ping from different node

[selvialagar]

i'm doing icmp implementation in vc++.net 2003.when i receive icmp packets, it comes from the different system..what is the reason?is it correct?

[Plater]

The icmp packet should be coming from someone else yes.
Did you look at the docs on icmp?

[selvialagar]

Reply comes from the node different from what i am expected.

When i gave ping 172.20.20.23, reply comes from other system...is it correct

or not?

[Plater]

Well they get changed.
If a series of devices are connected, where lowercase is a computer and uppercase are routers:

a - B - C - d

If you ping d from a, your icmp response will come from B, since each packet gets stopped on the way I believe.
I *think* this is what you are seeing. Another explanation could be a byte order mistake, like you think you're pinging one address but really it's different one due to a byte order mistake?

[selvialagar]

Thanks for your reply..

iphe =Dns::Resolve(s); 
		Console::WriteLine(S"Host Entry :{0}",iphe->HostName->ToString()); 
		IPAddress* ipad = __try_cast<IPAddress*>(iphe->AddressList[0]);

		Console::WriteLine(S"IP Address : {0}",ipad->ToString()); 
		IPEndPoint* ipe = new IPEndPoint(ipad,80);
EndPoint* senderRemote = __try_cast<EndPoint*>(ipe);
		Console::WriteLine(S"Sender Remote :{0}",senderRemote->ToString());  

DateTime dt=DateTime::Now;	
		int iRet;
		st->SetSocketOption(SocketOptionLevel::Socket,SocketOptionName::IpTimeToLive,32);
		st->SetSocketOption(SocketOptionLevel::Socket,SocketOptionName::SendTimeout,500000);
Byte RecvByte[]=new Byte[256]; 
			  iRet=st->ReceiveFrom(RecvByte,RecvByte->Length,SocketFlags::None,&senderRemote);
     	      TimeSpan ts=DateTime::Now -dt;
			if(iRet==-1)
			{
					Console::WriteLine(S"Error Getting Data"); 
			}
			Console::WriteLine(S"Reply From :IP={0,-20} TTL={1,-10}  Time={2,3}ms",senderRemote->ToString(),RecvByte[8].ToString(),ts.Milliseconds.ToString());

this is my code..here before i got reply from the destination,the IP address is printed correctly.But after i getting reply the destination address has changed..

My assumption is.. the packet from the destination comes through different node..the actual reply is from the actual destination..


Another problem is i am getting very late response...even i ping my node response is very late.what is the reason for that?can i minimize the response time?

i'm awaiting for your reply..

[Plater]

What happens when you ping with a regular ping command in windows?
Or use the actual ping implementation in .NET?

If you do a traceroute to that same address, does the "next hop" have the ip address you are seeing on the return of YOUR ping?

[selvialagar]

In Regular ping commad, the response comes immediatly.I used the actual ping implementaion.

When i checked the IP datagram header,the TTL always 128.If the packet comes from the different node, TTL field might be decremented by 1 or 2.but in my case the TTL always 128.

Here is my output of my program.I displayed first 60 bytes of the returning IP packet.when i send ping 172.20.20.24,th e reply comes from 172.20.20.6 which is the server.Sometime s the reply comes from other IP address

IP Address : 172.20.20.24

Data Sending to 172.20.20.24:80

Reply From :IP=172.20.20.6 :0 TTL=128 Time=213ms

69 0 0 60 148 184 0 0 128 1 37 190 172 20 20 6 172 20 20 28 0 0 65 94 2 0 20 0 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 65 66 67 68 69 70 71 72 73
Data Sending to 172.20.20.24:80

Reply From :IP=172.20.20.6 :0 TTL=128 Time=213ms
69 0 0 60 148 186 0 0 128 1 37 188 172 20 20 6 172 20 20 28 0 0 64 94 2 0 21 0 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 65 66 67 68 69 70 71 72 73
Data Sending to 172.20.20.24:80

Reply From :IP=172.20.20.6 :0 TTL=128 Time=758ms
69 0 0 60 244 161 0 0 128 1 197 212 172 20 20 6 172 20 20 28 0 0 63 94 2 0 22 0 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 65 66 67 68 69 70 71 72 73
Data Sending to 172.20.20.24:80

Reply From :IP=172.20.20.6 :0 TTL=128 Time= 71ms
69 0 0 60 244 163 0 0 128 1 197 210 172 20 20 6 172 20 20 28 0 0 62 94 2 0 23 0 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 65 66 67 68 69 70 71 72 73