[Ilugc] [OT?] Many sites not opening - BSNL BB
Natarajan V
Am not very sure if it is an OT. But potential
solutions/troubleshooting guide could be of help.
I have a BSNL BB connection connected to a PC and a Laptop through an
ADSL router NATed to a NETGEAR WiFi router. The PC runs on Kubuntu
10.04 64 bit and the laptop runs on Kubuntu 9.04 32 bit. The browsers
that I tried are FireFox 11, Opera 11.62 for Linux, Google Chrome,
Konquerer, links, lynx, etc...
Some of the sites such as icicilombard, slashdot, some of my corporate
sites, hotmail, yahoo mail, the hindu, etc.. aren't accessible. Some
of these sites stop loading midway, while someothers do not respond
(timeout). I ran a traceroute to these sites and the response is
similar to the results from www.tracert.com. When I try to connect to
the internet through my Airtel 2G (laptop connected to cellphone),
these sites open up. I tried to open these sites from my brother's
place, which has BSNL BB (different telephone exchange) connected to
Kubuntu 32 Bit 11.10. These sites open without issues. I also verified
if there are issues with the DNS servers, and confirmed that it isn't.
This makes me think that there is some problem with the routing of the
BSNL routers in my exchange, or an issue with my router.. Is there a
way to confirm this? If that is the problem, is there a way to
circumvent the same?
with regards,
Natarajan
_______________________________________________
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Balachandran Sivakumar
On Sun, Apr 1, 2012 at 11:33 AM, Natarajan V <raj...@gmail.com> wrote:
> Hi,
>
> I have a BSNL BB connection connected to a PC and a Laptop through an
> ADSL router NATed to a NETGEAR WiFi router. The PC runs on Kubuntu
> 10.04 64 bit and the laptop runs on Kubuntu 9.04 32 bit. The browsers
>
I have a BSNL broadband connection, with a D-Link router(No
Wi-Fi, this is wired).
> Some of the sites such as icicilombard, slashdot, some of my corporate
> sites, hotmail, yahoo mail, the hindu, etc.. aren't accessible. Some
I am able to access all these. In fact, the hindu is something that
is always open in my browser :)
>
> This makes me think that there is some problem with the routing of the
> BSNL routers in my exchange, or an issue with my router.. Is there a
> way to confirm this? If that is the problem, is there a way to
I don't think they use different routers for each exchange.
Can you try to get your brother's router and use it from your
place(after the necessary config changes) ? That will help is identify
if the issue is with your router or with BSNL's. Thanks
--
Thank you
Balachandran Sivakumar
Arise Awake and stop not till the goal is reached.
- Swami Vivekananda
Mail: benig...@gmail.com
Blog: http://benignbala.wordpress.com/
0
> This makes me think that there is some problem with the routing of the
> BSNL routers in my exchange, or an issue with my router.. Is there a
> way to confirm this? If that is the problem, is there a way to
> circumvent the same?
>
It is most likely a local issue. Can you provide the following details ?
It will help debug the issue.
1. ping ilugc.in
2. ADSL Line Attenuation (Downstream & Upstream)
3. ADSL Noise Margin (Downstream & Upstream)
4. ADSL Connection Speed (Downstream & Upstream)
5. Do you have the modem connected after the splitter ?
You can get the ADSL details from the BSNL router. If you don't have the
username:password try the default admin:admin.
--
0
Akilan R
> I have a BSNL BB connection connected to a PC and a Laptop through an
[snip]
Set MTU to 1452 and check if the sites load.
--
அகிலன் (Akilan R)
[ blog.akilan.in ]
*I should have no use for a paradise in which I should be deprived of the
right to prefer hell.*
--Jean Rostand
"ம. ஸ்ரீ ராமதாஸ்"
> Is there a
> way to confirm this? If that is the problem, is there a way to
> circumvent the same?
/etc/resolv.conf
Natarajan V
> On 04/01/2012 11:33 AM, Natarajan V wrote:
>> Is there a
>> way to confirm this? If that is the problem, is there a way to
>> circumvent the same?
> set google nameservers (8.8.8.8, 8.8.4.4) or some other credible in
> /etc/resolv.conf
>
Thanks. I don't have issues with name servers. Infact, I have Google
nameservers added. Routing seems to be troublesome. Infact some sites
without any names, but just IP addresses (some BSNL Directory lookup
sites) also dont work.
with regards,
Natarajan
Girish Venkatachalam
In my rich networking experience, in fact I have never solved any problems
as networking problems in my whole life I have never come across
something like this.
However there are networking troubleshooting boys and certain OpenBSD devs like
Henning Brauer who play with BGP and SMTP internals.
I am not that caliber but then I am also not a sysadmin of a huge
network to troubleshoot
a lot.
Still from a programming and troubleshooting angle I do know something
about where what
could go wrong.
Your problem is bizarre.
It has nothing to do with routing is what I feel.
Probably some firewall, browser or some such thing.
If ping does not work, then your MODEM could be broken, your
switch/hub could be worn out,
your computer's NIC, it could be anything.
Best of luck.
-Girish
--
G3 Tech
Networking appliance company
web: http://g3tech.in mail: gir...@g3tech.in
Natarajan V
> On Sun, Apr 1, 2012 at 11:33 AM, Natarajan V <raj...@gmail.com> wrote:
>
>> I have a BSNL BB connection connected to a PC and a Laptop through an
>
> [snip]
>
> Set MTU to 1452 and check if the sites load.
