Essentially, despite differing source addresses, only one default gateway exists to send traffic to IPs not within the connected subnets and thus, traffic on any “secondary” subnet is rejected as a martian when leaving the host’s interface that is connected to its default gateway.

Some people would use bridged intefaces, although this is sadly not an option for me right now. Whilst the performance of VENET is supposedly better, we also have a large install-base of VENET guests that do not wish to be disturbed. So for now I still need a way to make this work with VENET interfaces (and also VETH if required later).

There are two methods around the return_path filtering, with the first being a terrible hack that should only be used temporarily, if at all… If you echo ’1′ to /proc/sys/net/ipv4/conf/all/log_martians, you will be able to see which interface is filtering martian packets. With that information you can then simply disable the rp_filter function by echoing ’0′ to /proc/sys/net/ipv4/conf/INTERFACE/rp_filter and martians won’t be filtered.

However, this isn’t a sensible option. A better solution is to actually create a routing rule to alter the default gateway used, based on the source subnet. It took me a little bit of digging, but I eventually managed to get this working after combing a few sources (including, but not limited to, the iproute2 man file).

For reference, here’s my routing table showing two networks and two /32 IPs assigned to a guest’s VENET interface (note that the networks are /23′s, not /24′s!):

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.9.159      0.0.0.0         255.255.255.255 UH    0      0        0 venet0
10.0.125.53     0.0.0.0         255.255.255.255 UH    0      0        0 venet0
10.0.8.0        0.0.0.0         255.255.254.0   U     0      0        0 br0
10.0.124.0      0.0.0.0         255.255.254.0   U     0      0        0 br1
0.0.0.0         10.0.9.1        0.0.0.0         UG    0      0        0 br0

Start by opening /etc/iproute2/rt_tables in your favourite editor. You’ll need to append a line to the bottom to create a new routing table:

# cat /etc/iproute2/rt_tables
#
# reserved values
#
255    local
254    main
253    default
0    unspec
#
# local
#
#1    inr.ruhep
100    vlan4

As you can see, I’ve appended a new table named ‘vlan4′ (picking a sensible name helps, in my case this is the VLAN name for 10.0.124.0/23)  and given it a priority of 100. As per my understanding, the priority should be decremented for each subsequent table defined.

Now you need to use ip to define the new rules & routing behaviour, taking advantage of the new table we’ve defined. First, create a rule matching traffic from your secondary subnet:

ip rule add from 10.0.124.0/23 iif venet0 table vlan4

For reference, the ‘iif’ attribute is not a mistake; “iif” not “if”. This was also a key part of the setup, as it only classifies traffic originating from the VENET interfaces, no-where else.

Now add a route to define the new default gateway for our new table of classified traffic and apply it:

ip route add default via 10.0.125.1 dev br1 table vlan4
ip route flush cache

You should now find that guest traffic from either network is routed correctly without having to change any rp_filter settings. At any time you can use the following two commands to see your configuration:

ip rule show

ip route show table vlan4

Be sure to re-apply the ‘ip rule’ and ‘ip route’ statements on your next reboot; under Scientific Linux 6.0 I’ve used the /etc/rc.local file, but you can just as easily apply them on ifup in Debian’s network configuration.

Anyone that’s had this happen to them will notice that you literally cannot find/retrieve these basic add-ons with via the Add-ons store, and most searches online bring back results related to the Google toolbar (not helpful).

Eventually I tracked-down this post and I am eternally grateful to the poster because, not only did it it allow me to fix the issue myself (copy the missing .xml files from /usr/lib/firefox-addons/searchplugins/en-US/ to the corresponding ‘en-GB’ folder) but I have also finally found a method to send my queries to google.co.uk instead of google.com… Just edit the appropriate .xml file, changing .com to .co.uk.

So no more having to deal with American shopping results!

My ADSL provider Andrews & Arnold have provided me with a /48 IPv6 subnet, which seems somewhat wasteful at 2^80 addresses (throw that in your calculator) but certainly useful for testing nevertheless. Whilst slowly getting my head around the task that is variable-length subnetting of IPv6 ranges – painful at best – I decided to just throw in a /64 subnet and set a static gateway address on m0n0wall‘s LAN interface to see if it would ‘just work’.

The result, is a working IPv6 LAN by simply enabling autoconfig from the m0n0wall box and telling Ubuntu’s Network Manager to use it. Et voila:

teh@desktop:~$ ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:01:29:fc:37:1d
inet addr:81.187.xxx.xxx Bcast:81.187.xxx.xxx Mask:255.255.255.240
inet6 addr: 2001:8b0:ff87:1:201:29ff:fefc:371d/64 Scope:Global
inet6 addr: fe80::201:29ff:fefc:371d/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1616524 errors:0 dropped:0 overruns:0 frame:0
TX packets:2224946 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:277202062 (277.2 MB) TX bytes:519498762 (519.4 MB)
Interrupt:18

You’ll notice that the last 80 bits of my IPv6 address on this host were assigned via autoconfig, using part of my MAC address (the part that doesn’t correspond to a certain manufacturer, IIRC) as well as some randomly-generated bits, too.

