Re: ISIS L1 vs L2

BTW I found this in ORD a couple of pages later...

"Deploying a pure L2 routing domain in IS-IS is not possible, because the
L2 routers do not know a path to the edge of the L2 routing domain. The L2
routing information that is contained in IS tables shows only information
on how to reach the next hop toward the destination; it does not provide a
path to the next hop. Instead, any 'L2 domain' that is discussed in this
chapter actually refers to an overlapped L1/L2 domain."

Thoughts? See Marko's previous email? :)

Ronnie

On Thu, Nov 29, 2012 at 8:28 AM, Ronnie Angello
<ronnie.angello_at_gmail.com>wrote:

> Yep, I understand and I agree with you. I think we beat this one up
> pretty good yesterday...
>
> I was not saying that you "have to have" flat L1/L2 in this particular
> design. I was replying to my previous email where I mistakenly said that
> L1/L2 mode is a Cisco thing. What I meant to say is that L1/L2 mode on by
> default is a Cisco thing. You would "have to have" the actual L1/L2 IS
> mode for IS that maintains adjacencies in both areas.
>
> Ronnie
>
> On Thu, Nov 29, 2012 at 2:12 AM, <shiranp3_at_gmail.com> wrote:
>
>> 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.
>>> >
>>> >
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>>> >
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>>
>>
>> --
>> Shiran Guez
>> MCSE CCNP NCE1 JNCIA-ENT JNCIS-ENT CCIE #20572
>> http://cciep3.blogspot.com
>> http://www.linkedin.com/in/cciep3
>> http://twitter.com/cciep3

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Received on Fri Nov 30 2012 - 09:26:23 ART