Four types of internet connectivity

Dial-access modems

The operation of the dial-in access is simple. You connect to an ISP (Internet Service Provider) via dial modem. When you dial in you connect to the ISP as another user on their network. You use their lines to connect to the internet. The maximum data rate is 56kbit/sec but is restricted by the FCC to only 53kbit/sec. There are virtually no distance limitations, wherever a clear voice can be heard on a phone line you can dial in. One advantage of this service is that it is versatile, widely available but the disadvantage is that it is very slow by today’s standards. This connection would suit someone doing occasional browsing and checking e-mail. The service cost is ~$9-20 dollars a month.


DSL is a technology used by many major phone companies to bring high speed internet to your home with the existing phone lines inside your home. The maximum data rate that can be achieved with DSL is 8mbits/sec with ADSL (Asymmetric Digital Subscriber Line.) However, with VDSL (Very high bit rate Digital Subscriber Line) you can achieve up to 55mbits/sec. The main advantage of DSL is you can use your existing phone line at the same time you are on the internet. The disadvantage is that the speed is directly limited by distance from a central office. The type of user that would benefit from DSL is a person who wants high speed browsing, relatively fast downloads but who also is close to a central office. Approximate monthly costs range from $27.00 to $40.00.

Cable Modems

Cable internet is very fast and stable. Basically the network is around most residential and business areas. The cable internet (e.g. Roadrunner®) infrastructure is already there – mostly fiber optics in this area. This allows for a massive amount of bandwidth to flow through the cable system. The maximum speed able to be obtained over cable is 10mbits/sec as determined by the cable modem and service providers. The main advantage is always on high speed internet. A major disadvantage, in areas where the network throughput overall is low, is slow speed because it is a shared network. The type of user that would benefit from this connection would be someone wanting to play online games with low ping times, and enjoy high speed downloads. The approximate monthly cost is $30-$50 depending on the provider.

Satellite-based Internet Access

Satellite internet is very interesting, I personally have used it and it is conceptually a very good idea but the latency of the satellite can bring the good idea to a screeching halt. When you connect you either use a dial up modem (receive only internet) where you dial to a separate ISP, then you send out a request via dialup then a tunnel is created to your satellite provider so your upstream can communicate with the provider so the received information can be beamed to your house from the satellite. This whole process takes up to 800 milli-seconds! This is very unacceptable for everyday browsing, but the advantages to some people make the service worth it. The main advantage is for users who have no access to higher speed internet. The downstream is about 512kbit/sec which isn’t too bad. (I’ve achieved 150-200kbyte/sec with it) but it is unacceptable for the ping times. The main disadvantage is the sheer space between the satellite and your home and the provider takes time to beam info back. The type of user who would benefit from this technology would be someone in the middle of nowhere. The cost of the service varies; usually you can lease the equipment for $99 dollars a month including service. Or you can buy the equipment for about $500-$600 dollars.

IPtables Port Redirection

Here’s the command-by-command reference of how to forward TCP port 80 on the local host to a remote host ( on TCP port 8080.

# iptables -F
# iptables -X
# iptables -t nat -A OUTPUT -d -p tcp –dport 80 -j REDIRECT –to-ports 8080
# iptables -t nat -A PREROUTING -d -p tcp –dport 80 -j REDIRECT –to-ports 8080

# /etc/init.d/iptables save
# /etc/init.d/iptables restart
# chkconfig iptables on

How to configure a new port with VLAN (Cisco)

Here’s how to hot port 5 on VLAN 1081 on a Cisco Catalyst 2950.

# enable
# config t
# interface fastethernet0/5
# switchport access vlan 1081
# switchport mode access
# no shut
# exit
# exit
# wr (writes configuration)

VMware ESX General Information

The main difference between ESX and regular VMware server is that ESX runs its own VMware kernel (loaded with GRUB) and allows for the virtualization technology to live closer to the hardware. VMFS, available in ESX, allows for larger files and offers higher performance over traditional file systems like EXT3. VMFS is tuned for large files and exhibits almost raw filesystem speed.

Key Terms
H.A – High Availablity
VMotion – Move live guest to different hosts in real-time
DRS – Distributed Resource Scheduler – allows for distributed resource management
VMFS – Large file support, provides near raw disk speeds

The ESX console is simply another virtual machine which has access to the VMKernel (through hostd process) and allows for management of the host. This console provides SNMP monitoring and all management functions for manipulating guests and the host configuration.


  • Default of 56 ports per virtual switch. Maximum of 1016 (8 reserved for trunking)
  • Three types of network connections.
    • Service console port (should be bonded)
    • VMkernel port – access to VMotion, iSCSI and NFS traffic traverses this port or portgroup
    • Virtual machine port group – access to VM networks
  • Creating Virtual Switches (Very simple)
  • Console command "esxcfg-nics -l" lists all NICs available on the host machine
  • Three methods of load distribution
    • Port-Based
             VMKernel decides which physical NIC will carry the packet to the outside world. This method does not require special switch configuration. This method
    • Source MAC-Based
             VMKernel maps VM to physical adaptors based on the source MAC hash. This method has low overhead but might not effectively spread the load to all physical adapters.
    • IP-Based
             VMKernel routes outbound and inbound traffic based on IP address. This requires VMKernel to inspect packets at Layer-3 and can introduce more CPU overhead and might not be the best option for high-throughput applications.

How to clear ESM logs in OpenManage

Hey all,

Sometimes it can be useful to clear the ESM logs in OpenManage if you do not have direct access to OMSA as a root user. To perform this action from the command line just enter the following:

omconfig system esmlog action=clear

The above command clears the ESM (hardware) logs in OpenManage. Sometimes this can clear amber lights on the front of the Dell servers.