Re: ISIS L1 vs L2

You do not "have to have" anything and just because Cisco default to L1/L2
does not mean your design should stick to defaults.

When implementing L1/L2 everywhere it is like you are running 2 igp's doing
the same thing, redundancy with no actual redundancy as they both run from the
same control plane and on the same process, so when event happen or any other
it will always take double the effort and resources, believe me as I am
working for a company that build core routers, it is not very nice when
convergence is double the time dose not meter how strong is your router, the
algorithm is the same ( for sure double the time of crs is not the time for
j2320 or t640 will converge much faster then 3900 ), also I would not go in
to the buggy software risk when doing everything double.

So you can see where I am going...

A good design is simple and flexible and scalable, L2 core will provide it
safe and clean even if you are doing now only one area.

W W)WW WW-iPad W)WW

W-28 WW WW 2012, WW)W"W 19:16, Ronnie Angello <ronnie.angello_at_gmail.com>
WW*W/W:

> Never mind that... you would have to have L1/L2. L1/L2 mode by *default* is
a Cisco thing if I remember correctly. I will shut up now...
>
> Sent from my iPhone
>
> On Nov 28, 2012, at 12:08 PM, Ronnie Angello <ronnie.angello_at_gmail.com>
wrote:
>
>> Good discussion, and I agree on all points. Actually now that I think
about it, that would be the "standard" answer anyway. Isn't L1/L2 a Cisco
concept? Maybe not at this point, but thought that was the case at one
point.
>>
>> Now I'm curious why ORD recommended L1/L2. I guess because it's the Cisco
default and performance hit on modern day routers would be "negligible."
However, the title of the book *is* Optimal Routing Design...
>>
>> Ronnie
>>
>> Sent from my iPhone
>>
>> On Nov 28, 2012, at 11:10 AM, Marko Milivojevic <markom_at_ipexpert.com>
wrote:
>>
>>>
>>> Personally, I'd rather go with a single L2 domain. That allows the
flexibility to add L1 domains in the future, simplifies database and removes
redundant hellos.
>>>
>>> --
>>> Marko Milivojevic - CCIE #18427 (SP R&S)
>>> Senior CCIE Instructor - IPexpert
>>>
>>> :: This message was sent from a mobile device. I apologize for errors and
brevity. ::
>>>
>>> On Nov 28, 2012, at 7:34, Ronnie Angello <ronnie.angello_at_gmail.com>
wrote:
>>>
>>>> So at least we agree don't do L1 only... I honestly haven't done much
real world IS-IS design, but my reference is Optimal Routing Design (Chapter
5, page 190).
>>>>
>>>> Ronnie
>>>>
>>>> Sent from my iPhone
>>>>
>>>> On Nov 28, 2012, at 9:56 AM, shiran guez <shiranp3_at_gmail.com> wrote:
>>>>
>>>>> L1/L2 everywhere is not making much sense as you will have redundant
database for both L1 and L2. normally Core you will work L2 edge to "stub" you
will do L1/L2 and stub networks you will set L1, L2 will provide you future
flexibility, even if you think that you will not expand or change, it is not a
good design to do a limit yourself from the start, it does not cost anything
to do it L2, but it will cost plenty if you will need to change Core in
future.
>>>>>
>>>>> my 2 cents :-)
>>>>>
>>>>>
>>>>> On Wed, Nov 28, 2012 at 3:18 PM, Ronnie Angello
<ronnie.angello_at_gmail.com> wrote:
>>>>>> A single L1/L2 domain would be best as it provides flexibility... That
way you already have a contiguous L2 domain. If the network grows, it's
easier to add an L1 routing domain than it is to add an L2 routing domain. You
just add an L1 IS to the edge and push the L1 domain into the network...
>>>>>>
>>>>>> Ronnie
>>>>>>
>>>>>> Sent from my iPhone
>>>>>>
>>>>>> On Nov 27, 2012, at 10:24 PM, Routing Freak <routingfreak_at_gmail.com>
wrote:
>>>>>>
>>>>>> > Hi all
>>>>>> >
>>>>>> > In my customer core network where we had a heated about wither OSPF
or ISIS
>>>>>> > and finally ISIS won the race for the core IGP due to some business
>>>>>> > decision and now my problem here is that when i was designing the
network
>>>>>> > with one large ISIS area with all the linka s L1, everyone opposed me
to
>>>>>> > not to configure L1 and go for L2.
>>>>>> >
>>>>>> > I know that L1 is within single area and L2 can be connected across
areas
>>>>>> > and also within a single area and it carries all the routes within L1
and
>>>>>> > L2.
>>>>>> >
>>>>>> > But in my design , i have single large area with all links as L1,
what is
>>>>>> > the problem in that, L1 or L2 it should be the same.
>>>>>> >
>>>>>> > I didnt understood what is the logic behind the fact that L1 should
not be
>>>>>> > used and L2 should be used.
>>>>>> >
>>>>>> > I thought may be when they are forming more areas, then l2 makes
sense, but
>>>>>> > they r not going to expand the site with another area, so why not
going for
>>>>>> > L1 will suffice the requirement .
>>>>>> >
>>>>>> > L1 is within one single area and doesnt know any other routes of
other area
>>>>>> >
>>>>>> > L2 router is one where all the areas merge and exchange routes in
one
>>>>>> > separate area. It can be any area and not area 0 and just all the
routers
>>>>>> > in that particular area should be running L2 adjacency with each
other.
>>>>>> >
>>>>>> >
>>>>>> > In one large area, which is better L1 or L2. Any ISIS Experts, be
sure to
>>>>>> > reply to this.
>>>>>> >
>>>>>> >
>>>>>> > Blogs and organic groups at http://www.ccie.net
>>>>>> >
>>>>>> >
Received on Thu Nov 29 2012 - 09:12:42 ART