Re: Nexus 5k / 7k Loop

Not sure if my last email went through. One thing I would check is to
ensure that you unique domain IDs between the pairs. For instance the N7Ks
should have the same domain IDs, but the 5Ks should have a unique pair of
domain IDs. Domain ID is used to seed the MAC address assignments so each
pair might be assigned the same MAC addresses. Thus when you plug them
together they see "themselves" talking back and assume a loop.

-Marc

On Wed, Sep 24, 2014 at 1:52 PM, Tony Singh <mothafungla_at_gmail.com> wrote:

> Hi David
>
> What codes were you running on the 5k and 7k's be a good one to search
> back on...
>
> --
> BR
>
> Tony
>
> Sent from my iPad
>
> > On 22 Aug 2014, at 02:18, david bloom <dbsg13_at_yahoo.com> wrote:
> >
> > In case anyone else has this issue - TAC has identified that this can
> actually
> > happen within the 77xx platforms and is a rare but known bug. B They
> have seen
> > this before, but are unsure of a root cause. B Either the L2FM or the
> port
> > index manager was not properly adding links to the vPC port-channel, and
> a L2
> > loop formed. B The fix can be as simple as a system reload, or in some
> cases
> > just flapping the links.
> >
> >
> > ________________________________
> > From: david bloom
> > <dbsg13_at_yahoo.com>
> > To: Cisco Certification <ccielab_at_groupstudy.com>
> > Sent:
> > Tuesday, August 19, 2014 10:58 AM
> > Subject: Re: Nexus 5k / 7k Loop
> >
> >
> >
> > As an
> > update - we just completed the 2nd uplink from the 5k to the 7k, created
> > port-channels and back to back vPC, however the loop still exists...
> > ________________________________
> > From: david bloom <dbsg13_at_yahoo.com>
> > To:
> > Cisco Certification <ccielab_at_groupstudy.com>
> > Sent: Tuesday, August 19, 2014
> > 9:38 AM
> > Subject: Nexus 5k / 7k Loop
> >
> >
> >
> > Hello Everyone,
> >
> > We have an odd
> > situation that I canb t quite understand - a L2 loop is happening.
> >
> > We have a
> > production 5k environment, and a new 7k lab
> > environment.B When I connect the
> > two
> > together, the 5kb s immediately report a loop and disables learning.
> > B While this happens, traffic in the production vlan is intermittent,
> i.e.
> > some pings go though, others dropped.
> >
> > Both the 5kb s and the 7kb s are in a
> > back to back vPC
> > configuration.B There is a single link
> > between 5k04 and
> > 7k02.B At first, we
> > set up that single link in a port-channel and vPC on both
> > the 7k and 5k.B We then removed the port-channel and vPC
> > config for the link
> > on both sides, and set the link as a standard trunk.B B Both scenarios
> > produced the loop b with the
> > detection showing on the 5k that the same MAC
> > was learned coming from the 7k,
> > and on the port-channel going to the upstream
> > 5k.
> >
> > My guess is that this is an unsupported config.B We do plan do add a
> > second link from the 7k
> > ot the 5k, this way we can run back to back vPC
> > between the 7k and 5k.B Ib m thinking this will solve the issue.
> >
> > Question
> > is why would the single link cause a loop?
> >
> > Mac address flooding coming in
> > from the upstream 5k goes through the link to the single 7k02. B The
> flood
> > goes out the port-channel (to both downstream 7k03 AND 7k04) and across
> the
> > vPC peer link, correct? B From there, each switch (other 7k01, and both
> > downstream 7k03, 7k04) receive the flood on a vPC port-channel, so it
> should
> > not flood back, either over the same port-channel, or through the
> downstream
> > vPC peer link?
> >
> > 5k01 B ---- B 5k02
> > B B | B B B B \ / B B B |
> > 5k03
> > B ---- B 5k04
> > B B B B B B B B B B B B |
> > B B B B B B B B B
> > B B B |
> > 7k01 B ---- 7k02
> > B B | B B B \ B / B B B |
> > 7k03 B --- 7k04
> > Each horizontal set is a vPC peer, and all cross links are
> > port-channels in a
> > vPC.B The single
> > connection is a standard trunk.B The loop
> > errors occur on
> > the 5k04 that is connected to the 7k02. B 5k03 also reports the errors -
> the
> > duplicate mac is seen on the vPC peer-link from 5k04, and the
> port-channel to
> > the upstream 5ks.
> >
> > David
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
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>

-- 
Marc Abel
CCIE #35470
(Routing and Switching)
Blogs and organic groups at http://www.ccie.net