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Thanks you for your time.
I have just set up a Postfix mail server which is running as MTA in one of my aws instances. I can successfully connect to the localhost through 'telnet localhost 25', and I can send emails to both external and internal email accounts when connected on localhost, however whenever I try to connect through 'telnet zwitch.it 25' or 'telnet mail.zwitch.it 25' I get a connection timeout.
I have set up all my records, including the MX record and the SPF record with the values "v=spf1 include:amazonses.com include:zwitch.it -all" and "spf2.0/pra include:amazonses.com include:zwitch.it ~all".
I really cannot find what is the problem here, if there is a firewall, or if the port is blocked, or maybe something is wrong with my postfix configuration... I would really appreciate if you could help me.
To set up my postfix mail server I followed the instructions at http://flurdy.com/docs/postfix/ where it mentions the installation of a simple postfix server.
I thank you in advance for the help.
EDIT:
Thanks to the answer below the problem was fixed. I only had to go on my aws security groups and add SMTP to the list!
It's one of three things:
1.) You need to edit your security group in AWS to allow port 25 from all external IP addresses.
2.) Your DNS entries for mail.zwitch.it do not point to the external IP address of the AWS instance.
3.) You don't have a static IP (elastic) address configured for the instance.
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When I type a domain URL in the browser (or send a ping or write code that fetches a particular IP) the browser gets the associated IP address based on DNS lookup in a distributed database system - the DNS name servers.
But once the IP is obtained - how does the browser know how to go to the particular computer that this IP represents?
import urllib.request
nf = urllib.request.urlopen("http://192.168.1.2")
The operating system will compare the target IP address with its own IP address. If both addresses are part of the same network, the OS will issue an ARP request to obtain the physical address (the MAC) of the target interface.
If both IP addresses are not part of the same network, the OS will forward the traffic to the gateway responsible for the subnet that is addressed. If it has no such a route, the OS will forward the traffic to the default gateway.
From there the game starts anew.
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I was to check this URL:
http://geotool.servehttp.com
Is this some sort of suspicious behavior? I can't understand.
My local hosts file (I am using Windows 7 - 64 bit) shows nothing about this domain.
I also made an online whois query on it and there I found 127.0.0.1 as its IP address!!!
What's the magic behind this?
Edited
When I point to this URL, using my browser, the localhost (WAMP server) homepage loads.
Whoever configured the DNS records for geotool.servehttp.com pointed that subdomain name to 127.0.0.1.
It is not usual to point a public hostname to a private IP address, but it is possible.
Here are the results from dig +trace geotool.servehttp.com A:
geotool.servehttp.com. 60 IN A 127.0.0.1
servehttp.com. 86400 IN NS nf3.no-ip.com.
servehttp.com. 86400 IN NS nf4.no-ip.com.
servehttp.com. 86400 IN NS nf2.no-ip.com.
servehttp.com. 86400 IN NS nf5.no-ip.com.
servehttp.com. 86400 IN NS nf1.no-ip.com.
;; Received 151 bytes from 83.222.240.75#53(83.222.240.75) in 153 ms
Four Years ago, I asked this question and now, I am posting an answer to it for any further reference.
DNS Information
TXT Record:
AUTHORITY
servehttp.com. IN SOA nf1.no-ip.com. hostmaster.no-ip.com.
This text record tells us that the domain geotool.servehttp.com probably belongs to no-ip.com.
Visiting internet website for http://no-ip.com (which currently redirects to https://noip.com), a simple slogan tells us everything:
Create an easy to remember hostname and never lose your connection again.
Our Dynamic DNS solution makes it easy to remote access any internet connected device.
That is, a Dynamic DNS service. It helps you reach your local hosted application or network through internet by assigning a dns name to your dynamic always changing ip address.
That's it.
The question asks 'why', so I would like to share my reason.
I wrote a proxy software called vproxy, so I bought domain vproxy.cc.
In the software it runs dns health check periodically to see if the dns server is still available (otherwise it will stop sending dns requests to that server).
The health check is enabled by default, so I have to choose a domain which simply does nothing but returning a constant A record (ipv4 address).
So here comes 127.0.0.1.special.vproxy.cc, which resolves to 127.0.0.1. The domain and address are hardcoded into the software as the default dns health check settings.
Using 127.0.0.1 is simply because it's a loopback address and if someone accidently send traffic to this domain/address, he/she would be sending to local and would not cause any trouble for other people.
And the reason I'm not choosing other 127.x.y.z ips is because they are not so well known as 127.0.0.1 do. Most people don't know that 127/8 are all loopback addresses, but people do know 127.0.0.1.
And for geotool.servehttp.com, maybe the maintainer simply want the same thing as I do? Just some const address which is choosen to be 127.0.0.1.
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My EC2 instance is up and running at ec2:8080 because my node server is listening on port 8080. But I want to connect my instance as a cname to my website under a domain (At namecheap). The cname only accepts ec2 not ec2:8080, so my code won't go up. This is probably an easy fix, any help? (my security group accepts all ports so its not that)
You need to point your domain's DNS settings to your public DNS or elastic IP provided by EC2. From there, you need to allow an exception in your security group granting HTTP traffic through to port 8080. Assuming the DNS changes propagate, you should be able to access your instance on node server running on port 8080 by:
http://your.public.dns.address:8080/
or
http://elastic.ip:8080
Hope that helps.
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Can I specify DNS servers for multiple domains.
For example there are 3 domains for which I know the DNS server which would resolve the domain name, so can I specify something like
b.com (domain)
u1.x1.y1.z1 (DNS server IP address which would resolve b.com)
l.m.n.o (default DNS server used if above DNS server unavailable)
c.com (domain)
u2.x2.y2.z2 (DNS server IP address which would resolve c.com)
l.m.n.o (default DNS server used if above DNS server unavailable)
d.com (domain)
u3.x3.y3.z3 (DNS server IP address which would resolve d.com)
l.m.n.o (default DNS server used if above DNS server unavailable)
please refer https://github.com/whitekid/dnspost
this provide max osx's resolver functionality.
Will following help. In /etc/resolv.conf I will specify,
search b.com
nameserver u1.x1.y1.z1
search c.com
nameserver u2.x2.y2.z2
search d.com
nameserver u3.x3.y3.z3
For d.com, NS u3.x3.y3.z3 will be used (other NS's i.e. u1.x1.y1.z1 and u2.x2.y2.z2 will not be tried for d.com)?
If input domain does not match any of the above given domains then local nameserver will be used?
Also local nameserver will be used if above nameservers are not available or respond with NO?
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I have a linux machine Iam using as a router with multible interfaces and multible internet connection
say eth0--isp1
eth1--isp2
eth2--isp3
the gateway is eth0 throw isp1
and eth3--local1 10.0.0.x
eth4--local2 192.168.1.x
i need local1 ip 192.168.1.10 to go throw isp3, eth2
thanks
You need to use policy routing for this. You create a new routing table and use it when the source IP is 192.168.1.10.
ip route add ... table $TABLENUM # your usual routes, for the new table
...
ip route add default via $ISP3 table $TABLENUM # gateway for the new table
ip rule add from 192.168.1.10/32 lookup $TABLENUM # use the new table for this IP
ip rule add to 192.168.1.10/32 lookup $TABLENUM # make it symmetric, for clarity
Try route add 192.168.1.0 netmask 255.255.255.0 dev eth4--local, on the assumption these are locally-connected networks. If not, you will need to specify a gateway machine to route the packets through also. Truthfully your question is malformed (and probably belongs on serverfault). If you already have addresses on those networks, these routes should already exist. If you do not, your problem is likely more complicated than you think it is.