bgpd: With suppress-fib-pending ensure withdrawal is sent (backport #17971) #17974
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When you have suppress-fib-pending turned on it is possible to end up in a situation where the prefix is not withdrawn from downstream peers. Here is the timing that I believe is happening: a) have 2 paths to a peer. b) receive a withdrawal from 1 path, set BGP_NODE_FIB_INSTALL_PENDING and send the route install to zebra. c) receive a withdrawal from the other path. d) At this point we have a dest->flags set BGP_NODE_FIB_INSTALL_PENDING old_select the path_info going away, new_select is NULL e) A bit further down we call group_announce_route() which calls the code to see if we should advertise the path. It sees the BGP_NODE_FIB_INSTALL_PENDING flag and says, nope. f) the route is sent to zebra to withdraw, which unsets the BGP_NODE_FIB_INSTALL_PENDING. g) This function winds up and deletes the path_info. Dest now has no path infos. h) BGP receives the route install(from step b) and unsets the BGP_NODE_FIB_INSTALL_PENDING flag i) BGP receives the route removed from zebra (from step f) and unsets the flag again. We know if there is no new_select, let's go ahead and just unset the PENDING flag to allow the withdrawal to go out at the time when the second withdrawal is received. Signed-off-by: Donald Sharp <[email protected]> (cherry picked from commit 4e8eda7)
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When you have suppress-fib-pending turned on it is possible to end up in a situation where the prefix is not withdrawn from downstream peers.
Here is the timing that I believe is happening:
a) have 2 paths to a peer.
b) receive a withdrawal from 1 path, set BGP_NODE_FIB_INSTALL_PENDING
and send the route install to zebra.
c) receive a withdrawal from the other path.
d) At this point we have a dest->flags set BGP_NODE_FIB_INSTALL_PENDING
old_select the path_info going away, new_select is NULL
e) A bit further down we call group_announce_route() which calls
the code to see if we should advertise the path. It sees the
BGP_NODE_FIB_INSTALL_PENDING flag and says, nope.
f) the route is sent to zebra to withdraw, which unsets the
BGP_NODE_FIB_INSTALL_PENDING.
g) This function winds up and deletes the path_info. Dest now
has no path infos.
h) BGP receives the route install(from step b) and unsets the
BGP_NODE_FIB_INSTALL_PENDING flag
i) BGP receives the route removed from zebra (from step f) and
unsets the flag again.
We know if there is no new_select, let's go ahead and just unset the PENDING flag to allow the withdrawal to go out at the time when the second withdrawal is received.
This is an automatic backport of pull request #17971 done by Mergify.