TCP/IP

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Transmission Control Protocol/Internet Protocol (TCP/IP) is the set of networking protocols that define end-to-end connectivity specifying how data should be packeted, addressed, transmitted, routed and received at the destination. This functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved.

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Our LAN uses 192.168.1.x IP addresses.  One of our vendors has just required us to connect to their VPN, then RDP to one of their computers to conduct business.  Their network also uses 192.168.1.x IP addresses.  Our network is small, so the effects have been minimal, but only by luck it would seem.  Sometimes we are forced to re-login to our own file server, and this is cumbersome and inconvenient.  How can we adjust settings on our end to minimize/eliminate IP address conflicts?  Our networking equipment is SOHO.  One perhaps obvious solution would to change our entire subnet internally, but that just doesn't seem like the best way to proceed.  Advice please?
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to setup new office what IP addressing is recommended as it is common to use 192.168.1.0/24 but I would like to go for something different and this network will have to be get connected over the VPN from other location and they may be using 19.168.1.0/24,  this new network yet to be setup will have internal dns and dhcp and leased line and mpls connectivity. the total users or end devices within this network will not be more than 75, I prefer other than 192.168.1.0/24 is there a recommend/best  practice in selecting a particular ip addressing for private lan network please suggest,  is it good to go with 192.168.0.1/24 or something like 192.168.100.0/24 or any other ip addressing recommended please suggest.
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I am needing a revolving server system that changes IP address once it starts getting hits from sever filters. It needs to be seamless and use the same email address that we establish to send emails out from, but configures a different IP with every 50 to 100 emails. This is what we need to get a marketing job done and the email messages we want to send have to fit the character count specifics and font type. The subject line is the most important and the size cannot exceed X kilobytes for the total email to reach target market.
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Hi,

Can you please advise why IP of server is changing like

C:\Users\Administrator>ping 113.255.213.114
Pinging 113.255.213.114 with 32 bytes of data:
Reply from 113.255.218.217: Destination host unreachable.
Reply from 113.255.218.217: Destination host unreachable.

Open in new window

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Recently, our W2012R2 RDS server has started giving users problems logging in. The message is:
The number of connections to this computer is limited and all connections are in use right now. Try connecting later or contact your system administrator.

I'm having a hard time finding any helpful information on how to resolve this issue other than on desktop versions of Windows.

In a bid to get around this issue, I've opened more ports (HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp 339x), and this has given some temporary reprieve.

It seems to me that the issue is pervasive. By that I mean that the message does not disappear even if existing users log off from their RDS sessions.

This RDS server has been working fine for years, and now, suddenly, this happens.
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We run a small network with less than 256 devices so we use static IP addressing (IP 192.168.0.1 subnet 255.255.255.0).
We recently expanded our equipment so I changed the subnet to 255.255.254.0 on all existing servers, workstations, printers, switches, routers, etc to accommodate new workstations in the 192.168.1.? range.

Any workstation (new or old) that I change to the 192.168.1.* range has communications problems. Most notably drive mapping on logon and being accessed by remove viewing products like VNC. Each time I change a machine back to the 192.168.0.* range the problems go away.

Any direction on how to troubleshoot this issue would help !
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Please include the detailed explanation of the following:
Physical layer
Data link layer
Network layer
Transport layer
MAC address
IP address
TCP port
Checksum check
Routing table
TTL
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Hello All,

I have integrated Kamailio 4.4 with asterisk 13 LTS and I think its been properly integrated. It also shows me the registered users but when i call from 101 to 102 it gives me the below error

[May  7 12:43:14] NOTICE[19838][C-00000000]: chan_sip.c:25545 handle_request_invite: Call from '101' (192.168.56.103:5060) to extension '102' rejected because extension not found in context 'public'.

