The command below will dump all of the reservations to a file named “reservations.txt”. findstr filters netsh output keeping just the info we need.

Each line in “reservations.txt” should look like this:

10.4.1.1 is the IP address for dhcpsrv1, the “source” DHCP server.

Open “reservations.txt” in a text editor, check that everything is fine and substitute the source DHCP server IP with the target’s one (i.e.: 10.4.1.1 becomes 10.4.1.2), save the file and run:

That’s it; not a fancy trick, but it may be useful nonetheless. Just beware that, when there are thousands of clients, netsh could take a while to complete its job (especially the “dump” step)…

I used the following command to check my MAC addresses:

Then resorted to the “show mac” switches facilites (some Cisco, some ProCurve) to know on which network ports that particular MAC lied… Only to discover that the cluster’s “logical” MAC address (00:09:0f:09:00:08) wasn’t really located where I expected it to be.
Well, FortiGate’s MAC addresses aren’t randomly generated. They have predictable values that depend on the firewall’s port number. The eight port (or wan1, in my case) will always have a virtual MAC as the one above. What will happen if you have two clusters (as we had) sitting on the same L2 network segment (on the same broadcast domain, that is)? You said MAC address conflict? You’re right.
The solution is simple, use the group-id directive to tweak the logical MAC address, i.e.:

Changes the second right-most bytes of the MAC, from 00 to 0a:

Point is that the “FortiOS High Availablity Handbook” explains the case very thoroughly! See page 192, paragraph “Diagnosing packet loss with two FortiGate HA clusters in the same broadcast domain”. We’re so used to discardable product documentation that sometimes we don’t even try to look for clues where they should normally reside.
Instead of troubleshooting, this time, I should really have Read The (unexpectedly) Fine Manual…

And here’s how to add the same “A” record (named “www”) to each of the zones created above.

As you may have guessed this is the typical scenario where you’ve got to re-create some external zones, on the internal DNS servers. That’s needed in order for the internal hosts to reach some server with the “public” DNS name, but the private IP.
For the sake of completeness, let me also mention that you could achieve the same effect by leaving DNS as it is, and configuring “loopback NAT”/”double NAT” on the router/firewall. E.g.: an internal Host wants to reach an internal Server, given it’s public hostname, mapped to a public IP address. It asks the (possibly internal) DNS to translate the name. DNS doesn’t know the zone, it forwards the query to an external DNS Server, obtaining a public IP address that it hands back to the Client. Since its address is non-local, while trying to talk with the Server, the Client sends packets to its default gateway (possibly the router/firewall). The firewall matches the server’s public IP addresses, substituting it with the right private one. It also changes the source IP, swapping the Client’s with the firewall’s LAN address. This way Client and Server are actually communicating through the firewall, even if they’re both internal hosts. And the Server can’t tell Client A from Client B since every connection to it comes from the firewall’s IP address. That’s the main reason why I prefer duplicating the public DNS zones on internal DNS servers, with private IP addresses: you avoid routing internal traffic through the firewall, and avoid NAT where there shouldn’t be any.

I wasn’t completely satisfied with NetEnforcer reporting functions and wanted something more dependable and realtime. Well, if you turn to the device’s CLI access (SSH), you’ll notice an interesting acthruput command.
It shows the current throughput per Interface, Line, Pipe and Virtual Channel. What more could you ask for?

As you can see, acthruput identifies Pipes by number. How do you relate this number to the actual mnemonic pipe name? Use “acstat -l pipe“, which also displays the total number of live connections per pipe .

Wrap acthruput in a while loop that adds a timestamp and a delay (→ sampling frequency). Start your terminal emulator logging facilities, hit enter, wait, ctrl-c, stop logging.

Eventually, clean the log a bit and feed it to the Perl script you’ll find at the end of this post.

The script outputs CSV formatted data:

And here’s what it looks like when opened up in OpenOffice Calc (sorry, no fancy formatting).

