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XRPi Documentation - Interfacing

Loopback

Name

LOOPBACK -- Loopback Interfacing.

Description

Loopback interfaces and ports reflect or "loop back" any packets sent to them. This facilitates self-connections, and is used mainly for test purposes.

They are not required for normal use, and may cause problems in certain circumstances, so it is recommended that you don't use them unless you really need to.

A typical INTERFACE and PORT for loopback purposes is shown below: 

	INTERFACE=3
		TYPE=LOOPBACK
		PROTOCOL=KISS
		MTU=576
	ENDINTERFACE

	PORT=3
		ID=Internal Loopback
		INTERFACENUM=3
	ENDPORT

The PROTOCOL directive specifies the encapsulation protocol for the interface, and this dictates the protocols that can be used for self-connects as follows:

Protocol  Supported protocols
NONEAX25, IP, ARP, ICMP
ETHERAX25, IP, ARP, ICMP
KISSAX25 only. Up to 16 PORTs may be attached.
SLIPIP, ICMP, ARP

The above self-connect protocols can in turn support many others. For example, AX25 supports NetRom and IP. IP supports TCP, UDP, AXIP and so on.

The use of any other PROTOCOL directive causes the interface to default to KISS mode.