03 Oct

Airtel 3G running CGNAT

Yesterday I was driving and radio was pretty boring. Next, I connected cell phone to car’s stereo (I use a PT-750 to wirelessly connected my devices to car’s audio system). Next I tuned into Gaana.com app and experience was overall good. The way whole setup was working itself is a wonder – wireless profiles keeping layer 3 link (IP address of device) consistent and handovers happening on layer 1. On top of that a while world of backbone routing across AS9498 backbone the hosting provider’s network of the app.
Now an interesting thing in this setup was the IP allocations. I that IP allocated by Airtel was

Is that an Airtel allocated IP range?

Let’s see whois data on it:

NetRange: -
NetHandle: NET-100-64-0-0-1
Parent: NET-100-0-0-0-0
NetType: IANA Special Use
Comment: This block is used as Shared Address Space. Traffic from these addresses does not come from IANA. IANA has simply reserved these numbers in its database and does not use or operate them. We are not the source of activity you may see on logs or in e-mail records. Please refer to http://www.iana.org/abuse/
Comment: Shared Address Space can only be used in Service Provider networks or on routing equipment that is able to do address translation across router interfaces when addresses are identical on two different interfaces.
Comment: This block was assigned by the IETF in the Best Current Practice document,
Comment: RFC 6598 which can be found at:
Comment: http://tools.ietf.org/html/rfc6598
RegDate: 2012-03-13
Updated: 2012-04-23
Ref: http://whois.arin.net/rest/net/NET-100-64-0-0-1

The IP is part of which is a well known pool for CGNAT or Carrier Grade NAT. Checkout wikipedia’s small into to CGNAT here. Basically Airtel is out of publically unique IP address pools and hence doing NAT at carrier level. This is something very common across 3G provider’s in India where they are getting a demand of high growth and “always on” connectivity where end users just grab an IP address and keep it for long time and carriers can’t re-use it anywhere else in network.

Why use ?

This is because other private pools from RFC1918 address space are already in use by lot of home and business networks for NATing inside a home or organization network. If carriers also use the same, it will cause a major conflict and routing will just fail. Imagine using on your home router and then getting a WAN IP of from your upstream. It will just not work. Thus a pool is just like other private IP’s but simply not used by CPE vendors as default pool for NATing. Further more is supposed to stay within an organization and not to be announced/leaked to any peer. It’s a one-to-many NAT and multiple IP’s in pool have a single public IP as source address.
Let’s check what is my public IP on same 3G connection from bgp.he.net.
So my public IP at that instant was This public IP has many such private IP’s behind it. It is part of pool announced by Airtel AS9498 in global routing table. Though technically is supposed to stay within a network and not hit global table at all but just like other routing issues, it’s very common to see this pool in global table. At the time of this blog post I see that BELTelecom in Belarus (AS6697) is leaking in the global routing table. Route has very limited visibility but does seems visible at Oregon route-views. Russian provider MegaFon AS31133 seems to be transiting it.

route-views.routeviews.org> show ip bgp long
BGP table version is 0, local router ID is
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale, R Removed
Origin codes: i – IGP, e – EGP, ? – incomplete
Network Next Hop Metric LocPrf Weight Path
* 0 200130 31133 6697 i
* 0 0 16150 31133 6697 i
* 0 202018 31133 6697 i
* 0 3267 31133 31133 6697 i
* 0 3277 3267 31133 31133 6697 i
*> 0 3303 31133 6697 i
Total number of prefixes 1

Next time when you are streaming music over 3G, think about all nuts and bolts running in background to keep it going. 😉

23 Dec

End of inter-circle roaming: Good or Bad move?

Today I read in news about Govt’s decision to finally end inter-circle roaming agreements between Airtel, Vodafone & IDEA.
Well, the case is not new. It has been up with doT from over months and got highlights when CEO’s of all 3 firms wrote letter to Prime Minister of India for his intervention.

Little background

In 3G auction held in 2010, none of the operators got pan India spectrum across 22 telecom circles. Most of them have license in around 10 circles (few in 9, few in 11 and so on) and thus no one can provide full Nationwide 3G coverage.

Why did that happened?

Well, it was already expected well before auctions as Govt. gave only 20Mhz of spectrum in 2100 band in most of circles. It was decided that each player will get just 5Mhz, which brings number of 3G operators per circle to just 4. In all circles one slot was reserved for BSNL & MTNL (infact they were allocated spectrum back in 2008) and hence in most of circles there was scope of just 3 more operators. This was a problem as we do have more then 3 mobile operators at pan India level and which are big and doing pretty good business. Airtel, Tata Teleservices, Reliance, Vodafone, IDEA, Aircel, and few other small operators. Hence it resulted in cases like Airtel getting spectrum in Delhi, while IDEA missing in Delhi and going in for Haryana, where we find Airtel missing. (Here’s detailed circle wise allocation)
Few months back , Airtel, Vodafone and IDEA eventually got in an agreement for inter-circle roaming. It was a situation where a user say of Airtel Haryana (where Airtel has no 3G spectrum) will use IDEA’s 3G network and will have seamless experience and no roaming or any extra cost.

Inter-circle roaming agreement: loss to Govt?

One of big controversies here is claim from Govt. that Inter-Circle roaming agreement was huge loss to Govt as operators who have not paid for a specific circle are offering service in that circle. Thus Airtel giving 3G in Haryana is like Rs 300 crore ($60million) loss to Govt. and same applied on IDEA giving 3G in Delhi – loss of $600million to Govt.
Is that true? Well, I am not a lawyer, nor I have read 3G agreement carefully from legal eyes to find if such sharing is permitted or not but from common technical sense I can say that’s just a bad judgement from Govt’s end.

Why bad judgement…

  • Less spectrum was auctioned initially (that too after years of delay) and operators had no choice but to go for just few circles. (mistake from Govt. end)
  • Broadband still suffers badly in India due to very poor policies of Govt. ranging from very poor management of BSNL to poor niXi tariff policies. We stand no where in top 50 list in terms of broadband speed and penetration. Checkout NSN’s Connectivity Score Card on India.
  • Since operators had limited spectrum, capacity is always limited.  Thus if Airtel is sharing 5Mhz with IDEA, it is still 5Mhz in total. Hence Airtel is probably not making an undue gain from the deal. Airtel has not paid to Govt. for Haryana circle but in a sense paying to IDEA for the same. They are not getting things for free!
  • All operators all already feeling hard on cash and another auction doesn’t makes sense + they are still investing a lot in building new network which is used by just a few users. Such sharing would have boosted up  usage significantly.

Well, based on above points, I don’t see any sense in not permitting such agreement. If it was illegal, then may be a policy should have been re-considered rather then causing another road block for broadband in India. What else Govt. of India expects from telecom players after getting $15billion in 3G auction that too just for 5Mhz block.
It is again one of decisions where I see Govt. to be less responsive towards pain of poor broadband in India and more concerned about making money from telcos which in-turn is passed on to end users of India.
With hope that India will have better broadband soon, Good Night! 🙂