z/OS TCPCS7

Static route statements for z/OS® TCPCS7:

BEGINRoutes                              
;
;Network/mask              FirstHop      LinkName   PacketSize
Route 9.67.106.0/24        =             CTC7TO4   MTU 1500       ;route1  
Route 9.67.100.0/24        =             CTC7TO8   MTU 1500       ;route2  
Route 9.67.102.0/24        =             CTC7TO3   MTU 1500       ;route3  
Route 9.67.103.0/24        =             CTC7TO6   MTU 1500       ;route4  
Route 9.67.107.0/24        =             CTC7TO5   MTU 1500       ;route5  
Route 4.4.4.4/32           9.67.106.4    CTC7TO4   MTU 1500       ;route6  
Route 10.1.1.0/24          9.67.106.4    CTC7TO4   MTU 1500       ;route7  
Route 20.1.1.0/24          9.67.107.5    CTC7TO5   MTU 1500       ;route8  
Route 30.1.1.0/24          9.67.103.6    CTC7TO6   MTU 1500       ;route9  
Route 130.200.0.0/14       9.67.100.8    CTC7TO8   MTU 1500       ;route10 
Route 130.200.0.0/14       9.67.102.8    CTC7TO3   MTU 1500       ;route11 
Route 130.203.0.0/16       9.67.102.3    CTC7TO3   MTU 1500       ;route12 
Route DEFAULT              9.67.107.5    CTC7TO5   MTU 1500       ;route13 
;
;Destination/PrefixLen     FirstHop      Interface  PacketSize
Route FE80::1:2:3:3/128    =             OSAQDIO76 MTU 5000 REPL  ;route14
Route FE80::1:2:3:4/128    =             OSAQDIO76 MTU 5000 REPL  ;route15
Route 2001:0DB8:0:A1B::/64 FE80::1:2:3:3 OSAQDIO76 MTU 5000 REPL  ;route16
Route 2001:0DB8:0:A1C::/64 FE80::1:2:3:4 OSAQDIO76 MTU 5000 REPL  ;route17
Route DEFAULT6             FE80::1:2:3:4 OSAQDIO76 MTU 5000 REPL  ;route18
EndRoutes                                              

BSDROUTINGPARMS statements for z/OS TCPCS7:

BSDRoutingParms TRUE                                                            
; Linkname    MTU    Metric    Subnet Mask     Dest Address                     
  CTC7TO8     1500        0    255.255.255.0   0                                
  CTC7TO3     1500        0    255.255.255.0   0                                
  CTC7TO6     1500        0    255.255.255.0   0                                
  CTC7TO4     1500        0    255.255.255.0   0                                
  CTC7TO5     1500        0    255.255.255.0   0                                
  VIPA1A      1500        0    255.255.255.252 0                                
  EndBSDRoutingParms                                                            
;                                                         

The sample configuration has an IPv4 supernet route for 130.200.0.0. An IPv4 supernet route means that the netmask for the route is smaller than the class netmask. In this case, 130.200.0.0 is a class B address. The default netmask for class B is 255.255.0.0. The netmask used for this sample is 255.252.0.0, which is less than 255.255.0.0, hence making this a supernet route. In routing, the stack prefers a route that has the most bits in common. Therefore, the stack chooses a route in the following order:

1. If a route exists to the destination address (a host route), it is chosen.
2. At this point, the route chosen depends upon the version of IP being used:
   • For IPv4:
     1. If subnet, network, or supernetwork routes exist to the destination, the route with the most specific network mask (the mask with the most bits on) is chosen.
     2. If the destination is a multicast destination and a multicast default route exists, that route is chosen.
   • For IPv6, if prefix routes exist to the destination, the route with the most specific prefix is chosen.
3. Default routes are chosen when no other route exists to a destination.

For example, for TCPCS4 (and when trying to reach 130.200.0.0), route12 in the list is used, which is the supernet route 130.200.0.0 with mask 255.252.0.0. If applying the mask of that route, 255.252.0.0, to the destination IP address, 130.200.0.0, the result is 130.200.0.0, which is the IP address of this route. Now, when trying to reach destination 130.203.5.2, the stack would use route13 in the list, which is a network route for 130.203.00 with mask 255.255.0.0. If applying the mask of that route, 255.255.0.0, to the destination IP address, 130.203.5.2, the result is 130.203.00, which is the IP address of this route.

For TCPCS4, route7 and route8 are examples of equal cost multipath routes to get to 9.67.103.0 subnet. This means that TCPCS4 has two different routes to get to this destination. If IPCONFIG MULTIPATH is not enabled, then only route7 will be used as long as it is active. This is because the stack chooses the first route and ignores route8. If route7 becomes inactive, then the stack will switch and use route8. If MULTIPATH is enabled, then the stack will use both routes according to the MULTIPATH specification.

In the preceding example, all of the IPv4 links have a subnet mask of 255.255.255.0 because this is what is specified for the links in the BSDROUTINGPARMS. Therefore, to determine the broadcast addresses for link CTC4TO3, AND the IP Address, 9.67.101.4, and the subnet mask, 255.255.255.0, to yield the subnet for this link, 9.67.101.0. Then, OR the subnet, 9.67.101.0, with the complement of the subnet mask, 0.0.0.255. This determines that the broadcast address for this link is 9.67.101.255.

For TCPCS4, route15 and route16 would be selected to reach host FE80::1:2:3:3 and host FE80::1:2:3:4 respectively. Route17 and route18 would be selected to reach any IPv6 address that had the first 64 bits of 2001:0DB8:0:A1B and 2001:0DB8:0:A1C respectively. Route19 would be selected for any other IPv6 destination.