[c-nsp] Monitoring L3 link status

[Bill Nash]

Apply some PBR fu to the subnet you're probing from. Set aside one IP 
address for use with each provider, and have the PBR force the nexthop to 
be one of your BGP peers. Use a tool that allows you to set your source 
address for the probes (or just use two different boxes) so the PBR traps 
the outbound probe, and you can force the traffic to take a left or a 
right at Albequerque. You can't gaurantee the return path with this setup 
but you can at least see the outbound.

I haven't done this inside an OSPF context, but I have successfully used 
this technique to monitor paths and perform network probes out as many as 
five different bgp peers, simultaneously. 

- billn

On Wed, 13 Dec 2006, Frank Bulk wrote:

> We're using two Cisco 3750-ME routers (B & C) that are connected to our
> upstream service provider's routers (D & E).  We started using ping checks
> to D & E from our server running SolarWinds, but because our internet
> traffic runs primarily over B-D or C-E it's not really a good link test.  If
> our traffic runs over C-E then ping checks to D run over C, E, and then on
> to D.  Link B-D could fail and we wouldn't know.
> 
>            |---OSPF---[B]---BGP---[W]---[EoS]---[EoS]---[D]
>            |           |                     / \         |
> server ----A         OSPF                   |   |       BGP
>            |           |                     \ /         |
>            |---OSPF---[C]---BGP---[X]---[EoS]---[EoS]---[E]
> 
> This can't be a new issue -- what's the easiest way to test L3 connectivity
> between B-D and C-E?  All our connections internally and to our upstream
> provider are Ethernet, transport is Ethernet over SONET) and testing for
> interface status is not reliable enough as our demarc with our upstream
> provider is a Cisco 2950 (W & X).  I believe our upstream provider uses
> Juniper routers.
> 
> Regards,
> 
> Frank
> 
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