[Xorp-users] Question on supporting multiple routing tables.

[Pavlin Radoslavov]

Ben Greear <greearb at candelatech.com> wrote:

> Hello!
> 
> I am curious how hard it would be to get Xorp to support
> multiple routing tables.  My goal is to support virtual routers (VR).
> 
> For instance, suppose eth0 and eth1 belong to one VR, and eth2 and eth3 to
> a second VR.  I'd associate eth0 and eth1 with routing table X, and eth2 and eth3
> with routing table Y.  I'd want the Xorp daemon to treat the two sets of
> interfaces completely separate, and update the correct routing table as needed.
> Xorp should NOT, for instance, think that eth2 can talk to eth0 unless OSPF
> messages or similar are received on the eth0 and eth2 interfaces allowing such
> communication.
> 
> I already have scripts to create the proper routing tables and a few patches
> to the kernel to make this work, but I'd like to support 'real' routing protocols
> as well.

What kind of isolation do you want between the VRs?
E.g., do you want to run a single XORP instance that will control
two forwarding tables, or do you want to run 2+ XORP instances
(one per forwarding table).

If you want to run 2+ XORP instances, you can probably do it with
just a little bit extra work:

* Right now all forwarding entries are installed in the main
  forwarding table RT_TABLE_MAIN.
  You need to modify the FEA such that it allows to specify the
  corresponding routing/forwarding table ID it should be
  manipulating. The table ID is used inside the
  fea/data_llane/fibconfig/ directory (search for rtm_table).
  There are total of three places where rtm_table is used. In all
  those cases it should take some pre-configured table ID.

  A new configuraion XRL should be added to the FEA that will be
  used to configure/specify the forwarding table ID.
  This XRL should be added to xrl/interfaces/fti.xif and should
  look like:

    /**
     * Set the forwarding table ID.
     *
     * @param table_id the forwarding table ID.
     */
    set_forwarding_table_id ? table_id:u32

  Then, obviously, the processing side for this XRL needs to be
  implemented inside fea/xrl_fea_target.hh and fea/xrl_target.cc

  Finally, inside etc/templates/fea.tp there should be a
  configuration entry for the forwarding table ID.

* Before starting each XORP instance you must specify a different
  port number to be used by the XORP Finder. E.g.:

  setenv XORP_FINDER_SERVER_PORT 20001
  # Start first XORP instance

  setenv XORP_FINDER_SERVER_PORT 20002
  # Start second XORP instance
 
* It is up to you to make sure that inside the XORP configuration
  for each XORP instance you configure/use only those interfaces
  that   correspond to the particular forwarding table. E.g., in the
  first XORP instance you should configure only eth1 and eth2, and
  in the second XORP instance you should configure only eth3 and
  eth4.

BTW, note that the above solution might work for unicast, but won't
work for multicast forwarding, because the UNIX kernel allows
only one open multicast routing socket per system.

If the above is sufficient for your need, then it is relatively easy
to implement it. It will be actually useful for XORP itself, so we
might actually implement it anyway (for free :).


However, if you want to run a single XORP instance that will control
2+ forwarding tables, this will be much more complicated to do.
For example, there should be somewhere a mapping which interfaces are
associated with each forwarding table. Futhermore, if each routing
process needs to be aware about the separation, then it will become
ever more complicated. This might lead to a design which will allow
you to configure, say, 2 OSPF instances each of them talking to 2
RIB instances.

If you have something else in mind, please provide more details.

Regards,
Pavlin

> Assuming this cannot currently be done, if anyone is interested in developing
> this (possibly for a fee), please contact me.  (off-list if the $fee option
> interests you).
> 
> Thanks,
> Ben
> 
> -- 
> Ben Greear <greearb at candelatech.com>
> Candela Technologies Inc  http://www.candelatech.com
> 
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