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Thread: How to route to a default gateway that is not on my subnet?




How to route to a default gateway that is not on my subnet?
user name
2006-12-13 21:23:20
Hi everybody.  I'm encountering some difficulties
configuring my
laptop to work on the wireless network setup at the
University of
Saskatchewan.  They use a Cisco Clean Access (CCA) system
which
blocks all network traffic until you have authenticated
yourself
to a CCA server.  This CCA server is supposed to be your
gateway.

They have a somewhat strange setup where the gateway is
actually
outside of the subnet configuration provided to the clients
through
DHCP.  This setup works fine under Windows XP (and MacOS,
though
I haven't seen that for myself). 

We've been able to figure out a recipe for route(8) to route
packets
to the CCA server so I can authenticate myself, but we can't
route
packets to any other machines.

I get the following information from DHCP:

    lease {
      interface "ath0";
      fixed-address 172.17.245.122;
      option subnet-mask 255.255.255.224;
      option routers 128.233.122.254;
      option dhcp-lease-time 1148;
      option dhcp-message-type 5;
      option domain-name-servers
128.233.3.1,128.233.150.126,128.233.119.73;
      option dhcp-server-identifier 128.233.150.112;
      option broadcast-address 255.255.255.255;
      option ntp-servers 128.233.154.245,128.233.150.93;
      option host-name "monolith";
      option netbios-name-servers
128.233.3.16,128.233.22.25;
      option domain-name "usask.ca";
      option netbios-node-type 8;
      renew 3 2006/12/13 20:46:39;
      rebind 3 2006/12/13 20:54:27;
      expire 3 2006/12/13 20:56:51;
    }

The router 128.233.122.254 is the CCA server.  Trying to add
the
provided router as the default gateway fails:

    # route flush
    # route add default 128.233.122.254
    route: writing to routing socket: Network is unreachable
    add net default: gateway 128.233.122.254: Network is
unreachable

Which makes sens as it's not on the subnet.

From talking to our ITS department, the CCA server
128.233.122.254
actually receives all traffic actually sent on ath0 -- the
subnet
is a virtual subnet rather than an actual subnet (I'm sure
I'm
butchering terms here, but I'm not a networking expert). 
Apparently
Windows is configured to simply forward all traffic onto the
interface and the right thing is done (and is done on this
laptop
if I'm in WinXP).

The following route(8) command actually allows pinging and
communicating with the CCA server:

    # route add -ifp ath0 -iface default 128.233.122.254

But we can't access any other machines -- from tcpdump, this
route
command causes NetBSD to think that everything is on the
local
interface and so it's doing ARPs to resolve the addresses.

ath0 isn't a point to point, so the following fails too:

    # ifconfig ath0 inet 172.17.245.122 128.233.122.254
    ifconfig: can't set destination address on
non-point-to-point link

What I think I really want is something like the following,
though
they don't work.

    # route add -iface 128.233.122.254 -ifp ath0
	# meaning: route packets to 128.233.122.254 directly to
ath0
    # route add default 128.233.122.254
	# and make 128.233.122.254 the default gateway

Any ideas?

Thanks.

Brian.

-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/

      "Amusement to an observing mind is study." -
Benjamin Disraeli
SOLVED: How to route to a default gateway that is not on my subnet?
user name
2006-12-15 22:28:55
Thanks to Greg Oster and other NetBSD developers, we have a
solution:

    $ route add -host <<CCAip>> -link ath0
-iface
    $ route add default -ifa <<ath0ip>>
<<CCAip>>

where <<CCAip>> is the IP address of the CCA
server, and <<ath0ip>>
is the IP address of my ath0 wireless.

Thanks Greg and the other NetBSD devs!

Brian.

On 2006.12.13 15:22:54 -0600, Brian de Alwis wrote:
> Hi everybody.  I'm encountering some difficulties
configuring my
> laptop to work on the wireless network setup at the
University of
> Saskatchewan.  They use a Cisco Clean Access (CCA)
system which
> blocks all network traffic until you have authenticated
yourself
> to a CCA server.  This CCA server is supposed to be
your gateway.
> 
> They have a somewhat strange setup where the gateway is
actually
> outside of the subnet configuration provided to the
clients through
> DHCP.  This setup works fine under Windows XP (and
MacOS, though
> I haven't seen that for myself). 
> 
> We've been able to figure out a recipe for route(8) to
route packets
> to the CCA server so I can authenticate myself, but we
can't route
> packets to any other machines.
> 
> I get the following information from DHCP:
> 
>     lease {
>       interface "ath0";
>       fixed-address 172.17.245.122;
>       option subnet-mask 255.255.255.224;
>       option routers 128.233.122.254;
>       option dhcp-lease-time 1148;
>       option dhcp-message-type 5;
>       option domain-name-servers
128.233.3.1,128.233.150.126,128.233.119.73;
>       option dhcp-server-identifier 128.233.150.112;
>       option broadcast-address 255.255.255.255;
>       option ntp-servers
128.233.154.245,128.233.150.93;
>       option host-name "monolith";
>       option netbios-name-servers
128.233.3.16,128.233.22.25;
>       option domain-name "usask.ca";
>       option netbios-node-type 8;
>       renew 3 2006/12/13 20:46:39;
>       rebind 3 2006/12/13 20:54:27;
>       expire 3 2006/12/13 20:56:51;
>     }
> 
> The router 128.233.122.254 is the CCA server.  Trying
to add the
> provided router as the default gateway fails:
> 
>     # route flush
>     # route add default 128.233.122.254
>     route: writing to routing socket: Network is
unreachable
>     add net default: gateway 128.233.122.254: Network
is unreachable
> 
> Which makes sens as it's not on the subnet.
> 
> From talking to our ITS department, the CCA server
128.233.122.254
> actually receives all traffic actually sent on ath0 --
the subnet
> is a virtual subnet rather than an actual subnet (I'm
sure I'm
> butchering terms here, but I'm not a networking
expert).  Apparently
> Windows is configured to simply forward all traffic
onto the
> interface and the right thing is done (and is done on
this laptop
> if I'm in WinXP).
> 
> The following route(8) command actually allows pinging
and
> communicating with the CCA server:
> 
>     # route add -ifp ath0 -iface default
128.233.122.254
> 
> But we can't access any other machines -- from tcpdump,
this route
> command causes NetBSD to think that everything is on
the local
> interface and so it's doing ARPs to resolve the
addresses.
> 
> ath0 isn't a point to point, so the following fails
too:
> 
>     # ifconfig ath0 inet 172.17.245.122 128.233.122.254
>     ifconfig: can't set destination address on
non-point-to-point link
> 
> What I think I really want is something like the
following, though
> they don't work.
> 
>     # route add -iface 128.233.122.254 -ifp ath0
> 	# meaning: route packets to 128.233.122.254 directly
to ath0
>     # route add default 128.233.122.254
> 	# and make 128.233.122.254 the default gateway
> 
> Any ideas?
> 
> Thanks.
> 
> Brian.

-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/

      "Amusement to an observing mind is study." -
Benjamin Disraeli
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