[Xorp-users] static qualified next-hop-router problem

Pavlin Radoslavov pavlin at icir.org
Mon Jan 14 11:40:42 PST 2008


Tuan Hoang <tuan.hoang at agilecommunications.com> wrote:

> Yes, that is correct.  This is a very simple network, so the static
> route (with qualified next-hop-router) was the easiest compared to using
> either RIP or OSPF.  Also as you suspected, my ISP's don't allow routing
> protocols...for obvious reasons.
> 
> So the only way for XORP to detect that my ISP gateway is down is if the
> network interface flags change right (i.e when unplugging the wire or
> basically breaking the link)?  If that is the case, then I'll go with
> the scripting method.

Correct. StaticRoutes can detect only changes to the interface flags
(including the unplugging of the cable) which is a local event.

Please keep us informed how it goes with the scripting method.

Regards,
Pavlin

> Thanks,
> Tuan
> 
> -----Original Message-----
> From: Pavlin Radoslavov [mailto:pavlin at icir.org] 
> Sent: Monday, January 14, 2008 12:36 AM
> To: Adam Greenhalgh
> Cc: Tuan Hoang; xorp-users at xorp.org
> Subject: Re: [Xorp-users] static qualified next-hop-router problem 
> 
> Adam Greenhalgh <a.greenhalgh at cs.ucl.ac.uk> wrote:
> 
> > Tuan,
> > 
> > You didn't say whether you were running any routing protocols.
> > 
> > Adam
> 
> My interpretation of Tuan's email is that the used protocol is "static
> routes".
> 
> The obvious solution would be to use a dynamic protocol like RIP or
> OSPF. Though, if your ISPs don't let you run any, then this is not an
> option for you.
> 
> The StaticRoutes solution can't track the status of remote gateways on
> its own; this is why there are dynamic protocols.
> 
> One possible work-around hack is to use an external script that helps
> StaticRoutes tracking the status of the gateways.
> 
> The script will run a periodic ping to the primary gateway. If the ping
> fails, then the script will use xorpsh to reconfigure XORP by changing
> the next-hop address to the secondary gateway.
> 
> Hope that helps,
> Pavlin
> 
> > On 09/01/2008, Tuan Hoang <tuan.hoang at agilecommunications.com> wrote:
> > >
> > >
> > >
> > > Hi,
> > >
> > > I'm using a XORP 1.4 under CentOS 4.5.  I have a router connected to
> 
> > > two ISP's and want to detect when my primary gateway is down on eth1
> (Note:
> > > ethernet link is still up but gateway is unreachable) and then 
> > > switch over my default route to my other ISP's gateway on eth2.
> > >
> > > I have the static route configured with the a simple next-hop-router
> 
> > > to eth1 with ISP1's GW and also a qualified next-hop-router to eth2
> with ISP2's GW.
> > > When I turn off my cable modem to ISP1, XORP does not change my 
> > > default route's GW to ISP2's GW on eth2.  The only way I've gotten 
> > > this to work is by removing the eth1 ethernet cable to cause the
> interface flags to change.
> > >
> > > FWIW, I've made sure that the ARP cache is flushed for the ISP1 GW.
> > >
> > > Thanks,
> > > Tuan
> > >
> > > P.S.  Please reply all since I am not subscribing to the list.
> > > _______________________________________________
> > > Xorp-users mailing list
> > > Xorp-users at xorp.org
> > > http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/xorp-users
> > >
> > >
> > 
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