docs: T9200: note no-ipv6-auto-ra doesn't stop already-active RA (#2195)

* docs: T9200: note no-ipv6-auto-ra doesn't stop already-active RA

no-ipv6-auto-ra only prevents future RA initiation; it doesn't
retroactively silence router advertisements already sent on an
established session. Confirmed on VyOS 1.5.1: neither a soft nor a
hard clear/reset bgp on the neighbor stopped it. Per FRR's
bgp_zebra_terminate_radv()/upstream PR FRRouting/frr#19487, that only
runs when the neighbor's remote-as is removed and re-added.

* docs: T9200: distinguish blast radius of the two RA workarounds

remote-as re-add only affects the one neighbor; a bgpd/frr restart
clears every BGP session on the router. The note listed them as
equivalent options - reframe the restart as a maintenance-window
fallback instead.

Flagged by CodeRabbit review on PR #2195.

* Make the note less wordy

---------

Co-authored-by: Daniil Baturin <daniil@baturin.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/docs/configuration/protocols/bgp.md b/docs/configuration/protocols/bgp.md
index d7310ba2..68902bfb 100644
--- a/docs/configuration/protocols/bgp.md
+++ b/docs/configuration/protocols/bgp.md
@@ -1507,6 +1507,16 @@ for BGP.**
 By default, FRR sends RAs on an interface when its BGP session has
 negotiated the Extended Next Hop capability, or when a BGP neighbor is
 configured by interface name (Unnumbered BGP).
+
+:::{note}
+In current VyOS versions, this only prevents router advertisements
+from starting on sessions
+established *after* the setting takes effect. It does not stop router
+advertisements already active on an established session.
+
+To stop advertisements on a already established sessions,
+you can remove and re-add `remote-as`, or restart the BGP process.
+:::
 ```
 
 ```{note}