LoadMaster shows server as "UP" but I can't access

Question

I'm setting up load balancing through KEMP LoadMaster. I've setup everything and got to the point where real servers are up, virtual server is up, ping works but http request doesn't go through.

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Now if I type h**p://192.168.252.199 (had to remove http from the link) in my browser I'd expect it's call to be redirected to 201 and shown the page (I can access the page if I type 201).

Is there any setting I missed?

Thanks in advance.

EDIT: It seems that balancer is working fine but the connection doesn't make it to the server. Looking at the statistics, seems like the requests are sent to the right machine (I'm using sticky sessions that's why it mostly goes on the server2), but the connection is never received from there.

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Can you try Round Robin load balancing method instead of least connection (Scheduler) ? — krisFR, Jan 06 '14 at 14:08
In that case can you check this and see if it helps ? http://workinghardinit.wordpress.com/2011/11/01/using-host-names-in-iis-in-combination-with-a-kemp-loadmaster/ — krisFR, Jan 06 '14 at 14:22
What is the IP address (and subnet mask) of the client from which you're trying to get to the service via the load-balancer? — MadHatter, Jan 06 '14 at 15:53

score 2 · Answer 1 · answered Jan 06 '14 at 14:53

I haven't fiddled with our KEMPs for some time now, but vaguely recall that the source NAT(snat) function is obscurely documented. Maybe that's what's missing?

It's purpose is to trick the real server by substituting the real client ip address in the request with one of the KEMPs ip addresses. With snat the real server will therefore send it's responses through the KEMP rather than directly to the client. If you do not have other NAT mechanisms in place further upstream from the KEMP, snat is mandatory as the client won't accept a reply from a different ip than it sent the request to (such as if it requested from the KEMP but got the reply directly from the real server).

You can easily sniff the truth out at the real server, for example if the source ip of the get request is your clients ip address rather than the KEMPs (snat:ed) address.

I cannot recall exactly what they called the option but vaguely recall it being one of the check boxes under Network Options. Looking quickly at the Configuration Guide it could have been for example 'Enable server nat' or 'Subnet originating requests'.

score 2 · Accepted Answer · answered Jan 06 '14 at 15:12

2

I solved this problem by deactivating L7 Transparency.

answered Jan 06 '14 at 15:12

Fedor Hajdu

161

Well done. I can't believe how poorly KEMP has documented this option, but now it's searchable on the internet, +1 to that and to the question. – ErikE Jan 07 '14 at 23:07

LoadMaster shows server as "UP" but I can't access

2 Answers2