[nos-bbs] Multiple routes to one destination

Barry Siegfried k2mf at k2mf.ampr.org
Mon Apr 14 14:54:28 EDT 2008

["(Skip) K8RRA" <k8rra at ameritech.net> wrote]:

> Greetings fellow NOS users.
> AMPRNET is my jnos home, and with a dynamic IP from my ISP
> I have chosen to remain with only a radio link to the world.  Another
> close jnos node has provided fine service in connecting me to the
> remainder of 44...
> Being VERY fortunate, there is a second equally qualified jnos in the
> opposite direction with equal access to 44... network.  It makes sense
> to me that I should be able to use that second path equally.  Well not
> for return packets -- they are routed to the first path and that breaks
> the symmetrical rule we try to follow [more on this below].
> As I read documentation, the "route add ..." command provides for a
> "metric" to break ties found in multiple routes.  That is logical --
> except jnos does not permit me to "route add ..." a second route to the
> same IP.  Therefore for example, I am prevented from specifying two
> gateways with different metrics.  Instead jnos replaces the original
> route with the new route, thus the route table *seems* to support only
> *ONE* route to any remote IP.
> SO -- is metric a documentation flaw or am I reading challenged?


'metric' is a field of data in the basic IP route structure that has
a numeric value.  To the best of my knowledge, nothing was ever done
in the xNOS code to implement an actual use for it except for in the
RIP module.  Otherwise, it means very little to the rest of the IP
routing code.  The xNOS code permits only a single IP route to a
given destination and a newly specified one WILL overwrite an
existing one.

> As I further read documentation, jnos supports "rspf" that I have
> not tested yet.  If I were to implement rspf to find a best route
> to a remote site, then it *seems* logical that I must modify the
> static route table to allow rspf to work its magic.  Likewise, the
> nodes carrying the response packet back to me must permit route
> table magic to permit a symmetrical route.
> Is anyone using rspf now?  Where might I find expanded documentation
> for this jnos feature?

I'm sure RSPF is still in use somewhere but I don't know where.  To the
best of my knowledge, we don't use it around these here parts and since
an RFC was never written for it, it never became "well known".

73, de Barry, K2MF >>
          <|>      Barry Siegfried
| Internet | bgs at mfnos.net              |
| HomePage | http://www.mfnos.net/~bgs  |
| Amprnet  | k2mf at k2mf.ampr.org         |
| PBBS     | k2mf at k2ge.#cnj.nj.usa.noam |

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