A coworker brought an interesting problem to me the other day.  He wanted to move a serverfarm from one server VLAN to another without taking an outage.  Since I didn’t want to have to come into the office late at night to do work, I decided to see what we could do.

It turned out to be pretty easy.  We tend to think of CSM VLANs as pairs – you have the client VLAN for the web servers where the vserver sits and the server VLAN where the serverfarm sits.  The CSM doesn’t know about these relationships; all it cares about is whether the servers are in a server VLAN, and we can use that to our advantage here.

Here are some more notes from my studies.  Of course, no one cares about them but me, but it’s my blog.  I’m sure someone will find it useful.  Please help to correct dumbass mistakes.

• Congestion

  • Speed mismatch - traffic leaves a lower-bandwidth interface than the one it came in on
  • Aggregation problem - lots of links with one egress of equal bandwidth
  • Confluence problem - a bunch of traffic needs to egress out of the same interface

• Queuing

Here’s another set of notes from my ONT studies.  I’m sure someone will find it useful.  Please help to correct dumbass mistakes.

• Classification is done with traffic desriptors

  • Ingress interface
  • CoS value on ISL or 802.1P frames
  • Source/destination IP address
  • IP Precedence or DSCP value
  • MPLS EXP
  • Application type

• Layer 3 QoS

  • Type of Service (ToS) is 8-bit field.
  • First 3 bits of ToS are the IP precedence.
  • First 6 bits of ToS are the DSCP value.
  • Last 2 bits of ToS are explicit congestion notification (ECN).

• Layer 2 QoS

I’ll try to keep it a little shorter this time.

Major issues for converged enterprise networks

• Available bandwidth: competition among applications
  • Fixes
    • Increase bandwidth: More power!
    • Properly queue based on classification and marking: QoS
    • Compress: cRTP, TCP header compression, etc.
• Delay: Lead time to get a packet to the destination
  • Types of delay
    • Processing delay: routing, switch delay
    • Queuing delay: how long a frame stays in an output queue
    • Serialization delay:  how long to put the frame on the wire
    • Propagation delay: the time to cross the physical medium
• Jitter (delay variation): Variation is the delay
  • Different delays mean different arrival times
  • De-jitter buffers save up packets to reduce jitter (like the old CD writers)
  • Fixes
    • More bandwidth
    • Prioritize sensitive data and forward first
    • Remark (reclassify) packets based on sensitivity
    • Enable L2 payload compression: make sure compression delay isn’t worse than the jitter
    • Use header compression
• Packet loss: Packets are lost in the network somewhere
  • Fixes
    • More bandwidth
    • Increase buffers space: more room for the queue on the interface
    • Provide guaranteed bandwidth: Queuing and QoS
    • Congestion avoidance
      • Random Early Detection (RED) and weighted RED (WRED) drop packets before the queue is full
      • Selective dropping is better than FIFO or LIFO dropping

QoS History

Here are some of the notes I’ve been taking while reading over the ONT book. I hope it benefits somebody.  Feel free to correct any stupid mistakes as a paraphrase to avoid a lawsuit.

There’s way too much info here.  I’ll refine the process a little better for the next topics.

Benefits of Packet Telephony Networks

• More efficient use of bandwidth and equipment - Packet telephony networks don’t dedicate channels or a static bandwidth to a call; it’s just another network application.
• Consolidate network expense - The common infrastructure (IP-based networks) keeps you from having to support another distinct network for voice like in traditional PBX implementations.
• Improved employee productivity - The phone can be used for more than just phone calls by utilizing the XML interface to run applications or provide content from the network.
• Access to new communications devices - IP phones can communicate with computers, network gear, PDAs, etc., and not just the PBX.

Packet Telephony Components

It seems that we have another piece of evidence that Cisco doesn’t like the CSM.  From what I’m able to creatively interpret, the software developers didn’t think anyone would be running the CSM for very long, so they set a variable that expires CSM-inserted cookies at 01:01:50GMT on 1 January 20101.  If you’re using cookies to make connections sticky, that means you may see some unexpected results; this shouldn’t affect the web servers’ cookies.

Here we are at the end of another year.  It’s been a pretty good one for me - the wife got a new job, we have a new house, we’re in good health.  I hope that you, too, have had a great year.

Here are some highlights from 2009 to read over while your boss is out on vacation.  I know that I’m a little wiser thanks to the many, many network-related blogs out there, and I hope that I was able to give someone an answer or just some new knowledge in 2009.

I took and passed the ISCW test today.  I was super-nervous going into it, which is weird for me, but I finally calmed down after the first few questions.  Here’s my take.  I don’t want to get into any trouble so I’m not going to include very much detail.

The testing center wasn’t very good at all.  It’s in an old building on the busiest road in town, and the noise from the street was barely dampened by the 1960s building materials.  I can tell you that there are three different pipes in the walls since their vibrations resonated through the room every time somebody flushed or brewed some coffee.  There was also a little foot traffic, which can be expected anywhere; they were working through some software problems on another testing station and were very respectful, so it wasn’t too bad.  The worst part of the whole ordeal, though, was the Microsoft class I sat through while taking the test.  They were across the hall, but it sounded like they were in the room with me.  Usually, you hear the instructor yelling at the top of his lungs so the whole class can hear, but I could hear questions being asked and papers being moved.  I think I can go pass a test of AD replication, though.  I certainly won’t be using that facility for any more tests.

I coworker sent over a link today that got me thinking about an old adage that I’ve been sharing for years.  The link actually has nothing to do with the philosophy but did trigger a random spewing of words from my brain.

Here’s what I tell everyone.  When I deliver these lines, I usually picture myself as Socrates talking to a bunch of Greeks in togas.