Dr. I Doctor

Sharing Internet for Redundancy

Mon, 01 Sep 2008 16:06:39 -0700

Dear Doctor, A neighboring company with a high-speed Internet connection similar to ours, but from a different provider, has proposed that we pool our resources so that one company's connection can support the other company...

Missing Incoming Email

Mon, 01 Sep 2008 16:04:16 -0700

Dear Doctor, We've recently seen a sudden increase in reports of lost email — email our users send that recipients never receive. Last month we moved our System i email server to a collocation facility,...

Choosing Between FC and iSCSI SAN

Fri, 01 Aug 2008 01:01:02 -0700

Dear Doctor, We're moving to server virtualization and are planning for a Storage Area Network (SAN) array to provide disk storage for all our virtual machines. My problem is choosing between the two SAN technologies,...

Backscatter Spam

Fri, 01 Aug 2008 01:01:01 -0700

Dear Doctor, Over the last few weeks, our users have seen an alarming increase in e-mail bounce messages that claim we are sending spam. The messages have subjects such as "Message rejected as spam" and...

Fiber Optic Transceiver ARP Caching

Tue, 01 Jul 2008 01:01:02 -0700

Dear Doctor, One interface on our System i box connects to an Ethernet switch that connects through a fiber-optic transceiver (FOT) and cable that runs 3,000 feet to our training center, where another FOT turns...

Duplicated Incoming Email Messages

Sun, 01 Jun 2008 16:00:48 -0700

Dear Doctor, We're a total i5/OS shop and run several different kinds of mail servers: Lotus Notes, CommuniGate Pro, and the native i5/OS SMTP server. Each server provides e-mail for a specific suborganization of our...

VoIP echo on POTS lines

Sun, 01 Jun 2008 15:54:10 -0700

Dear Doctor, Our VoIP system has two kinds of trunk connections to the local exchange carrier (LEC): an ISDN PRI T1 circuit with six channels for long distance and another four plain old telephone service...

Clipped Speech During VoIP Calls

Thu, 01 May 2008 16:28:58 -0700

Dear Doctor, I installed a Voice over IP (VoIP) phone system for our office, initially set up to use Internet VoIP trunks. The reliability and sound quality of Internet phone calls was too poor for...

Windows Remote File Copy Timeout Errors

Thu, 01 May 2008 16:27:03 -0700

Dear Doctor, Our remote offices' Windows servers nightly perform file copy operations from our central System i server for database synchronization. Recently, however, the file copy operations have begun randomly failing. Some nights they all...

Slow File Transfers in Windows Vista

Tue, 01 Apr 2008 16:32:42 -0700

Dear Doctor, Our branch office network recently upgraded many workstations to Windows Vista. We've noticed that file transfers to and from these machines and the Internet is much slower — about 10 times slower —...

Deploying Domain Key Identified Mail (DKIM)

Tue, 01 Apr 2008 16:30:55 -0700

Dear Doctor, In an effort to reduce the amount of phishing e-mail going to our users, I've been asked to set up processing for something called Domain Key Identified Mail (DKIM). I gather DKIM is...

T1/T3 Circuit Troubleshooting Using Loopback

Sat, 01 Mar 2008 16:42:23 -0700

Dear Doctor, We have several T1 and T3 circuits between our main office and branch locations. These all connect to a central router, which relays traffic between the branches and to our centralized server farm....

Proxy ARP Timeouts

Sat, 01 Mar 2008 16:40:19 -0700

Dear Doctor, Our System i is in a secure collocation facility with redundant upstream Internet feeds connected to redundant firewalls. Between the firewalls and the System i are two Ethernet switches, one connected to each...

Switch Port Broadcast Flooding in ISA Server Load Balancing

Fri, 01 Feb 2008 16:46:27 -0700

Dear Doctor, Our network border is controlled by a pair of Windows servers running Microsoft's Internet Security and Acceleration (ISA) Server 2004 in a load-balancing configuration. We process a high volume of SSL transactions, and...

Jumbo Frames on Virtual Ethernet Interfaces

Fri, 01 Feb 2008 16:44:24 -0700

Dear Doctor, Our System i includes a couple of Linux LPAR partitions that we use to collect data from other systems; the data is then manipulated nightly in a very I/O intensive process. I discovered...