ASDM 6.x conflicts with JRE 1.6.11+

 Posted by at 11:43 pm  Network Administration, Network Research  Comments Off on ASDM 6.x conflicts with JRE 1.6.11+
Jun 072010

Working with an under powered ASA 5520 with merely 256MB of RAM whose IOS and ASDM image have not been updated since delivery from the factory, there is a conflict between the ASDM and the Java Runtime Environment (JRE). Sometimes you can back level the version of JRE on the workstation (on Windows clients for instance) unless the older versions are not listed, then you’ll need to acquire the older version and install it in order to back level to it.

The JRE must be 1.6.11 or less, but there may be a workaround, here more on these topics here:

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The OSI Reference Model

 Posted by at 5:02 am  Network Administration, Network Research  Comments Off on The OSI Reference Model
Apr 082010

The OSI Reference model is the fundamental design of internet communication, and lays out a schematic for the assembly of internet based information, how it is organized and transmitted from one computer to another.� Information is organized like an onion, with layers over layers, and each layer communicates information. The layer effect is called encapsulation, and as encapsulation occurs, the information changes name so that we can speak about it contextually.� Low level information is referred to as bits, slightly higher level information is called a frame, then packets, and then segments, and finally data. Looking at it from the perspective of a user in a word spreadsheet application placing a link to another document in one of the cells, the process begins at the Application Layer.

Starting with some information called data, encapsulating it with a header and footer to create a segment, passing it to the Presentation Layer which adds a header and footer again, and on to the Session layer with another header and footer, and so on down the stack until the bits are transmitter across the network.� Arriving information is then incrementally stripped of its header and footer as it moves up through the layers, until it arrives on a different computer where the linked data resides.� The process happens many time per second, but understanding the process is fundamental to understanding how to troubleshoot the network.

The reference model has seven layers:

  1. Physical
  2. Data Link
  3. Network
  4. Transport
  5. Session
  6. Presentation
  7. Application

Although I’ve listed the layers in ascending order here, the stack is often shown with the Application layer on the top, and the model really becomes helpful when depicted as part of a diagram.

Ports to Remember

 Posted by at 4:33 am  Network Administration, Network Research  Comments Off on Ports to Remember
Apr 082010

Port Protocol��� Description

20� TCP��������� FTP, Data

21� TCP��������� FTP, Control


23� TCP��������� Telnet

25� TCP��������� SMTP


43� TCP � � �� � WHOIS


67 UDP���������� BOOTP, DHCP Client

68� UDP��������� BOOTP, DHCP Server

69� UDP��������� TFTP


110 TCP���������� POP3

135 TCP ��������� Client/Server Communications, Exchange Administrator, DHCP Manager,

137 UDP � � � � � File Shares Name Lookup, Browsing requests to NetBIOS

138 UDP���������� Browsing datagram responses of NetBIOS

139 TCP���������� File Shares Session

143 TCP���������� IMAP

389 TCP���������� LDAP


636 TCP���������� LDP over TLS/SSL

989 TCP/UDP �� FTPS data; FTP over TLS/SSL

990 TCP/UDP��� FTPS control; FTP over TLS/SSL

993 TCP���������� IMAP (SSL)

995 TCP���������� POP3 (SSL)

1433 TCP��������� SQL Session

3389 TCP��������� RDP, Terminal Server

Fundamentals of WAN Optimization

 Posted by at 7:50 am  Network Administration, Network Research  Comments Off on Fundamentals of WAN Optimization
Sep 202009

The goal of WAN Optimization is to make applications work more efficiently over long links, such as offices connection to data centers.� The devices to perform the optimization are meant to reduce bandwidth utilization, accelerate application performance, and prevent or reduce the need to purchase more bandwidth. A WAN optimization device should pay for itself in three years or not be purchased.

Key features of WAN Optimization devices:

  • Compression–reduces the number of bits transferred from sender to received, and minimizing transmission time as a result.
  • TCP Acceleration–mistaking latency for congestion is a problem for TCP, so helping TCP discern the difference accelerated the TCP traffic rate with device loacted at both ends of the WAN
  • File Caching–the storage of frequntly used files on disk within a WAN Optimization device to speed up delivery.
  • Traffic Shaping–the classification and prioritization of WAN traffic setting limits how much bandwidth is granted to certain classifications

From an article in Network World magazine titled, “The ABCs of WAN Optimization,” by Tim Greene.

Cisco CCNA lab stack

 Posted by at 7:36 am  Cisco, Network Administration  Comments Off on Cisco CCNA lab stack
Aug 032009

I’m slowly assembling a collection of routers, switches and firewalls with which to test my knowledge and try-out things which are not possible in production. I know I can use simulators but there is no replacing hands on experience, so I’m building out the lab stack. In my present Sys Admin day job we have Cisco 2600 premises router with a T-1 module, into a pair of ASA 5520s and 3750s for failover to the data center. Fun to administer but not much room for service interuption, but then there never is.� The home stack is two Cisco 36406416 and one 1720T1 routers, and a PIX 515E firewall. Next I need to acquire a switch or two, and so here are some canidates…

  • Cisco Kits–Dual 2501 16/16 Routers & Dual 2924 Switches (est. $359.00) this would also let me do those labs requiring four routers since I’d gain two additional routers for my stack. One of the switchs is a modular version
  • Cisco Kits–2924M-XL-EM Switch (est. $69.00)
  • Cisco Kits–Catalyst 2950 24 port switch (eat. $125.00)


OK, I made the decision and a stack of two routers and two switches now sit on my sofa, waiting for a more appropriate home. Both of the switches are modular 24-port 2924’s, and there are two transievers to simulate a WAN connection. I think I’ll pickup another transciever to grow the possibilities further yet. I had already procured the two 3640’s, the 1720 and the Pix, so my stack is sufficient to start the experiments. I’m looking forward to it; I think I’ll post a photo of the stack for posterity.� I actually have a rack, but I don’t think my wife would appreciate me brining the rack into the spare bed room. Come to tink of it I’ll have to do some creative wiring, and or be careful when powering up, and then there will be the noise-polution… hmm, perhaps I should bring it the rack, and enclose it and… more things to think about. is the place where I made the purchase, and I actually got an extended warrantee for $36.99, because I rationalized that the 30-day default might expire before I got the whole thing up and running.� The secondary projects take backseat to the paid gig, and those weeks pass so fast. Shipping was about $45.00 so I spent the better part of $500.00 for this gear.� Eventually, when I pass the certification, and get a better job these expense will be money well spent. So “manos de los obras” as wife would say, which translates as “hands to the tasks.”