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JUNOS 10.1 Network Interfaces Configuration Guide
The packet is not accepted when either of the following is true:
Unicast RPF Behavior Without a Default Route
If you do not configure a default route, or if the default route does not use an interface
configured with unicast RPF, unicast RPF behaves as described in "Configuring
Unicast RPF Strict Mode" on page 215 and "Configuring Unicast RPF Loose Mode" on
page 216. To summarize, unicast RPF without a default route behaves as follows:
Unicast RPF with Routing Asymmetry
In general, we recommend that you not enable unicast RPF on interfaces that are
internal to the network because internal interfaces are likely to have routing
asymmetry. Routing asymmetry means that a packet s outgoing and return paths are
different. Routers in the core of the network are more likely to have asymmetric
reverse paths than routers at the customer or provider edge. Figure 8 on page 218
shows unicast RPF in an environment with routing asymmetry.
Figure 8: Unicast RPF with Routing Asymmetry
In Figure 8 on page 218, if you enable unicast RPF on interface
destined for Router A is not rejected. If you enable unicast RPF on interface
traffic from Router A is rejected.
If you need to enable unicast RPF in an asymmetric routing environment, you can
use fail filters to allow the router to accept incoming packets that are known to be
arriving by specific paths. For an example of a fail filter that accepts packets with a
specific source and destination address, see "Example: Configuring Unicast RPF" on
page 219.
218
Configuring Unicast RPF
The source address of the packet does not match a prefix in the routing table.
The interface does not expect to receive a packet with this source address prefix.
Strict mode—The packet is not accepted when either of the following is true:
The packet has a source address that does not match a prefix in the routing
table.
The interface does not expect to receive a packet with this source address
prefix.
Loose mode—The packet is not accepted when the packet has a source address
that does not match a prefix in the routing table.
, traffic
so-0/0/0
so-1/0/1
,
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