[j-nsp] EX4200 missing ARP entry work-around

[James Jones]

Have you contacted JTAC about this issue?



On Wed, Jan 11, 2012 at 2:14 PM, Jeff Wheeler <jsw at inconcepts.biz> wrote:

> We have decided on a better work-around for our missing ARP entry
> problems on the EX4200 and friends.
>
> As you may recall, the EX4200 will sometimes have an ARP entry in the
> control-plane, but it will not be present in the data-plane.  You can
> investigate by checking your destination IP address with the command
> `show halp-rt route ip rtt-index 0 prefix 192.0.2.2 prefix-length 32`
> which will produce output like this:
>
> PFEM0(vty)# show halp-rt route ip rtt-index 0 prefix 192.0.2.2
> prefix-length 32
>
>  Route                    Type Paths RtIdx Rpf SipSa Row:Col:Row:Col
>  --------------------     ---- ----- ----- --- ----- ---------------
>  192.0.2.2              ECMP 0     2037  No  No    439:0:0:0
>
>  Dev0 (RtIdx:2037)
>  -----------------
>  Command           : Route              CpuCode        : 3
>  AppSpCpuCodeEn    : 0                  UcSipFiltEna   : 0
>  TtlDecEna         : 1                  TtlOptChkBypass: 0
>  IngressMirror     : 0                  QoSProfileEn   : 0
>  QoSProfileIndex   : 0                  QoSPrecedence  : 1
>  ModifyUp          : 2                  ModifyDscp     : 0
>  CounterSet        : 2                  ArpBc2Cpu      : 0
>  SipAccessLevel    : 0                  DipAccessLevel : 0
>  IcmpRedirExpnMirr : 0                  MtuProfileIdx  : 2
>  Ipv6ScopeCheckEn  : 0                  Ipv6DstSiteId  : 0
>  NhTnnl            : 0                  NhTnnlIdx      : 0
>  NhVlan            : 6                  NhIf           : VIDX4095
>  NhArpIdx          : 138
> Device: 0
>  ArpEntry Idx 138  : 00:2b:f0:19:87:01
>  Hit/Miss          : N
>
> Notice above a reference to NhArpIdx 138.  In order for forwarding to
> work correctly, there must be an entry # 138 in the `halp-nh
> arp-table.`  Since there isn't one, the NhIf shown is VIDX4095, not a
> port.  However, if you want to verify that there is no NhArpIdx 138 in
> the hardware, you can examine the table with `show halp-nh arp-table`
> and scroll down to where # 138 should be.  You won't find it!
>
> PFEM0(vty)# show halp-nh arp-table
> Device: 0
> ... lots of scrolling ...
>  ArpEntry Idx 136  : 00:18:8b:f8:b6:6e
>  ArpEntry Idx 137  : 00:0e:b6:2d:01:a0
>  ArpEntry Idx 139  : 00:19:b9:f9:24:2a
>  ArpEntry Idx 140  : 78:2b:cb:3c:91:60
>
> How do you get the switch to populate that entry?  Well, since `clear
> arp` on the EX4200 doesn't actually do what it is supposed to do, what
> we have been doing in the past is deleting whole subnets, impacting
> potentially many machines, and then re-adding them.  This is not good
> but it does work.
>
> Our new solution is much better.  We just add a bogus static arp entry
> for 192.0.2.2, pointing to some made-up MAC address, and then we
> commit, roll back, and commit again.  Like magic, the ARP entry will
> re-populate correctly.  Almost as if you really did have a `clear arp`
> command on the EX4200, one that worked right!
>
> After adding and then deleting the bogus static ARP for 192.0.2.2 you
> can re-examine the PFE and see the results.  Also, your customer's
> Internets will begin working correctly again.
>
> I hope this helps.
> --
> Jeff S Wheeler <jsw at inconcepts.biz>
> Sr Network Operator  /  Innovative Network Concepts
>
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