Can LLT heartbeats communicate between NICs with different device names?

[zhangchao]

One 2-node vcs cluster, the heartbeat NICs are eth2 and eth3 on each node,

IF eth2 on node1 down, and eth3 on node2 down. Does this mean the 2 heartbeat Links both down, and the Cluster is in split brain situation?

Can LLT heartbeats communicate between NIC eth2 and NIC eth3?

Since the 《VCS Installation Guide》requires the 2 heartbeat Links in different networks.We should put eth2 of both nodes in the VLAN (VLAN1), and put eth3 of both nodes in another vlan (VLAN2). So in this situation heartbeats cannot communicate between eth2 and  eth3.

But, in a production cluster system, we found out the 4 NICs--eth2 and eth3 of both nodes are all in a same VLAN. and this lead me to post the discussion thread to ask this question:

IF eth2 on node1 down, and eth3 on node2 down, What will happen to the cluster (which is in active-standby mode) ?

Thanks!

[zhangchao]

When configureing VCS heartbeat link, there are 3 options, and we configure as this:

First private heartbeat link:   eth2;

Second private heartbeat link: eth3

Low-priority heartbeat link: eth4

And we use the same NICs for private heartbeat links on all systems

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IF eth2, eth3, eth4 on all nodes are all in a same VLAN,

1) Can heatbeat communicate between eth2 on node1 and eth3 on node2?

2) Can heartbeat communicate between eth2 on node1 and eth4(Low-pri) on node2 ?

3) IF there is only one heartbeat NIC up on the Master node, Will all the cluster members be in jeopardy?

[zhangchao]

We put all heartbeat NICs in a same VLAN, the syslog gave Warnings "Heartbeat Links are in same network", Will this kind of warning eventually lead to VCS faults?

Since the installation guide suggest using different networks for different heartbeat Links. Is there really any problem IF putting all  heartbeat NICs in a same VLAN?

[mikebounds · Accepted solution]

You should not put heartbeats in the same VLAN - they are not supposed to cross over and if they do they can cause interferance and issues such as mising heartbeats 

LLT can communicate on different device names, but they must Communicate on only one - i.e you could actually have eth2 on first node connected to eth3 on 2nd node and eth3 on first node connect to eth2 on 2nd node, but this would be silly as it would be confused, but if NICs are not the same on each node, then it is fine to connect heartbeats with different device names, but it is a one to one pairing.

So in answer to original question, if eth2 on node1 down, and eth3 on node2 down then you will have split brain unless you have configured a 3rd heartbeats (low-pri or hi-pri).

Mike

[zhangchao]

Thanks! you make this clear.

[stinsong]

And answer your question of 

3) IF there is only one heartbeat NIC up on the Master node, Will all the cluster members be in jeopardy?

No, only Master node will put into jeopardy status on this situation.

And for low priority LLT, it's usually on a public NIC and only transfer heartbeat package when there is other LLT link up. But when all other high priority are LLT down, low priority LLT will transfer configure info and command message to other nodes.