How Hosts Find Their Destination
Mar 4, 2011
I have several Cisco switches connecting our network. Switch N connects to the gateway, Switches Y & Z connect to some hosts. Switch N connects to Y and Y connects to Z. Assume our gateway IP is a Class B address with a netmask of 255.255.254.0 and all the hosts attached on switches Y & Z have static IP addresses assigned to them. This gateway connects to the internet.In addition to this IP address, some of the hosts also have a second IP address assigned to the same NIC. This IP is Class A (10.0.###.###) and have a netmask of 255.255.0.0 A second gateway address is not defined.
The hosts that have 2 IP's bound to their nic, use the 10. address to communicate with each other. (Programs running on the hosts are specifically configured to use 10. address).I have several questions regarding this setup:
1) Assume Host has only 1 IP (Class B) - if the destination is on the same network, does the host system send the packet to the gateway first to find the destination on the network or does the host send a "where are u" packet to the broadcast address to find the destination?
2) Assume Host as 2 IPs (Class A & B) - if the destination is a 10. address, how does the host go about finding it?
Since there is no Gateway defined for the Class A address, does the host simply send out a packet to the broadcast address for the Class A network? or does it go to the gateway defined in the Class B network as it was defined first (i'm assuming primary connection)
3) Assume Switch N's connection to Switch Y is disabled - how will this affect communication between hosts on Switches Y & Z that have a 10. IP trying to share data with each other, using the 10. Address. If the answer is this should not affect it, what additional circumstances are required that may cause the systems with a 10. address to be unable to communicate when the connection from Switch Y to N is terminated?]
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Jul 7, 2011
I need a tool to find all the hosts connected on my network. I need something that will tell me the MAC and host type/name. I ran an IP Address tracker and got all the IPs in use, but that doesn't tell much beyond the IP address. Don't really need to do a full in-depth nmap port scan. My concern about using nmap is it can bog down a router...Although I can't say for sure if there are ways to scale the scan back in nmap so it won't cause any issues?
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May 23, 2012
Do you have any suggest for network scanning software?Something who can find IP address and hosts in the network?
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Jul 24, 2011
I have a situation which requires some non best practice stuff to be done. There is a box behind an ASA that has a lot of code that references public DNS names and therefore needs access to itself and a number of other boxes on the same subnet via the public DNS names (that obviously resolve to public IPs). This traffic is dropped on some pretty fundamental ASA characteristics.I know this isn't really ideal, and it should be handled by DNS nstead, but I'm in somewhat of a bind and need to know if the ASA can allow this traffic.I figure I could match the traffic and exempt it from state-checking and that would probably work, but it's not a very graceful solution.
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Feb 27, 2013
I configured dns on the router on this command ip name-server 4.2.2.2when i tried to ping www.google.com showing no valid routeTranslating "www.google.com"...domain server (4.2.2.2) [OK]Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 2800:3F0:4001:807::1013, timeout is 2 seconds:
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May 12, 2012
i have my 9 computers 1 prolink modem/router h5200 and tplink switch...for 3 months my connection is quite good..but in the 4th month its starting to Reply 192.168.1.1 Destination net Unreachable..i called up a technician from the network..He changed my modem/router with the same model and it runs for an hour... 5-6 hrs..the problem starts again it begins to ping Reply 192.168.1.1 Destination net Unreachable...b4 my TCP/IP i configured it automatically but now i try to put it manually...my modem/router starts with 192.168.1.1 my first unit starts in 192.168.1.2 and so on.
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Aug 2, 2012
a) one router with two ethernet interfaces (LANs) and a serial interface. The serial interface is connected to the internet, dynamic nat is used for hosts in the two lans. A web server has a private address of 172.168.50.10 and it is being translated to the internet with serial's interface 68.32.x.x (public ip) with static nat. Clients in the internet type the public address to access the web server.
b)Problem: clients inside the LANs cannot access the web server by typing the public address, they use the server's private address instead, this create a problem with DNS static entries in the HOSTS file in the OS. It is a test server and is only available to authenticated users (lock and key ACLs), so no need to make a real DNS record. The entry in the HOSTS file points to the public address.
c)Question: how can a create a route map to change the public address in the HOST file to the private address of the test web server everytime a user in the LANs type the domain name.
