Meaning of “Loose” Flag in Routing Table

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A question mark next to the route in the routing table symbolizes a  “loose” flag.


This flag is often used for routes coming from BGP protocol because the next-hop attribute is not being changed among iBGP neighbors, so routed process should do reverse routing lookup to determine the real next-hop IP of given route.


See this example:


> show routing route
flags: A:active, ?:loose, C:connect, H:host, S:static, ~:internal, R:rip, O:ospf, B:bgp,
Oi:ospf intra-area, Oo:ospf inter-area, O1:ospf ext-type-1, O2:ospf ext-type-2
VIRTUAL ROUTER: default (id 1)
destination nexthop metric flags age interface next-AS
... ?B 92699 0 10 A S ethernet1/2


owner: djoksimovic

Tags (5)

Is there a problem with this flag being present? It is happening to me between 2 inter-vr iBGP peers, but the routes are still installed and functioning correctly. 

To expand on mbryan's question above - 


Are there any negative repercussions for a route being loose? Will this negatively impact NAT rules, or security policy (proper source/dst zone identification for example?)

I think it isn't called reverse route lookup but sort of route resolution to find directly connected next hop.