1. For EBGP,
the next hop is always the IP address of the neighbor specified in the neighbor
command. For IBGP, the protocol states that the next hop advertised by EBGP
should be carried into IBGP“You would need to be running internal IGP in order
for the default behavior to work. To change the default behavior, you would use
neighbor X.X.X.X next-hop-self
2. Networks
originated via an “aggregate” command will have a next hop of 0.0.0.0.
3. A rule of
aggregation is “Aggregation applies only to routes that exist in the BGP
routing table. An aggregated route is forwarded if at least one more specific
route of the aggregation exists in the BGP routing table”.
4. If you
see (s>) under show ip bgp, it specifies the route is suppressed (Not Being
Advertised by design).
What are the well known communities of the BGP community attribute?
A. The community attribute is a transitive, optional attribute designed to group destinations in a certain community and apply certain policies (such as accept, prefer, or redistribute). This table shows the well known BGP communities.
Community Description Local-AS Use in confederation scenarios to prevent sending packets outside the local autonomous system (AS). no-export Do not advertise to external BGP (eBGP) peers. Keep this route within an AS. no-advertise Do not advertise this route to any peer, internal or external. none Apply no community attribute when you want to clear the communities associated with a route. internet Advertise this route to the internet community, and any router that belongs to it.
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