[j-nsp] EX4200 missing ARP entry work-around
jsw at inconcepts.biz
Wed Jan 11 14:14:59 EST 2012
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
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
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
... 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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