Using as set a list of routes to advertise

[William]

On 13/05/2023 4:12 pm, Ross Tajvar wrote:
> What are you using the prefix set for in the first place?
In this particular case it is used to filter inbound and restrict 
outbound advertisements with upstream BGP routers to ensure that site 
doesn't receive its own routes back, but also protect the rest of the 
network from accidentally advertising the wrong routes (like default route).

In some situations the routes may be directly connected (and so fed into 
the route tables by direct protocol entries), others via downstream 
hosts like I mentioned and that point we need to add the routes 
one-by-one into the tables.

> On Thu, May 11, 2023, 2:34 AM William <bird at is.unlawful.id.au> wrote:
>
>     On 10/05/2023 19:46, Maria Matejka via Bird-users wrote:
>     > Hello!
>
>     Thanks for replying.
>
>     > On 5/10/23 11:13, William wrote:
>     >> Hi All,
>     >> I've been digging around trying to find a nice way of doing it but
>     >> can't seem to find a valid answer.
>     >>
>     >> Is there a way to use a prefix set to create static routes?
>     >
>     > No, this is not possible and implementing this would be surprisingly
>     > difficult as the prefix sets are implemented as a compressed trie
>     > optimized for fast lookup and not enumeration.
>     >
>     > Also imagine this:
>     >
>     >   define my_route_set = [ 2001:db8/32+ ]; # note the plus sign
>     >   protocol static { ipv6; route my_route_set via
>     2001:db8::dead:beef; }
>     >
>     > This short code would generate approx. 7.9e28 routes.
>
>     Yeah, that could hurt.
>
>     >
>     > If you could elaborate more precisely what you are trying to achieve
>     > as a whole result, we may try to help you find how to do it in
>     the way
>     > BIRD is designed.
>
>     We have a number of remote sites where there are non-dynamically
>     routed
>     downstream subnets that we need to add as static routes (anything
>     from 1
>     to 20+ per site) but also advertise upstream back into the WAN.
>
>     Instead of specifying each prefix as an individual static route I was
>     hoping to be able to use the existing prefix set to act as a list of
>     routes to add.  If there was a way to iterate over the set in a loop
>     fashion then that would suffice.  In our instance there aren't
>     modifiers
>     on the masks (no -'s, +'s or {minlen, maxlen}) hence the idea of
>     being
>     able to use the set as "just a list" - this could be a condition of
>     using it for that function.
>
>     For example (twist on my original):
>
>     define my_route_set = [ 10.1.2.3/24 <http://10.1.2.3/24>,
>     172.20.4.2/24 <http://172.20.4.2/24>, 10.200.0.0/23
>     <http://10.200.0.0/23> ];
>
>     protocol static route_set {
>        ipv4 {
>          table Some_Routes;
>        }
>        for ThisRoute in my_route_set {
>          route ThisRoute via 192.168.55.2;    # downstream static gateway
>        }
>        route 5.6.7.8/32 <http://5.6.7.8/32> via 192.168.55.1;
>     }
>
>     Resulting in:
>     bird> sh route table Some_Routes
>     Table Some_Routes:
>     10.1.2.3/24 <http://10.1.2.3/24>           unicast [route_set
>     2023-05-10] * (200)
>             via 192.168.55.2 on ens256
>     10.20.4.2/24 <http://10.20.4.2/24>          unicast [route_set
>     2023-05-10] * (200)
>             via 192.168.55.2 on ens256
>     10.200.0.0/23 <http://10.200.0.0/23>         unicast [route_set
>     2023-05-10] * (200)
>             via 192.168.55.2 on ens256
>     5.6.7.8/32 <http://5.6.7.8/32>          unicast [route_set
>     2023-05-10] * (200)
>             via 192.168.55.1 on ens256
>     192.168.55.0/24 <http://192.168.55.0/24>       unicast [Local_Ints
>     2023-05-10] * (240)
>             dev ens256
>     bird>
>
>     Hope that explains better what I'm hoping to achieve.  I couldn't
>     see a
>     way of doing it with if..then..else or case statements. The only
>     other
>     option would be to have a script scrape the set out of the config and
>     prepare an include file *shudder*.
>
>     Regards,
>     William
>
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