Re: OT: GS Archives Search

Thanks Narbik, perhaps I was over thinking the logic. Theoretically I understand and accept what they are and what they do.

I struggled to appreciate the need for the design of RDs while I was reading that RFC. But now I get it; I understand the design needs now, but the designers could have reused RTs to extend the normal IPv4 32bits to whatever to make the routes unique within MPBGP.

Only VPNv4 routes are allowed within MP-BGP "vehicle". To convert IPv4 routes into these, we need to add additional 8 octet. When we do this, the route becomes unique since we don't want to mix up customer routes during transit. Ok, when the routes get to the egress control plane's PE, it gets converted back to IPv4 and needs a logic to know which vrf to import it into.....that is where RT comes in.

Yemi Salau
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On Mar 26, 2012, at 21:17, Narbik Kocharians <narbikk_at_gmail.com> wrote:

> Since we all know what VRFs are. Remember that the VRF is NOT operational
> without an RD.
> What is an RD? An RD is a 64 bit value that is attached to the customer's
> IPv4 address, to make it a Unique 96 bit address called VPNv4. These
> addresses are ONLY exchanged between the PE routers. In Brians example,
> RDs distinguish one route from another, in his example 10.0.0.0:A from
> 10.0.0.0:B.
>
>
> I think that the name VPNv4 is the worst name they could assign to these
> addresses, because many people think that RDs define the VPN, and they DO
> NOT define the VPN.
>
>
> Once the PE router attaches the RD to the CE routes, it then sends the
> VPNv4 address/es to the other PE router/s. The receiving PE router strips
> the RD from the VPNv4 prefix, and its left with an IPv4 address.
>
>
> NOWHow does the receiving PE know which VRF does the IP address belong
> to? The answer is Route-Target.
>
>
>
> The Route-target is a BGP extended community that indicates which routes
> should be exported from a given VRF or imported into a given VRF.
> I hope this helped.
>
> On Mon, Mar 26, 2012 at 6:27 PM, Brian McGahan <bmcgahan_at_ine.com> wrote:
>
>> 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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>>
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>>
>>
>>
>>
>
>
> --
> *Narbik Kocharians
> *CCSI#30832, CCIE# 12410 (R&S, SP, Security)
> *www.MicronicsTraining.com* <http://www.micronicstraining.com/>
> Sr. Technical Instructor
> YES! We take Cisco Learning Credits!
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>
>
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Received on Fri Mar 30 2012 - 08:20:48 ART