[Babel-users] Question about source specific routing

[Matthieu Boutier]

Hello,

This is an interesting problem.

> Router A had address 10.0.200.1 and has a default route, which babel shares using src-prefix 10.0.0.0/16 <http://10.0.0.0/16>.

> root at B:~# ip rule show
> 0:    from all lookup 128 
> 1:    from all lookup local 
> 100:    from 10.0.100.0/16 <http://10.0.100.0/16> lookup 10 

Not the actual problem, but this should be 10.0.0.0/16 instead of 10.0.100.0/16.  Is your A configuration file correct?

> My question is: Shouldn't the route for 10.0.100.0/24 <http://10.0.100.0/24> appear in the source specific table of router B?

It's "normal", but not desirable in this case.  It's a "not implemented" part (kernel routes are not considered).  The point is that considering kernel (FIB) routes is not an obvious choice: at which point should we correct the FIB.  For instance, we probably don't want to see Babel inserting additional routes when there is only kernel routes.

1. Should we add a (D, S) route (with the corresponding rule) for each "src-prefix <prefix>" configuration directive ?

2. Should we fix the FIB ? (detecting rules associated to imported tables, and fixing the routing)

3. Should we fix the redistributed routes of the FIB ? (creating rules for "src-prefix" config, adding additional entries in that table, even without receiving routes)

4. Should we fix routing for redistributed routes and babel routes pairs ?

Now, I would say "Probably" for the 1, "No" for 2, "Unclear" for the 3, and "Yes" for the 4.

Dealing with redistribution is always difficult…  I'll sleep on that before writing a patch.  Don't hesitate to give your opinion.  Before a suitable solution is written, you may be able to temporarily fix your problem with some kind of "ip rule add prio 90 to 10.0.100.0/24 table 254".

Matthieu

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