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Re: LAN failover

 
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Wim Van den Wyngaert
Honored Contributor

Re: LAN failover

Antoniov,

Correct me if I'm wrong.

The network cards both have a an ethernet address. When decnet starts, it corrects this address to the well known AA. IP starts after decnet.

If decnet is using both cards with the same decnet address, all communications use the same ethernet address. The other nodes don't know that there are 2 cards.

So, for IP it should be possible to use either card too. Not ?
Wim
Uwe Zessin
Honored Contributor

Re: LAN failover

You typically use the DECnet end-node license. Last time I checked it used only one active circuit at a time. When that one went down it used the next.

Many networks are switched. If you put two NICs with the same MAC address on the same switch he at least stops traffic on one port - I have seen it and could diagnose it thanks to extensive counters within DECnet-Plus. If you put them on different switches you will screw up the internal tables, because they suddenly will see frames with the same MAC address comming in from different ports.

In that case you need to separate the segments by DECnet routers. Nothing new.

LAT works differently. It build multiple virtual circits and can cope with different MAC addresses.
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Antoniov.
Honored Contributor

Re: LAN failover

I hope I can explain in simple way using my broken english.

All the network devices send data togheter using MAC (you have called AA). Theorically doesn't exist 2 NIC (Network Interface Card) with same MAC. All lowset network protocols use this information.
IP address is an abtraction of network to permit eterogeneous machines exchange information; however, socket need physical network to reach destination host and need MAC to make this. Conversion between IP address and MAC is automatic and is called ARP; you can see this table of conversion on your host typing
$ arp -a
if you have define unix like command or else
TCPIP>SHOW ARP
where MAC is called physical address.
ARP tables of all network device are dynamically updated, so your problem may be theorically solved; the trouble is the time-out of ARP table; using short time-out you can substitute a card with another but increase network traffic.
Usually the ARP table are valid ffor few minutes (from 1 until 30) and this is the time for complete substitution of NIC in network.

@Antoniov
Antonio Maria Vigliotti
Antoniov.
Honored Contributor

Re: LAN failover

Wim,
found this page can explain better than my post
http://members.cox.net/~ndav1/self_published/The_ARP_cache.doc

@Antoniov
Antonio Maria Vigliotti
Wim Van den Wyngaert
Honored Contributor

Re: LAN failover

Antoniov,

There is a 2nd feature : arp broadcast. When there is a change in network setup, a node can broadcast the new arp settings. In UCX 4.2 it was used in the cluster alias context.

Wim
Wim Van den Wyngaert
Honored Contributor

Re: LAN failover

Uwe,

If this causes problems, can it also cause problems on 7.3-2 ?

We use decnet PLUS. Last time I checked, decnet used the 2 ports simulaniously.

Is anyone using a solution that is not DNS based ?
Wim
Antoniov.
Honored Contributor

Re: LAN failover


There is a 2nd feature : arp broadcast. When there is a change in network setup, a node can broadcast the new arp settings. In UCX 4.2 it was used in the cluster alias context.


ARP tables of all network device are dynamically updated, so your problem may be theorically solved [...] increase network traffic.

Antonio Maria Vigliotti
Uwe Zessin
Honored Contributor

Re: LAN failover

Hello Wim,
it's been some years since I worked with this, but I recall that one could disable PHASE IV addressing within DECnet-Plus and then it did not alter the physical address of the interface.

Unfortunately I don't have the commands handy to check the counters and as I don't run DECnet-Plus I cannot find out easily, sorry.
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Wim Van den Wyngaert
Honored Contributor

Re: LAN failover

OK.

I'm going to install a 2nd card in my station and test it. To be continued ...
Wim
Steve Reece
Advisor

Re: LAN failover

"We use decnet PLUS. Last time I checked, decnet used the 2 ports simulaniously."

For a Phase IV installation, the two network interfaces would have to be on entirely separate physical networks.

For a Phase V (a.k.a. DECnet-Plus) installation, only ONE network interface will have the Phase IV compatible address running on it. The other network interface would either be on a completely separate network (as with Phase IV) or would not be running with a Phase IV compatible address and so probably wouldn't have the MAC address of the interface changed.

As a side issue, can LAT run on two network interfaces? I assumed it couldn't after a system that I have here used the wrong one for LAT when initially configured. Only one interface was used by default.
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