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New Member

MPLS multicast load balancing

Hi, we will have multicast running over the MPLS VPN with ASR 9K as PE, CRS as P. I checked the ASR 9K multicast configuration guide v4.0 but didn't find any info for multicast load balancing. I found some old threads said we have to use GRE tunnel for this, but not sure if IOS XR could have any new features on it. Any suggestions?

Thanks. Leo

Cisco Employee

MPLS multicast load balancing

Hi Leo,

I assume you are doing MVPN  (only default MDT, no data MDT) to transport  multicast traffic across  MPLS/VPN network.

What kind of load balansing you would like to achieve?

If you are using LinkBundle on ASR9K and would like to

know if the multicast traffic will be loadbalanced across the bundle

members, then the answer is - the load balancing on the bundle for Multicast traffic is only done on

egress and the egress LC is chosen based on the multicast Groud ID.

On the egress LC, the egress NP is chosen based on the same criteria and

only at the NP level, we are doing a more granular (L3 or L5-tuple hash) LB.

On CRS we have new 7-tuple hash algorithm will be supported for IPv4, IPv6, and MPLS flows

starting for 3.6 release for load balancing.

Could you please provide more details to have more precise answer?



New Member

MPLS multicast load balancing

Hi Vadim, thanks for your reply. The current network setup is CRS as P, C6500 and R7200 as PE. I can see following mdt config on PE router. I don't have any ideas for the multicast load-balancing, but seems current P and PE config doesn't have this function.

ip vrf xxx

mdt default

mdt data threshold 400

mdt mtu 1476

mdt log-reuse

ip multicast-routing

ip multicast-routing vrf xxx

Now we are planning to replace all PEs with ASR 9K and building the lab to test. I just found this command 'multipath' under the multicast-routing on IOS XR. Does it only one command I need to enable the load-balancing for multicast on P and PE? Any other configuration we can try?

Thanks. Leo

Cisco Employee

MPLS multicast load balancing

Hi Leo,

Yes, the multipath is the only command needed to enable the multicast load balancing in the core. The configuration allows multiple equal cost paths toward a PIM source or RP using a hash function based on a mcast Source and Group.

Note, as the balancing is based on S,G hashing, and in mVPN the address of a PE router would be always a source for the mdt, the balancing would be done based only on varying MDT data addresses.

For example, when PE1 start using group, hashing based on (PE1, will be always the same, so if there are several end customers’ mcast groups use the same MDT, they’d use the same core path.



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