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End-host IPs showing for some hosts even though the SVI is in a VRF?

Techie
Posts: 16
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I opened a support case, but thought I would post it here as well. I don't understand what is going on.

We utilize VRFs in our Cisco Nexus datacenter. I have understood that NetMRI cannot currently parse the VRFs to obtain ARP and routing tables. However, I am confused because there are a small number of datacenter switchports that NetMRI has been able to (correctly) identify the IP address of a switchport for a vlan that is in a non-default VRF. I would like to understand why and find out if there is a way to expand this capability to other switchports.

For example, we have a vlan that is in our "Enterprise" VRF with a SVI on Nexus 7010s with subnet 10.42.4.0/22. Yet somehow in Switch Port Manager  - End Hosts Present, I am able to see several of these host IPs which are correctly mapped to switchports. I'm only seeing data for a few hosts out of the hundreds in this subnet, but why am I able to see any at all?

I am not sure what's

Adviser
Posts: 353
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I am not sure what's happening here, it will need a closer look. I have seen older devices that still report the interface IP addresses for non-default VRFs through SNMP. For example, you'll the the IP of two SVIs in the interface address list even though those are in different VRFs. But to see end hosts is another thing. We have also seen a Nexus bug that was exposing HSRP VIPs across VRF contexts. 

Are those hosts you are seeing directly attached to the Nexus? And perhaps the hosts you do not see are not? Or, could there be some reason those hosts would show up in the ARP tables of another router in that VRF for which we are collecting data?

The forwarding tables will not be per-VRF, since they are layer 2. So, we would get the MACs for the end hosts from the switch port forwarding tables. If we find the IP in another ARP we can make the association.

 

Spot on again John! You were

Techie
Posts: 16
4164     0

Spot on again John! You were correct about it coming from another device. The end-hosts I am seeing are connected to Nexus 5596s which are L2 only, and the SVI gateways live upstream on a VRF on the 7010s. However, the managmenet SVI of the 5596 is in the same vlan as the end-hosts I was seeing in NetMRI. So, the 5Ks have a small ARP table in default VRF from hosts in that subnet, I presume from any hosts that are sending gratuitous ARP.

So mystery solved at least. Hmmm, maybe I'll schedule some ping sweeps on the 5Ks to keep their ARP table populated for this subnet...

Thanks!

The more I think about it I'm

Techie
Posts: 16
4164     0

The more I think about it I'm getting tempted to setup a L2 device with a SVI in all datacenter vlans and do ping sweeps. That will provide a work-aound for NetMRI's end-host identification until they support VRFs. It sounds pretty rediculous though hah!

NetMRI - Mac tables for nexus 5k's

Not applicable
Posts: 1
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Hi

I have a problem with my v6.9.4 NetMRI

I am not getting MAC addresses / End hosts populated - On cisco Nexus 5k's

The device has forwarding tables support - yes

But is not "Available"

What does this mean?

Is there a fix ?

 

 

Re: NetMRI - Mac tables for nexus 5k's

Adviser
Posts: 65
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Is this issue resolved now ? Is snmpv3 used for polling ?


@dstevens wrote:

Hi

I have a problem with my v6.9.4 NetMRI

I am not getting MAC addresses / End hosts populated - On cisco Nexus 5k's

The device has forwarding tables support - yes

But is not "Available"

What does this mean?

Is there a fix ?

 

 


 

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