These are the ip configurations of the interfaces on the servers.

Server A

eth0 ( 192.168.1.100, running Bind9 and listening on this IP)

eth1 (192.168.2.100)

Server B

eth0 ( 192.168.2.101)

Problem:

Server B issues a DNS lookup to Server A and gets a timeout.  I didn’t have this problem with another multi-homed machine running RHEL5.

I did a tcpdump -i any host 192.168.2.101 and port 53 on Server A and saw that packets are indeed coming to come Server B, but there are no return packets. Bind is definitely running fine. The problem definitely has to be due to RHEL 6 and caused by asymmetric routing.

A Google search asymmetric routing issues on RHEL6 gave me the answer immediately.

In RHEL5, rp_filter is disabled. So packets can be routed via another interface in another Layer 3 domain i.e. eth0 source ip on Server A can answer to Server B via routing rather than going through eth1 in the same broadcast domain.

In RHEL6, rp_filter is enabled, so Server A checks the routing table and finds that eth1 is the optimal route to Server B. Trouble is that the request from Server B arrived from eth0, so rp_filter kicks in and drops the packet silently!

The immediate solution is to set the rp_filter to 2 on Server A, which is Loose Checking mode. I edited /etc/sysctl.conf and changed net.ipv4.conf.default.rp_filter = 1 to net.ipv4.conf.default.rp_filter = 2

I like to be very explicit when defining configurations, so I added the following too.

net.ipv4.conf.eth0.rp_filter = 2

net.ipv4.conf.eth1.rp_filter = 2

The configuration in /etc/sysctl.conf makes the setting permanent after reboots. For realtime change, do

echo 2 > /proc/sys/net/ipv4/conf/eth0/rp_filter

echo 2 > /proc/sys/net/ipv4/conf/eth1/rp_filter

More information on rp_filter or Reverse Path Filter:

http://www.wlug.org.nz/ReversePathFiltering

https://www.redhat.com/archives/rhelv6-list/2011-January/msg00080.html (Google: “rhel 6 asymmetric routing”)

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I have been getting consistent performance on FileSonic, so it’s worth the money that I’m paying, both for the account and the fibre broadband.

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Prelude:

Neighbour goes to HDB and complain that their ceiling is leaking. HDB comes to inspect their place and came knocking on my door. No one’s at home, so they called me a couple of days later to fix a day to come to my place to check the toilets.

HDB folks came, took a quick look at my toilets and started to tell me about procedures, how to repair and stuff. What makes them so sure it’s my toilet that’s leaking then? I asked them to do some conclusive tests before we start to arrange for repairs. Who knows the water might be leaking from some other places. So another couple of days later, they came to do a flood test.

Note: Other than flood test, there are 2 more kinds of tests.

First is the dry test, where they seal your toilet for a week to keep it dry and after that, if the leak continues then the origin is somewhere else other than the toilet.

Then there’s the dye test, where they flood the toilet and put a dye into the water. That would be very conclusive to show the origin of the water because your neighbor’s ceiling, walls, whatever, will be stained with the dye if the leak is indeed from your toilet. Not something that I want to do to my poor neighbors.

Anyway, after the flood test, we went down to our neighbor’s place and saw water leaking. Not the very severe kind, but the droplets were forming quite quickly. Not 100% conclusive but I went with the opinion of HDB that my toilets needed repair.

So, as responsible people, we arranged with HDB to send their contractor for an evaluation and make arrangements to start the repair. Another couple of days for this arrangement.

There were some unhappiness after this with my neighbor because they didn’t agree with the date that I chose to start work. Anyway, I don’t to talk about it here.

Repair starts 3 weeks later after a hectic rush to arrange the logistic for the repair. I had to arrange for my baby girl to stay at parents’ place, clear my work before going on leave etc etc.

Preparation:

The hacking of the floor is going to create a big mess. The whole house is going to be very dusty, based on experiences shared by friends who went through the same repairs. So make sure you get enough protection and covers for your furniture.

Day 1:

The workers came and hack down my toilet floor. Drilling is a pain. The noise is terrible!

End of the day, they coat the floor with this non-shrink grout thing to prepare for the cement and water proofing the next day. Dust was everywhere as expected. It’s very very dusty. Don’t underestimate the mess.

Day 2:

This is a fast one. One guy to finish the job in like half a day.

First they put apply the water proofing. The water proof layer dried very quickly with fans blowing, so lend them the fans if you can.

After that, the cement goes in. Very quickly done. The cement has to be dry before the tile can be laid on the next day.

Day 3:

The 3rd day is for tile laying.

Day 4:

The contractors come back to tie up lose ends, wash up the toilet.

Problem:

After washing, we inspected the place and discovered defects.

1. My tap was damaged.

2. The old tiles were badly chipped at some areas. I went to a friend’s place and look at their repair which was completed about 2 weeks before. Their’s was nicely done. No chips and cracks.

3. The toilet drainage was clogged after the washing.

We called up HDB to come and look at the defects and also inspect the site to make sure the repairs were in order. HDB didn’t turn up at the agreed timing. Wasted my time waiting for them. In fact, I don’t think the HDB people even had intention to come. They were pushing everything to their contractors, which I think is utterly irresponsible.

We are still pursuing this with HDB and the contractors. They are wasting a lot of time and energy. The last straw is bringing this to the media.