>
Great! That worked. Now, let me try to find out how that happened :-)
Thanks a lot!
with regards,
Natarajan.
Girish Venkatachalam
> On Sun, Apr 1, 2012 at 12:48 PM, Akilan R <akil...@gmail.com> wrote:
>> On Sun, Apr 1, 2012 at 11:33 AM, Natarajan V <raj...@gmail.com> wrote:
>> Set MTU to 1452 and check if the sites load.
>>
>
> Great! That worked. Now, let me try to find out how that happened :-)
> Thanks a lot!
>
>
I see. Such pointed tech answers are rare in LUG.
This is wonderful. I am happy for both of you.
However this is bad advertisement for Linux.
How can something so silly bite you?
-Girish
--
G3 Tech
Networking appliance company
web: http://g3tech.in mail: gir...@g3tech.in
Natarajan V
<girishven...@gmail.com> wrote:
> On Sun, Apr 1, 2012 at 8:01 PM, Natarajan V <raj...@gmail.com> wrote:
>> On Sun, Apr 1, 2012 at 12:48 PM, Akilan R <akil...@gmail.com> wrote:
>>> On Sun, Apr 1, 2012 at 11:33 AM, Natarajan V <raj...@gmail.com> wrote:
>>> Set MTU to 1452 and check if the sites load.
>>>
>>
>> Great! That worked. Now, let me try to find out how that happened :-)
>> Thanks a lot!
Well, this documentation seems to be concise enough:
http://www.dslreports.com/faq/695
The following is what *think* might have happened.
MTU is largest size of each packet. The default value is 1500. But
seems like this size is too big for some networks. When I observed
more closely, some sites just didn't load at all. The othersites (such
as thehindu & slashdot), start to load, and they keep waiting for
ever. The site has been waiting indefinitely for some content to be
loaded from other domains whose routes accept smaller than 1500.
That's why some sites stopped loading midway, while others never
loaded at all.
>
> I see. Such pointed tech answers are rare in LUG.
Don't you remember that iLugC is one of those rare LUGs where you do
get such answers :-)
> However this is bad advertisement for Linux.
No it isn't. It's just a good documentation for others who might also
face a similar problem.
> How can something so silly bite you?
:(
1. Am not a network-admin, but more of an App Developer
2. I couldn't relate the symptoms with the cause.
with regards,
Natarajan
Raja Subramanian
> The following is what *think* might have happened.
> MTU is largest size of each packet. The default value is 1500. But
> seems like this size is too big for some networks.
Actually the issue is more like this:
The link between your DSL modem and DSLAM (other end ISP equipment
your DSL modem connects to) uses encapsulated PPP - it's either PPP over
Ethernet or ATM.
Since 1500 is the MTU on Ethernet networks, when you add PPPoA/E
the packet size increases due to encapsulation overhead.
PPPoE add 8 bytes overhead. So the MTU should be 1492 bytes to
ensure that even after adding encapsulation overhead you are still
at the 1500 byte MTU limit.
* I don't use BSNL to verify, so please let us know if MTU 1492 works for you.
Note that the same issue is present when you use VPN tunnels - you
need to use a lower MTU on the tunnel to accommodate VPN overhead.
There are a couple of ways around manual MTU setting:
Routers can fragment and reassemble packets so that they can pass through
packets with smaller MTU sizes, but this has a lot of overhead. In fact it has
so much overhead that IPv6 does not support fragmentation/reassembly.
It simply drops the packet, sends a "packet to big" ICMP error condition.
This forces sender/receiver to perform path MTU discovery.
> When I observed
> more closely, some sites just didn't load at all.
> The othersites (such
> as thehindu & slashdot), start to load, and they keep waiting for
> ever. The site has been waiting indefinitely for some content to be
> loaded from other domains whose routes accept smaller than 1500.
> That's why some sites stopped loading midway, while others never
> loaded at all.
Sites which load are successfully able to perform path MTU discovery
so they automatically discover the lower MTU on your DSL modem.
To be certain use "tracepath" which is similar to traceroute but reports
the path MTU at each hop. It will be great to see the tracepath output
for your various websites.
- Raja
Mohan Sundaram
<rajasu...@gmail.com> wrote:
> On Sun, Apr 1, 2012 at 8:21 PM, Natarajan V <raj...@gmail.com> wrote:
>> The following is what *think* might have happened.
>> MTU is largest size of each packet. The default value is 1500. But
>> seems like this size is too big for some networks.
> so they automatically discover the lower MTU on your DSL modem.
>
> To be certain use "tracepath" which is similar to traceroute but reports
> the path MTU at each hop. It will be great to see the tracepath output
> for your various websites.
This has been an issue for a long time now. Many sites do not open as
packets get dropped when encapsulation happens. It is seen more often
when you have control connections getting dropped. PPP control
connections is one such case.
I've also noticed this more often in sites that are served out of
large web farms/ CDNs which have some kind of indirection/ reverse
proxy. LinkedIn is a standing example.
-- Mohan Sundaram
Mohan Sundaram
> This has been an issue for a long time now. Many sites do not open as
> packets get dropped when encapsulation happens. It is seen more often
> when you have control connections getting dropped. PPP control
> connections is one such case.
>
> I've also noticed this more often in sites that are served out of
> large web farms/ CDNs which have some kind of indirection/ reverse
> proxy. LinkedIn is a standing example.
Apologies for replying to my own post. To get rid of this problem
across networks that I move in and out of, I've set my ethernet MTU to
1300 ( a safe number) to account for a few encapsulated hops.