Articles in the Networking category

1. Preserve Cisco Router DHCP Bindings Across a Reboot

   Posted on October 07, 2008 in Networking

   Preserve Cisco router DHCP leases across a reboot by configuring a DHCP database agent, verifying successful writes, and choosing a storage target that fits the platform.

2. Quality of Service (QoS) Resources

   Posted on September 22, 2008 in Networking

   Last week I mentioned that I was working on a Quality of Service (QoS) project. For those who are curious about QoS and how to get it working, here are the resources I found most useful. These resources are mostly Cisco specific, but the principles should be applicable in many …

3. Work in Progress: Cisco QoS Classification ACLs

   Posted on September 12, 2008 in Networking

   I decided I needed a standardized set of Quality of Service classification access-lists for some work I'm doing. Check out my Cisco QoS Classification ACLs page and let me know what you think.

   If you have any ideas on how I can improve the lists, leave a comment here or …

4. Cisco Catalyst 12.2(46)SE May Break SNMP ifIndexes

   Posted on September 10, 2008 in Networking

   This week I tried upgrading a Cisco Catalyst 2960 to the newest software release — 12.2(46)SE. The upgrade went just fine, but I noticed that the monitoring software was throwing SNMP errors.

   In case you don't know much about SNMP, an ifIndex identifies a specific interface on a …

5. Cisco QoS Classification ACLs

   Posted on September 04, 2008 in networking

   I've been working on a standardized list of access lists to use in conjunction with QoS on Cisco routers and switches. I've tried to adhere as closely as possible to the Cisco QOS Baseline (pdf).

   As I refine the ACLs, I'll keep this page up to date. If you have …

6. Locked out of your Cisco? Break in!

   Posted on August 13, 2008 in Networking

   I recently had the pleasure of working on a client's Cisco 2600 series router that had not been used in quite some time. Access lists on the vty lines and a misconfigured con line meant I was locked out. In a situation like this, the only way to gain access …

7. Cable Tag Definition

   Posted on June 16, 2008 in Networking

   Laurence F. Sheldon, Jr. just gave a great cable tag definition on the NANOG mailing list.

   The tags should have a short (two or three word) description, the authority for the patch (person's name or position, order number, or trouble ticket number) and where the [other]{.underline} end of the …

8. Cisco, NAT, and Port Range Resolution

   Posted on February 09, 2008 in Networking

   As you might recall, I had previously taken umbrage with Cisco's inability to forward a range of ports to a particular host. Many readers have offered suggestions and links to other documents around the Internet offering various solutions, but none of them really sat quite right with me.

   In hindsight …

9. Tired of ISP Traffic Shaping? Beat It!

   Posted on January 31, 2008 in Networking

   I've written a lot of posts about various methods for blocking <acronym title="Peer-to-Peer">P2P</acronym> traffic, especially with Cisco's Network Based Application Recognition (NBAR). Although these posts are probably of interest to smallish Internet Service Providers and administrators of business networks, they don't have much use for the average …

10. Gotcha! Upgrading Catalyst to New Feature Set

    Posted on January 17, 2008 in Networking

    Error: The image in the archive which would be used to upgrade
    Error: system number 1 does not support the same feature set.
    

    I just got this error message while upgrading a Cisco Catalyst 3560 from 12.2(35)SE5 to 12.2(44)SE. The older version was IP …

11. Cisco's New ip verify unicast source reachable-via

    Posted on January 16, 2008 in Networking

    Oops! I guess I'm way behind the times.

    For quite a while, I've been using ip verify unicast reverse-path to prevent packets with spoofed source addresses from crossing my routers. Apparently, as of IOS 12.0 (12.4 is current as of this writing), that command has been replaced with …

12. Find Cisco Serial Numbers with the IOS Command Line

    Posted on January 14, 2008 in Networking

    "How do I find a Cisco serial number remotely through the command line?"

    This is one of those frequently asked questions that I see over and over. So, here's the quick and dirty answer:

    You can find Cisco serial numbers from the IOS command line by using the show inventory …

13. Installing PDLMs for Cisco NBAR

    Posted on December 17, 2007 in Networking

    I've talked about using Cisco <acronym title="Network-Based Application Recognition">NBAR</acronym> frequently (check the Related Posts section below for more articles). One thing I've never pointed out is that not all versions of Cisco <acronym title="Internetwork Operating System">IOS</acronym> come with all protocol descriptions built in.

    Not …

14. Cisco ASA / PIX Logging Facilities

    Posted on December 11, 2007 in Networking

    When setting up a Cisco ASA or PIX to send logs to a remote syslog server, you need to specify which facility to use. This can cause a bit of disconnect since the syslog server configuration uses names and the logging facility command in the Cisco Adaptive Security Appliance Software …

15. 2 AM and ssh_exchange_identification Silliness

    Posted on December 02, 2007 in Networking

    I could blame it on the late hour, but the truth of the matter is that I'm just a bonehead.

    I'm currently installing a new Cisco ASA 5520 to replace an old Cisco PIX. This new device is going to use <acronym title="Secure SHell">SSH</acronym> and TACACS+ to …