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Aug 3, 2011
Test a destination port if it blocked or not by my ISP
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Mar 13, 2012
Here is a snippet from "show ip cache flow", from a border router of our network; [code] To clarify, Gi0/3 faces our customers, Fa1/0 faces a transit provider. These results have come from configuring "ip flow egress" on Fa1/0, facing the transit provider. 1.2.3.4 is a static IP we have assigned a customer. I know this customer has a firewall terminating this connection so I want to understand the cache flow results on this route. Why is the destination address an RFC1918 address? Is it possible that the customers firewall is trying to connect to these addresses, the flow gets as far as this border router, and drops? I assume that to be false, and only successfully initiated flows are recorded?
Also, looking at those figures it's IP protocol 0x11 which is UDP (17) and source port 62023 to destination port 161. 161 is SNMP? Without asking the customer what they are doing I suppose I can never know at that level, but I'm really more interested in why these flows are showing at all, when 192.168.1.0/24 isn't in this routers FIB?
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Feb 25, 2012
I am trying to perform destination NAT through a VPN tunnel.my scenario traffic coming from 172.29.11.135 needs to connect to address 192.168.1.1 from the source device traffic will have a source IP address of 172.29.11.135 destination will be 172.30.14.1 traffic will hit the asa 5510 and the traffic source will stay as 172.29.11.135 but the destination needs to change to 192.168.1.1.
I have tried the different types of NAT but been unsucessful with all. My VPN tunnel will connect if the destination address does not change (NAT Exemption used). This scenario is even possible on Cisco devices. I have seen discussion that NAT the source address but not the destination address.
example config
access-list FROM_INTERNET extended permit esp any any
access-list FROM_INTERNET extended permit ah any any
access-list FROM_INTERNET extended permit gre any any
access-list FROM_INSIDE extended permit ip host 172.29.11.135 host 172.30.14.1
access-list VPN-TUNNEL extended permit ip host 172.29.11.135 host 192.168.1.1
**I have left other config statements off as the NAT config used previous has not worked and the VPN tunnel does build when using NAT exempt.
**All ACL have been applied in the inbound direction on the respective interfaces. Two static routes have been applied to the FW directing inside traffic inbound and all unknown traffic outbound. I have not defined a specific static roule for the VPN traffic allowing the default static to perform that function.
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Jul 15, 2012
i have a situation where i have a deployed asa5505 running 8.4.1.The client has an existing mail server that is located on their lan and has Port Nat's configured for the normal mail ports, 25,110,993,587 etc.
This works fine for mail inbound and for any user popping mail off the server externally or visiting the webmail interface from outside the network.However when users inside the LAN try to connect through the ASA back inbound to the IP on the External Interface of the ASA they are unable to do so.
One solution i came up with is Split DNS. and well this works it rely's on the users not changing their dns servers.I was wondering if it's possible to do some sort of NAT that rewrites traffic destined for the above ports on the external IP to the Internal LAN Ip instead.
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Dec 16, 2011
Im running 10 units of computers, anyhow my server has no internet connection, the other 9 units has net connection,when i ping the diagnosis is destination host unreachable.I'm using windows XP.
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Dec 15, 2012
My old router recently died and my ISP was kind enough to offer this Thomson one free. But ever since I got it, my PCs cant see each other on the homegroup. They can all get onto the internet - and by using programs like Dropbox or Teamviewer I can share info from one to the other- but I'd like to get my homegroup working again, Both my PCs are running Win 7, connecting wirelessly to the network. When trying to tracert from one to the other it gives this message: Tracing route to GLaptop.lan [192.168.1.79] over a maximum of 30 hops: 1 GDesktop.lan [192.168.1.82] reports: Destination host unreachable. The problem persists when firewalls on both PCs are disabled, and I've attempted to delete the homegroup on both PCs and re-create it.
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Mar 31, 2011
how to get details of any destination location through google earth?
