bin/111493: routed doesn't use multicasts for RIPv2 via P2P interfaces

[Dan Lukes]

The following reply was made to PR bin/111493; it has been noted by GNATS.

From: Dan Lukes <dan at obluda.cz>
To: Vernon Schryver <vjs at calcite.rhyolite.com>
Cc: freebsd-gnats-submit at FreeBSD.org, bms at incunabulum.net,
        carlson at workingcode.com
Subject: Re: bin/111493: routed doesn't use multicasts for RIPv2 via P2P interfaces
Date: Sun, 22 Jul 2007 21:24:57 +0200

 Vernon Schryver napsal/wrote, On 07/21/07 15:45:
 > If an interface is point-to-point (it sets the IFF_POINTOPOINT bit),
 > is it right to send to the RIPv2 multicast address?
 
 	Why not ?
 
 	To send or not to send the multicast is question related to "is 
 supported or is not supported multicasting on interface". It isn't 
 related to question "is the interface of type X".
 
 > Even on a GRE tunnel, why isn't it better to unicast to the router at
 > the other end of the tunnel instead of multicasting?
 
 'it is better' and 'it is right' is questions of wo different 
 categories. The answer for the first is "yes, there is no reason to 
 forbid multicast addresses on P2P interface when if network stack 
 support it". There is no reason to punish GRE users even if we don't 
 like the protocol personally.
 
 	The answer for the second is not simple. "Better" is subjective 
 category - I don't know the all details of all network specifications of 
 all networks.
 
 	If you trust the administrator to decide on ethernet interface, I see 
 no reason not to trust them on P2P interface as well.
 
 > Consider the error of the missing () in the first change:
 > +                if (ifp->int_if_flags & IFF_POINTOPOINT && ! ifp->int_if_flags & IFF_MULTICAST) {
 
 	You are true.
 
 > description of the failure with the current code.
 
 	The descripion "of the failuter" is simple. The administrator of other 
 side use not FreeBSD nor your routed. It's policy is - RIPv2 on 
 multicasts. The RIPv2 on unicasts are blocked by firewall. He says that 
 RIPv2 daemon on multicast link shall be able to use multicast, unless 
 it's implementation is incomplete.
 
 	I don't want dispute about it's mad policy decision. I dislike the GRE 
 tunnels as you.
 
 	Despite of it, there is no technical reason not to allow RIPv2 
 multicasting over a multicast capable interface, so the statement about 
 incomplete implementation seems to be true.
 
 	The required changes in the current code is simple, but the final 
 decision is yours.
 
 	Please note my knowledge of english language is far from perfect.
 
 					Dan