Using 2 Cross-over LAN cable for Heartbeat in Serviceguard

[Mohanasundaram_1]

Hi Folks,

I have a strange customer requirement which I would like to dicuss here and take some expert opinion.

Customer wanted to use cross-over cable for the heartbeat LAN. I quoted the statement from Melwyn Burnard about the limitations of such a solution.

Now customer has come-up with a modified request. He wants to use 2 Cross-over LANs for heartbeat. That is, configure 2 different IPs to carry heartbeat so that the failover limitation is handled. Customer wants to avoid using the switches for the heartbeat LAN. Is it feasible to have such configuration (I personally believe it should be ok, but want to know the pitfalls of this, if any).

Secondly, customer says he does not want the Local LAN failover for the Heartbeat LAN to happen (This heartbeat is going through switch). We have a production LAN and a Heartbeat LAN and one standby LAN. In reality if the production or heartbeat LAN fails, it fails over to standby. So, customer wants to ensure that only production LAN fails over to the standby LAN. Is it possible to configure? if so,how?

Answers will be rewarded with points.

With regards,
Mohan.

[RAC_1]

First, What version of SG?? The lastest (I think the ones after 11.14) do not support crossover cables hearbeat setup. If you are bellow 11.14, you can. Putting two hearbeats is OK. But do not understand why not local LAN failover. It is certainly a SPOF, and not good. Other than that two crossover cable hearbeat should not be a problem.

[Mohanasundaram_1]

Hi RAC,

Thanks for your reply. The SG version is A.11.13 on HP-UX 11.0. But I do not find any information of cross cable not supported on 11.14 or 11.16. Have you really seen the documents stating that?

For some unspecified reason the customer wants to avoid connecting the heartbeats to switch. Hence these requirements.

I will wait for more response.

With regards,
Mohan.

[RAC_1]

With 11.13, you can do that. Somewhere while reading realease notes for 11.15 or 11.16, I recall that crossover cable heart is not supported. But you do not need to worry about it as you are on 11.13.

So in you setup aprt from "no local lan failover" all seems ok.

[melvyn burnard]

Well first comment is that 11.13 of Sg is no longer supported, you shoul dupgrade to a supported version and patch it.
Secondly, there is nothing saying we do not support the crossover cable in later versions of SG.

If they have a data/user lan, they should also put the heartbeat across this lan for redundancy.
As for the crossover cableing question, I advise against using these wherever possible, for the reasons stated before, and also from experience, so to suggest having two of them would make me concerned.
You are introducing more areas for possible problems, for the sake of saving money for a small hub or switch ( a small 100BT hu/switch does not cost much)

[Mohanasundaram_1]

Hi Melvyn,

Thanks for the response. I will provide more information at this stage to clear the picture.

The customer wants to avoid any package switching in case both his core switch fails. Hence he wants to use the cross cable for heartbeat ( I have explained to them that both the core switch failing should be considered as a disaster, but customer still insists on cross cable).

He does not have issues in putting the heartbeat LANs in a seperate switch provided HP categorically says that cross cable is not supported. I have configured the cluster in such a way that the data LAN will carry the heartbeat as well, so they claim cross cable is not a single point of failure. At this stage we proposed APA with additional LAN card for teaming 2 LANs in cross cable (this is supported as per APA manual).

But customer does not want to buy APA. They just want to configure 1 more LAN connceted through cross cable as a second heartbeat. Hence I have come up with this query.

At this juncture, it would help me to know what were the problems faced by SAs in their experience due to a Heartbeat on cross-over cable.

As you stated, I do not find any mention of "not supported" for cross cable in any of the new serviceguard manuals.

The secondary part of the question from customer was, if cross cable is not supported then he does not want the heartbeat to perform local LAN failover because the data LAN will conduct the heartbeats. Therefore, is it possible, by configuration, to prevent the heartbeat LAN alone to perform a local LAN failover?

With regards,
Mohan.

