[Xorp-users] New to this multcast - Can this work with xorp?

[Pavlin Radoslavov]

>   I have a linux box that I want it to route multicast trafic from a gre tunnel.
> 
> 
>   The linux box has only 1 network interface. The multicast trafic
> gets in from the tunnel interface and needs to get out to the "real"
> physical interface eth0. Do you think that this setup can work?

Yes, but with a bit of extra tweaking (see below).

>   We are using PIM-SM and a cisco router 2811.
>   I enabled IGMP only on xorp and disabled all the other routing
> protocol, RIP, OSPF, and such.

You need to configure PIM-SM as well on your XORP box.
See the following URL for a sample PIM-SM configuration:

http://xorpc.icir.org/cgi-bin/cvsweb.cgi/xorp/rtrmgr/config/multicast4.boot?rev=1.1&content-type=text/x-cvsweb-markup

The XORP User Manual explains the details of the configuration, but
here are few high-level things you need to be aware of:

The Cand-RP set in all PIM-SM routers must be same. You can use the
following xorpsh command to see it inside XORP: "show pim rps".
There are two ways of setting it in XORP: the dynamic Bootstrap
mechanism and the "static-rps" mechanism.
The Bootstrap mechanism will work if it is enabled on all PIM-SM
routers.
However, for debugging purpose if you know the IP address of the
elected PIM-SM RP (Rendezvous Point) you could use "static-rps"
XORP configuration to point to that RP.
Just be careful that in general there could be more than one RPs
(per multicast group prefix), so make sure there is no mismatch
between the Cisco's RP info and your XORP router. Typically, there
is a single RP (for the whole 224.0.0.0/4 multicast prefix), so
hopefully you have similar setup.

Currently XORP doesn't support the GRE configuration (yet), so you
need to configure it before starting XORP (including its IP
address). Then, it is better to configure it inside the XORP
"interfaces" section like:

interfaces {
    interface gre0 {
        default-system-config
    }

    interface eth0 {
        ...
    }
}

For the eth0 interface you have to option of using the
default-system-config setup (if it already has the IP address(es)
assigned), or explicitly configuring the IP addresses as specified
in the PIM-SM sample configuration.

There is some more GRE-specific setup. See the XORP User Manual
Section 13.3.2 "Configuring Multicast Tunnels on UNIX Systems" for
details.

In general, I would strongly recommend reading at least the
multicast-related chapters in the user manual: Chapters 11--14.
It also contains a brief introduction to multicast and PIM-SM which
you might find useful.

>   So since I am kinda new in all this, is there a way for me to see if
> my setup works? I do a ping to 224.0.0.1 and I get no anser.

In general, ping to a multicast address shouldn't work.

>   I did not set any route for 224.0.0.1, is it XORP that will create
> those routes or I do need to set this route on all my interfaces, on
> the tunnel and on the physical?

XORP (PIM-SM) should set any multicast-related routes.
However, you won't see them with unicast route commands like
"netstat -rn". On Linux you need to use a command like
"cat /proc/net/ip_mr_cache" to show the multicast forwarding cache
in the kernel.

> I will probably have more questions ;)

Feel free to ask them, as long as you read first the
multicast-related sections in the User Manual :)

Regards,
Pavlin