Forwarding IP Irule

Jason replied here:

 

 

http://devcentral.f5.com/Community/GroupDetails/tabid/1082223/aff/25/afv/topic/aft/1179270/afc/1251283/Default.aspx

 

Yes, that's possible. Check out the RESOLV::lookup command in the wiki: http://devcentral.f5.com/wiki/default.aspx/iRules/RESOLV__lookup.html

 

 

Aaron

many thanks people! :)

Hi,

 

 

I was wondering if anyone tell me if the below rule will simply forward any traffic it receives toward cluster.messagelabs.com? I think it will use the dns server (172.1.1.1) to resolve the address cluster.messagelabs.com, but once it has resolved it, will it actually forward traffic toward cluster.messagelabs.com?

 

 

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Select the first returned IP address as the destination IP (inherits the destination port from the client's destination port).

 

when CLIENT_ACCEPTED {

 

log local0. "cluster.messagelabs.com is currently at IP [RESOLV::lookup @172.1.1.1 "cluster.messagelabs.com"]"

 

 

Get IP(s) for hostname cluster.messagelabs.com against 172.1.1.1 name server

 

set ips [RESOLV::lookup @172.1.1.1 -a "cluster3out.eu.messagelabs.com"]

 

 

Log result. If there are multiple IP's it could be a TCL list like {1.1.1.1 2.2.2.2 3.3.3.3}.

 

log local0. "Looked up cluster3out.eu.messagelabs.com and found $ips, parsed first element: [lindex $ips 0]"

 

 

Check if the first list element was empty

 

if {$ips eq ""}{

 

 

Select the IP

 

node [lindex $ips 0]

 

}

 

}

 

 

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Sorry if this is a numpty question, but I'm new to this! :(

 

 

May thanks,

 

Pete

That looks pretty close. Make sure you have a port on your node command, but other than that, it should work, assuming you can always resolve the host address.

 

 

Funny, I don't think I've seen anyone do that before. You're basically creating a dynamic DNS setup for the back-end server(s) with your LTM. Interesting. :)

 

 

Colin

never seen it before eh....well i am special! ;) lol

 

 

Thank you for the response Colin, nice to know its close! :) I dont suppose you know how i could make it select a node from a pool that I have created do you? The current setup is ok, but if one/that node goes down then my mail wouldnt be routed out! :(

 

Pete

How would you select what pool to direct it to? I suppose if you have a list of the resolved IP -> pool mapping stored somewhere within the iRule (a Data Group most likely) you could do a lookup with RESOLV::lookup to find the IP of the host, then check that IP against the Data Group and determine which pool to send it to based on that.

 

 

I.E. If the IP is 10.10.10.1-6 go to poola, if 192.168.7.5-17 poolb, etc.

 

 

Does that sound like what you're looking for?

 

 

Colin

erm, well I only have one pool that I want to use....and 3 nodes in that pool... its not a case of selecting a pool, more selecting a node/load balancing the traffic to the nodes! :)

So you want to choose a particular node out of the pool, without allowing the pool to do the actual load balancing? What is it you want to do to select the node out of the pool? Some kind of static mapping or a metric or...what?

 

 

This is definitely doable it's just a matter of figuring out the specific logic you want to apply.

 

 

I.E. "If a request comes in from subnet A, always send it to member A unless it's down, in which case send it to member B", that kind of thing.

 

 

Colin