How does DHCP assigns unique addresses to a network and does DNS lookup need to be changed
I recently got to know about DHCP that it dynamically assigns ip addresses to a computer. But what if two DHCP servers across the world assign a same ip address to two different computers. Doesn't it conflicts with the uniqueness property of ip addresses. For example two DHCP servers assign ip address x to computer1 and computer2 and i wanted to send a mail to computer1 by looking at DNS server it should be send to ip address x. But there is a conflict as two different computers have same ip address x. could someone please clear my doubt.
Let say I want to contact a server whose domain name is example.Com and ip address stored in DNS server is 127.18.1.1 and DHCP changes the ip address for this server to some random value 127.19.1.1 then how is the address resolved since I'm contacting to example.com which has 127.18.1.1
There are a number of ways that this problem is avoided.
Firstly, by keeping networks small, segregating machines into specific functions, geographic areas, etc you reduce the risk of having a large pool of addresses in use.
Secondly, if you must have multiple DHCP servers on a network, then the address space should be split between them. So if you have 192.168.0.0/24, one server would handle 192.168.0.0/25 and another would handle 192.168.127.0/25
Thirdly, most DHCP servers will ping the IP address that they are going to offer before offering it. If the address gets a response it will be marked as Conflicted and won't be offered again.
See also questions close to this topic
Wireless Connection Location
I am developing emergency notification system and running windows service to check active alerts based on logged-in user's location however when user connects with wireless then i do not know the location because I use centralized network and only wired connections have IP range but no IP range for access points. I have over 50 buildings and some of them so close to each other they may overlap wireless connections.
How to know user's building if h/she use wireless connection? or what else can i try to overcome this?
IIS hosted Web API doesn't pick up incoming requests
Some background: I'm working on setting up a Web API in IIS. Everything works locally in Postman/web browser, big surprise. I also have a small no frills client/server program I wrote (C# console application) a while back that was known to work between computers at the time, I've since moved and have a different ISP (CenturyLink).
More background: I have DynDNS set up (I don't have a choice, I'm locked into it for hardware/ISP reasons), and I have Port Forwarding setup to go to the box I want. When I check my port, 18960 for what it's worth, using http://www.canyouseeme.org/, it's open. My website is also bound to that Port.
What I've tried: When I ran my client program to connect to the server, it failed, which I assumed was due to firewall issues on the computer I was running the client on, so I moved on. Interestingly, my server will output "Client Connected" when I use "canyouseeme" to check the Port. I can also use my phone to use one of the GET URLs and see it come in through WireShark, so I know my requests are getting to the endpoint, presumably meaning my Ports and DDNS stuff is setup correctly.
The issue is that when I have my server running, I get the Port check traffic, and I can see the GET request come in, but when I turn off the server and start the website... nothing. I'm still very new to IIS, so I thought perhaps IIS wasn't listening on the Port, but doing a quick search on that train of thought led me to believe that's silly.
How to set vrf and source-interface ios_logging ansible
To configure switch as shown below from ansible, how can we write playbook for the last 4 lines of this config files? Any comments and suggestions appreciated.
... logging trap informational logging console informational logging vrf MGMT host 10.2.5.7 logging host 10.5.3.7 5454 Logging vrf MGMT source-interface Management1 Logging source-interface Loopback0
- name: config trap logging and level ios_logging: dest: trap # Is it available? level: informational state: present - name: config console logging and level ios_logging: dest: console level: informational state: present - name: config vrf and host # not enough documentation I could find ios_logging: dest: # how to get the vrf VRF or is it host? name: 10.2.5.7 # only if the dest. is host state: present - name: config host and name ios_logging: dest: host name: '10.5.3.7 5454' state: present - name: config vrf and source-interface # not enough documentation I could find ios_logging: dest: # how to get the vrf VRF or is it host? name: ? # source-interface part state: present - name: config source-interface # same issue ios_logging: dest: source-interface # is this a way? name: Loopback0 # someone tell me this is a way state: present
Reproduce `Temporary failure in name resolution`
How can I reproduce manually the
Temporary failure in name resolutionerror, when doing
ping google.comin linux?
Probably, I can add a broken DNS server by my own and specify it in
I need this for testing my project.
AWS route 53 inaccessible domain in www
I'm currently deploying my first SAAS on AWS. I am using a free Amazon Linux 2 EC2 with a domain name on Route 53.
I can access my domain in http and even in https: https://booda.me redirection without problem.
Alternately, when using www (www.booda.me), the domain is inaccessible. When I created my https certificate, I got the following error message for www.booda.me:
I did not change the apache config other than the virtual host as shown in the AWS doc tutorial:
<VirtualHost *: 80> DocumentRoot "/ var / www / html" ServerName "booda.me" ServerAlias "www.booda.me" </ VirtualHost>
Here are the DNS (image below) of the routing of my domain.
Where do you think it could come from?
EDIT I added a type A DNS for "www.booda.me" and now the HTTPS certificate is passed. However the domain www.booda.me is still inaccessible.
I tried to add the same type A DNS as an alias but still no result. www.booda.me does not redirect to the HTTPS version and displays a 404 instead. [DNS A]
[Alias] [404 not found]
EDIT thank you everything works now, sorry I'm really new to the subject. Thank you for helping me. Have a good day :)
Centos7.4 DNS Issue: Unable To Resolve Domains via Ping But NSLOOKUP Working
I have been unable to resolve domains via ping however DIG, NSLOOKUP and HOST are resolving domains just fine.
