[Xorp-users] How to change loopback interface?

Bruce Simpson bms at incunabulum.net
Thu May 7 08:04:17 PDT 2009


Alejandro Berna wrote:
> Hi, I am trying to configure OSPF changing the loopback interfaces of my 
> XORP routers. I have not found how to do with Xorpsh therefore I have 
> done with ifconfig linux command. But when I try to run my config.boot 
> file with the OSPF configuration it fails because XORP still thinks that 
> the loopback address is 127.0.0.1, here is the trace of the error:
> ...
>
> When I again put with ifconfig the loopback to 127.0.0.1 it doesn't 
> fail. I want to define my loopback address as the router-id, 
> 192.168.0.1, how can I change the property my address? And how can I 
> change the loopback address with XORP? Thanks for everything,
>   

I can't understand why you want to configure your loopback interface 
with an RFC 1918 prefix, this is going to break a lot of networking 
software, not just XORP :-)

You need to do one of these following things:

1. configure a separate loopback interface instance using your operating 
system's capabilities to do this, and configure it in the router 
manager, *OR* :-
2. configure *both* the 127.0.0.1 address and another address on the 
default loopback interface. This is usually named lo or lo0.

It is best not to remove 127.0.0.1 from most IPv4 capable hosts. XORP in 
particular assumes the existence of 127.0.0.1 and uses TCP sockets bound 
to this interface address as the default IPC mechanism. It is just one 
of many pieces of software which do this, so please don't remove this 
address.

To the best of my knowledge, XORP's OSPF implementation doesn't need the 
loopback address to be configured with the router ID; as far as I know 
the router ID is an opaque identifier. It is used for winning DR 
elections, sure, but XORP doesn't need to see it on the loopback 
interface. Of course, the normative reference is the code.

cheers,
BMS




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