Re: OT: GS Archives Search

Yemi,
by now you should have a clear idea of the complexity of the topic.
Instructors debate as to what the best way of teaching this stuff is!

I like the "understanding comes after confusion" moto, so I'd add yet
another look at how it goes. And yes, I think it is a good idea to be
able to search GS archives. The current interface seems to bring no
results (http://www.groupstudy.com/cgi-bin/search) so I'm asking Paul to
take a look.

So RDs are, as the name implies, route distinguishers. They make "would
be identical" routes, different. One and only one RD can/has to be
assigned to each VRF, i.e., each router context.

As Brian and Marko and books and manuals say, they make custommer A net
10 different from custommer B net 10, so the common core routing
protocol iBGP does not confuse them. We need them or else we would not
be able to route custommers independently.

Even though RDs is all that might be needed to implement VPNs, RTs are a
standardized way of making things easy (yes, believe it or not, this is
easy). It's a way of marking (at origin) the routes to later be able to
pick the ones you need at destination. This is needed because all routes
share a common iBGP, a common bag if you will.

This enables not only independent "simple" VPNs to be deployed (which
would have been easy to do with just a common RD at all places) but to
do complex interlaced VPNs where some sites of custommer A can talk to
some sites of custommer B (C and D...).

Fun stuff, that makes some of us compete for the better explanation :)

-Carlos

Brian McGahan @ 26/03/2012 22:27 -0300 dixit:
> Personally that seems overly confusing to me. Yes Route Targets are an attribute of the route, but that attribute is not part of the BGP Bestpath Selection. I'm not sure how it ties together. It's simpler to think of it this way:
>
> It's given that customers of a Service Provider will have overlapping IP addressing in their VPNs, e.g. you will have more than two customers who use the 10.0.0.0/8 network. The RD is how you tell them apart. If you have customer "A" with RD "A" and customer "B" with RD "B" the routes "A:10.0.0.0/8" and "B:10.0.0.0/8" become unique. This is all the RD does.
>
> The Route Target tells you which VRF table the route belongs to. You have to separate the two attributes because sometimes you want the same route to belong to multiple VRF tables. This is common in what's known as "Central Services VPNs". For example if the Service Provider hosts email for customers, that route to the mail server would have to be in the routing table of multiple customers. This doesn't break the rule of the route having to be unique though, which is what the RD does.
>
> Like I said you may be able to find more clarification in this video: http://goo.gl/Y0imB.
>
> Brian McGahan, CCIE #8593 (R&S/SP/Security)
> bmcgahan_at_INE.com
>
> Internetwork Expert, Inc.
> http://www.INE.com
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Marko Milivojevic
> Sent: Monday, March 26, 2012 6:00 PM
> To: Yemi Salau
> Cc: ccielab_at_groupstudy.com
> Subject: Re: OT: GS Archives Search
>
> Simple reason - prefixes are passed on through the bestpath selection process where the best one is chosen based on attributes. RT is a community, which is an attribute. This means that given two prefixes with different RTs would be treated as equals when it comes to bestpath selection. With RD we extend the prefix space to 86 bits and then use those for comparison instead of 32bit ones.
>
> [ iPhone, brevity, etc disclaimer :-) ]
>
> --
> Marko Milivojevic - CCIE #18427
>
> :: This message was sent from a mobile device. I apologize for errors and brevity. ::
>
> On Mar 26, 2012, at 14:44, Yemi Salau<salauolayemi_at_yahoo.co.uk> wrote:
>
>> Thanks Marko, reading RFC 4364, I was trying to figure out why RT
>> couldn't
> do the same job of RD for uniquely separating VPN-IPv4 routes within the provider MPLS cloud. I'll watch your video when I get home. Many Thanks.
>>
>> From: Marko Milivojevic<markom_at_ipexpert.com>
>> To: Yemi Salau<salauolayemi_at_yahoo.co.uk>
>> Cc: ccielab_at_groupstudy.com
>> Sent: Monday, 26 March 2012, 16:25
>> Subject: Re: OT: GS Archives Search
>>
>>
>> Yemi,
>>
>> I'm not sure about the Archive search, but I can certainly help you
>> with RD
> and RT. Almost two years ago I hosted a free online training session called "MPLS 101". You can find it, together with all other recorded vLectures on many other subjects here:
>>
>> http://bit.ly/vLecture
>>
>> Please go ahead and watch it and if you have any questions feel free
>> to ask
> them here.
>>
>> --
>> Marko Milivojevic - CCIE #18427 (SP R&S) Senior CCIE Instructor -
>> IPexpert
>>
>> On Mon, Mar 26, 2012 at 10:18, Yemi Salau<salauolayemi_at_yahoo.co.uk> wrote:
>> Guys,
>>
>> I remember a time where I was able to search the GS archives for
>> stuffs. Is
> this still available today? I want to search out some stuffs on RD vs RT.
>>
>> Yemi
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net