I think the added functionality probably outweighs the possible issues.  I am in favor.

I propose that MICE enable BGP ADD-PATH capability (RFC 7911) on the route servers (in TX mode only). This is negotiated BGP capability, so we do not need any per-participant setting for it.

ADD-PATH is useful if the best path route is being filtered but another route would not be. We discussed adding this at a UG meeting years ago.

There are other IXPs that have this enabled. For example, this one: https://www.bcix.de/ixp/content/0/route-servers

In terms of timeline, I propose something like this:

• January 9: Enable it on Route Server 1.
• January 16: Enable it on Route Server 2.

The actual change looks like this for the RS1-only piece, and then the conditional would be removed when we want to deploy to RS2:

--- a/roles/ixpmanager/files/mice/api/v4/router/server/bird2/neighbors.foil.php
+++ b/roles/ixpmanager/files/mice/api/v4/router/server/bird2/neighbors.foil.php
@@ -315,6 +315,9 @@ protocol bgp pb_<?= $int['fvliid'] ?>_as<?= $int['autsys'] ?> from tb_rsclient {
             import filter f_import_as<?= $int['autsys'] ?>;
             table t_<?= $int['fvliid'] ?>_as<?= $int['autsys'] ?>;
             export filter f_export_as<?= $int['autsys'] ?>;
+<?php if( $t->router->router_id == "206.108.255.1" ): ?>
+            add paths tx;
+<?php endif; ?>
         };
 <?php if( $int['bgpmd5secret'] && !$t->router->skip_md5 ): ?>
         password "<?= $int['bgpmd5secret'] ?>";

-- 

Richard

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