PIM RPF override configuration
Overview of PIM RPF
Reverse Path Forward (RPF) checking is a core multicast routing mechanism which ensures that the multicast
traffic received has arrived on the expected router interface derived from the L3 table prior to further processing. If
the RPF check fails for a multicast packet, the packet is discarded.
For traffic arriving on the SPT, the expected incoming interface for a given source/group multicast flow is the
interface towards the source address of the traffic (as determined by the unicast routing system.) For traffic
arriving on the RP tree, the expected incoming interface is the interface towards the RP.
RPF override is a feature that allows the override of the normal RPF lookup mechanism and indicates to the
router that it may accept multicast traffic on an interface, other than the normally selected interface by the RPF
lookup mechanism. This includes accepting traffic from a source directly connected to the router when the source
IP address is invalid for the subnet or VLAN to which it is connected. Traffic may also be accepted from a valid
PIM neighbor that is not on the reverse path towards the source of the received multicast traffic.
RPF checking is applied to all multicast traffic and is significant in preventing network loops. Up to eight manual
RPF overrides can be specified.
NOTE:
These static RPF override entries are not distributed.
The manually configured static multicast RPF override is restored on subsequent reboots. The command is
executed in PIM context.
rpf-override
[no] rpf-override [source-ip-addr/mask-length] [rpf-ip-addr]
Add, edit, or delete up to eight RPF override entries. The multicast RPF override has a multicast source address
[source-ip-addr/mask-length]
and an RPF address
[rpf-ip-addr]
pair.
The
no
form of the command deletes the RPF override.
NOTE:
Only host-specific addresses are supported (i.e. “/32” addresses.)
[source-ip-addr]
The IPv4 address of the host from which the multicast flow originated.
[mask-length]
The length, in bits, of the mask used to indicate the range of addresses from
[source-ip-addr]
to which
the RPF override command applies. Currently, only a 32–bit mask is supported, that is, only one host per
entry. Eight individual entries are supported.
[rpf-ip-addr]
The IPv4 address indicating one of two distinct RPF candidates:
1.
A valid PIM neighbor address from which forwarded multicast traffic is accepted with a source address of
[source-ip-addr]
.
2.
Alocal router address on a PIM-enabled VLAN to which
[source-ip-addr]
is directly connected. The
local router will assume the role of DR for this flow and registers the flow with an RP, if configured.
The following example shows how to configure a manual multicast RPF override and saving it in a config file.
switch(config)# ip routing
switch(config)# ip multicast-routing
Chapter 4 PIM-SM (Sparse Mode)
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