Prefix not making it through two iBGP sessions

[Brooks Swinnerton]

Hello,

I'm having trouble understanding why certain routes aren't making it
through to an iBGP session on BIRD 2.0.7.

My network layout looks something like below. I have three BIRD instances
running, *Router 1* is connected to *Upstream 1*, *Router 2* is connected
to *Upstream 2*, and *Router 1* and *Router 2* are connected to each other
via iBGP. This all works great.

Upstream 1         Upstream 2
    ▲                  ▲
    |                  |
   eBGP               eBGP
    |                  |
 Router 1 ◀--iBGP--▶ Router 2
    |
   iBGP
    |
    ▼
 Router 3

The problem comes with *Router 3* not receiving routes from *Router 2*.

The iBGP export filter on router1 looks like this:

    export filter {
      if is_v4_bogon() then reject;
      if is_v4_default() then reject;
      if is_v4_peering_net() then reject;
      if is_v4_own_net() then accept;
      if source = RTS_BGP then accept;
      reject;
    };

And if I test each of these functions out manually I can see the prefix
should be allowed through:

bird> show route filter { if is_v4_bogon() then reject; } 174.202.0.0/16
bird> show route filter { if is_v4_default() then reject; } 174.202.0.0/16
bird> show route filter { if is_v4_peering_net() then reject; }
174.202.0.0/16
bird> show route filter { if is_v4_own_net() then accept; } 174.202.0.0/16
bird> show route filter { if source = RTS_BGP then accept; } 174.202.0.0/16
Table master4:
174.202.0.0/16       unicast [cologuard4 21:17:56.850 from 169.254.3.3] *
(100) [AS22394?]
        dev bdr-cologuard

Unfortunately if I look at the session from *Router 1* to *Router 3*
(core_nyiix_14), it is not let through:

bird> show route export core_nyiix_14 174.202.0.0/16
bird>

I've added all of the relevant configuration in this Gist
<https://gist.github.com/bswinnerton/6b7527bc9d78215275c1ae75e64d34cd>.

Any help would be much appreciated.
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