HOWTO: Learning recursive routes from kernel protocol

[Сергей Попович]

 Deploying VLAN per user with IP unnumbered schema using Linux as access server
we face with following problem:

  BIRD's kernel protocol does not learn routes with nexthop, that resolves trought
  another route (recursive routes).

This is reproducable for both IPv4 and IPv6.
----------------------------------------------------------

While for IPv4 this has minimal impact, as typically customer gets its /32 ip address and
entire LAN part of the customer connection uses addresses from RFC1918 and NAT.

For IPv6 this becomes more complicated:
  - there is no NAT in such view as with IPv4, (ok)
  - as with IPv4 customer gets one IPv6 address on its WAN interface (ok)
  - customer gets additional IPv6 block with 64 long prefix for its LAN interface (fail)

So for typical IPv6 deplyment with IP unnumbered schema we need:
# ip -6 route add fd11::2/128 dev vlan10 proto static src fd11::1
# ip -6 route add fd22::/64 dev vlan10 via fd11::2 proto static src fd11::1
# birdc 'show route filter { if proto = kernel254 then accept; reject; }'
BIRD 1.3.9 ready.
fd11::2/128 dev qinq22.226 [kernel254 12:57] * (10)

Last route MUST be advertised using dynamic routing protocol (BGP in our case).

Example of such routes for both IPv4 and IPv6 is:
------------------------------------------------------------------

# ip -4 route add 192.168.1.2/32 dev vlan10 proto static src 192.168.1.1
# ip -4 route add 10.0.1.0/24 dev vlan10 via 192.168.1.1 proto static src 192.168.1.1
# birdc 'show route filter { if net = 10.0.1.0/24 then accept; reject; }'
BIRD 1.3.9 ready.

# ip -6 route add fd8e:579a:623c:826a::2/128 dev vlan10 proto static src fd8e:579a:623c:826a::1
# ip -6 route add fd8e:579a:623c:ffff::/64 dev vlan10
# birdc 'show route filter { if net = fd8e:579a:623c:ffff::/64 then accept; reject; }'

Kernel protocol configuration
---------------------------------------
protocol kernel kernel254 {
    persist no;
    scan time 120;
    learn yes;
    device routes no;
    kernel table ipt_main;
    import filter {
        # Import only 'static' routes
        if krt_source != ipp_static then
            reject;
        accept;
    };
    export all;
}

Workaround
-----------------
Use static protocol with routes not learned from kernel.

protocol static static254 {
  route fd8e:579a:623c:ffff::/64 drop;
}

Any ideas about solution/other workarouns for this problem are welcome.

--
SP5474-RIPE
Sergey Popovich
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