[lvs-users] ipvsadm and packets leaving a gre tunnel

Joseph Mack NA3T jmack at wm7d.net
Tue Jul 22 15:16:54 BST 2008

On Tue, 22 Jul 2008, Marco Lorig wrote:

> I´ve read the section but as i understand correctly the 
> only solution in a LVS-NAT env is to set the MTU by hand 
> on each route or interface on the realservers, which 
> unfortunately I haven´t access to.

Ratz's solution is on the director, and sets the MTU for the 

> We have been running this env since 2002 with Kernel 
> 2.4.19 with no problems (running director on 
> gre_interface). Actually we have upgraded our systems to 
> kernel 2.6.18 which causes this problems.


a lot of stuff broke going to 2.6.x

> The gre tunnel exists between the directors because of 
> failover reasons ( each director is located in a seperate 
> datacenter interconnected by WAN).
> Copying files like this:
> Client ---scp----> Director ---GRE Tunnel nopmtudisc --> Director ----scp ---> Server and vice versa.

not sure what you're doing here. Is it one connection with 
this route?


I assume you have two directors in some standard failover 
setup and only one is directing when your LVS is up?

> works fine but if the ipvsadm is enabled on the second 
> director to serve multiple servers, the mtu problem 
> happens.

the copy has nothing to do with LVS? ie you can do the copy 
when there is nothing in the ipvsadm table in the 2nd 
(inactive) director, but as soon as you put entries into 
ipvsadm on the backup director, the gre tunnel breaks?

If so, are there any entries you can put into ipvsadm that 
won't break the tunnel? Are the any which guarantee to break 
the tunnel? What if the ipvsadm table is empty on the active 


Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!

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