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BFC: Network Interface Node Scan From – Includes Switch Assignment Details - nwd.pl

This can be used to verify a customer's network layout in case they are not telling you the whole truth or you need more info. This does not require any 3rd Party tools to be installed on their systems.

nwd.pl is what AppLogic uses do determine a node's network config. We can output this to a text file for our reviewing pleasure. It does include switch config details ( STP, CDP, LLDP, etc. ) and which node interface connects to each switch... This can be very useful in determining a correct configuration.

Change directory to the scripts directory under the appropriate applogic version.

cd /opt/bfc/applogic_versions/3.5.19/aldlib/scripts

Will probably need to use full path to perl to execute the script. You may list several nodes to test seperated by only a space and direct the output to whatever location you'd like.

/usr/bin/perl nwd.pl 192.168.10.1 192.168.10.2 > /tmp/data.txt

The following is quoted text from AppLogic dev.

nwd.pl retrieves the vlanID from the LLDP or CDP packets that are emitted by the switch. Specifically, for LLDP, it looks for a tag 0x7f (127), with data containing
00 80 c2 01 xx xx (oc = IEEE802.1, subtype=vlanID). Similarly, VLAN ID is also available in CDP, if CDP is used, in tag 0x0a.

If the appropriate tag with the VLAN info is found in the LLDP data, then the ID will be appeneded as a 4-digit hex number to the switch ID, like this: a4:18:75:37:54:40:0004

If the received LLDP (or CDP) packets have no VLAN info, then nwd.pl will append ":0000".

NOTE that from the data that I have, for the ports that detected the switch ID as something:0000, I don't know if nwd.pl got LLDP packets with no VLAN info at all or it got packets with vlan info, but having vlanID=0 (in both cases, nwd.pl will do the same - add ":0000".

FYI: I don't actually know how switches decide what vlan ID data to send in the LLDP packets, if at all.

Here is my best guess about this, based on the experimental data that I have and on what seems like common sense to me:

• Normally, when a port is configured in 'access' mode (i.e., the port belongs to a single VLAN, and packets sent to/from it do not have VLAN tags), e.g., in Cisco config terms, if you have something like:

  switchport mode access
  switchport access vlan 4
  

  then the switch will report the VLAN ID of the configured VLAN in the LLDP data. It is typically non-zero as you can never configure "access vlan 0" (for that matter, no one should be sending network data with vlan-tagged Ethernet packets that carry a tag of 0 - but that's irrelevant for the LLDP decoding done by nwd.pl for the puropses of identifying a switch).

• If the port is configured in 'trunk' mode (multiple vlans, packets are sent out with

  vlan tags and expected to have one on input), I am not at all sure what vlanID will be reported in the LLDP packet. Likely, if a default vlan is defined for the port (e.g. "switchport trunk native vlan 2") , then you'd get this one.

Like I noted above, the 'vlan ID' part of the switch IDs has nothing to do with how "our" traffic is routed - nor does it bear any relationship to the AppLogic-configured VLANs, if you have any. For example, you can have your external network carry multiple VLANs (the switch ports will be in 'trunk' mode), but also have native vlan configured on those switch ports for traffic that has no vlan tags.

NOTE that you need to have the ports configured to forward native packets in all cases, otherwise the AppLogic network detection won't work - we don't support working with switches that require all traffic to contain vlan tags in the Ethernet packets).