I have followed the below for installation and configuration.

http://kb.asipto.com/asterisk:realtime:kamailio-4.0.x-asterisk-11.3.0-astdb

The user database is fetching from remote host in which kamailio has been installed. Users are showing in asterisk node as well

asterisk*CLI> sip show users
Username                   Secret           Accountcode      Def.Context      ACL  Forcerport
101                                                          public           No   No
102                                                          public           No   No

So how can i debug this or is there any clue that what might be wrong. Please find below  the extension.conf details as well.

exten => _1XX,1,Dial(SIP/${EXTEN})
exten => _1XX,n,Voicemail(${EXTEN},u)
exten => _1XX,n,Hangup
exten => _1XX,101,Voicemail(${EXTEN},b)
exten => _1XX,102,Hangup

Thanks and looking forward for some clues from this community

Regards,
Atif Ramzan
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Public IP configuration for two different network. I got error when I assign public ip address on port 1 and 2 with same subnet. 1.1.1.1/24 for port 1 and i got error when I try to set up 1.1.1.2/24 on port 2, "same subnet on port 1" I am using Cisco 1926.  How do I make this work? Any advise?
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I am getting error 1m ipv4 tcp listen drops
"the number of TCP listen socket drops during the last minute"
Last night i tried to enables https on server with following steps
Added virtual host file but i reverted the changes.
I also executed the following commands: is it efected something on server.
sudo iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPTED
sudo lsof -iTCP -sTCP:LISTEN -P
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I'm sure this is simple, but I can't remember and I don't have time to figure it out, so...

I have a Windows 10 "All In One" lenovo computer.

The PC needs to connect to a small personal NAS via Ethernet, AND, the only way it can get Internet is Via Wireless.

The PC has both wireless and Standard RJ45...

I just can't remember how to do both at the same time.

Or, am I over thinking things: Just set a common IP for the RJ45 and the NAS , and then connect the wireless and I'm done...

Just not sure, and when I get there to set it up, it'll be too late to figure it out.

Thanks!
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I have a law firm client who has a network for his suite of offices covering a whole floor, 192.168.101.x  The firm has two open offices so they leased them to a different attorney and his paralegal.  The lease included 'internet'. Because the main law firm has ample (100x30) capacity (and a limited budget) I tapped the network (as though it were WAN) into a little netgear wifi router (creating 10.1.10.x).  All this worked fine. Because of the double NAT, the 10.1.10.x network has slightly increased latency but it is negligible.

Last week the 10.1.10.x attorney's paralegal contacted me saying that the lease was supposed to include access to the firm's printer/copier/scanning systems (Ricoh, running Nuance software). It was easy enough to create credentials for them to Copy, and I set up a scanning protocol that uploaded their PDF's to BOX.COM. But they want to print large jobs on the Ricoh printers (192.168.101.203 and 192.168.101.205 - everything on the big law firm is Static IP with MAC-ID).

How do I create a printer path on the 10.1.10.x network (two machines, paralegal is Win10, attorney is Mac, both current rev) to 192.168.101.203 and 192.168.101.205?
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I tried the below code and it showing output like SSH-2.0-OpenSSH_5.3 that means connected i hope.

 declare c  utl_tcp.connection;  -- TCP/IP connection to the Web server ret_val pls_integer;
 BEGIN c := utl_tcp.open_connection(remote_host => 'ftp.******.******.com'
                                   ,remote_port =>  21 ,charset => 'US7ASCII' --                              
                                   ,wallet_path     => '****************' --                              
                                   ,wallet_password => '**********' );  -- open connection
--  ret_val := utl_tcp.write_line(c, 'GET / HTTP/1.0');    -- send HTTP request
ret_val := utl_tcp.write_line(c);
BEGIN LOOP dbms_output.put_line(utl_tcp.get_line(c, TRUE));  -- read result
 END LOOP;
EXCEPTION
WHEN utl_tcp.end_of_input THEN NULL; -- end of input
END;
utl_tcp.close_connection(c);
END;
/
Could someone help me on next steps on How to open and read the .csv file present in SFTP/FTP server and load it into Oracle DB table ?
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We have a TCP/IP interface between a Millennium SPA POS system and Oracle Opera PMS system at our Hotel. There are a total of 8 interfaces and 7 of them have no issues. This specific one keeps disconnecting on the POS side. I have a packet capture that shows all traffic over the specified port and it looks like every 15 minutes exactly the interface disconnects.  On the POS side, we get an error message a pop up that must be clicked. Once you click ok on the pop up, the systems immediately automatically reconnect with out issue. As far as i can tell there is zero traffic unless someone is actually sending a transaction across. There is absolutely no keep alive being sent as far as i can tell.

