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ICMP Router Discovery (RDISC) Protocol in Solaris

The RDISC Protocol implemented in Solaris by in.rdisc daemon sends and receives router advertisement messages pertaining to default routes. RFC 1256 specifies the format of related ICMP messages.

• Routers that run the in.rdisc process with the -r option advertise their presence using the 224.0.0.1 multicast address every 600 seconds (10 minutes).
• Non-routers, running the in.rdisc process that is started with the -s option, listen to the 224.0.0.1 multicast address for these router advertisement messages.
• The in.rdisc process builds a default route entry for each router from which an advertisement is received.

Some advantages of the RDISC Protocol are that it:

• Is routing protocol independent
• Uses a multicast address
• Results in small route tables
• Provides redundancy through multiple default route entries

Some disadvantages of the RDISC protocol are:

• An advertisement period of 10 minutes can result in a black hole. A black hole is the time period in which a router path is present in the table, but the router is not actually available. The default lifetime for a non-advertised route is 30 minutes (three times the advertising time interval).
• Routers must still run a routing protocol, such as RIP, to learn about other networks. The RDISC Protocol provides a default route from hosts to routers, not between routers.

The basic syntax for the in.rdisc process is:

/usr/sbin/in.rdisc [-s]
/usr/sbin/in.rdisc -r [-T interval]

The first syntax example is used by non-router systems and is called the host mode. The -s option causes the process to solicit input from routers.

The second syntax example is used by routers and is called the router mode. The -r options causes the in.rdisc process to advertise the system as a router.

The in.rdisc process sends three solicitation messages when it starts to quickly discover available routers.

qTo change the interval for router advertisements to 100 seconds from the default of 600 seconds, use the following command:

# /usr/sbin/in.rdisc -r -T 100

Quiz

Q1: Which statements indicate ways by which default route entries could be generated and appear in the route table? (Choose two.)

1. Running the in.routed daemon.
2. Running the in.rdisc daemon.
3. Making an appropriate entry in the /etc/default/routers file
4. Making an appropriate entry in the /etc/default/gateways file.

A: b,c