[root@xxx ~]# cat /etc/resolv.conf | grep nameserver nameserver 127.0.0.1 nameserver 18.104.22.168 nameserver 22.214.171.124 [root@xxx ~]# cat /etc/nsswitch.conf | grep hosts hosts: files dns myhostname mdns [root@xxx ~]# ping 126.96.36.199 -c 1 PING 188.8.131.52 (184.108.40.206) 56(84) bytes of data.<br/> 64 bytes from 220.127.116.11: icmp_seq=1 ttl=117 time=71.1 ms --- 18.104.22.168 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 71.173/71.173/71.173/0.000 ms [root@xxx ~]# [root@xxx ~]# ping google.com ping: google.com: Name or service not known [root@xxx ~]# host google.com google.com has address 22.214.171.124 google.com has IPv6 address 2a00:1450:401a:804::200e google.com mail is handled by 40 alt3.aspmx.l.google.com. google.com mail is handled by 50 alt4.aspmx.l.google.com. google.com mail is handled by 30 alt2.aspmx.l.google.com. google.com mail is handled by 10 aspmx.l.google.com. google.com mail is handled by 20 alt1.aspmx.l.google.com. [root@xxx ~]# nslookup google.com Server: 127.0.0.1 Address: 127.0.0.1#53 Non-authoritative answer: Name: google.com Address: 126.96.36.199 [root@xxx ~]# dig google.com ; <<>> DiG 9.9.4-RedHat-9.9.4-51.el7 <<>> google.com ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 64421 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 9 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;google.com. IN A ;; ANSWER SECTION: google.com. 290 IN A 188.8.131.52 ;; AUTHORITY SECTION: google.com. 172790 IN NS ns3.google.com. google.com. 172790 IN NS ns4.google.com. google.com. 172790 IN NS ns2.google.com. google.com. 172790 IN NS ns1.google.com. ;; ADDITIONAL SECTION: ns2.google.com. 172790 IN A 184.108.40.206 ns2.google.com. 172790 IN AAAA 2001:4860:4802:34::a ns1.google.com. 172790 IN A 220.127.116.11 ns1.google.com. 172790 IN AAAA 2001:4860:4802:32::a ns3.google.com. 172790 IN A 18.104.22.168 ns3.google.com. 172790 IN AAAA 2001:4860:4802:36::a ns4.google.com. 172790 IN A 22.214.171.124 ns4.google.com. 172790 IN AAAA 2001:4860:4802:38::a ;; Query time: 1 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Fri Oct 19 12:13:50 CAT 2018 ;; MSG SIZE rcvd: 303 [root@xxx ~]#
How to see devices ip in child TP-Link Routers from Main Modem?
Actually i wanna see all devices connected in Child Modems... Details:
1.) I have a Modem with ip-address/Default-Gateway 192.168.10.1, i have ip address of 192.168.10.4(My Laptop's ip)
2.) A tp-link1 router connected on ip address 192.168.10.2 with its own gateway of 192.168.10.1, subnet 255.255.255.0 and ip range 192.168.0.100-199
3.) Another tp-link2 router connected on ip address 192.168.10.3 with its own gateway of 192.168.10.1, subnet 255.255.255.0 and ip range 192.168.0.100-199
Now i wanna see list of devices with nmap or any tool connected with tplink1 and tplink2...
i disabled firewall on both tplink routers but it doesn't helped... and modem doesn't have any firewall i guess... Any help will be much appreciated...
Can only send emails when using IP of SMTP host
I have this annoying issue:
- When sending an email when debugging in VS, it works fine (I'm using
After publishing to the server, I get this error:
System.Net.Mail.SmtpException: Failure sending mail. ---> System.Net.WebException: The remote name could not be resolved: 'mail.company.co.za'
However, if I change the smtp host to the IP address, it seems to work fine.
I got the IP by calling
ping mail.company.co.zain CMD (When calling this on the server it can't find the address, but it can ping the IP)
Since I'm not sure whether the IP is static or not, I don't know if its safe to just use the physical IP. Why would the server not recognise the
Note that I am debugging and hosting the application on the same network. This suggests to me that it is not a firewall issue, but maybe I'm wrong about that?
- When sending an email when debugging in VS, it works fine (I'm using
How to fetch ISP internet connection type using python?
My program has a requirement to dynamically adjust some parameters based on the internet connection type provided by the ISP.
For instance if the connection type is DHCP, my program will behave slightly differently and if it is PPPoE, it will behave otherwise.
But is there a way to fetch these details using Python?
A quick google search brings up ways to fetch details like public IP, hostname, etc. But no mention of connection type anywhere.
Any help is appreciated. Thanks! :)
PowerDNS Master Slave Configuration
I deployed 4 powerDNS instances. 2 in NJ (nj-ns1 and nj-ns2) and 2 others in LA (la-ns1 and la-ns2).
Configured pdns in pdns.conf as, nj-ns1 as master. nj-ns2 la-ns1 and la-ns2 as Slaves.
Each of the NS also run DHCP. The 2 NS in NJ only manage NJ host and 2 NS in LA only mange LA hosts. I configured DHCP to update DNS with the leases.
My question is, If I create a dns zone (called la.test) with la-ns1 as master ns, would dhcp in LA be able to add A records to it? even though it is not a "powerDNS master"? I am basically confused about the difference between setting Master in pdns.conf vs. on the zone itself.
Issue setting up Open vSwitch on GCE (DHCP client not working)
I am trying to simulate an on-premises solution on GCP. I am not able to bridge with the GCE NIC and get DHCP working on that.
I have isolated the issue and also successfully tests the similar thing on a sandboxed Vagrant (VirtualBox) setup.
Both approaches are scripted and available on the following repos: https://github.com/htssouza/ovs-gcp-issue