I have attached a packet capture here.

I have not dealt with these serial/ip interfaces very often and dont really know what i am looking for in the packet capture. But it does look like the PMS system is sending a RST packet which from what i am reading terminates the connection.  Can anyone confirm this is what is going on based on the attached packet capture? I appreciate any assistance here. We have been battling this for 2 weeks now and both sides vendors are telling us it is the other sides problem.

port5010-traffic.pcapng
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Cloud based application having issues with ldaps bind to our Domain Controller in DMZ.
The application vendor is seeing the follwoing log entries on their side:
           [7:Public User][1024:application notice][R] (:) - Unable to bind to the LDAP server.

Based on this they have taken a wireshark capture and seen the following sequence of packets:-
Source -> destination (DC)   TCP    49662->636 [ACK] Seq=805 Ack=12910
Source -> destination (DC)   TLSv1  Application data
Source -> destination (DC)   TLSv1  Encrypted Alert
Source -> destination (DC)   TCP    49662->636 [FIN, ACK] Seq=927 Ack=12910
destination (DC) -> Source   TCP    636->49662 [ACK] Seq=12910 Ack=928
destination (DC) -> Source   TCP    636->49662 [RST,ACK] Seq=12910 Ack=928

They are saying that the reason packet analyser highlights the [RST, ACT] packets in red is because after the connection closure by Cloud Application server (source) [FIN, ACK] , server is expecting a final [FIN, ACK] from Domain Controller  (destination) but [RST, ACK] arrives instead. And thus they believe that it could be a issue with the Domain Controller.

Is this claim correct?
What can we do to troubleshoot this further?
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Windows 10 Pro machine with a USB 4G card changes the TCP/IP v4 settings to a blank IP address when connecting to the mobile network. If I change this back to dhcp as soon as I connect again it reverts back. This is the second machine I have had this problem on and cannot find a solution.
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I am receiving intermittent issues on a client server. After a while, users cannot access the internet or internal servers. Unfortunately, I am not on site and only have access to the logs as we need to restart the server before I can get there to minimise down time for all users.

Once the server is restarted, all users can access the internet/internal servers/share drives etc.

This has only come up over the couple of months randomly. Previously the DNS servers on the server had another IP which is the virtual server NIC (nic 2) and the TCP/IP V4 DNS had 127.0.0.1. The 169.x.x.x has been removed and the 127.0.0.1 has been changed to 192.168.1.1.

Would really appreciate what else I should be looking at as this has me stumped. Are there any ports on the firewall that need to explicitly be open?

The errors at the times of the issue commencing is Netlogon error 5774 entries. I have copied one below however have slightly changed the DNS record of the internal domain name. The IP Address 192.168.1.1 is the Server 2012 R2 DC. It is the only one on the network.

The dynamic registration of the DNS record 'DomainDnsZones.DOMAINNAME.local. 600 IN A 192.168.1.1' failed on the following DNS server:  

DNS server IP address: 192.168.1.1
Returned Response Code (RCODE): 0
Returned Status Code: 10054  

For computers and users to locate this domain controller, this record must be registered in DNS.  

USER ACTION  
Determine what might have caused this failure, …
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Need to know about vpn services,vpn name and there related circuit id function?
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Ethernet and T1 service-
How they are related to CLLI?
Is there any link between switch and service wire center CLLI?
What are LATA? How it used in modern communication?
Thanks
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I have a kernel module, in which :

It changes the saddr field of outgoing packets and fixes it back(daddr) in incomming packets ...
I'm calculating new checksum for ip and tcp headers ...
So in client side I change ip - server side receives it(SYN packet) and sends (SYN-ACK) packet - but client side - sends (Reset) packets and trying again to process tcp handshake ...

