Factors Affecting Internet Connectivity

Here is a brief discussion of the various factors that can affect connectivity on the Internet.

Packet loss: If there is any router or line overload between any two points on the Internet, this will show up as a very slow speed of data transfer. The 'ping' command will usually show you if there is any noticeable packet loss. From the UNIX shell on any a2i machine, type 'ping -s <hostname>', wait a few seconds, then hit control-C to abort the ping and print packet loss statistics. Ideal is 0% packet loss (no packets lost). More than about 5% packet loss is not good.
Web server overload: If a web server responds very slowly, this is usually caused either by packet loss (above), or due to the web server itself being overloaded.
Routing changes: When any path on the Internet goes down, backbone routers normally try to find alternative paths automatically. While such a path change is occurring there will be a temporary loss of connectivity for a minute or two.
DNS, forward resolution: When you initiate a connection to any location by name, the first step is always to convert that name into an IP address. This is done by querying a DNS server. That DNS server may need to query other DNS servers, and those may need to query yet more DNS servers. If any DNS server in the chain is not properly responding, there will be a delay before conversion is complete. DNS queries can also hang for a long time. Once the conection is completed, there should be no more delays (until you connect to another location).
DNS, reverse resolution: When you connect to a remote location, the remote host normally knows you by IP address. To record the connection in its log files, the remote host will query a DNS server to convert your IP address into a domain name. As with forward resolution (above), there may be a delay in this conversion. Many sites on the Internet have misconfigured reverse DNS resolution, and users at such sites may encounter delays when connecting to other sites. Once the connection is complete there should be no more delays. Failure of DNS reverse resolution is the most common reason for mysterious problems doing telnet, ftp, or web accesses. To see if the DNS reverse resolution for your host is misconfigured, telnet to rahul.net and try to log in as the user 'id'. (No password is needed.) If you manage to log in, you will see a line like this:
```
      id       ttyp3   Nov 20 10:12   (some.host.name)
```
and you will be automatically logged out. In place of 'some.host.name' you should see the name of your own host. If you don't see a name, but you see an IP address (four numbers separated by dots), it means your DNS reverse resolution is misconfigured and you may encounter connectivity problems. Contact your service provider and ask for a fix. If the login attempt hangs, it also usually indicates the same problem.

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