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Date:	Mon, 26 May 2008 13:23:18 -0700
From:	Ben Greear <>
To:	NetDev <>
Subject: Adding multiple multicast routing tables.

I am working on adding support for multiple multicast routing tables, and
would welcome some feedback if anyone has comments.

It looks like there are several globals currently.  I would plan to wrap 
in a 'mroute_table_entry struct and have the global be a hash of these
routing tables.

Inside this table, I'd add a hash of vifs (no more max limit for vifs),
the mroute_socket for this table, and 32-bit vif_index (routing-table id).

In the ip_mroute_setsockopt, add a 32-bit table-id to all of the
optnames.  This will increase the optlen by 4 for all options,
so we can know it's the new API.  For MRT_INIT, could pass
in something like this, for instance:

struct foo {
  uint32 mrt_table_idx;
  uint32 mrt_version;

Or, use entirely new MRT_* sockopts so there is no chance
of confusion.  I plan to update xorp to support this API, so I can be 
flexible on
the API.

User space will need a way to detect the new API.  I could probably
just try to INIT with a larger optlen.  2.6.25 (and probably many previous kernels) 

appears to error nicely if optlen != sizeof(int), so I can trigger on that.

The mcast table ID would be associated directly with the 'regular' routing
table index, so if the mcast is table-id 4444, then any routes 
associated with it
should be added to the unicast routing table 4444.  Or, it could be mapped,
but I am not sure there is much benefit for that added complexity.

getsockopt and the ioctl would need similar changes to the setsockopt.

ip_mr_input looks interesting...not sure how to decide which mroute_socket
it uses...maybe it doesn't matter?

And, for things like pim_rcv*, might need some sort of table lookup to
map a skb->dev into a mroute table so that it can handle the reg_vif_num
thing.  To make this really fast, a new member could be added to struct netdev.

A netdev may belong to no more that one mcast routing table.  If someone 
to share NICS, they can use something like mac-vlans to multiplex the 

Suggestions are welcome.


Ben Greear <> 
Candela Technologies Inc

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