[c-nsp] OSPF router gets separated from a broadcast domain

Jeff Tantsura jeff.nsp at gmail.com
Thu Feb 7 13:08:14 EST 2008


Hi,

It is not as difficult as you might think, imagine VPLS in between and
incorrect LSP's setup :)

> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Christopher E. Brown
> Sent: maandag 4 februari 2008 5:14
> To: Gabor Ivanszky
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] OSPF router gets separated from a broadcast domain
> 
> Gabor Ivanszky wrote:
> > Peter Rathlev wrote:
> >>
> >>> That makes sense. But our experience in a real life scenario is that
> >>> the partitioning of  "OSPF speaking transport network" creates the
> >>> blackhole as well. I will try to build this in the lab. May the root
> >>> cause of the blackhole wasn't the network separation, but something
> >>> else...
> >>
> >> If you only use these networks as OSPF transport networks, it's not a
> >> big problem if they're black holed. Since they're not destinations,
> >> neither clients nor servers ever see them in anything but a trace.
> >>
> > But not only the transport network itself get blackholed, but all the
> > networks which are reachable through it.
> 
> 
> Important follow on bits.
> 
> 
> Declare the "one true IP" for the router on a Loopback as a /32
> enable OSPF on this loopback
> declare the OSPF router-id to be this IP
> make use of "source" statements so that telnet, tacacs, snmp, ntp, etc.
> all use this one true address
> whenever you refer to or connect to, use the "one true IP"
> 
> 
> Example
> 
> interface Loopback0
> ip address 10.1.1.1 255.255.255.255
> !
> router ospf 10
> router-id 10.1.1.1
> network 10.1.1.1 0.0.0.0 area 0
> !
> 
> 
> The IPs within the split subnet may be blackholed, but since we never
> speak to/from those IPs...
> 
> 
> The one exception is a non-uniform split.  Assume 3 routers A, B, C, if
> a can talk to B and B to C but not A to C than even with OSPF things
> outside of the transport subnets may also be blackholes, but it takes a
> very screwy/evil network to create a non-unifor L2 split.
> 
> 
> --
> ------------------------------------------------------------------------
> Christopher E. Brown   <chris.brown at acsalaska.net>   desk (907) 550-8393
>                                                       cell (907) 632-8492
> IP Engineer - ACS
> ------------------------------------------------------------------------
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/



More information about the cisco-nsp mailing list