Re: [load balancing] F5 load balancing problem

From: sezen eren <sezen_eren [izzat] yahoo.com>
Date: Wed Nov 21 2007 - 02:49:35 EST

Hi Tony,

The network guys checked the network and everything is normal. I say normal because the self IP of F5 is assigned to the F5's internal interface. Therefore it is normal to see this self IP at F5's internal network. When I take a tcpdump I see this self IP only in the internal network.

What is abnormal when I make requests to the my new VIP, I see that this self IP is in external interface. F5 sends the packets from external interface although it should have sent from internal interface.

My question is why dows F5 send the packets from external network while it supposed to use the internal network? what could be the reason of this misworking?

here I can show it from tcpdump results, here 10.200.146.12 is the F5' self IP in its internal interface, 10.201.147.175 is the server at F5's pool is:

[root@1stF5:Active] config # tcpdump -v -i external host 10.200.146.12
tcpdump: listening on external
09:26:12.155355 10.200.146.12.1314 > 10.201.147.175.1800: S [tcp sum ok] 3141430394:3141430394(0) win 4380 <mss 1460,nop,nop,sackOK,nop,wscale 0> (DF) (ttl 255, id 56330, len 52)
09:26:15.154802 10.200.146.12.1314 > 10.201.147.175.1800: S [tcp sum ok] 3141430394:3141430394(0) win 4380 <mss 1460,nop,nop,sackOK,nop,wscale 0> (DF) (ttl 255, id 61077, len 52)

[root@1stF5:Active] config # tcpdump -v -i internal host 10.200.146.12 and port 1800
tcpdump: listening on internal
09:26:12.163677 10.201.147.175.1800 > 10.200.146.12.1314: S [tcp sum ok] 2393155742:2393155742(0) ack 3141430395 win 49640 <mss 1460,nop,wscale 0,nop,nop,sackOK> (DF) (ttl 60, id 57643, len 52)
09:26:12.163693 10.200.146.12.1314 > 10.201.147.175.1800: R [tcp sum ok] 1:1(0) ack 1 win 0 (DF) (ttl 255, id 56351, len 40)
09:26:15.162967 10.201.147.175.1800 > 10.200.146.12.1314: S [tcp sum ok] 2394450063:2394450063(0) ack 3141430395 win 49640 <mss 1460,nop,wscale 0,nop,nop,sackOK> (DF) (ttl 60, id 57644, len 52)
09:26:15.162979 10.200.146.12.1314 > 10.201.147.175.1800: R [tcp sum ok] 1:1(0) ack 1 win 0 (DF) (ttl 255, id 61110, len 40)

thanks in advance
//sezen

Tony Bourke <tony@vegan.net> wrote: Hello Sezen,

The F5 doesn't control what interfaces the responses come from, the
servers would. Perhaps you have a default route configured on the
servers that point to a self IP on the Internal interface?

For 2, the F5 would send a RST most likely, which appears to be what
you're seeing.

I would check to see what default route you have on your servers, and
also check your LAN configuration. Something is causing the servers to
respond to the Internal interface.

Also, show a tcdump for both the External and Internal network
interfaces for a single connection attempt.

Hope that helps,

Tony

sezen eren wrote:
> Hi all,
>
> I have an F5 and I need to confugure this F5 to provide load balancing
> between two servers.
>
> However, there is a problem and it is not working. As much as I could
> troubleshoot, I saw that the F5 sends the packets from the external
> interface to the servers those are in the F5 pool, but the replies
> from the pool server comes to the F5's internal interface, I don't
> know why. (all interface IPs and the F5's Self IP are in the same
> network.F5's Self IP is assigned at external interface and AutoSNAT
> option is enabled at VIP) and F5 sends RST packets to the server for
> the packets that are received from internal interface.(unfortunately
> the F5 and Pool servers are in different networks so I cant assign a
> static route at pool servers)
>
>
> my questions are:
> 1 - Why does packets are sent from the F5's external interface and the
> replies are received from internal interface?
> 2 - What does F5 do if it send the SYN packets from external interface
> and it receives SYN+ACK packet from internal interface?
> 3 - What can I do to solve this problem?
>
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Received on Wed Nov 21 02:50:11 2007

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