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

Hmmmmmm....I'd have to lab it up again but I would expect something a
bit different. I would expect that PE1 would NOT have the label to
PE2's loopback at all for the same reason -- It's IGP is telling him
it is a /32 and LDP from P1 in this case is telling him it is a /24.
What I would expect to happen is that CE1 sends traffic destined for
CE2 and when it hits PE1, PE1 will not have a label for the BGP
next-hop of PE2 and thus can not correctly push 2 labels on to the
MPLS stack (inside label for the VPN, outside label for the next-hop).

I would however expect that IP traffic would work between PE1 and PE2
because as you said if there are no labels it will fallback to IP
routing -- and the P routers are also running OSPF and will have
routes in the global routing table. The thing that needs
clarification is this -- At PE1 does it just NOT send the frame at all
because it has no label for the next-hop PE OR does it send the frame,
but only with the inner VPN label, which would cause issues when the P
router receives the frame (the P router would have no idea what to do
with a VPN label)

On Fri, Jan 22, 2010 at 5:18 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:
> 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
>>>> >> > Fax: +1.810.454.0130
>>>> >> > Community: http://www.ipexpert.com/communities
>>>> >>
>>>> >> --
>>>> >> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
>>>> LW7 EQI Argentina
>>>> >>
>>>> >>
>>>> >> Blogs and organic groups at http://www.ccie.net
>>>> >>
>>>> >>
>>>> _______________________________________________________________________
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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
>

-- 
Regards,
Joe Astorino CCIE #24347 (R&S)
Sr. Technical Instructor - IPexpert
Mailto: jastorino_at_ipexpert.com
Telephone: +1.810.326.1444
Live Assistance, Please visit: www.ipexpert.com/chat
eFax: +1.810.454.0130
IPexpert is a premier provider of Classroom and Self-Study Cisco CCNA
(R&S, Voice & Security), CCNP, CCVP, CCSP and CCIE (R&S, Voice,
Security & Service Provider) Certification Training with locations
throughout the United States, Europe and Australia. Be sure to check
out our online communities at www.ipexpert.com/communities and our
public website at www.ipexpert.com
Blogs and organic groups at http://www.ccie.net