North American Network Operators Group


Re: OSPF multi-level hierarchy: Necessary at all?

  • From: Jessica Yu
  • Date: Fri May 28 16:18:59 1999

>But please stop talking about _a lot of interface changes_ etc withouth 
>referencing to the type of network. In case of leased-links network I can 
>built the network of ANY size; and limitations depends of the link 
>stability, not of the network size. 

I was talking about ISP network which mostly is leased-line based.
It depends on link stability and router stability.  As I pointed out
in my previous message, the more router and link a network has (i.e.
the large scaled network), the large chance of having link flapping
and router crashes (if you think in percentage sense), the more flooding,
SPF calculation and LSDB update all routers in the network have to
handle.  If there is a hierarchy, then only a portion of routers (not all 
the routers) would need to handle flooding, SPF calculation and LSDB update.

Also, the large the size of network (lots of routers and links), the
bigger the LSDB and the higher complexity of SPF calculation.