R I P & RIPv2 summary

Generals

RIP (Routing Information Protocol) is and old protocol but still used.

It is an IGP (Interior Getaway Protocol) very useful for small homogeneous networks.

It uses the UDP in broadcast mode to exchange the routing information.

• Updates are done every 30 seconds.
• If no update info is received within 180 seconds, it marks the routes used as useless.
• If no update info is received within 240 seconds, it removes all corresponding routing tables info.

Characteristics:

· The routing calculation is based on the hops number (hop count).

· Each new routing info that is learned is set to the administrative distance of 120.

· A directly connected network has a distance of 0, whereas an inaccessible network is set to 16.

Configuration

• Launching:

The command line “router rip”, in the configuration mode, allows to:

- Set up the configuration mode

- Activate the Rip protocol

This done, you need to enter the network addresses directly connected to the router for updates.

This includes all the networks that need to receive the routing updates.

By using this command line “network {address}” from the configuration mode.

· Unicast update:

The default updates are set to broadcast.

You can change this by using the command line ”neighbor {address}”, being in config mode.

· Calculation offsets:

The learned routing table values are usually set to the sum of the values found in the update packet and the value of the link between the local router and the router to update.

You can add a selective increment mechanism to this calculation.

The command line “offset-list [acl] {in | out} {value} [{type} {number}] “ of the config. mode is the way to do it.

- [acl]: name or ACL number used to reduce the offset-list (optional parameter).

- {in | out}: the offset-list will be in use at the reception or the emission.

- {value}: the number to add to the routing calculation.

- [{type}{number}]: you can use this command line for a specific interface too(optional).

· Timers:

All routing protocols are using different timer types.

This is used to manage the routing table.

Timers used by RIP:

- update timer: transmission gap of the update packets(default is 30 seconds)

- invalid timer: non updating time for a route before it is marked as useless (default is 180 s).

- hold-down timer: after this time, the non updated entry is not scanned anymore for the best route calculation.

- flush timer: after this time, the non updated entry will be suppressed from the routing table(default is 240 s).

Using the command line “timers basic {update} {invalid} {holddown} {flush} from the config mode does this,

.

· RIP version:

You can specify the RIP version used for updates sent and received.

Here is the chart for the command lines:

Command line	Description
version {1 | 2}	Send or receive version 1 or 2 only
ip rip send version {1 | 2 | 1 2}	Send update packets for version 1 or 2 or 1 and 2
ip rip receive version {1 | 2 | 1 2}	Same for reception.

· RIP authentication:

RIPv2 is using authentication, so you can find a couple of command line to configure this.

- ip rip authentication key-chain {word}: character chain used to authenticate.

- Ip rip authentication key-chain {text| md5}: this character chain can be encrypted (md5).

These command lines can be used in the config mode, from the considered interface.

Authentication config must be done for each connected router.

· Routes grouping:

RIPv2 is a classless protocol.

It means that it can manage also sub-network routes.

Not reserved for a certain kinds of predefined address classes.

One of the specifications of RIPv2 is the possibility of grouping routes, usually called “route summarization”.

This allows simplifying the routing tables by grouping several sub-network routes within a solely generalized one by using the corresponding class-full network.

Using the “auto-summary” command line from the config mode can do grouping the routes.

· Source IP addresses validation:

A router validates the update ource packet ip addresses.

If this address is useless, the router drops down the update.

Using the “validate-update-source” command line from the config mode can do the source IP address validation.

· Split horizon:

Split horizon is activated by default for all media types except for SMDS and Frame Relay.

Using the “ip split-horizon” command line can do the activation of a specified interface.

If you have an interface configured with one or several secondary ip addresses and split-horizon validated, the updates won’t be done for every secondary ip address.

Only one update will be performed for each network.

· Inter-packet delay:

RIP sometimes performs several update packets at the same time.

These updates are immediately sent one after another.

By using the command line “output-delay {delay}” from the config mode, you can set a delay in a matter of 8 to 50 milliseconds.