I was delighted when I got access to Cisco’s Application Control Engine (ACE) XML Gateway/Web Application Firewall (WAF) box. This box is the perfect intersection of three fields that really interest me: networking, security and Web programming. To my huge disappointment, though, all the real configuration can only be done through the Web interface. I understand that casual users of a device prefer a graphical user interface (GUI) over text commands (and Generation Z has never seen a terminal window, DOS prompt or, God forbid, an actual terminal), but you can achieve so much more with a simple text-based configuration approach:

This is a nice MPLS question I’ve received from one of the readers:

I have understood the Penultimate Hop Popping (PHP) process, but I don’t understand when a router would use UNTAGGED instead of POP TAG?

Instead of answering the question directly, let's walk through a series of simple Q&A pairs that will help you understand the whole process (remember: knowledge, not recipes!).

I received an interesting comment on one of my knowledge/certification-related posts:

I used to think that certifications were a useful indicator of knowledge or at least initiative, but I’m changing my mind. [...] I feel like I’ve gotten a lot out of studying for certifications, especially CCIE, but I’m starting to wonder if that’s the exception.

I guess a lot of prospective internetworking engineers are thinking along the same lines, so here’s my personal perspective on this issue.

The Network World recently published a story describing the results of an independent security product testing lab, where they’ve discovered (surprise, surprise) that adding security features to Cisco routers “presents a tremendous bottleneck” and “can turn a 60G router into a 5G one or even a 100M bit/sec device”.

The test results haven’t been published yet; I’ve got all the quotes from the NW story, so they might be the result of an ambitious middleware.

We don’t need “independent experts” for that. Anyone who has ever configured VPNs in a high-speed environment can tell you how to kill the performance. The basics are always the same: make sure the dedicated silicon can’t handle the job, so the packets have to be passed to the CPU. Here are a few ideas:

The November Technical Services News from Cisco included the Annotating Troubleshooting Sessions document from the Cisco’s support wiki. The document describes two well hidden features of Cisco IOS:

• The send log exec-level command writes a line in the syslog, allowing you to delineate logging or debugging outputs.
• The exclamation mark used as the first character in any IOS command line (not just in the configuration) serves as a comment. If you’re logging the TTY session, you can use these comments to document the session.

When I chose the word “unfortunately” in my post describing how Cisco IOS performs DNS lookup when you enter a host name in an access list, I’ve triggered several responses that disagreed with my choice of words. Here’s why I still think IOS ACL could be improved with dynamic DNS lookup:

When I was configuring the access list that should prevent spammers from misusing my workstations, I obviously had to figure out the IP address of the ISP’s SMTP server (access lists and object groups accept IP addresses). I almost started nslookup on my Linux workstation, but then decided to try entering a hostname in an IOS ACL … and it works. Unfortunately, IOS performs a DNS lookup when you enter the hostname (assuming you have configured the ip name-server) and stores the resulting IP address in the ACL definition:

We’ve spotted some of our best engineers when they were in the final years of their undergraduate studies. To continue the trend, NIL offers a student-engagement program that attracts highly promising candidates each year. They offer them CCNA training (after which the students have to pass the exam), a few weeks of hands-on instructor-led introductory bootcamps and the first CCNP course. These training courses should give students a solid foundation and a framework that they can expand on their own—which is the point where it's time to stress-test them with advanced bootcamps.

My MPLS QoS: Implementing the best model for guaranteed service article published by SearchTelecom gives you a high-level overview of the pipe and hose QoS models in the MPLS VPN environment. I’m also describing basic DiffServ QoS mechanisms available in an MPLS backbone.

If you’re new to IP QoS, you should start with the IP QoS: Two generations of class-of-service tools article.

I always thought that there was no need to restrict outbound sessions across a firewall in low-security environments. My last encounter with malware has taught me otherwise; sometimes we need to protect the rest of the Internet from our clumsiness. OK, so I decided to install an inbound access-list on the inside interface of my SOHO router that will block all SMTP traffic not sent to a well-known SMTP server (and let the ISP’s SMTP server deal with relay issues).