GRE devices and MULTICAST flag.

3 messages, 2 authors, 2011-09-23 · open the first message on its own page

GRE devices and MULTICAST flag.

From: Ben Greear <hidden>
Date: 2011-09-23 19:56:36

I was under the impression that GRE tunnels could support MULTICAST
traffic, but the MULTICAST flag is not set.  This is making the xorp
router crap out because it checks the MULTICAST flag and will
not start multicast on the interface if it's not set....

Is it supposed to be set?

7: gre0: <NOARP,UP,LOWER_UP> mtu 1476 qdisc noqueue state UNKNOWN
    link/gre 0.0.0.0 brd 0.0.0.0
8: netb: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1476 qdisc noqueue state UNKNOWN
    link/gre 192.168.100.223 peer 192.168.100.138
    inet 10.0.1.1/32 scope global netb


Thanks,
Ben

-- 
Ben Greear [off-list ref]
Candela Technologies Inc  http://www.candelatech.com

Re: GRE devices and MULTICAST flag.

From: Ben Greear <hidden>
Date: 2011-09-23 20:42:53

On 09/23/2011 12:56 PM, Ben Greear wrote:
I was under the impression that GRE tunnels could support MULTICAST
traffic, but the MULTICAST flag is not set. This is making the xorp
router crap out because it checks the MULTICAST flag and will
not start multicast on the interface if it's not set....

Is it supposed to be set?

7: gre0: <NOARP,UP,LOWER_UP> mtu 1476 qdisc noqueue state UNKNOWN
link/gre 0.0.0.0 brd 0.0.0.0
8: netb: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1476 qdisc noqueue state UNKNOWN
link/gre 192.168.100.223 peer 192.168.100.138
inet 10.0.1.1/32 scope global netb
Well, ifconfig netb multicast seems to add the flag,
so maybe all is as it should be.

Thanks,
Ben

-- 
Ben Greear [off-list ref]
Candela Technologies Inc  http://www.candelatech.com

Re: GRE devices and MULTICAST flag.

From: David Lamparter <hidden>
Date: 2011-09-23 21:16:30

On Fri, Sep 23, 2011 at 01:42:53PM -0700, Ben Greear wrote:
On 09/23/2011 12:56 PM, Ben Greear wrote:
quoted
I was under the impression that GRE tunnels could support MULTICAST
traffic, but the MULTICAST flag is not set. This is making the xorp
router crap out because it checks the MULTICAST flag and will
not start multicast on the interface if it's not set....

Is it supposed to be set?

7: gre0: <NOARP,UP,LOWER_UP> mtu 1476 qdisc noqueue state UNKNOWN
link/gre 0.0.0.0 brd 0.0.0.0
8: netb: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1476 qdisc noqueue state UNKNOWN
link/gre 192.168.100.223 peer 192.168.100.138
inet 10.0.1.1/32 scope global netb
Well, ifconfig netb multicast seems to add the flag,
so maybe all is as it should be.
I distinctively remember that the MULTICAST flag is supposed to be an
input to the kernel, not a feature-indication flag output. I'm quite
unsure where I picked this up, but I remember using it in that way that
xorp does and then finding out it's wrong.


-David
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