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Solaris route command

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Routing is the process of forwarding a packet from one computer to another. It is based on an address in the messageís layer-3 header. But thereís more involved than just reading a layer-3 address, though.

The Solaris IP stack maintains a special database called a routing table. When Solaris forwards a packet, it first refers to the routing table to decided where to send the packet. If the host tries to connect to a host which is the same network it just sends packet to the destination (direct routing). If the target host is on another network than host's own, then it sends the data to the router (indirect routing). Often only one router is defined as the 'default gateway'.  In this case from the hostís point of view it outsources all the processing of "non-local" packets to this gateway. If there is no default gateway and the router doesnít find an entry in its routing table that matches the destination network address, the router discards the packet.

The Solaris route command enables manual manipulation of the route table. The routing table contains a list of networks that the router knows it can send packets to, and states over which link to send the packets. These can be static routes, (entered by a system administrator) they can be default routes (a special static route to send unknown destination IP addresses to), or they can be dynamically discovered routes, found using a routing protocol. In case of dynamic routing routers talk to each other and share information about networks they are connected to. That sounds scary and it really is. It also creates the infinite possibilities of misunderstanding. At the same time, dynamic routing takes the building of the routing table out of your hands and puts it into the hands of specific routing protocol. Your job then becomes the monitoring of the routing tables to make sure that the routers are playing nicely with each other. See Routing for more details.

Route command gives the possibility to specify static routes. The syntax of the command is somewhat complicated:

route [-fn] add | delete | get [net|host|default] [destination] [gateway]

With keywords add and delete the default for optional [net|host|default] troika is host.

Here are some examples that might help to learn the intricacies of the command: 

Notes:

  1. Netmask  is used to specify which part of the address is the network number part, and which is the host part. This is accomplished by a logical bitwise-AND between the Netmask and the IP address. The result specifies the network number. For Class C, the Netmask will always be 255.255.255.0; for Class B, the Netmask will always be 255.255.0.0; and so on.
  2. The metric between two machines increases by one each time a new router (gateway) is encountered in the path. RIP routing protocol automatically chooses the path with the lowest metric. The metric information for a path is kept in the kernel's routing table in cache.
  3. When deleting entries from or flushing the routing table, the process in.routed stops listening for RIP broadcasts but continues listening for RDISC advertisements. This freezes the current table. The appropriate process must be manually restarted to have it continue listening for RIP broadcasts.

Specifing default route with /etc/defaultrouter

As we already discussed there are two types of routing:

A default route is a route table entry that allows a host to define default routers to use if no other specific route is available. The default routers must be reliable. There is no need to define every reachable network. All indirectly connected packet destinations go to the default router.

A default router is identified by entries in /etc/defaultrouter.  It contains hostname or IP address entries that correspond to one or more routers. Upon rebooting, this prevents the startup script (/etc/rc2.d/S69inet) from launching the in.routed and in.rdisc dynamic router processes. Default route table entries may also be added by the in.rdisc daemon.

Advantages of default routing are:

Disadvantages of default routing:

Quiz

Q1. Which command manipulates the routing table ?

 A: route

 Q2: Command to add a route to server1 via router1:

 A: route add host server1 router1

Q3. Which command will add a route to the network 128.251.0.0 via 128.144.1.254 ?

 A: route add net 128.251.0.0 128.144.1.254

Q4. Which command would delete a route to host server1 via router1 ?

 A: route delete host server1 router1

Q5. Which command will delete the route to the network 128.251.0.0 via 128.144.1.254 ?

 A: route delete net 128.251.0.0 128.144.1.254

Q6. Which command will remove all entries from the routing table ?

 A: route flush

Q7. Which command allows you to monitor the routing requests that are not getting resolved from the routing table ?

 A7: route monitor

Q8. Which script starts the in.named daemon ?

A:  Depend on the Solaris version:


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Last modified: March 23, 2010