Cluster I/O Protocols (CIP) Configuration and Management Manual (H06.16+, J06.05+)

Network routes are configured on the CLIMs. You specify static routes by using CLIMCMD climconfig
commands. Dynamic routes are created by the system as the result of various protocol events. CIP
keeps separate routing tables for IPv4 and IPv6 destinations. Default routes have a prefix or
subnet-mask length of zero and indicate where to send packets or connections when no other
routes match the destination address. Default routes can be static or dynamic. A CLIM that does
not have a default route cannot route to arbitrary destinations.
If a CLIM is configured to join multiple providers, an independent set of routes is maintained for
each of the providers. When sending packets, only routes for the provider that was used to send
the packet are used.
Each CLIM uploads a copy of the statically-configured entries, entries added for each local IP
address, and the dynamic default entries in its routing tables to the NonStop host system for each
interface as it reports that the interface is up. Each CLIM continues updating the host as changes
are made to its tables. The host merges the routing tables from all the CLIMs in a Provider into one
IPv4 and one IPv6 table for the Provider. When the host needs to use a destination address to
decide which CLIM gets an outgoing connection or packet, it consults the corresponding table. If
it finds that more than one CLIM could be used, it uses round-robin selection to help balance the
load among them. Once the connection or packet gets to the CLIM, the CLIM uses its own tables
to decide on an interface and first-hop destination.
In many environments, nearly all CLIMs have default routes defined and most traffic uses these
routes, so simple round-robin selection may not be adequate. The ROUTE object on the NonStop
host system allows additional control of default route use. Each ROUTE object indicates a CLIM to
use for a default route and a PRIORITY for its use. The PRIORITY is a number from 1 to 100 where
higher numbers indicate higher priority. The CLIM is considered only if it actually has a default
route defined in its routing table for the desired address family. When a default route is needed,
the CLIM with the highest priority is selected. If more than one CLIM has the highest priority,
round-robin selection is used. If no ROUTEs have an available CLIM, any CLIM with a default route
defined is used. If no CLIMs have a default route, the packet cannot be routed.
Every CLIM contains a loopback interface (lo) and the loopback addresses for the configured IP
address families (IPv4 127.0.0.1 and/or IPv6 ::1). When a NonStop host system application
connects or sends to a loopback address or to a local address, the connection or data is sent to
a CLIM and is looped back to the host using the loopback interface. If the sending socket is bound
to a specific local IP address other than a loopback address, then the CLIM containing that address
is chosen. If the socket is not bound or is bound to INADDR_ANY, the CLIM containing the
destination address is used. If the destination is a loopback address, any CLIM can be chosen.
NOTE: If a socket is bound to a specific local address and connects or sends to a local address
on a different CLIM, the data is passed from one CLIM to the other over the external network. Even
though the addresses are both local in the Provider, a path through the external network is required.
Sockets bound to a loopback address are replicated in all the CLIMs of the Provider like sockets
bound to INADDR_ANY. If the socket is later used to listen for incoming connections or packets,
it can get them at that address no matter to which CLIM they are directed.
The NonStop host system performs these steps to select a CLIM for an outgoing connection or
packet in Providers with multiple CLIMs:
1. If the socket has bound to a specific local IP address other than a loopback address (127.0.0.1
or ::1), use the CLIM containing that address.
2. If the destination address is a loopback address, make a round-robin selection of any CLIM.
3. If the destination address is a local address in one of the CLIMs, use that CLIM.
4. If the destination address matches one or more network-route entries that are not default routes,
make a round-robin selection of one of the CLIMs containing the entries with the same longest
matching prefix or subnet-mask length.
5. Make a round-robin selection of any available CLIM that has a default network-route entry.
When selecting a CLIM containing a default route, only the available CLIM(s) with the highest
The CIP Subsystem for Internet Protocols (IP CIP) 35