The graph above shows that the 8Mbps link (the “Line”, in Allot’s parlance) is not saturated. Problem was that, during that timeframe, we were also trying to make Iperf “consume” all of the available bandwidth. We couldn’t make it because one of the firewalls was acting as a bottleneck if presented with certain workloads (many connections, see this) . Being able to generate these kinds of report proved very useful in troubleshooting…

How do you find out why this is happening?

The possible causes boil down to:

1. Router/Firewall¹ is not pleased by “something”. Could be an attack or a bug in the device firmware.
2. Too many connections. Maybe they’re not passing much traffic, but the internet gateway can’t keep up with their number. I’ve seen firewalls perform very badly in this respect. E.g.: 3 connections trying to download/upload as fast as they can, and a total, aggregate, b/w of 10Mbps. Those 3 plus 3000 “normal” connections and a total b/w of 6Mbps.
3. A reasonable amount of connections, effectively eating all of the available bandwidth.

I’ll skip case A, for now.
In case B you’ll likely want to know the firewall’s idea of “netstat”, meaning the complete listing of TCP/UDP/other connections. No big deal if the device has got some sort of CLI access: capture its output, import it into a spreadsheet, or use awk/sort/grep² to build your stats. Usually, computing total number of connections by source IP address and sorting accordingly, is enough to gain some insight about what’s going on.
Case C… For long-running (days) data analysis, you could use a tool like NTOP. But if, like me today, you need to act quickly (perhaps because you know that the issue will disappear soon), iftop can hardly be beaten.
Both tools require the machine they run on to be able to “sniff” all the traffic passing through the firewall. This can be accomplished by configuring monitoring/monitored port(s) on a switch. Monitored ports get their inbound/outbound traffic copied to the monitoring one. Different vendors call the thing a different way, port mirroring is also a good keyphrase. Here are a couple of resources:

• (Old) 3Com Superstack: Monitor Port on 3Com 4400
• HP ProCurve, pretty straightforward to set up using the “menu” interface: How do I attach a LAN Analyzer to a Switch 208t/224t port to monitor LAN traffic for diagnostic purposes?
• ProCurve switches are not limited to mirroring ports that belong to the same device/chassis: How to configure remote and intelligent mirroring on ProCurve switches
• Low-end HP switches (like the ProCurve 1800 one I encountered here), though, are only manageable via a web gui:
  
  

  Port Mirroring on a ProCurve 1800

• Cisco: Port Mirroring, Configuring a Cisco Catalyst Switch SPAN mirroring port

(You could as well use a hub instead of a switch and get implicit mirroring of any port, to any port of the hub. Just unplug the firewall, link the hub to the switch, plug firewall and monitoring host in the hub. Kludgy but quick and easy, if you can afford the temporary cabling changes, and the bottleneck introduced by the hub…)

So:

• Find the switch where the firewall is connected to. Which side of the firewall? It depends on where you believe the issues originates from. Let’s say the culprit is most likely to lie on the LAN → switch port A.
• Connect your laptop/monitoring machine to the same switch → port B.
• Set up monitoring: port A is monitored, port B is monitoring.
• Run iftop, maybe telling it to also show port numbers (“-P”, without this switch, you’ll only see totals by source/destination IP addresses couple), don’t display hostnames “-n”, the interface “-i eth0″ and provide a meaningful filter (here I’m selecting packets whose source is not on the LAN³. The “-p” option instructs iftop to capture packets in promiscuous mode. Without it, iftop won’t lift off the wire packets that aren’t addressed to the machine on which it is running.
  iftop -p -P -n -i eth0 -f 'not src net 192.168.200.0/23'

  Iftop will produce a realtime table of running connections, sorted by how demanding they are in terms of bandwidth (10s average, by default). See the screenshot below; the top connections are due to two running video conference streams stealing 1Mbit/second worth of bandwidth, each.
  

  

  iftop's output

  
  Once everything is set up and you’re able to read iftop’s output, spotting the “top talkers” of your net becomes kids play, enjoy!
  1. for brevity, I’ll just say “firewall” from now on. ↩
  2. Yuri is king at doing that. See his AWK weekly series. ↩
  3. iftop will still show these source addresses, since its output is always made of bidirectional “connections”. Only, counters pertaining to the LAN → outside direction, won’t increase. ↩
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