LAN failover

[Wim Van den Wyngaert]

I have a GS160 with double everything. Except double network connection. I would like to plan the activation of the 2nd card (on a 2nd switch). I have VMS 7.3 and I am unable to upgrade (even install patches).

For decnet, I can enable the 2nd card and decnet will use both cards.

For LAT, I can create a link for the 2nd card.

For IP, I can assign a second IP address. AND I don't want to do that because my clients are unable to use it.

Is there a way to let IP use 2 cards with 1 IP address ? My IP version is 5.3 ECO 2.

And for those who know DSM/MUMPS : how will DDP use the second card ?

[Mobeen_1]

Wim,
Thats a good one. What we have been doing is, having 2 cards configured to 2 different IPs, one for production use and the other for backup network (for carrying out backups without clogging the production network).

It would be interesting for me to see if we could have one IP assigned to 2 n/w cards and know what benefits one could get in such a configuration.

regards
Mobeen

[Wim Van den Wyngaert]

Mobeen,

FYI : 7.3-2 has LAN failover. 1 card can fail and the other takes over. But I don't know if this would also work if the switch behind it fails. But this is another subject.

[Antoniov.]

Hello Wim,
I think you can't use same IP on two different cards; main problem is not in software but it's inside TCP/IP techinal characteristics.
When any host send a socket into network, this soccket have to reach the destination host; IP address tell to all network device where socket have to go; low level network, however doesn't use IP addres but use MAC (Medium Address Card), the hex number stored in every network device; two specific part of TCP/IP standard determine how IP address is associated to MAC and theese feature have named ARP and RARP.
If you assign same IP to 2 different NIC, some network device (mainly the routers and bridges) can be confused and can't deliver the socket.
This means, if can assign same IP to 2 different NIC you have disable one fo two devices.
I hope I can explain in simple way.

@Antoniov

[Ian Miller.]

TCPIP V5.4 has failover for ip if you can upgrade tcpip.

Why the restrictions on upgrading?

[Mobeen_1]

Wim,
Yup, i am aware that 7.3-2 supports n/w failover, but i thought thats assuming that the 2 cards have different IP addresses and not a single IP assigned to your 2 network cards

regards
Mobeen

[Wim Van den Wyngaert]

Ian,

I don't upgrade because "on paper" all applications must approve the new system.

We need to keep the platform as stable as possible. The migration of 6.2 -> 7.3 took 2 years !!!

[Jan van den Ende]

Ha Wim,

there is a recent thread
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=385987
that is mainly concerned with IP cluster alias stuff.
The thread also discusses DNS round-robin (kind of poor-mans cluster alias, or maybe more exactly: as close as Unix can get to cluster aliasing). Using this mechanism it IS possible use both cards (we are doing it, over 2 cards each of 4 nodes).
The way it works: any existing connection is to MAC address and stays where it is. After a round-robin step the service name (functional analogous to DECnet cluster adddress, but NOT the IP cluster alias!) is changed to the next MAC address, and new connections (IF using DNS, not router-cache!) get connected to the other NIC. No real load-balance, but more or less even connection-time based spread.

hth.

Jan

[Wim Van den Wyngaert]

Jan,

I found that one too. But DNS is a too big change for us. We are still using host files.

It is rather strange that since years redundant machines are sold while the network protocols are not able to use it.

Also : it would like that when the network goes down on 1 card that IP retransmits the packets on the other card.

Did someone test all this (network failure, card failure) ?

Excellent would be that in case of failure, all connections stay up and act as if the packets were lost.

Btw : how is decnet/lat reacting in case of a failure ? Is something lost ?

[Antoniov.]

Wim,
I understand my answer don't like you but TCP/IP suite is based on MAC (physical address of card) so, today is not possible use a secondary network card to backup a primary card :-(
Every change of card require a manual modify or else require some minutes (from 1 to max 30 minutes, depending network complex) to upgrade all ARP table of network device.
You can use DNS to solve or you have ready to accept some minutes of waiting for activation of new card.
Ortherwise don't use TCP/IP (but I think also other protocol have same limitation).
Sorry for unhappy news.

@Antoniov