Engineering Sense
Why didn’t they ask Evans?
For those who haven’t read the famous Agatha Christie novel, the entire point revolves around a man uttering these words just before dying. Who is Evans? What does this person know that can lead to the murderer of the man on the golf course? Bobby and Frankie, the heroes of the story, are led on one wild goose chase after another, until they finally discover it’s not what Evans knows but who Evans knows that really matters.
Okay… But this isn’t a blog about mysteries, it’s about engineering. What does Evans have to do with engineering? Troubleshooting, as Fish says, is often like working through a mystery novel. But I think the analogy can be carried farther than this. Engineering, even on the design side, is much like a mystery novel. It’s often the context of the question, or the context of the answer to the question, that solves the mystery. It’s Poirot straightening the items sitting on a mantelpiece twice, it’s the dog that didn’t bark, and it’s the funny footprints and the Sign of Four.
Just like the detective in a mystery novel, the engineer can only solve the problem if they can Continue reading
Well Known Intervals
Listed below are many events which occur on network devices at well-known intervals. The list is provided to serve as an aid while troubleshooting recurring network disruptions. Please consider helping to expand this list by adding other recurrent issues you encounter not already listed.
This list was generated by Jeremy Stretch from PacketLife, but lost after he took his wiki down. Luckily I had previously saved it, as I found it useful, and with his permission I’ve reposted it here.
Short (<=5 minutes)
1 Second
- Default VRRP hello timer
- Default EAP-Identity-Request Timeout (Unified WLAN)
- Default EAP-Request Timeout (Unified WLAN)
- Default EAPOL-KEY Timeout (Unified WLAN)
- CleanAir AP Sampling Interval (Unified WLAN)
- Default Group Specific Query interval (Maximum Response Time of 10) for IGMPv2
2 Seconds
- Default IEEE 802.1D Continue reading
Four Reasons Why Whitebox Networking is Cheaper
Whitebox & Whitebrand network equipment has a lower purchase price than branded products. But why ?
The post Four Reasons Why Whitebox Networking is Cheaper appeared first on EtherealMind.
Network Change Management Best Practices
No one wants to be that person who caused the network to crash while implementing a change. Here are some steps to help ensure successful network changes.A10 Health Monitors
This post is an equivalence check of A10 vs ACE probes/health monitors.
-
ACE
ACE-A# show probe
probe : tcp-3121-probe-1
type : TCP
state : ACTIVE
----------------------------------------------
port : 3121 address : 0.0.0.0 addr type : -
interval : 10 pass intvl : 30 pass count : 2
fail count: 2 recv timeout: 5
--------------------- probe results --------------------
probe association probed-address probes failed passed health
------------------- ---------------+----------+----------+----------+-------
serverfarm : vip-11.95.79.90_3121
real : ip-11.95.79.68[3121]
11.95.79.68 1286028 1104 1284924 SUCCESS
interval – the time period health checks for a healthy server are sent
pass intvl – the time period health checks for a server marked “DOWN” are sent
pass count – the number of successful probes required to mark a server as “UP”
fail count – the number of unsuccessful probes required to mark a server as “DOWN”
recv timeout – timeout before a probe fails
a10-1[test-1]#show health monitor
Idle = Not used by any server In use = Used by server
Attrs = Attributes G = GSLB
Monitor Name Interval Retries Timeout Up-Retries Method Status Attrs
---------------------------------------------------------------------------------
tcp-443-monitor-1 30 2 5 2 TCP In use
Interval – the time period Continue reading
SDN Controller Benchmarking
There’s been a lot of talk of late on the performance of centralized network controllers (such an odd thing to say when you think about it, but there it is). Ethan recently had a post up on the topic of scaling and SDNs that overlaps with this topic, and SDN Testing ran some interesting tests […]
The post SDN Controller Benchmarking appeared first on Packet Pushers.
Cisco ASA: VPN with over overlapping addresses and twice NAT
IP addressing design is a topic that follows every networker from the basic to the architect level of experience. Usually we just pick a random range from RFC1918 and address all the devices. But then VPN happens, and with VPN…IPv6 and the Swinging Technology Pendulum
35 years ago, mainframes, single-protocol networks (be it SNA or DECnet), and centralized architectures that would make hard-core SDN evangelists gloat with unbridled pride were all the rage. If you’re old enough to remember IBM SNA, you know what I’m talking about.
