NTP time synchronization in offline machines - time

I have a couple of offline nodes in a cluster. I want their time to be synchronized, so I configured one of the nodes to be the NTP server.
This is the configuration file of my NTP server:
# node's ip:192.168.17.11
driftfile /etc/ntp.drift
server 192.168.17.11
fudge 192.168.17.11 stratum 1
restrict 192.168.17.0 mask 255.255.255.0 nomodify notrap
restrict -4 default kod notrap nomodify nopeer noquery
The problem is that the other machines can not synchronize their time with this machine.
Is this configuration file correct for acting as NTP server?
Thank you,
Ali

Using 127.0.0.1 as the server IP you are not allowing other compututers in the LAN to communicate with the NTP server.
Try changing 127.0.0.1 by the LAN IP of the server in the configuration file.

Related

Mikrotik PPPOE Routing

I have setup PPPOE Server successfully in Mikrotik. All is Good. I am able to give out public ips to clients over PPPOE. But I have some issues. For example I have 2 clients with public ips that would want to be able to connect to each other this is not working. Both public ips cannot reach each other.
Client 1
Local IP Remote IP
a.a.a.a b.b.b.b
Client 2
a.a.a.b b.b.b.b
Is there a way for these two IPs talk to each other?
Although its a very old question.
Answer:
1. Both the clients will be connected using ppp link to the pppoe server.
2. Enabled ipv4/ipv6 routing the pppoe server, if it's linux you need to enabled ip forwarding.
The above is logical answer, I haven't tried it myself.

the dns server ping use is different from the dns server nslookup use

on my computer(windows 10), the dns server that ping.exe use is different from the dns server nslookup use. i set 192.168.123.1 to be my computer's dns server, which is my router. so nslookup uses it as the dns server:
PS C:\Users\peter> nslookup.exe fm.zju.edu.cn
server: RT-N14U.lan
Address: 192.168.123.1
name: fm.zju.edu.cn
Address: 10.214.0.99
this ip address ic correct, which is school-internal ip.
but the ping result is different:
PS C:\Users\peter> ipconfig.exe /flushdns
Windows IP Configuration
Successfully flushed the DNS Resolver Cache.
PS C:\Users\peter> ping fm.zju.edu.cn
Pinging fm.zju.edu.cn [210.32.157.99] with 32 bytes of data:
then i use wireshark to find out that ping.exe send dns request to another dns server 114.114.114.114. i used to use this dns server, but i doesn't use it for about a month.
i reset the network settings, but the ping.exe still use 114.114.114.114 as its dns server.
i don't know how to solve this problem.
i don't know why this problem disappear today, what i did yesterday was:
change the mtu value of network card from 1500 to 1280 and many other things.
if this problem never appears again, just let it pass.

Elasticsearch cluster configuration is not discovering any nodes under both unicast and multicast

I've been trying to use the lovely ansible-elasticsearch project to set up a nine-node Elasticsearch cluster.
Each node is up and running... but they are not communcating with each other. The master nodes think there are zero data nodes. The data nodes are not connecting to the master nodes.
They all have the same cluster.name. I have tried with multicast enabled (discovery.zen.ping.multicast.enabled: true) and disabled (previous setting to false, and discovery.zen.ping.unicast.hosts:["host1","host2",..."host9"]) but in either case the nodes are not communicating.
They have network connectivity to one another - verified via telnet over port 9300.
Sample output:
$ curl host1:9200/_cluster/health
{"error":{"root_cause":[{"type":"master_not_discovered_exception","reason":"waited for [30s]"}],"type":"master_not_discovered_exception","reason":"waited for [30s]"},"status":503}
I cannot think of any more reasons why they wouldn't connect - looking for any more ideas of what to try.
Edit: I finally resolved this issue. The settings that worked were publish_host to "_non_loopback:ipv4_" and unicast with discovery.zen.ping.unicast.hosts set to ["host1:9300","host2:9300","host3:9300"] - listing only the dedicated master nodes. I have a minimum master node count of 2.
The only reasons I can think that can cause that behavior are:
Connectivity issues - Ping is not a good tool to check that nodes can connect to each other. Use telnet and try connecting from host1 to host2 on port 9300.
Your elasticsearch.yml is set to bind 127.0.0.1 or the wrong host (if you're not sure, bind 0.0.0.0 to see if that solves your connectivity issues and then it's important to change it to bind only internal hosts to avoid exposure of elasticsearch directly to the internet).
Your publish_host is incorrect - This usually happens when you run ES inside a docker container for example, you need to make sure that the publish_host is set to an address that can be accessed via other hosts.