[Steven E. Protter]

Shalom Mohan,

I'm using it right now between two D boxes 11.16 SG.

Works fine for heartbeat.

In real scenarios, I generally want to have a second heartbeat on the regular lan. This is helpful if the cable gets pulled accidently.

SEP

[Mohanasundaram_1]

Hi SEP,

Thanks for the post. I wanted to know real life instances, as you have mentioned.

I have already configured the data LAN to carry the heartbeat to account for the cross connection failure.

But since the very reason of going for a seperate heartbeat is to avoid using the data LAN, we wanted to have a fall back for the cross cable heartbeat. Now I am reasonably confident that I can configure 1 more cross connected LAN to carry heartbeat in addition to the existing heartbeat (cross connected) LAN.

I would like to see more posts to indicate to me the real life problems faced in having a crossover cable for the heartbeat LAN.

with regards,
Mohan.

[A. Clay Stephenson]

There are two big disadvantages to using xover cables:

1) They are useless whenever the cluster expands beyond 2 nodes -- a not uncommon scenario.

2) It's difficult to tell which end of the connection is having the problem.

It's so cheap to purchase inexpensive hubs that they are worth it for the "winky-blinky" indicators alone -- and you now know which end of the connection is having trouble.

[Yogeeraj_1]

hi mohan,

see also the following post:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=883197


hope this helps too!

kind regards
yogeeraj

[Mohanasundaram_1]

Hi Clay and Yogeeraj,

Thanks for your reply. Customer is aware of the 2 limitations indicated by Clay and is ready to accept it.

The hub is another option, but customer does not want the heartbeat LAN to perform a local LAN failover. For this requirement, 2 * cross over LAN each running heartbeat + the production LAN also carrying the heartbeat seems to be a good option. Is there another option to prevent the local LAN failover only for the Heartbeat LAN?

Yogeeraj, Customer does not want to purchase APA and he feels the 2 LANs for heartbeat should sufficiently handle the SPOF concerns.

Any other real life experiences before I close this thread?

With regards,
Mohan.

[John Bigg · Accepted solution]

Firstly, I would like to put an end to the rumour that crossover cables are not supported on some releases. Crossover cables have always been supported on all releases up to and including 11.17 and I know of no plans to change this in 11.18 or any other future release.

I think you are already aware of the disadvantages of crossover cables so I'm not going to repeat them here. They do have the advantage that they are very reliable since there is only 1 piece of hardware which can go wrong. The cable itself!

With regards to heartbeat, you should always run heartbeat over all your lans for extra redundancy. The heartbeat overhead is small and I've seen too many problems where clusters have had downtime due to heartbeat failures when there were non heartbeat lans working within the cluster.

If you do not want a package to failure when a lan goes down, simply do not configure this as a monitored subnet in the package configuration.

Lastly, if you do not want a lan to failover to another lan the only way you can do this is to ensure that there are no standby lans configured which are bridged to the primary lan you do not want to failover.

If there is a standby lan on the same "bridged net" as a primary then Serviceguard will allow local lan failover for this primary. There is no way to configure Serviceguard not to do this. The only way is to ensure the primary lan is isolated from any standbys.

[Mohanasundaram_1]

Hi John,

Thanks a lot for the BIGG answer I was looking for. Your post had cleared my doubts about all the queries I raised in this thread.

I have a request to HP. It will be useful if HP posts this statement about using a cross-over cable in Serviceguard on the website. I can see a lot of people raising this query and there is no official document on the web (as far as I know).

I have made a similar request to Melvyn through this forum earlier. It will be convenient to all concerned to have an official document in HP's web site .

With regards,
Mohan.

[Mohanasundaram_1]

Thanks to RAC, Melvyn, SEP, Clay, Yogeeraj and John for their valuable time and useful responses.

I am closing this thread now.

[melvyn burnard]

The simple answer about posting this info on the web is that I have posted the same info a number of times on the ITRC.
We cannot and do not post official documents stating every single possible supported/unsupported permutations.