And to make my night, ping6 worked straight away, too:

teh@desktop:~$ ping6 2001:08B0:FF88:0001::1
PING 2001:08B0:FF88:0001::1(2001:8b0:ff88:1::1) 56 data bytes
64 bytes from 2001:8b0:ff88:1::1: icmp_seq=1 ttl=64 time=3.81 ms
64 bytes from 2001:8b0:ff88:1::1: icmp_seq=2 ttl=64 time=0.130 ms
64 bytes from 2001:8b0:ff88:1::1: icmp_seq=3 ttl=64 time=0.132 ms

--- 2001:08B0:FF88:0001::1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 0.130/1.358/3.813/1.735 ms

Now to plan how I’m going to roll this out at work…

Wrong. I tried at least three of the twenty I purchased (for a few quid) and none of them would even begin writing. Brasero/K3B both complained about incompatible media types.

Remembering that my DVD drive, a trusty NEC 3500A, was designed, built and purchased somewhere between 2004 and 2005 (4-5 years ago at this point) and that I hadn’t ever updated the firmware, I set about researching ways and means into doing this.

I came across this website, run by a pair of firmware hackers named Liggy and Dee whom have (between them) released, and continue to host, many firmware releases (both official and unofficial) for a wide variety of NEC optical drives.

What’s more, their binflash (or ‘necflash’) utility was even released as a Linux binary and it even provides compatibility for reading the official NEC .exe firmware releases! I was sceptical that it would work under Ubuntu 9.10 at first, but much to my delight it worked perfectly. With a little reading, I was able to dump my current firmware (2.16) to file and subsequently flash two different firmware releases: 2.58 (an OEM firmware release) and the latest, official NEC firmware 2.1A release.

The full output of my escapades for anyone curious:


~$ sudo ./necflash -flash -v -s Desktop/NECND350_v21A.exe /dev/sg2
Binflash - NEC version - (C) by Liggy and Herrie
Visit http://binflash.cdfreaks.com

Identified drive: 4 - 3031
Detected drive from Firmware: 4

You are about to flash your drive with the following firmware:

Vendor: _NEC
Identification: DVD_RW ND-3500AG
Version: 2.1A

Remember no one can be held responsible for any kind of failure!
Are you sure you want to proceed? (y/n) y

Entering safe mode
Sending firmware to drive at 0x006000
Sending firmware to drive at 0x00e000
Sending firmware to drive at 0x016000
Sending firmware to drive at 0x01e000
Sending firmware to drive at 0x026000
Sending firmware to drive at 0x02e000
Sending firmware to drive at 0x036000
Sending firmware to drive at 0x03e000
Sending firmware to drive at 0x046000
Sending firmware to drive at 0x04e000
Sending firmware to drive at 0x056000
Sending firmware to drive at 0x05e000
Sending firmware to drive at 0x066000
Sending firmware to drive at 0x06e000
Sending firmware to drive at 0x076000
Sending firmware to drive at 0x07e000
Sending firmware to drive at 0x086000
Sending firmware to drive at 0x08e000
Sending firmware to drive at 0x096000
Sending firmware to drive at 0x09e000
Sending firmware to drive at 0x0a6000
Sending firmware to drive at 0x0ae000
Sending firmware to drive at 0x0b6000
Sending firmware to drive at 0x0be000
Sending firmware to drive at 0x0c6000
Sending firmware to drive at 0x0ce000
Sending firmware to drive at 0x0d6000
Sending firmware to drive at 0x0de000
Sending firmware to drive at 0x0e6000
Sending firmware to drive at 0x0ee000
Sending firmware to drive at 0x0f6000
Sending firmware to drive at 0x0fe000
Sending checksum to drive
Erasing flash block 2
Erasing flash block 3
Erasing flash block 4
Erasing flash block 5
Erasing flash block 6
Erasing flash block 7
Erasing flash block 8
Erasing flash block 9
Erasing flash block 10
Erasing flash block 11
Erasing flash block 12
Erasing flash block 13
Erasing flash block 14
Erasing flash block 15
Erasing flash block 16
Erasing flash block 17
Erasing flash block 18
Writing flash block 2
Writing flash block 3
Writing flash block 4
Writing flash block 5
Writing flash block 6
Writing flash block 7
Writing flash block 8
Writing flash block 9
Writing flash block 10
Writing flash block 11
Writing flash block 12
Writing flash block 13
Writing flash block 14
Writing flash block 15
Writing flash block 16
Writing flash block 17
Writing flash block 18
Leaving safe mode

Whilst the 2.58 OEM release didn’t fix my problems, 2.1A did and I now have a freshly-burnt copy of Windows 7 Pro to go and play games with. Nice one, Liggy & Dee.

Whilst I’m not a programmer, and exist far from the plain of ever pretending to be one – I do have some professional interests in playing with this. I’ll probably update this post a little later with some more, specific information when all can be revealed, but for now here’s a little taster:

root@gotest:~# 6g hello.go
root@gotest:~# 6l hello.6
root@gotest:~# ./6.out
hello, world

It works! This machine is an openvz container, running Ubuntu 9.04 x86_64 and it works a treat, with the only exception that I couldn’t build Go with the standard ‘all.bash’ make script. I had to use the ‘make.bash’ script, instead for it to work – something about probing the network devices not working with the former script. Thanks go to Rob Pike from Google, whom seems to have been working pretty darn hard in the #go-wild IRC channel on Freenode recently!

Update: 34SP.com are now offering Google Go development environments, for those wishing to dabble!