Apache Cassandra: Unable to gossip with any seeds

I have built Cassandra server 2.0.3, then run it. It is starting and then stopped with messages:
X:\MyProjects\cassandra\apache-cassandra-2.0.3-src\bin>cassandra.bat >log.txt
java.lang.RuntimeException: Unable to gossip with any seeds
at org.apache.cassandra.gms.Gossiper.doShadowRound(Gossiper.java:1160)
at org.apache.cassandra.service.StorageService.checkForEndpointCollision
(StorageService.java:416)
at org.apache.cassandra.service.StorageService.joinTokenRing(StorageServ
ice.java:608)
at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:576)
at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:475)
at org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.ja
va:346)
at org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon
.java:461)
at org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.jav
a:504)
What I can change to run it?
I had a similar problem with my cassandra v2.0.4 cluster running a single node.
Check your cassandra.yaml and make sure that your "listen_address" and "seeds" values match, with the exception that the seeds value requires quotes around it.
You might get this problem if your private IP address is different than the public one (like on AWS). For example, the host thinks it's "172.31.0.2" when it's visible as "55.70.33.10".
The solution to this problem is:
listen_address: 172.31.0.2
broadcast_address: 55.70.33.10
in cassandra.yaml
Make sure your cluster_name entry match on all the nodes in the cluster
(you may need to delete your storage if you changed the cluster name)
Verify that all nodes can ping to each other
broadcast_rpc_address and listen_address should be set to local IP
(not localhost or 127.0.0.1)
seeds should point to the IP address of the seed(s)
If you are on AWS and use the Ec2MultiRegionSnitch you will need to set the seeds to the public IP addresses rather than the private IPs.
I had the same problem on Ubuntu 16.04. I'm not sure which of these changes made it work, where XXX.XXX.XXX.XXX is your public facing IP address, below are selections from cassandra.yaml
seed_provider:
# Addresses of hosts that are deemed contact points.
# Cassandra nodes use this list of hosts to find each other and learn
# the topology of the ring. You must change this if you are running
# multiple nodes!
- class_name: org.apache.cassandra.locator.SimpleSeedProvider
parameters:
# seeds is actually a comma-delimited list of addresses.
# Ex: "<ip1>,<ip2>,<ip3>"
- seeds: "XXX.XXX.XXX.XXX"
listen_address: XXX.XXX.XXX.XXX
broadcast_address: XXX.XXX.XXX.XXX
broadcast_rpc_address: XXX.XXX.XXX.XXX
listen_on_broadcast_address: true
start_rpc: true
rpc_address: XXX.XXX.XXX.XXX
I also needed to restart my Virtual Machine for some reason. ¯_(ツ)_/¯
For a quick single node setup on RHEL, I did the following:
Get info about your network interface setup:
# /sbin/ifconfig -a
It will list the interfaces and the ip addresses they are attached to.
Usually it will show an "Ethernet" interface and a "Local Loopback".
Get the associated ip addresses.
Then edit conf/cassandra.yaml:
rpc_address: [Local Loopback address]
broadcast_rpc_address: [Ethernet address]
listen_address: [Local Loopback address]
broadcast_address: [Ethernet address]
listen_on_broadcast_address: true
seed_provider:
- class_name: org.apache.cassandra.locator.SimpleSeedProvider
parameters:
- seeds: "[Ethernet address]"
Then also, open the correct ports on Linux firewall, being 9042, 7000 and 7001. More info about opening ports on Linux here:
http://ask.xmodulo.com/open-port-firewall-centos-rhel.html
in cassandra.yaml, I update the seed from domain name to IP address. and it works.
Happened to me because in my configuration the "intial_token" settings was specified (I think because I just copied to configuration file over from another cluster member). After clearing the data directory, commenting out the setting and restarting the node, it worked fine for me.
I experienced this error today...
I could not find any reason for the error other than timing issues.
I restarted many times and after a while it sticked. It looks like they expect a bi-directional communication on the gossip channel and if it does not happen quickly enough (which looks like a very small amount of time to me) then they drop the line and generate that error.
In my case I just upgraded my software and restarted the computer. So it was clearly not a connection issue between the computers (I have firewalls and SSL, to complicate matters) and the node was connected before... So the one entry I found in that regard from datastax did not apply...
