Re: ISIS L1 vs L2

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
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Received on Thu Nov 29 2012 - 08:28:45 ART