11-04-2008 02:14 PM - edited 03-06-2019 02:18 AM
Are there any issues I should be concerned about with receiving multicast on interfaces with secondary IP addresses?
Thanks,
Mike
11-05-2008 08:35 AM
Mike
I am not aware of any issues with receiving multicast on interfaces with secondary addresses. The processing of multicast and access to multicast is dependent on the broadcast domain. So whether the interface has a single unicast address or has more than one unicast address (through the secondary address) should not impact multicast.
Is there some particular reason for asking? Is there some specific thing that you are trying to address?
HTH
Rick
11-05-2008 10:10 AM
Rick,
Thanks for the reply. It doesn't work on secondary addresses in the configuration I have. I was looking to see if it might be a code issue or can't be done. The secondary IP Address never gets put into being a PIM interface.
Mike
11-05-2008 10:40 AM
Mike
I am a bit confused. Are you saying that if you configure an interface with ip pim
Or are you saying that when you have configured the interface with PIM that it identifies the interface using the primary address and not the secondary address?
Perhaps it would help if you would post the interface configuration and what you expect it to do that it is not doing.
HTH
Rick
11-05-2008 10:56 AM
The secondary IP address does not become a PIM interface. I am connecting from a 6504 to 2 seperate routers. The 2 routers are on seperate subnets, but in same vlan. So under the interface VLAN X, the config has a primary ip address going to 'Router 1' and a secondary IP address going to 'Router 2'. The RP and source of the multicast is off of 'Router 2'. This configuration does not work. Multicast traffic does not come down the link of 'Router 2'.
11-05-2008 11:14 AM
Mike
Would you post the configuration of the interface on Router 2 and of the VLAN interface? It would also help if you would post the output of show ip pim interface.
HTH
Rick
11-05-2008 11:25 AM
11-05-2008 02:24 PM
Mike
Thanks for the additional information. Your comment that if you swap primary <-> secondary that it works is interesting and helpful. It is best practice when configuring secondary addresses on router interfaces that routers that connect to each other should both use the same subnet as the primary address. In your current config they are mismatched and when you swap them then they match (for router 2) for the PIM upstream.
Most of the routing protocols need their neighbors to be in the same subnet that they are in. Apparently PIM also has that requirement.
HTH
Rick
11-05-2008 06:18 PM
Rick,
Thanks for the response. I guess then there is no way to provide redundancy in this case without manual configuration changes.
Mike
11-06-2008 04:36 AM
Hi Mike
The routers are connected in the same vlan but with differnet subnets. Have you thought of moving the secondary address to a new vlan, so it will be the primary address on that. Then it will work.
/Mikael
11-06-2008 06:02 AM
Mikael,
We can only have the one VLAN.
Mike
11-06-2008 04:37 AM
Mike
A big part of the issue is the implementation that has the connection to router 1 in one subnet and the connection to router 2 in a different subnet but has them both in the same VLAN. Is there a reason why it needs to be that way? Would it be possible to have a separate VLAN per subnet?
HTH
Rick
11-06-2008 06:00 AM
Rick,
The VLAN has to be the same. We have no control over that.
Mike
11-06-2008 11:42 AM
You are experiencing a typical problem with secundary addresses. Running multiple subnets on the same VLAN is a bad idea and generates only problems (DHCP, IGP neighbors,etc..), i can say from experience, but i know: it is so easy to add extra ip addresses, no ?
What you could try. Do you have another port that you can configure as router port ?
I know it is messy, but you could try the following:
current situation
int x/x
ip add
ip add
ip pim sparse-mode
suggestion:
int x/x
no switchport
ip add
îp pim sparse-mode
int x/x+1
no switchport
ip add
ip pim sparse-mode
and you connect BOTH interfaces to a switch where you put both interfaces in the same vlan for example.
11-06-2008 12:29 PM
First, i understand the design is flawed, but it can't be changed. I agree with your suggestion, but it can't be done in our case because the links to 'Router 1' and 'Router 2' are trunks.
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