PIM-BiDir for IPv6

Load multicast.init.cfg

#IOS-XE
config replace flash:multicast.init.cfg
 
#IOS-XR
configure
load bootflash:multicast.init.cfg
commit replace
y

Configure XR4 as the RP for all IPv6 multicast groups. Advertise the RP mapping using BSR. Use BiDir for these groups.

Answer

#XR4
multicast-routing
 address-family ipv6
  interface Loopback0 enable
!
router pim
 address-family ipv6
  bsr candidate-bsr 2001::14
  bsr candidate-rp 2001::14 bidir

Explanation

PIM-BiDir for IPv6 works the same way as IPv4. The DF election is used to ensure a loop free topology for upstream traffic that is unconditionally forwarded towards the RP.

To begin, we can confirm that we learn the RP mapping via BSR, and that XR4 identified as the RP in bidir mode. For IPv6 PIM, BiDir support is enabled by default on both IOS-XE and IOS-XR. The BD flag appears to mean BiDir.

To make this simpler, we will just join a group from R5’s loopback. This mimicks a host joining on a physical interface.

#R5
int lo0
 ipv6 mld join-group ff08::5

We see on the RP that the tree is built to the receiver and the outgoing interface is the link to XR1.

Let’s now ping this group from R1:

At R7, the traffic is forwarded towards the BiDir RP unconditionally. Interestingly, we see no entries at all under show ipv6 mroute or show ipv6 pim topology. However, we can see the ff00::/8 BiDir entry using show ipv6 mrib route:

R7 is accepting on all interfaces that are DF or upstream interfaces, and only forwarding out the upstream interface. Just like BiDir for IPv4, we can check the DF election results. R7 did not win the DF election with XR1, so this interface is not available as an incoming interface.

A similar command can be used on IOS-XR:

A note on IPv6 PIM-SM with PIM-BiDir

For IPv4 on IOS-XE, we cannot use the same loopback for the RP for both PIM-SM and PIM-BIDIR. This is because the command overrides itself when you try to use the same loopback for two separate PIM RP commands.

This is again an issue for IPv6 when using BSR on IOS-XE.

ipv6 pim bsr candidate rp 2001::9 group-list PIM_SM_V6
ipv6 pim bsr candidate rp 2001::9 group-list PIM_BIDIR_V6 bidir <---- This just replaces the previous command

However, it is not an issue when using static IPv6 RP assignment on IOS-XE:

ipv6 pim rp-address 2001::7 PIM_SM_V6
ipv6 pim rp-address 2001::7 PIM_BIDIR_V6 bidir  <--- Both commands are taken

Like we saw for IPv4 on IOS-XR, IPv6 on IOS-XR allows both commands for either BSR or static RP.

router pim
 address-family ipv6
  rp-address 2001::14 PIM_SM_V6
  rp-address 2001::14 PIM_BIDIR_V6 bidir
!
! or
!
router pim
 address-family ipv6
  bsr candidate-rp 2001::14 group-list PIM_SM_V6 priority 192 interval 60
  bsr candidate-rp 2001::14 group-list PIM_BIDIR_V6 priority 192 interval 60 bidir