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Why can I ping, but not

I have to ping it like this


Is it because of DNS record of NASA?

Also how does a ping response time improve?

time 44 msec
time 10 msec

edit: new query If I am correct, isnt WWW one level below the nasa node in a DNS tree? Then as most of the addresses we use in the browser are with WWW, does that mean that the A record is with the WWW node or with the nasa node or with both?

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migrated from Jul 14 '11 at 13:24

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Every ping packet may take a different time to reach its destination and come back. This depends on the load of the hops on its way. – slhck Jul 14 '11 at 13:30
Ping times depend more on the route taken than load in my experience. Routers may send packets to their destination by different routes at different times. – CarlF Jul 14 '11 at 13:37
Did any of you who actually picked Tom Frey's answer actually try pinging (minus the www) or do an NSLOOKUP? That answer is so wrong. The same firewall he says is dropping them, responds to ping It is because it is lacking a DNS A record for – KCotreau Jul 14 '11 at 15:35
up vote 27 down vote accepted

Because for some reason, they have not added a DNS "A record" for, so it does not resolve, and returns a host unknown. Most administrators do configure their DNS to respond to requests, especially for HTTP, to both the and You can ping though.

Although, not in this case, another reason would be if they chose to drop ICMP ping requests, which is configured on a firewall or router.

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One more thing: In general, it is usually ignorance that leads to this situation, but I find it strange that one of THE most technically-oriented agencies in the world would do this by accident. I can't think of their reason, but I sure hope for the last Shuttle in space right now, they did not overlook something so simple. – KCotreau Jul 14 '11 at 13:34
4 does have DNS records and resolves fine. It just doesn't have any addresses (A/AAAA records). It used to be relatively common for websites to be hosted on the www subdomain (similar to mail for mail servers, etc.) – grawity Jul 14 '11 at 14:01
Of course, I meant A records since we are talking about resolving to a host. Think" "Context" of the question please. – KCotreau Jul 14 '11 at 14:31
Also try pinging for comparison. It will also drop the requests. Also why does this answer get like 19 thumb-ups in 6 hours(!!) and my answer on… which is almost the same question (only difference here being the DNS the error) only gets one? ;D. Yes, I'm jelly :O – sinni800 Jul 14 '11 at 20:31
I didn't miss this, read my comment: (only difference here being the DNS the error). I know the sentence is messed up, sorry for that! – sinni800 Jul 14 '11 at 20:42
$ host mail is handled by 10 mail is handled by 10 mail is handled by 10 mail is handled by 10 mail is handled by 10 mail is handled by 10

So you can send mail to, but there is no machine to connect to.

$ host is an alias for is an alias for is an alias for has address has address

So when you ping you are really pinging an Akamai machine via several indirections.

The NASA mail server is run by NASA directly. It doesn't reply to ping requests:

$ host has address
$ whois
National Aeronautics and Space Administration NETBLK-NSI (NET-198-116-0-0-1) -
$ ping
PING ( 56(84) bytes of data.
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NASA's firewall is probably dropping ICMP (ping) packets, thus your pings will time out. The largest factor of latency is physical distance, the further away your target, the bigger the latency (speed of light is the top limiting factor)

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but why is there is an improvement of performance between successive runs of ping to same host? – zcqwevb Jul 14 '11 at 13:32
it increase and decrease, each packet you send doesn't necessarily take the same route to reach the final destination. Routes are dynamic and constantly changing to avoid bottle necks. – squarebear Jul 14 '11 at 13:40
Also, routers consider ICMP low priority, thus depending on the router's load, they may schedule to reply to ICMP at a later time once higher priority packets have been processed – TJF Jul 14 '11 at 14:37
my default gw is my router I guess, so ARP request wont be needed as I already did some ping's before. – zcqwevb Jul 14 '11 at 15:48
-1: I can ping (hosted in But doesn't resolve, so no address, so no packet sent. Nothing for a firewall to drop. – Richard Jul 14 '11 at 16:04

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