Ip

One of things which people often asked me around in past was on how to have multiple IPs on Linux machine under various circumstances. I know there are ton of blog posts about this but very few explain how it works and possible options under different use cases etc.   I will share router side and server side config with focus on how it should be done from server end. Assuming server side config to be for Ubuntu/Debian. You can find similar concept for CentOS.   Say you have a router on IP 10.10.10.1 and server on IP 10.10.10.2 on a /24 (255.255.255.0) subnet. Assming that entire 10.10.10.0/24 is available for server’s connectivity. Setup would be like: Configuration so far is super simple. You have got 10.10.10.1 placed on R1’s interface (g1/0) which connects to server01 and server01 has 10.10.10.2.

And finally academic session over. Done with all vivas and related stuff. Next will be exams likely in June. Time for me to get ready for travel. :)   Anyways an interesting topic for today’s post - Google Public DNS. Lot of us are familier with popular (and free) DNS resolvers 8.8.8.8 and 8.8.4.4. I have covered reason in previous posts on why it tends to fail with Content Delivery networks like Akamai which rely on anycasting at bottom DNS layer and simple unicasting on application servers. Anycasted DNS nodes point to application servers based on various factors like distance, load, cost etc out of interesting algorithms these CDN networks use for load & cost management.   Anyways today’s post focus is not CDN issues with these resolvers but Google Public DNS itself. Are these servers located in India and everywhere else where Google has PoPs?   Let’s do a simple trace to get forward path from Airtel to Google’s 8.8.8.8:

And an interesting day full of bit frustrating drama. Today was “External viva” for Major Project at college. It went good with external teacher but “internal ones” tend to cause un-necessary issues. Quite a few people put personal egos and frustration on top priority to an extent that they violate their own points for which they are arguing. They go completely unethical in way they deal with world.

I am saying this with full responsibility for couple of teachers from my college who have completely lost some “fundamentals of life” as taught in childhood to most of us. Some key principles like staying cool & calm, being humble, making best possible use of time and just being good with everyone. In last 4 years they haven’t learn how to give respect & talk with sense and they expect students to be learning “technology” from them? What an absurd!

Whenever I see a new unknown IP range, it gets hard to find exact source of that IP within command shell. Recently, I found a very interesting source of that information from Team Cymru.

I figured out (with a friend’s help) that using their whois server - v4.whois.cymru.com one can actually grab limited information as required. 

E.g

anurag@laptop:~$ whois -h v4.whois.cymru.com "  -v 8.8.8.8"
AS      | IP               | BGP Prefix          | CC | Registry | Allocated  | AS Name

15169   | 8.8.8.8          | 8.8.8.0/24          | US | arin     | 1992-12-01 | GOOGLE - Google Inc.

As we can see -v gives all possible information. All I needed was AS number, AS Name, BGP Prefix, Country code - this gives enough information for an IP address. Thus command turns out to be with -c & -p.