Humbledown :: VLAN tag stripping in Virtualbox actually, Intel NICs et al.

Humbledown :: VLAN tag stripping in Virtualbox actually, Intel NICs et al..

This article saved me some time and trouble. Apparently the Intel Pro/1000 adaptors in Virtual Box strip 802.1Q VLAN tags – I discovered this after examining packets sent to the vboxnet host-only network. The solution is to use the PC-Net adaptors.

Virtual Box Network Adaptor

Virtual Box Network Adaptor

FreeBSD 802.1Q Vlans

It’s possible to implement 802.1Q VLAN tagging with FreeBSD (as long as the hardware supports it). The documentation is rather sparse on this. All the intricate details are hidden in the man pages for vlan(4) and rc.conf(5).
Possible application for this are:

  • A Router-On-A-STick – for inter-VLAN routing via a switch’s trunk port.
  • Distribution of NTP to isolated subnets via a switch’s trunk port.

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Installing SDM On a Dynamips or GNS3 Router

I’ve seen several comments on the forums where folk have not been able to install SDM to the router memory. The IOS is usually a 12.4T series one. Here is a workaround which involves using a 12.4 or earlier IOS. In this case I used a 3725 with a 64MB flash card.
First attempt to install onto 12.4T with empty flash – reports

"Unable to eastablish connection with the router"

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SDM on Dynamips/GNS3 Routers

I’m a long way from home and my real router lab this week so having to make do with the amazing DynaMips emulator, which just happens to run real IOS images. I have the choice of running this either with the Dynagen package on Mac OSX or GNS3 on Windows.

I wanted to configure some C3725 images for CCNA Security simulations and as part of that, install SDM 2.5 into the router flash memory. Unfortunately this proved difficult with IOS 12.4T but I managed to persist and find a workaround.

First attempts using IOS c3725-advsecurityk9-mz.124-15.T14.extracted.bin – No luck, the Windows SDM installer continually fails with the message “Unable to establish connection with the router”.

So next I roll back my IOS to c3725-advsecurityk9-mz.124-25d – I ran the installer again and was able to load SDM into the virtual router flash.

Finally, re-configure with IOS 12.4T and I can launch SDM running on the router

Cisco Console Cable Differences

The console cable RS232 lines used vary between Routers and Catalyst Switches.

  • Router console does not use RTS/CTS (pins 1 and 8).
  • Router aux port uses all pins.

Auxiliary Port, Console Port, And Adapter Pinouts For Cisco 1000, 1600, 2500, 2600, And 3600 Series Routers

  • Some Catalyst switches do not use DSR/DTR (pins 2 and 7) but do use RTS/CTS (pins 1 and 8).

Connecting a Terminal to the Console Port on Catalyst Switches

This solves an issue I’ve been having with connecting some Catalyst switches to my Lantronix ETS-16 terminal server – the cables are only connected to RJ45 pins 2-7. The solution is to make up a cable with 1 looped to 8 (RTS – CTS) on the RJ45.

The Cisco RJ45 – 9D-Female rollover cable works perfectly as I would expect!

Setting Your Source Interface

Problem: I’ve set up VPN between the LANs on two routers and I want to test the link from LAN 1 to LAN 3.[R1]--[R2]--[R3]--

Default ping/telnet/ssh will fail because it will use the source address of the interface closest to the destination.


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 0 percent (0/5)

Solutions: Continue reading


I’ve finally reached a working solution for SDM with the aid of the brilliant multi-platform VirtualBox. I can run this set-up on OSX Snow Leopard or XP/Vista.

I used a Windows 2000 Professional VM that I had available and I’ve set it up to meet the SDM requirements.

  • Internet Explorer 6 SP1 as w2K ships with IE5.
  • Java JRE 1.6.0_03 – This can be found in the Oracle Java Archives.
  • Disable Java Updates in the Java settings in Windows Control Panel.
  • Set the Java User Runtime parameter to -Xmx256m in Java Runtime Environment Settings, otherwise you’ll get an error message from SDM when you try and access the IPS menu item.
  • Install SDM 2.5.

Please understand that W2K is no longer supported by MS so this should only be used for SDM in a controlled environment. Continue reading