Show Lan display in system analyzer

[M C_1]

Hello all,

I was looking in the system analyzer at the SHOW LAN display for protocols on my LAN Adapters and I noticed one that was unfamiliar.

Client State
------ -----
LOOP 009D STRTN,UNIQ,SHARE,STRTD,SHRDEF



I understand the other bindings like LAT and IP etc.. but not sure what LOOP is? I see it referenced in some documentation but nothing specific. Anyone know what its used for?

MC

[Volker Halle · Accepted solution]

MC

this protocol type corresponds to the Ethernet LOOP protocol type 90-00. It's used for LOOPBACK messages at the datalink level.

You can generate these LOOP packets with:

MC NCL LOOP MOP CIRCUIT csmacd-n ADDRESS xx-xx-xx-xx-xx-xx

or

MC NCP LOOP CIRCUIT xxx-0 PHYSICAL ADDRESS xx-xx-xx-xx-xx-xx

You can check, whether your system has received/sent any messages with this protocol type with SDA> SHOW LAN/FULL/DEVICE=xxx where xxx is the LAN device unit UCB name from column 1 of the SHOW LAN protocol summary display (for the LOOP client line).

Volker.

[M C_1]

Volker - thanks for the quick response. I checked SHOW LAN/FULL/DEVICE=xxx on the UCB and most counters were 0.

So what is this really used for? Is there a specific part of the OS that needs it? I don't see it on other systems that I manage.

In the not too distant past, we used MOP for some of our old VXT's, could this LOOP binding have been established as part of that?

MC

[Volker Halle]

MC,

I've also checked on a couple of systems. Looks like this protocol is only set up, if you are running DECnet-Plus and have MOP enabled on that LAN interface (MOP CIRCUIT xxx).

Datalink level loopback testing may come in handy, if you have problems in your network equipment. With NCL LOOP you can send packets to an individual LAN interface, varying things like packet length, packet contents (0/1/mixed) etc.

Volker.