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Peter Fabian from ottawa facing Networking problem

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#1 peterfabian


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Posted 29 September 2012 - 01:12 AM


I want to share a query with you all about the networking issue:

There are 2 hosts A and B & two switch named as Switch C and Switch D and a Router E
Host A is part of Vlan 100 of Switch C
Host B is part of Vlan 200 of switch D
And both Switch C and switch D are connected to Router E

Can someone please answer me, what all packets will get exchanged between the Host A and Host B if we start a ping from Host A to Host B


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#2 simonhud


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Posted 29 September 2012 - 02:45 AM

hello Peter Fabian from ottawa,

Since your attempting a ping from A ->B ICMP protocol which runs over IP protocol, Layer 3 communication),for that to happen the host device would need to know the
1) Source and destination IP info
2) Source and destination mac-address

Assuming the source has the ip info and its own mac address but destination info is unavailable, the host will send an Arp broadcast to all hosts.
The destination host will then respond to the arp broadcast with its source mac-address.
Once the host receives this packet, now it has all info to packetize and send it and the destination will response since all info is available to it in the packet.

To summarize, the ping has worked on layer 3 using layer 2 and layer 1 communication.

What Ping can tell you:-
Ping places a unique sequence number on each packet it transmits, and reports which sequence numbers it receives back. Thus, you can determine if packets have been dropped, duplicated, or reordered.
Ping checksums each packet it exchanges. You can detect some forms of damaged packets.
Ping places a timestamp in each packet, which is echoed back and can easily be used to compute how long each packet exchange took - the Round Trip Time (RTT).
Ping reports other ICMP messages that might otherwise get buried in the system software. It reports, for example, if a router is declaring the target host unreachable.

#3 Sneakycyber


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Posted 29 September 2012 - 06:10 AM

To confuse you a bit more If the devices are on the same LAN, same subnet, with no security on interface vlan100C or vlan200D and the router is not a configured firewall and the hosts are not blocking icmp request via thier firewall u will get an acknowlegemnt. If you give us the make and model of your switches, security setting, and or what problem/s you are having we can help more. Do u want to be able to ping? are you trying to filter ports or protocols on your switches? Create subnets?

Edited: grammer, punctuation (I think its better)

Edited by Sneakycyber, 29 September 2012 - 06:12 AM.

Chad Mockensturm 
Network Engineer
Certified CompTia Network +, A +

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