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May 11, 2012
My internet connection started to disconnect after an office mate used my PC. I thought it was just the cables but it's not. I pinged my ip address and its okay (sent=4; received=4). But when i ping Yahoo! and other websites, it said that "Destination host unreachable" (sent=4;received=0;lost=4;100% loss). What should I do to make my connection okay? I didn't ask assistance from our IT personnel bcoz they said if i want to reconnect/reinstall connection, I have to get an approved request from our bosses. And I don't like being asked bcoz they are like tyrant bosses.
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Jan 28, 2013
I wanted to know how, if there are any script which will send an alert once a file has reached a destination over an TCP network.
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Jun 17, 2013
One of end costumers is trying to configure IP Accounting on 7206 running version 12.4(4)XD8,The issue we are having is that while the physical interface is up (the sub interface is part of a metro line which is directly connected) we dont see packets being accounted if the destination IP is down.
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Apr 16, 2012
I have a internal subnet 192.168.3.0/24 sitting behind an ASA firewal 8.2 and would behind accessing to web server 192.168.11.54 which sits behind the outside interface of the ASA firewall.The access would be like this:
1) 192.168.3.0/24 will be accesing to the web server http://192.168.11.54
2) We would like to translate the source 192.168.3.0/24 to the firewall outside IP address
3) We would like to translate the destination web server 192.168.11.54 to 202.90.197.146 as well
How to perform this simultaneous source and destnation address translation in ASA firewall 8.2? Could this be done in ASA firewall 8.2?
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Jun 11, 2013
I need configure destination NAT in my ASA 8.2 version only for a specific origin.
Today, the network 10.84.25.0/24 access the web server with IP 172.17.3.150, i need Nat the IP 172.17.3.150 to 10.96.202.10 only for
10.84.25.0/24 network.
How i can configure this in 8.2 version?
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Dec 9, 2011
How to get into the ip hosts on vista?
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May 7, 2011
I have 2 brand new systems, a desktop running Windows 7 Pro connected with a had line, and a laptop running Windows 7 Home Premium connected wirelessly. Both can access the router, both can access the internet, both can be pinged from the router. However, they absolutely cannot see each other on the network. If I try to ping by name, the addresses don't resolve. If I try to ping by IP, I get either no reply or the "destination host unreachable."I've disabled firewall completely on both. I've double, triple, quadruple checked all sharing settings (network discovery is enabled on both, sharing enabled everywhere, etc. etc.). I've tried disabling all other network adapters on the laptop, no difference. I've tried all of the online tips about repairing winsock.
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Jan 23, 2012
im lookin to establish a a multiple L2L ips tunnels ( one tunnel for each subnet) from my cisco asa 5510 to the same destination. should the cisco asa capable of this ?
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Apr 2, 2013
I have Cisco RV180. I can not set static route with destination to all IPs (0.0.0.0/0.0.0.0). It always shows errors. It asked me to input non zero number. I can do this on Cisco RV042 without any problem.
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Apr 25, 2013
i have a general Question regarding buildings SA´s between two peers.Can I establish more than one SA between two Peers with the same IP Address?Actually I have 3 DMVPN´s running in parallel in different VRF´s using the same SA.They have all the same IPSEC encryption AES256.Now I need to reduce the encryption to 3DES in one of the three DMVPN´s.Is that possible or do I need a differnet IP Address so that the SA Pair is unique?Thats how I stared, with a Phase 2 failure that it is not acceptable.
crypto keyring preshared
pre-shared-key address x.x.x.x key ....ncvnbxcnbLsaYiKtxc4ex4U99Tn...
pre-shared-key address x.x.x.x key ....qerqwerJLsaYiKtxc4ex4U99Tn...
pre-shared-key address 0.0.0.0 0.0.0.0 key ....JLsaYiKtxewrc4ex4U99Tn...
[code]....
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Feb 12, 2013
1. the LAN network (multiple subnets) needs to access server 1(outside) - NAT translation works fine no issues
2. a subnet from the LAN e.g SUB-TEST currently acceses server1 but I need to change it to access TESTserver 2 (outside) instead (temporarily)
I dont want to change the original setup .I am trying to implement NAT on the local router such that
- any traffic from SUB-TEST that enters the inside interface and is going to Server1 then change the destination and NAT it to TESTServer 2
- all other LAN traffic is allowed to go to server 1.
i am using a 1941 router for this
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May 25, 2011
The Cisco ASDM or the event manager show wrong source/destination for teardown tcp messages:In this example the communication is an ssh session;from 1.1.1.1 -> 2.2.2.2 ssh and the connection is reseted by 2.2.2.2
The message build outbound is correct, i.e. source is 1.1.1.1 (message id is 302013)
But the teardown is incorrect, i.e. source for the connection is 2.2.2.2 which is definitely not true (message id is 302014)
Also there seems to be a documentation bug in syslog messages for ASA 8.4 since the message for the teardown 302014 is gone!
