp_recvspace               Set Socket Buffer Space for Receiving      True
tcp_sendspace 65536         Set Socket Buffer Space for Sending        True