IS-IS reference

Alex P. Rudnev alex at
Tue Sep 14 17:17:27 UTC 1999

> OSPF (and any other dynamic routing protocol) introduces and removes
> routes every time a link or device goes up or down - or perceived
Yes. For the 100-router backbone, it should happen once/day (failed link, 
failed router), or once/hour, not more often. Through OSPF route even 
dynamil dialup addresses as well - withouth any instability.

> to go up and down.  A typical scenario can be like: connecting a PC
Hmm, what is PC doing in the CORE backbone built by the L2 switches and 
running 100TX or 1,000TX ethernet? And how often does anyone plug in the 
broken cards?

No, the myths about the dynamic routing instability is not more than a 
myth - until someone don't try to readvertise 60,000 router from BGP to 
OSPF or back... I can't understand what all you are flames about - the 2 
level schema (IGP for the CORE hosts and networks, IBGP for the 
multi-home clients, OSPF-ASE or IGP for the STATIC and DialUP clients) 
have not visible disadvantages (except now you can choose IS-IS instead 
of OSPF if you use CISCO - can't argue against this).

> Additionally _no_ exising IGP has anything resembling protection
> from malfunctioning routing software _or_ malicious or negligient
> operators of host-based rotuing software.  I had to track down people
> who enable gated on their linux boxes just for the fun of it, and
> screw the entire network up in the process, more times than i care
> to count.
Yes, but do not mix the customer's and core networks; use OSPF 
authentication if you can't avoid this. And even if you mix networks, 
plug in broken linux with the wrong configured gated - the worst thing 
you can do in the real life is to stole DEFAULT (from the default-less 
backbone -:) - no one even notify this).

No, we had a lot of problems from the wrong static routes, from the wrong 
readvertisements, from the wrong aggregations - and never from the plain 
simple OSPF itself... 

Boths OSPF and IS-IS have a long history, designed well and realised very 
stable (if you don't use something absolutely new and untested). And 
there is a very simple ways to prevent the possible sources of 
instability (dividing the roiuting to the CORE-IGP and USERS-IBGP is one 
of them).

> > No, the comparation between OSPF and STATIC looks like the comparation
> > between the old (from 1950 year) and modern (Mersedess-600) cars - the
> > first is very simple implemented and difficult to drive; the second is
> > very complex implemented but very simple to drive (but if you are to be
> > starving on the unhabitant ireland with the good roads, you'll choose the
> > first car; but it seemd for me you just choose something more complex in
> > the real life).
> Did you notice that it takes a highly trained specialist with appropriate
> (and rather expensive) equipment to diagnose and fix a problem in a Mercedes?
> A hammer and few expletitives usually suffice for a Packard.
Yes, of course; but let's guess what was chosen by your wife?

The OSPF and IS-IS and other MODERN pritocols was designed for the 
brain-less usage; if you don't write too many config lines and prevent 
some hellish words, you are absolutely safe. The safest config is

 router ospf 1
 network area 0


(you can add 'unnumbered' interfaces to this example as well).

> That's the real difference.  People who understand routing protocols
> and how they interact with level-2 transport are still extremely rare
> and rather expensive.  Even the major ISPs here in US have serious staffing
> problems.  An average corporate MIS department is best characterized as
> clueless (what other explanation is here for the Microsoft dominance? :)

> At least he'll be able to understand what's broke when the network goes down.
> BTW, dealing with heaps of statics is very simple: do a numbering plan first,
> so the routes are aggregable.  That is helpful for dynamic routing, too.
Ok, some day I'll ask you to restore normal routing from the heap of 
STATIC routes - I did such work twise, and do not want anymore (this was 
not in our network, through).

> --vadim

Aleksei Roudnev, Network Operations Center, Relcom, Moscow
(+7 095) 194-19-95 (Network Operations Center Hot Line),(+7 095) 230-41-41, N 13729 (pager)
(+7 095) 196-72-12 (Support), (+7 095) 194-33-28 (Fax)

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