Pinging same address multiple times

icmpnetworkingping

I am just wondering if it is possible to ping the same ip address from the same source multiple times (ie fast enough so they get pipelined) and still get a valid result. By a valid result, I mean that you record a valid round trip time for all ping packets.

What I am getting at is that is there a possibility that packets could get mixed so the receiver does not know which packet is which, and thus the recorded round trip time not be accurate. Are there any mechanisms with ICMP or IP that number ping packets so they are distinguishable from the other pings to the same address.

Best Answer

In the ICMP header there is an Identifier and a Sequence number, used for exactly this purpose. They occupy bytes 5-7.

See RFC792 page 15:

The identifier and sequence number may be used by the echo sender to aid in matching the replies with the requests. For example, the identifier might be used like a port in TCP or UDP to identify a session, and the sequence number might be incremented on each request sent. The destination returns these same values in the reply.

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Ping replacement that shows real time

You can add timestamps using perl like this:

ping 127.0.0.1 | perl -pe 'BEGIN {use POSIX;} print strftime("%Y-%m-%d %H:%M:%S ", localtime)'

Intermittent high ping/latency problem

WISP? Meaning Wireless ISP? If so, there's your likely answer. Wireless is unreliable and you're seeing proof of that.

You can't really fix it because your medium (the atmosphere) is really awful for transmitting data. First because air is a hub instead of a switch so you're sharing it with anybody around you and colliding packets, second because CSMA/CA is slower than CSMA/CD, third because wireless is generally half-duplex instead of full duplex, and fourth because there are orders of magnitude higher interference through the air versus copper. [Microwaves, for example, operate at the same wavelength as 802.11b/g... but the microwave operates at about 500-1000 Watts vs your wireless antenna's 100 milliwatts. Microwaves are shielded, but shielding isn't perfect and microwaves aren't regulated by the FCC so it's not illegal if they cause interference.] Plus the fact that you're going through 10+ hops just to get to the Internet. That can't be helping, particularly if there's any NAT or firewalling going on.

As @dbasnett says, the traceroute ping latency to a given host only indicates the state of the entire network in between the interfaces taken as a whole at that point in time. That's why the response times go down sometimes. They're spiky because the network is unreliable. Your pathping looks good because it is running a large number of queries instead of just 3 that tracert is running. So pathping shows you what the network is doing over a period of 325 seconds (by default), and tracert is showing you what 3 packets per hop on the network are doing.

Best Answer

Related Solutions

Ping replacement that shows real time

Intermittent high ping/latency problem

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