A few years later, everything changed.
Read more ...Writing a Custom IPAM Application
Four years ago, I lamented the lackluster selection of IPAM applications available for service providers. Unfortunately, it seems not much has changed lately. I was back to exploring IPAM offerings again recently, this time with the needs of a cloud hosting provider in mind. I demoed a few tools, but none of them seemed to fit the bill (or they did, but were laughably overpriced).
So, I decided to write my own. In my rantings a few years back, I had considered this option:
Could I create a custom IPAM solution with everything we need? Sure! The problem is that I'm a network engineer, not a programmer (a natural division of labor which, it seems, is mostly to blame for the lack of robust IPAM solutions available). Even if I had the time to undertake such a project, I have little interest in providing long-term maintenance of it.
My opinion has not changed, but I've come to realize that if I want a tool that fits my requirements, I will need to build it. And after surprisingly little time, I'm happy to report that I have now have a kick-ass IPAM tool that does exactly what I want it to.
Writing a Custom IPAM Application
Four years ago, I lamented the lackluster selection of IPAM applications available for service providers. Unfortunately, it seems not much has changed lately. I was back to exploring IPAM offerings again recently, this time with the needs of a cloud hosting provider in mind. I demoed a few tools, but none of them seemed to fit the bill (or they did, but were laughably overpriced).
So, I decided to write my own. In my rantings a few years back, I had considered this option:
Could I create a custom IPAM solution with everything we need? Sure! The problem is that I'm a network engineer, not a programmer (a natural division of labor which, it seems, is mostly to blame for the lack of robust IPAM solutions available). Even if I had the time to undertake such a project, I have little interest in providing long-term maintenance of it.
My opinion has not changed, but I've come to realize that if I want a tool that fits my requirements, I will need to build it. And after surprisingly little time, I'm happy to report that I have now have a kick-ass IPAM tool that does exactly what I want it to.
Writing a Custom IPAM Application
Four years ago, I lamented the lackluster selection of IPAM applications available for service providers. Unfortunately, it seems not much has changed lately. I was back to exploring IPAM offerings again recently, this time with the needs of a cloud hosting provider in mind. I demoed a few tools, but none of them seemed to fit the bill (or they did, but were laughably overpriced).
So, I decided to write my own. In my rantings a few years back, I had considered this option:
Could I create a custom IPAM solution with everything we need? Sure! The problem is that I'm a network engineer, not a programmer (a natural division of labor which, it seems, is mostly to blame for the lack of robust IPAM solutions available). Even if I had the time to undertake such a project, I have little interest in providing long-term maintenance of it.
My opinion has not changed, but I've come to realize that if I want a tool that fits my requirements, I will need to build it. And after surprisingly little time, I'm happy to report that I have now have a kick-ass IPAM tool that does exactly what I want it to.
Many to Many Multicast – PIM BiDir
Introduction
This post will describe PIM Bidir, why it is needed and the design considerations for using PIM BiDir. This post is focused on technology overview and design and will not contain any actual configurations.
Multicast Applications
Multicast is a technology that is mainly used for one-to-many and many-to-many applications. The following are examples of applications that use or can benefit from using multicast.
One-to-many
One-to-many applications have a single sender and multiple receivers. These are examples of applications in the one-to-many model.
Scheduled audio/video: IP-TV, radio, lectures
Push media: News headlines, weather updates, sports scores
File distributing and caching: Web site content or any file-based updates sent to distributed end-user or replicating/caching sites
Announcements: Network time, multicast session schedules
Monitoring: Stock prices, security system or other real-time monitoring applications
Many-to-many
Many-to-many applications have many senders and many receivers. One-to-many applications are unidirectional and many-to-many applications are bidirectional.
Multimedia conferencing: Audio/video and whiteboard is the classic conference application
Synchronized resources: Shared distributed databases of any type
Distance learning: One-to-many lecture but with “upstream” capability where receivers can question the lecturer
Multi-player games: Many multi-player games are distributed simulations and also have chat group capabilities.
Overview of PIM
PIM has Continue reading