Re: Is there a methodical way to check full reachability?

Joe,
can we go into detail about this ?

> The issue with the /24 loopbacks is that you will actually not have a
> label for the LER in the MPLS cloud.

And by cloud I guess you mean all P routers ?

The actual problem happens at the router that is just before the exit P.
If you have CE1 - PE1 - P1 - P2 - PE2 - CE2, the blackhole of traffic
from CE1 to CE2 is seen at P2.
That is because, as you said, PE2 has the /24 in the RIB and it's
sending via LDP a label for it, but P2 has the /32 in its RIB and so
there is no match. P1 will have the /32 and a valid label though, as PE1.

Interestingly, IP traffic from PE1 to PE2 will work! being mpls framed
from PE1 to P2, and will be IP forwarded to PE2. The "Untagged" tag
in P2's LIB is the "culprit"...

It behaves just like as if you were doing PHP one hop early, thus my
comment.

-Carlos

Joe Astorino @ 22/01/2010 16:22 -0300 dixit:
> The issue with the /24 loopbacks is that you will actually not have a
> label for the LER in the MPLS cloud. What will happen is that by
> default OSPF will advertise that /24 loopback as a /32. LDP on the
> other hand will advertise the /24. Since your LFIB is based in part
> by your existing routing table, and the label you received does not
> match the prefix in your RIB (/24 vs /32) the label will never be
> installed.
>
> On Fri, Jan 22, 2010 at 1:58 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:
>> The PHP will occur one hop early.
>> That's why I asked if MPLS is present in R&S lab :)
>>
>> Divin Mathew John @ 22/01/2010 15:49 -0300 dixit:
>>> Wht will happen?
>>>
>>> On Sat, Jan 23, 2010 at 12:17 AM, Joe Astorino <jastorino_at_ipexpert.com
>>> <mailto:jastorino_at_ipexpert.com>> wrote:
>>>
>>> Indeed....using MPLS and having a broken LSP somewhere in the middle
>>> can result in having routes but no reachability : ) Try running MPLS
>>> L3 VPN with OSPF over frame-relay in your SP "core" and make your PE
>>> loopbacks /24s and see what happens : )
>>>
>>> On Fri, Jan 22, 2010 at 1:18 PM, Divin Mathew John
>>> <divinjohn_at_gmail.com <mailto:divinjohn_at_gmail.com>> wrote:
>>> > R1--- r2--- R3
>>> > R1 thinks R2 is next hop for R3 Lo0. and R2 Thinks R1 is next hop
>>> for R3'
>>> > Lo0
>>> >
>>> >
>>> > On Fri, Jan 22, 2010 at 10:27 PM, Carlos G Mendioroz
>>> <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
>>> > wrote:
>>> >>
>>> >> Would you please show a simple example where you have routes and
>>> >> not reachability ? Obviously without ACLs blocking traffic.
>>> >>
>>> >> -Carlos
>>> >>
>>> >> Marko Milivojevic @ 22/01/2010 8:54 -0300 dixit:
>>> >> > On Thu, Jan 21, 2010 at 23:51, Carlos G Mendioroz
>>> <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
>>> >> > wrote:
>>> >> >> Or you can use the thoughtfull (sp?) way of verifying that all
>>> your
>>> >> >> networks have indeed routes in all your routers, and that you have
>>> >> >> no routing (change) activity (i.e. debug routing).
>>> >> >
>>> >> > Having routes in the routing table does not mean reachability :-).
>>> >> >
>>> >> > Having pings working, doesn't mean full routing convergence :-).
>>> >> >
>>> >> > --
>>> >> > Marko Milivojevic - CCIE #18427
>>> >> > Senior Technical Instructor - IPexpert
>>> >> >
>>> >> > Mailto: markom_at_ipexpert.com <mailto:markom_at_ipexpert.com>
>>> >> > Telephone: +1.810.326.1444
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>>> >> --
>>> >> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
>>> LW7 EQI Argentina
>>> >>
>>> >>
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>>> >
>>> >
>>> >
>>> > --
>>> >
>>> > Sent from Bengaluru, Karnataka, India
>>> >
>>>
>>>
>>>
>>> --
>>> Regards,
>>>
>>> Joe Astorino CCIE #24347 (R&S)
>>> Sr. Technical Instructor - IPexpert
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>>> Sent from Bengaluru, Karnataka, India
>> --
>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>
>
>
>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net