[xio-user] XIO client-side interface binding logic?

[John Bresnahan]

hOlle Mulmo wrote:
> Hi,
> 
> Question first:
> 
> Does the XIO (TCP) client honor GLOBUS_HOSTNAME when
> selecting what address to bind() a socket to?

we dont have an environment variable for binding to an interface.  by default we listen on all 
interfaces and use GLOBUS_HOSTNAME env for reporting contact strings.  There are ways to set a 
specific interface, just not with an environment variable.  Look into the xio tcp driver control 
GLOBUS_XIO_TCP_SET_INTERFACE

> 
> Background:
> 
> I have a VLAN overlayed on a normal network the two endpoints
> happen to have a connection as well. The two connections share
> the same physical network card on the computers (eth0 and eth0:1)
> -- the traffic then splits into separate paths later depending
> on the destination IP.
> 
> This means that in order to get traffic over my special route,
> I need to e.g. do "ping -I <src ip>", otherwise the src IP will
> be the public IP, not the VLAN IP, which results in assymmetric
> routing: the reply will go across the public network on the way
> back.
> 
> This is by design: everything should be routed on the "public"
> network by default, and only selected traffic for certain
> applications should go on the VLAN. On such application is
> the one I have written on top of XIO.
> 
> At first I thought I could control the src IP by using
> GLOBUS_HOSTNAME, but that does not seem to be the case: as far
> as I can tell, the src IP will always be the public one. In my
> case, this results in assymmetric routing.
> 
> I understand this is an uncommon and rather obscure setup, but
> it made me wonder if I just have goofed up, have missed setting
> some XIO attribute, or whether XIO clients don't look at
> GLOBUS_HOSTNAME at all when calling bind()?
> 
> /Olle
>