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Apr 14, 2013
I know that 255.255.255.255 is the broadcast address to send message to all hosts that are in LAN. what i want here is, i want to send a mail to all hosts using this address.
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Aug 1, 2011
I am working on a Perl script to be ran on our different subnets to see what hosts are down (and make the assumption that if the host is down the IP address is free to be used). This is not being ran on a Linux system, so I can't use grep to filter out everything except down hosts. I know there are modules for Nmap that would make this task easier, but my plan is to install Nmap to our network monitoring server, compile the script for Windows, and have it create the report for what addresses are down. I don't want each person running the script to have to have all the modules installed, etc. Or can you compile the script with the modules in it?
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Jun 7, 2011
We have a modified hosts file on each of the computers here at work. This way we can have multi servers, in multi locations that can all be used by everyone for email & our finance program.However, there is one user who the hosts file keeps disappearing. Over the last 2 days it has disappeared 3 times (at least).The user has ran the symantec corp antivirus (at least a couple of times). All risks found have been quarentined and deleted, ran again and nothing found. Also ran Malwarebytes, which was clean. And ran ComboFix.At this point the hosts file has been fixed after running ComboFix.
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Mar 17, 2013
ping 10.0.0.1 -t give me destination host unreachable in the same time when i wright ping 192.168.1.1 -t it give me the correct reply but the net doesnt work
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Oct 17, 2011
when do we get Desteination host Unreachable and time to live exceeded while trying to ping .
From 10.1.1.1 icmp_seq=2 Destination Host Unreachable
From 10.1.1.1 icmp_seq=4 Destination Host Unreachable
From 10.1.1.1 icmp_seq=7 Destination Host Unreachable
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Aug 8, 2012
my WRT54G has been configured to block any and all incoming connections.continue to have disabled all port forwarding, port triggering, the DMZ, and QoS, via the applicable tabs under the [Applications & Gaming] Panel. The WRT54G continues to be configured to operate as a Gateway.No static routes are defined. The routing table show four entries, none of which are remarkable or match in anyway the partial address identified above.So I am under the impression that my WRT54G should be ignoring everything from the WAN-side.Even pinging the WAN-side of my router from the outside internet times out.My WRT54G ver 6 is at firmware level 1.02.8, which, as far as I can tell is the latest issued by Cisco.I am completely perplexed how such a connection is being established, and do not know if it is or has the potential of causing any harm. My own research indicates port 520 is typically used for RIP protocol, but I have almost zero knowledge of such.
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Apr 12, 2012
Cisco Linksys E3000
I have different types of network clients connecting to both bands of router (5 ghz and 2.4 ghz), and both bands set to WPA2 only. Everything has been set up and working for the past year with no problems.
Suddenly this morning, none of the 2.4 ghz clients can connect and get authenticated. When I attempt to ping them from a Windows 7 desktop connected by a LAN cable, I get Destination Host Unreachable.
The 5 ghz clients are fine and have had no problems. I tested this with the New iPad connected to the 5 ghz band.
Rebooted the E3000 router and the Comcast cable modem, then installed the newest firmware on the E3000 using the web access portal at 192.168.1.1, and still not working.
Changed the WPA2 Personal security mode for the 2.4 ghz band to WPA2 Personal/WPA Mixed Mode, and now all the clients are connected and authenticated and working OK, albeit slower.
What happened? And how can I fix this so I can change the security mode for the 2.4 ghz band back to WPA2 Personal?
P.S. The types of clients that connect to the 2.4 ghz band are 2 Windows 7 desktops, a Windows 7 laptop, and 5 Cisco Wireless N Internet Home Monitoring Cameras. The camera feeds have slowed down considerably using this Mixed mode.
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