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9.6 | ![]() |
BGP Attributes | |
9.6.4 | ![]() |
Next Hop behavior on NBMA networks |
On an NBMA network, the many-to-many direct interaction between
routers is not guaranteed unless virtual circuits are configured from
each router to all other routers. The primary reason that most
organizations implement a hub-and-spoke topology is because of cost
considerations. In a hub-and-spoke topology, multiple remote sites
have virtual circuits connected to one or more routers at a central
site. Figure
![]() The only difference between the environments illustrated is that
the medium in Figure
RTA gets a BGP routing update about 11.11.11.0/24 from RTC and
would try to use RTB, 10.10.10.3, as the next hop. This is the same
behavior as on multiaccess media.
Cisco IOS supports a special case parameter that remedies this situation. The next-hop-self keyword forces the router, in this case, RTC, to advertise 11.11.11.0/24 with itself as the next hop, 10.10.10.2. RTA then directs its traffic to RTC to reach destination 11.11.11.0/24. The syntax for this option is as follows:
For RTC, issue the following command:
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