802.1Q type 0x3737 frames

[stuartkendrick]

I am seeing odd frames flowing over a vPC Peer Link (between two N9K).

802.1Q VLAN header type 0x3737

9007 bytes in size, i.e. near-max jumbos

The data portion follows immediately after the 802.1Q frame and consists almost entirely of the repeated pattern "0b".

googling for 0x3737, I notice that the following ACL shows up, in discussions of N7K COPP

mac access-list copp-system-acl-mac-gold
    permit any any 0x3737

What function Cisco loads onto this protocol?

--sk

[Christoph Viethen]

Hello,

I'm seeing this on Nexus 7700, M3 line cards (NX-OS 8.2).

It is clearly related to the "GOLD" online diagnostics of the machine.

On my machine, I see those packets every five minutes.

"show diagnostic module all" yields the following:

Module 1: 10/40 Gbps Ethernet Module

Testing Interval
ID Name Attributes (hh:mm:ss)
____ __________________________________ ____________ _________________
1) ASICRegisterCheck-------------> ***N******A* 00:01:00
2) PrimaryBootROM----------------> ***N******A* 00:30:00
3) SecondaryBootROM--------------> ***N******A* 00:30:00
4) EOBCPortLoopback--------------> C**N**X**T** -NA-
5) OBFL--------------------------> C**N**X**T** -NA-
6) PortLoopback------------------> *P*N***E**AD 00:15:00
7) RewriteEngineLoopback---------> *P*N***E**AD 00:01:00
8) SnakeLoopback-----------------> *P*N***E**ID 00:20:00
9) IntPortLoopback---------------> *P*N***E**AD 00:05:00
10) FIPS--------------------------> *P*NO*XE*T** -NA-
11) BootupPortLoopback------------> CP*N**XE*T** -NA-

So, "IntPortLoopback" looks suspicious.

Indeed, configuring the following:

diagnostic monitor interval module 1 test IntPortLoopback hour 00 min 02 second 00

... causes the type 0x3737 frames to appear every two minutes now.

So there you go.

Probably could switch off IntPortLoopback diagnostics to avoid those packets, but I guess they're doing no harm to your network, right?

Cheers,

  Christoph