[ECOS] Second ethernet port?

[Colin Ford]

Many thanks for the explenation. It clears things up. I was 
thinking it was something like that. I've just tested it with two
networks and weyhay! it works great.

Many thanks again,
Col.



On 11 May 2001 11:51:56 +0100, Hugo Tyson wrote:
> 
> > From: Colin Ford <colin.ford@pipinghotnetworks.com>
> 
> > I've included my output below. The odd thing is,
> > is that I can ping from my Linux box both:
> > 
> > 1.1.2.239 & 1.1.2.187
> 
> Yep, looks like both interfaces are up and working OK.  That eth1 was left
> up following the error is probably a "feature" - or it might be talking
> through eth0.  Not important.
>  
> > after eCos has run and aquired thoes addresses.
> > Everthing seems to work apart from eCos thinking 
> > that eth1 failed when it did not?
> >
> > I think the "SIOCIFADDR 2" origanates from:
> > packages/net/tcpip/current/src/lib/bootp_support.c
> > 
> > // Must do this again so that [sub]netmask (and so default route)
> > // is taken notice of.
> > addrp->sin_addr = bp->bp_yiaddr;  // The address BOOTP gave us
> > if (ioctl(s, SIOCSIFADDR, &ifr)) {
> >      perror("SIOCIFADDR 2");
> >      return false;
> > }
> 
> Right, that's setting the address with the correct netmask.  But the system
> already has a route to that very address with the same netmask set up via
> the default routing for eth0.
> 
> > I'm not sure what your saying about the network segment?
> 
> ...snipped to keep the important details...
> 
> > BOOTP[eth0] op: REPLY
> >      client IP: 0.0.0.0
> >          my IP: 1.1.2.239
> >      server IP: 1.1.1.1
> >     gateway IP: 0.0.0.0
> >        subnet mask: 255.255.0.0
> > BOOTP[eth1] op: REPLY
> >      client IP: 0.0.0.0
> >          my IP: 1.1.2.187
> >      server IP: 1.1.1.1
> >     gateway IP: 0.0.0.0
> >        subnet mask: 255.255.0.0
> > SIOCIFADDR 2: File exists
> > Network initialization failed for eth1
> > Starting Interfaces
> > Running Ping Test on eth0
> 
> You have connected your board up thus, with both interfaces on the same
> network segment == the same logical IP address space, with netmasks of
> 255.255.0.0:
> 
>         1.1.2.239 eth0 ---------+-------network 1.1.x.x
>   BOARD                         |
>         1.1.2.187 eth1 ---------+
> 
> So the code sets up a route to all nodes called 1.1.x.x via eth0.  This is
> the correct thing to do.  It then tries to set up an implicit route to
> 1.1.2.187 via eth1 as well.  This is also (usually) the correct thing to
> do.  But this causes an error because the system already knows a route for
> 1.1.x.x, which includes 1.1.2.187, via eth0.  Bringing up 1.1.2.187 locally
> would conflict with that so it is rejected.
> 
> OK, I probably have the details wrong of what's happening internally to the
> stack, but I hope you understand the issue... the system expects 1.1.2.187
> to be outside on the net because of the way eth0 was already set up, not
> right here in the same box.
> 
> The initialization code that we provide assumes that different interfaces
> will be on different network segments, for example:
> 
>         1.1.2.239 eth0 ----------------network 1.1.2.x
>   BOARD                         
>         1.2.2.187 eth1 ----------------network 1.2.2.x
> 
> That way, the route to 1.1.2.x via eth0 does not conflict with a new route
> to 1.2.2.x via eth1.
> 
> The reason we assume this is that connecting both interfaces to the same
> network is kinda pointless, it doesn't let you do anything that you can't
> do with a single interface.  (Except testing your code, but it's a poor
> test, it could be going wrong in lots of ways that you wouldn't know)
> 
> The linux box on my desk, which I use to test many targets with multiple
> interfaces, itself has two interfaces, one onto our house network
> (191.17.17.x), and one onto a private net all of my own (10.17.17.x)
> 
> The target board has one interface connected to the house network, and one
> to my private net.  I run my own DHCP server to serve the private net, of
> course.  So my two interfaces have IP addresses like 191.17.17.99 and
> 10.17.17.99 (deliberately picking the same last part as an aide memoire,
> nothing more).
> 
> To use multiple interfaces meaningfully, you need multiple networks.
> 
> (Or set up the netmasks and routes &c yourself, with care...)
> 
>       - Huge



-- 
===========================================
Colin Ford               PipingHot Networks
Software Engineer        +44 (0)1364 655510