Routing and Reachability Question

Answered Question
Feb 4th, 2009
User Badges:

If I have a data center router that is running OSPF on a serial WAN interface - and that interface is connected to a remote spoke router, will that remote router be reachable from the rest of the enterprise if it is not running OSPF but is simply connected to the data center router's serial interface?

<br /><br />

<br /><br />I imagine it should because the data center router is advertising the /30 subnet to its OSPF neighbors, so when traffic destined for the peer remote router reaches the data center router, the remote router will be viewed as a "directly connected" route.

<br /><br />

<br /><br />Is that correct?

<br /><br />

<br /><br />Thank you

Correct Answer by Richard Burts about 8 years 1 month ago

Joe


Your logic is partly right - but also perhaps partly wrong.


You are right that the remote spoke router is reachable since the IP address of its serial interface is in a subnet that is advertised by the data center router. So anyone in the network would be able to ping the router serial interface (or perhaps to telnet to the router serial interface). If that is all that you care about then you are right.


But your logic has not considered that no other address on that router will be known. Any device connected to the LAN of the remote spoke will not be known and not be reachable. And it is the devices connected on the LAN that we generally care about when considering routing issues.


To overcome this you would either run OSPF on the remote spoke or you would configure static routes on the data center router and redistribute those static routes into OSPF.


HTH


Rick

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Loading.
Correct Answer
Richard Burts Wed, 02/04/2009 - 13:16
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Joe


Your logic is partly right - but also perhaps partly wrong.


You are right that the remote spoke router is reachable since the IP address of its serial interface is in a subnet that is advertised by the data center router. So anyone in the network would be able to ping the router serial interface (or perhaps to telnet to the router serial interface). If that is all that you care about then you are right.


But your logic has not considered that no other address on that router will be known. Any device connected to the LAN of the remote spoke will not be known and not be reachable. And it is the devices connected on the LAN that we generally care about when considering routing issues.


To overcome this you would either run OSPF on the remote spoke or you would configure static routes on the data center router and redistribute those static routes into OSPF.


HTH


Rick

ex-engineer Wed, 02/04/2009 - 13:56
User Badges:

Any device connected to the LAN of the remote spoke will not be known and not be reachable. And it is the devices connected on the LAN that we generally care about when considering routing issues.


To overcome this you would either run OSPF on the remote spoke or you would configure static routes on the data center router and redistribute those static routes into OSPF.


Rick:


I completely agree and realize this. In this circumstance, I am only concerned with reaching the device so that it can be configured by an engineer. A low-level tech, who is on site and in possession of the new switch has to configure the device to be reachable remotely, though, hence my question. I am trying to make it as simple for the tech as possible.


[EDIT] I should also mention that I need to have the tech configure a default route (ip routing) or default gateway to make the device reachable. [EDIT]


Thanks



Richard Burts Wed, 02/04/2009 - 14:23
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Joe


With that clarification you are right that the router will be reachable for telnet. And you are right that it would need a default route.


Also be aware that for telnet to work the router probably needs a password on the vty lines. And for enable access you probably need an enable password or enable secret.


I guess I am not clear about what might be preconfigured on the router when it is sent out vs what needs to be configured in the field.


HTH


Rick

Actions

This Discussion