At 15:11 28.05.99 +0400, Alex P. Rudnev wrote:

Btw. Flat network...

Routers now have - 128 or 256 MB RAM, 300 - 400 Mhz CPU. I guess you can built flat betwork with 5,000 routers withouth hard problems.

Mmm...I wouldn't be so sure, actually. Recall we need to refresh each LSA every 30 minutes not to let some bugs drive our network crazy. Also the more routers you have in the flat network the greater is the size of LSDB (or whatever table is used) and, since all routers see all other routers and links, the more CPU time we need to spent calculating our SPFs, maintaining the RT, etc...

Through it's not the question. There is _already_ 2 levels; you can use multi-zone OSPF (independent OSPF networks connected by _redistribute_). The question was _is 2-level hierarchy enougph__?

Externals in OSPF can also become a scalability issue---Type5 LSAs have domain-wide flooding scope....so, unless you want your areas to be stub, you have all your externals crossing all areas and installed into LSDBs of all routers, making them spend more time on SPF, while it is understood that the lower the level of hierarchy a router is in, the less granularity of external routing info it needs. Alex. ------------------------------------------------------------------ Alex D. Zinin, Consultant CCSI #98966 CCIE #4015 AMT Group / ISL Cisco Systems Gold Certified Partner http://www.amt.ru irc: //EFNET/#cisco, //irc.msn.com/#NetCisco [Ustas]