[smokeping-users] Re: Re[2]: logging multiple connections

hkclark at yahoo.com hkclark at yahoo.com
Sat Jan 15 14:18:09 MET 2005

Hi Peter,

Thank you for the clarification.

You should be able to get what you want if you add the
appropriate "host route" to "hack" the routing table
on your smokeping unix box (a “host route” is a route
where the netmask is 32 bits long [ or
/32 depending on how you want to represent it].  For
example, say you represent the next-hop routers to
each ISP connection as A (Telenet) and B (Skynet) and
that the IPs for these 2 devices are 10.1.1.A and
10.2.2.B.  Then say you have your default gateway on
your smokeping server set to use 10.2.2.B.  That
should result in a route in the server with
a next hop of 10.2.2.B; meaning that *all* traffic off
the local subnet goes through 10.2.2.B (assuming there
are no other routes on the box).  What you want to do
is override this default route, but *just* for one of
the outside servers you want to monitor.  Let's say
these outside servers are server-1 and server-2 with
the IP addresses and respectively. 
Without a host route, both servers will follow the
default route and ping through Skynet via the 10.2.2.B
router.  But, if we add a host route to the
destination and specify a next hop of
10.1.1.A, then only traffic to the exact IP address will go through Telenet.  The Linux command
should be something like: 
  route add -net gw 10.1.1.A

Does that sound like what you are looking for?


PS – I should point out that I’m more of a network guy
than a huge Unix admin type of person.  For this to
work, I’m assuming that your Unix/Linux box does what
is called “longest match routing” (or “longest prefix
routing”).  Things like Cisco routers have done this
by default for years now (the “Router Requirements
RFC” has mandated this since something like 1995), and
I would think all modern Unix-like OSs would be the
same.  However, I could be wrong. :-)

--- Peter Mees <peter at cts.be> wrote:

>    I will try to be more specific.
>    In my local network there's one machine that is
> the smokeping machine.
>    It has 2 nic's in it , one is connected to isp 1
> (Telenet), the other to my
>    lan switch. On that lan switch , there is a
> connection with another
>    small router that is connected to isp 2 (Skynet).
>    Skynet and Telenet are the main internetproviders
> for Belgium.
>    I have 2 other machines which are placed in 2
> different datacenters
>    to host websites.
>    What i want to do , is use the smokeping machine
> to verify the
>    connection to my 2 other server on both isp
> connections.
>    Why ? Because isp1 (Telenet) sometimes has a
> route problem to one
>    of my other servers. Then clients starting to
> call me because
>    theirs websites arent accesible from within the
> Telenet network.
>    So if i can use smokeping for this purpose ,
> clients can check
>    themself if it is a connection problem with
> Telenet.

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