https://support.datastax.com/hc/en-us/articles/209691483-Bootstap-fails-with-Unable-to-gossip-with-any-seeds-yet-new-node-can-connect-to-seed-nodes
I got the same error. There can be more than one solution. Hope my mistake is what you have done.
I had my localhost IP pointing to some domain name (and I did that in order that my Spring boot application's server context is some domain name like www.example.com:8080 instead of localhost:8080, and I had the following entry in my hosts file on Windows system).
127.0.0.1 www.example.com
While my cassandra batch file was looking for localhost which it didn't find. So, I made another entry for localhost too in my hosts file as:
127.0.0.1 localhost
127.0.0.1 www.example.com
After adding it, I opened new command prompt, ran cassandra batch from the cassandra bin directory and it then worked.
Disable the firewall and SELINUX and try again
In our case ssl was enabled, and cassandra.yaml configuration looks fine as per above comments. Then we enabled ssl debugging by by adding below jvm paramter in cassandra-env.sh -Djavax.net.debug=ssl:handshake
After starting the node again we noticed below in cassandra log file
MessagingService-Outgoing-geo2_host/xx.xx.xx.xx, Exception while
waiting for close javax.net.ssl.SSLHandshakeException: Received fatal
alert: certificate_unknown
After further investigating the ssl debug logs we got to know that the certificate was not valid. After fixing this ssl issue node was able to join the cluster.
Thanks to elvingt
His answer just remind me , I need to verify that all node needs to be able to talk to each other.
https://support.datastax.com/hc/en-us/articles/209691483-Bootstap-fails-with-Unable-to-gossip-with-any-seeds-yet-new-node-can-connect-to-seed-nodes
Gossip communications must be bi-directional.
To verify use this commnd, and you need test from BOTH SIDE
nc -vz {your_node_ip} 7000
Then I recollect that I turned on my ubuntu firewall last night. I open it by
sudo ufw allow 7000/tcp
And it is working now
Getting error during startup/bootstrap
Unable to gossip with any seeds
indicates there is some issue with broadcast_address. broadcast_address is responsible for communication with other nodes not with clients.
This address must be set in seed node(mandatory for seed node), If you are using cloud VMs you might have different IPs(public and private) hence its recommended to use your private IPs for broadcast_address this will save your n/w cost as well.
# Address to broadcast to other Cassandra nodes
# Leaving this blank will set it to the same value as listen_address
broadcast_address: 10.11.xx.xxx
In my scenario I was using IBM and once I set broadcast_address in seed nodes issue got resolved.
Please make sure you are starting your seed node first then other node, this order is mandatory.
in cassandra.yaml
changing listen_address value from localhost to domainName solved my issue
I had same issue, I checked port, used tcpdump, netcat to test connections and finally it comes to expired SSL certificates on internode_encryption. I modified internode_encryption to make it 'none', restarted all nodes and it worked.
Before all neighbor nodes were down. And node repair command was failing with:
"Did not get positive replies from all endpoints"
P.S Dont leave internode_encryption as none for a long time, just regenerate certs and enable it back.

ssh windows 7 connection refuser

trying to connect from localhost
ssh <MyLogin>#localhost - connected
trying to connect from another computer in my local network
ssh <Mylogin>#<MyServerLocalIp> - connected
trying to connect from internet
ssh <Mylogin>#<InternetIp> -conection refused (it not appears in my log file)
i'm check 22 port in this site http://www.canyouseeme.org/ - 22 port is open and it appears in my log file
trying use telnet
telnet InternetIp 22 - not connected
but when i'm trying another port
telnet InternetIp 21 - connected
This sounds like you are behind a NAT Router.
If this is the case, what you will need to do is first ensure your machine has a static IP address. This will likely be something like 192.168.1.x. You can configure this in your router by either mapping your machines MAC address to a DHCP assigned address or just configuring you machine with a static IP and checking that that IP is not in the DHCP range.
Then you will need to configure your Router to forward inbound port connections to the local IP address of your machine. Here is an article on Wikipedia about Port Forwarding: http://en.wikipedia.org/wiki/Port_forwarding
Your best bet is to download the manual for your specific Router and look up the section on port forwarding. It is often in the section about the routers Firewall.

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