routing
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... But Strict Reverse Path Forwarding has some problems of its own.
First, the test is only applicable in places where routing is
symmetrical - where IP datagrams in one direction and responses from
...
... ISPs, which normally use asymmetrical "hot potato"
routing. Also, if BGP is carrying prefixes and some legitimate
...
... There are operational techniques, especially with BGP but somewhat
applicable to other routing protocols as well, to make strict RPF
work better in the case of asymmetric or multihomed traffic ...
... well, and are valid for consideration. The list is populated using
routing-protocol specific methods, for example by including all or N
(where N is less than all) feasible BGP ...
... methods, for example by including all or N
(where N is less than all) feasible BGP paths in the Routing
Information Base (RIB). Sometimes this method has been implemented
...
... ISP e.g., due to route-maps or
other routing policies not being up-to-date. The failure modes are
typically similar to "operationally enhanced Strict RPF", as
...
... RPF is a very powerful
tool in certain kinds of asymmetric routing scenarios, but it is
important to understand its operational role and applicability
...
...
The questionable benefit of Loose RPF is found in asymmetric routing
situations: a packet is dropped if there is no route at all, such as
...
...
Like Loose RPF, this is useful in places where asymmetric routing is
found, such as on inter-ISP links ...
... ingress filtering mechanism towards a peer (e.g., Strict RPF) works
just fine as long as the routing between the peers is kept reasonably
symmetric. It might even be considered useful to be able to filter
...
...
Where asymmetric routing is preferred or is unavoidable, ingress
filtering may be difficult to deploy using a mechanism such as strict
RPF ...
... network, if multihoming is being used for robustness or
to change routing from time to time depending on measured ISP
behavior, the simplest approach will be to ensure that its ISPs ...
... network.
When a routing protocol is not being used, but rather the customer
information is generated from databases ...
... RPF assumes the consistent origination and
propagation of routing information to work; the implications of
this must be understood especially if a prefix advertisement
...