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Problems with Multilink PPP between Cisco and Junipers?

 
 
Andrew Gideon
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      03-21-2005

We'd a one of two T-1s in a Multilink PPP bundle go down. Annoying. But
this also appears to have somehow "broken" the Multilink itself. Very
Annoying.

I'm on the Cisco side: a 3662 running 12.2(23a). I've removed the "bad"
serial line from the Multilink, as did a fellow on the Juniper side, but
the link didn't return to a working state.

When the broken serial line is fixed, we'll be able to do a little more
testing. It *might* only be a coincidence that both the Multilink breaking
and the serial line going down occurred at the exact same time. But I've
my doubts.

Anyone have any thoughts or ideas?

I've no minimum number of member links set on my side, and the Juniper side
had a minimum of one (and we did confirm that the remaining T-1 was
working). The Multilink reported itself as up on both sides, but we
couldn't ping each other's IPs. I couldn't even ping my own!

Both IPs could be pinged from elsewhere, however.

The configuration for the multilink on my side is pretty basic:

interface multilink 2
description Upstream 2
no ip address
ip address a.b.c.d 255.255.255.252
ip nat outside
ppp multilink
multilink-group 2
ip access-group 101 in
ip access-group out-to-world out
no ip directed-broadcast
no ip unreachables
no cdp enable

with a couple of serial interfaces "joining" via:

encapsulation ppp
ppp multilink

Any thoughts or suggestions welcome...

Andrew


 
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aunraza
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      03-21-2005
Did you try pinging from the inside? Or sourcing the ping on the router
from the internal interface?

 
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Hansang Bae
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      03-22-2005
Andrew Gideon wrote:

>
> We'd a one of two T-1s in a Multilink PPP bundle go down. Annoying.
> But this also appears to have somehow "broken" the Multilink itself.
> Very Annoying.
>
> I'm on the Cisco side: a 3662 running 12.2(23a). I've removed the
> "bad" serial line from the Multilink, as did a fellow on the Juniper
> side, but the link didn't return to a working state.

[snip]
> Any thoughts or suggestions welcome...


Let us know how it turns out. Might be a Cisco/Juniper thing.


--

hsb


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Andrew Gideon
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      03-22-2005
Hansang Bae wrote:

> Let us know how it turns out. Might be a Cisco/Juniper thing.


The T-1 was brought back into service. The Multilink was reestablished on
both sides, and all was well. I could ping both my side of the link and
the remote site, and traffic moved properly.

I'm leaning slightly towards the Cisco/Juniper "thing" idea, except I'd be
hard pressed to describe the details of the thing. I know that I (on the
Cisco side) had at one point completely removed the Multilink interface and
rebuilt it with the lone working circuit. I believe that this was done on
the Juniper side too.

Yet that didn't provide a working Multilink. How could that not, unless one
cannot build a Multilink out of a single circuit between Cisco and Juniper?

Another puzzle to me within the larger puzzle is why I couldn't ping my side
of the Multilink. How could that not be possible?

- Andrew

 
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Andrew Gideon
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      03-22-2005
aunraza wrote:

> Did you try pinging from the inside?


I don't recall doing this. I suspect that it would have worked, but gone
"the long way round". That is, the pings to those IPs would have left my
"inside" via another egress path and then worked their way back.

> Or sourcing the ping on the router
> from the internal interface?


I did source the ping to the far side of the Multilink from the near side's
IP to no effect. I didn't try sourcing the pings to the near side from
anything in particular; I'm not sure what source would have been
"interesting".

- Andrew

 
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Rob
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      03-23-2005
Yes, there is a known issue between Cisco and Juniper doing MLPPP. At
least that is what Global Crossing told me when they wouldn't let me
do it until Juniper fixed their code. That was back in December.
Now, I don't know if this fix was specific for the ISP Global Crossing
or public. You'll have to ask Juniper.

BTW, it works fine now. I have several Cisco routers (mostly 2600XM
series) doing MLPPP with either two or four T1's to Global Crossing,
and they only run Juniper. There were some specific commands that
needed to be done, like turn off MLPPP fragmentation on both sides,
and an MTU bug which affects only OSPF, but that's it.

-Bob



On Mon, 21 Mar 2005 14:23:14 -0500, Andrew Gideon <(E-Mail Removed)>
wrote:

>
>We'd a one of two T-1s in a Multilink PPP bundle go down. Annoying. But
>this also appears to have somehow "broken" the Multilink itself. Very
>Annoying.
>
>I'm on the Cisco side: a 3662 running 12.2(23a). I've removed the "bad"
>serial line from the Multilink, as did a fellow on the Juniper side, but
>the link didn't return to a working state.
>
>When the broken serial line is fixed, we'll be able to do a little more
>testing. It *might* only be a coincidence that both the Multilink breaking
>and the serial line going down occurred at the exact same time. But I've
>my doubts.
>
>Anyone have any thoughts or ideas?
>
>I've no minimum number of member links set on my side, and the Juniper side
>had a minimum of one (and we did confirm that the remaining T-1 was
>working). The Multilink reported itself as up on both sides, but we
>couldn't ping each other's IPs. I couldn't even ping my own!
>
>Both IPs could be pinged from elsewhere, however.
>
>The configuration for the multilink on my side is pretty basic:
>
> interface multilink 2
> description Upstream 2
> no ip address
> ip address a.b.c.d 255.255.255.252
> ip nat outside
> ppp multilink
> multilink-group 2
> ip access-group 101 in
> ip access-group out-to-world out
> no ip directed-broadcast
> no ip unreachables
> no cdp enable
>
>with a couple of serial interfaces "joining" via:
>
> encapsulation ppp
> ppp multilink
>
>Any thoughts or suggestions welcome...
>
> Andrew
>


 
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