Lan Question

[Filosofo]

Hello,
I execute lanadmin command to display lan information....
I see
Deferred Transmissions = 20

This is heartbeat lan, can somebody tell me what is it?

Thanks

Filo

[Jeff Schussele]

Hi Filo,

Believe this has to do with the nnd parameter tcp_deferred_ack_max which is the upper limit of bytes that can be sent without receiving an ACK from the destination. This would be like a telephone conversation with someone & you're not receiving indications that they are actually connected. You think the connection has dropped & you stop to wait for that indication.
Now in a heartbeat situation, this is not a good thing. Are your heartbeats in a private LAN? This could indicate that the network becomes saturated at times & this could lead to missed heartbeats causing pkg failovers or even worse TOCs.

Rgds,
Jeff

[Bill McNAMARA_1]

heartbeat for what? serviceguard?

[Filosofo]

Yes,
it is the heartbeat for MC/ServiceGuard, it is a cross cable.

Thanks

Filo

[doug mielke]

If this is a statistic counter:
this seems to be the count of the times that an ethernet frame needs to be sent, but at that moment the cable is busy.

These should almost never occur in a switched network with short cables. A few as cable length increases even in a switched lan.

Can you clear this statisic, and see how often they are happening. If just a few, it is of no real concern.

[doug mielke]

On a crossed cable this would be the count of the times that both NICs tried to send at the same time.

I guess there would be similar numbers on both servers.

A small % ( less than 10% of total packets sent, even in a heartbeat) should be of no worry.

[Filosofo]

On node-A this value is 20 and on node-B is 10.......



Filo

[doug mielke]

Are the nics set for full duplex? In theory, there should be zero deferred trans on a crossed cable running full duplex. Both nics should be able to communicate at once.

Also, you can get things like this if the cable is moved or disturbed after the system is up.

I'd clear the statistics and watch to see if you get any more

[Filosofo]

Are set 10 Half Duplex



Filo

[doug mielke]

At half duplex then the occasional deferred transmission is possible, but the delay at this point is minimal.

Collisions are also possible, and become more likely as cable length increases. Even this is not a real issue.

If you start seeing multiple collisions in your statistics, then there will be some delay in getting the heartbeat message through, which could be cause for concern. Deley before retransmission doubles after each collision.

Given just the handfull that you've seen, I'd not yet be concerned.