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Fired up TweetDeck in my Chrome, and saw a Tweet from @davegirouard talking about new features in Gmail. There’s now better integration with Google+ which allows filtering based on Circles.

We can now add people to our circles from Gmail. I think this will tremendously help to boost the sign up for Google+ now with everything on one screen.

On a side note. The Google+ interface is still a bit unnatural somehow. It’s not as fluid as Facebook as I feel personally. Hopefully Google+ can take off in a much bigger scale. I like the circle concept much more than the Facebook lists.

Oh, 1 more upcoming. Facebook Timeline. Watch out for this. Very interesting.

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Initially, I thought I could do 15 frames per second with my new M1 Fibre Broadband connection, but because of some issues with routing, I need to settle for about 5 frames per second. That takes up about 2Mbps of my upstream bandwidth.

Recently, there’s some improvement to the routing. The latency improved from close to 300ms to about 40ms, so I can now do 15 frames per second. The image is now less laggy, but upstream bandwidth is 5Mbps! My upstream is 25Mbps, so I’m still coping well. In the long run however, I need to find another camera that does H.264. That should cut the upstream bandwidth by 50% at least. :)

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I came across the Raspberry Pi by chance some time last week and it has already gotten me immensely interested. Here are some things that I think I would want to build

Megapixel IP Camera

The megapixel camera out there are tooooooooo expensive for home use. I’m going to try to get a minimum 1 megapixel camera module and DIY an IP camera for home surveillance. Going to experiment with OpenCV for object tracking and stuff, e.g. where my daughter hides my iPhone.

Home Automation

Raspberry Pi is going to be a very low powered but nimble platform a X10 controller. The lowest powered PC I could find is still too expensive keep powered on all the time.

Weather Monitoring

Have been wondering if I could build something with humidity sensor and photosensors. Then I can write some scripts and build some simple mechanisms to open and close the house windows. Could cool the house considerably by the time I get home. I was contemplating doing this with Arduino, but it’s another learning curve.

These are the ones that I can think of currently and I think I could do this with maybe just 1 Raspberry Pi? :)

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Now, the next thing that I’m anticipating is iMessage coming to OS X. iMessage is instant messaging. It should and has to be on the desktop.

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In my opinion however, what Siri really threatens is Google’s advertising business.

For those unfamiliar with Google’s advertising business, Google basically has 2 products, namely Adsense and Adwords. In Adwords, advertisers bid for keywords and air their advertisement on websites that displays Google Adsense. Google decides what advertisement to display based on user’s history, keywords on that user search etc. One problem with this model is that users are searching for contents and information, not the advertisements.

In Siri however, the search is very specific. If I tell Siri I want to get a pair of shoes, Apple can throw very specific advertisements to me. The conversion rate and effectiveness of the advertisement is significantly higher because Google Adsense is very passive compared to Siri. The advertising experience become personal rather than guesswork in Google’s case.

Apple has not done targeted advertisements yet in Siri’s search results, but I think they would do so soon as Siri matures more over the next few months. When this comes, Google’s going to be in an awkward position since their main revenue source is from advertisement. Bear in mind that Facebook has already splitted a portion of the pie, so Google is going to lose more should Apple grow the advertising business.

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A friend posted this article on my Facebook wall.

http://theunderstatement.com/post/11982112928/android-orphans-visualizing-a-sad-history-of-support

This article talks about how the various generations of Android phones are left behind while newer phones get the latest Android.

I don’t to leave this open-ended and have people think that I’m an Apple fanboy. I’m a Linux admin and I have been using Linux on my office laptop for a very long time. So why iPhone and not Android phones?

Upgrade Woes

I have never owned an Android phone. The number 1 reason is that I dislike the customizations that the individual phone makers do to the OS. The implication is that certain models will be left behind in the upgrade process. We have been this in the Windows PDA phones in the past. Because of the difference in hardware, there’s tremendous effort for the phone makers to ensure that every single model runs the most current OS. So the easy way out is to leave them behind. I forecasted this since the very first version of Android and I have been proven right all these while.

Android vs iOS

So came the Nexus One. Google supported, plain vanilla Android. I was actually contemplating getting that but I chose the iPhone 3GS. Why? My choice was very much affected by my experience on the Mac.

While I still use Linux on my office laptop, I find myself doing most of my work on my Mac. I bought my first Macbook in 2007 and after using OS X, the impression was: It just works! No tinkering. No fiddling. I don’t getting into the situation where I need to solve the machine problem even before I get down to doing work. It’s a lot of time wasted.

Similarly on the iOS, a lot of things just work out of the box. One example was configuring of L2TP over IPSEC VPN on the iPhone. It takes less than 2 mins to get the iPhone setup and connected. 3 steps to get to the configuration screen, enter configuration details and we are done. My colleague tried it on their Android phone. The first phone took us close to 10 mins to figure out how to configure the connection. He later gave up his Samsung Galaxy for a new iPhone  4.

Now Google has announced that the Nexus One is not getting the latest OS. To fair, I haven’t read the details and I’m not sure what’s the rationale. But if you look at the chart, even the iPhone 3GS gets iOS 5. While some features are not available, the major key enhancement are made available to the 3GS user. They are not left behind.

I was thinking of getting the Nexus Galaxy actually after looking at the features of Android 4, but it looks like my next phone will still be a Apple phone after all.

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