[c-nsp] Monitoring L3 link status

[Phil Mayers]

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.

For probing / monitoring, the ip sla / rtr functionality from B-D and 
C-E would be the normal way (assuming D and E answer pings). It doesn't 
run continuously and getting the results back via SNMP can be a pain, 
but it's a reasonable solution.

http://www.cisco.com/go/saa

For actually detecting failures on the link, something like BFD or 
802.3ah would be the correct solution. I don't know if the 3750ME 
supports either, and the latter is quite new and still therefore raw.