This year I decided to run for the NANOG Board of Directors and I wanted to elaborate what I would like to accomplish if elected. Please see below for more details and hope to have your support.
What is CHI-NOG (Chicago-NOG)
Over the last year, I haven’t been writing many new blog posts. I have been pretty busy with a new job, but also starting a new networking group called the Chicago Network Operators Group (CHI-NOG). The idea behind it is that there aren’t that many places where network engineers can meet to talk about technology,…
Pseudowire FAT Interoperability
I usually don’t think much about Pseudowires Sub-TLV until I encountered two IOS-XR boxes that didn’t use the same value and didn’t forward any packets. There is a special corner case of pseudowires using Flow Labels Transport (FAT) that can cause unexpected behavior and if you don’t watch out you might drop traffic. In this…
New GNS3 – Redesign changing networking again
GNS3 has been a crucial tool used by many network engineers to emulate computer networks. It has proven to be fundamental studying for all network certification levels such as CCNA, CCNP and CCIE. It has been crucial for network design validations within many companies. With the news of Cisco’s VIRL, many said that GNS3 will…
Anycast DNS with IP SLA DNS
Recently I came across an idea to implement anycast DNS within an enterprise environment. The concept is similar to Google’s public DNS, but at an enterprise level. Using IP SLA DNS, a static tracked route and some redistribution it makes it an easy solution. The biggest benefits is that all internal clients can use the…
RSVP Per Flow Limit and RSVP Call Rate
When configuring RSVP, the “ip rsvp bandwidth (bandwidth) [per flow limit]” command there is an optional parameter which limits the per flow bandwidth of individual RSVP reservation. When using Call Admission Control for VoIP, that is the rate of an individual voice call in one direction, but the behavior is not as clear cut as…
RSVP Bandwidth on DMVPN Tunnels
Configuring RSVP on DMVPN mGRE tunnels requires few extra steps and a little bit of calculations to figure out the additional overhead. Without correctly configured overhead, the mismatch between RSVP and available LLQ bandwidth can cause degraded VoIP call performance.
Making RSVP work over DVMPN
When using RSVP Call Admission Control (CAC) for VoIP, DMVPN and RSVP have limitations that prevent RSVP from working over DMVPN. If you have VoIP and you can’t use location based CAC, RSVP is the only answers. So what’s the problem with RSVP over DMVPN? The root of the problem is RSVP’s loop prevention mechanism….
CCIE SP Lab
At Cisco Live I was able to attend the CCIE Service Provider technical session by Vincent Zhou who is the product manager of CCIE SP. It was a very good informative session (BRKCCIE-9163) that gave a nice insights into the lab test. Below are my notes from the session, hopefully you’ll find them useful.
VIRL – Why you need to know about it!
At Cisco Live in Orlando I had the chance to demo the Virtual Internet Routing Lab (VIRL). It is Cisco’s answer to GNS3 or Junipers’ Junosphere using virtualization to create virtual network topologies. This tools will be as revolutionary as GNS3, but at a much larger scale. It is an awesome tool that can be…
Nexus – iBGP with BFD
I’ve been trying to setup a BFD neighbor for a link connecting two important sites on a Nexus 7010. That link is only using iBGP for routing. This seems like a really easy thing to, unless you run into bad documentation with few key missing facts.
Which IPv6 source address to choose
In the good old days of IPv4, an interface on a host could have only one IPv4 IP address. Things were very simple, every IP host would use that one address as the source IP for all communication. When we get into IPv6, each interface can have multiple IPv6 addresses. These addresses have different scopes…
EIGRP Filtering with Offset-list and Delay
EIGRP Offset-list is usually used to increase the metric of routes being advertised over a link, but can it be used to filter EIGRP prefixes? I thought about using offset-list in RIP to filter specific routes and thought how about doing the same thing in EIGRP? I haven’t run into any examples or blog posts…
Intenet Access with Dot1q Tunnel
Is there a way to provide internet service over a dot1q tunnel using VLAN tunneling? Yes, there is a way, it is not the most intuitive method but works nicely.
CCDE Group Study by INE
Over the weekend I attended the CCDE group study sponsored by INE in Chicago. Discussion and material were let by Petr Lapukhov and Brian McGahan. I’m very excited to see high level networking event in my hometown. We had about 15-20 people in the class. This was my first
Password Recovery – Nexus 5548
Recently I had to recover the admin password on the Nexus 5548. The Cisco doc was a little bit uncleared so I figured I’ll make some notes on it. First thing reboot the switch. The power supplies on these don’t have a on/off switch so you’ll have to pull the power cable.
CCIE Review Questions
I updated the CCIE page to include CCIE Supermemo questions. Please go to CCIE Supermemo Questions. As time progresses I’ll update more and more of these.
BGP Decision Process
Cisco’s BGP decision process basically decides which BGP route to take when comparing multiple prefixes to the same destination. It is a rather long process and somewhat tricky. Below, I created a quick reference to its steps.
When NTP access-control needs ACL for 127.127.7.1?
The very simple answer is when the local NTP master controller is synching to the IP address 127.127.7.1 instead of 127.127.1.1. Ok, I think I need to clarify few things. In a number of CCIE workbooks, you’ll get a task to configure NTP access-control on the master NTP router to only peer with R1. After…
OSPF Area Range – Active vs Passive Advertisment
I was troubleshooting an OSPF area range summarization and came upon something I haven’t seen before called Passive Advertisement. There weren’t too many Cisco documents that explained it so I decided to post a really quick description explaining it in little detail and where you could see it . This could be useful for the…
Can’t remember the IPv6 6to4 conversion?
What is IPv6 6to4 tunnel address? 2022::/16 or 2002::/16? How do you convert the IPv4 address into IPv6 6to4 tunnel address? Well there is the long way, which you should understand and then there is the easy way in case you need to configure it really quickly. I found this nice method where you can…
IPv6 ACL Explicit vs Implicit Deny Any Any
Reading the IPv6 Configuration Guide (Implementing Traffic Filters and Firewalls for IPv6 Security), I came across a little known fact that seems to be very important when configuring IPv6 access-lists on IOS. Usually when I configured an IPv4 ACL, I explicitly defined a deny ip any any at the end, which seems like the best…
BGP – Modifying the AD of Backdoor networks
As you may know that the backdoor feature of BGP changes the AD to 200. But is there a way to modify it? There is a way, it’s not very intuitive. When you configure a network as a backdoor network you are creating a local-route that you don’t originate to others. To modify a local-route…
Redistribution RIP-OSPF Distance
Complex redistribution can be quite a challenging task to encounter studying for the CCIE R&S lab. There doesn’t seem to be that many clearly define general rules out there. So I thought why not dissect each individual case that could cause tricky redistribution problems. RIP and OSPF are a perfect example of two protocols that when…