I've seen to another kernel-module examples - dnat/snat - my code is analogical ? My be ebtables make my hooks to work incorrect ?

Interfaces: eth0 - XXX.XXX.XXX.1 eth0:0(alias) - XXX.XXX.XXX.2
Client (original ip XX.XX.XX.1(eth0) and XX.XX.XX.2(eth0:0))
                                                               SERVER (ip YY.YY.YY.YY)

     USER-SPACE app creates tcp-socket and connects to (YY.YY.YY.YY)

     1) 
     TCP (SYN) -----------(packet ip XX.XX.XX.1-YY.YY.YY.YY[ip.sum1, tcp.sum1] )----->
     NF_INET_POST_ROUTING ( ip XX.XX.XX.2-YY.YY.YY.YY[ip.sum2, tcp.sum2] )
     ================================================================================>


     2)
     <-------TCP (SYN ACK) ------(packet ip YY.YY.YY.YY-XX.XX.XX.2[ip.sum1, tcp.sum1])
     NF_INET_PRE_ROUTING ( ip YY.YY.YY.YY-XX.XX.XX.1[ip.sum2, tcp.sum2] )
     <================================================================================


     3)

     TCP (RST) - against TCP (ACK) - that is the question ....
     ================================================================================>

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/* 

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I have two questions about "under the hood" processes executed by Webrequest and the getresponse method.

1) I have noticed while packet capturing that, when doing a webrequest with a payload, packets starting a TCP/IP connection are sent and received *before* the getresponse method?  I would have expected the payload to be cached and sent only when the getresponse was called?

2) I have a webrequest case that has me puzzled.  It is an HTTPS URI.  All proceeds as expected (443 TCP/IP connection made before getresponse called) until the getresponse is called.  When that happens, the process attempts to create a new TCP/IP connection to the server, this one being on port 80 (not HTTPS).  Since the request is not HTTPS, the server ignores it and the process times out with a "no response from server".

What would cause the getresponse method to spawn a new connection, and why would it send it via HTTP when the original connection was made via HTTPS?  The certificate for the server is valid, and I have tried turning off the check-certificate functionality.

Thanks for any insight on both questions.

Bryan Hunt
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Need to access an application on a company Windows Server from outside using an iPad, Server has a private Static IP (10.x.x.x). The office router has Public Static IP interface. How can I access the server from outside on an iPad? Can I access the server using a public IP is this situation? Please advise.
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I have a Juniper QFX. My infosec team wants me to disable the TCP timestamp as per the ID: 80091

Now I know how to disable ICMP timestamps, but not the TCP timestamps. And I don't want to disable it for the whole QFX. If it can be done for an interface, that will be awesome.

Any help will be appreciated.
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Hello , does anyone knwo how to transfer iPhone contacts and messages to Android phone without any loss ? i've tried many ways to transfer them , but always fail ,and i don't how to connect the differen operation phones ,
Pls
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Hi Networking Gurus,
Sorry if i sound stupid but i am very new to networking.My application work as ESME  for the smsc  and it seems that recently we observing huge delay in ack of submitted  message or ack not coming at all.I can see in netstat output of linux send queue is increasing hugely.Taken a tcpdump in which i can  see to much [TCP Dup ACK],[TCP Out-Of-Order],[TCP Retransmission]

Also i see in wireshark
Smsc send mesg with seq:1 ACK:1 Len: 51 -->"213.132.40.140 -> 192.168.40.8 SMPP SMPP Deliver_sm"
but we reply by
 192.168.40.8 -> 213.132.40.140 TCP 42758 > dynamid [ACK] Seq=4141 Ack=52 Win=128 Len=0
That means are we losing frames.Pls help
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TCP/IP

11K

Solutions

17K

Contributors

Transmission Control Protocol/Internet Protocol (TCP/IP) is the set of networking protocols that define end-to-end connectivity specifying how data should be packeted, addressed, transmitted, routed and received at the destination. This functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved.