Posted on in networking
One of my pet peeves is Cisco switch and router interfaces that remain unlabeled. There is nothing worse that trying to debug a network problem when the problematic interface is unlabeled. Instead of spending valuable time working on the actual problem, you've got to trace down where this cable goes …
Posted on in Networking
I've been in the situation before were I needed to discover the neighbors of a Cisco device programmatically. This is useful in a case where you want to crawl a network without hard-coding a list of devices into your script. By default, all Cisco devices have Cisco Discovery Protocol (CDP …
Posted on in Networking
If you are at all familiar with <acronym title="Simple Network Management Protocol">SNMP</acronym>, you've probably heard of "community strings". Community strings are similar to passwords. They define and grant access to a device's <acronym title="Management Information Base">MIB</acronym>. If you've used SNMP in conjuction with a …
Posted on in Networking
You might have a situation where you have multiple network segments utilizing <acronym title="Dynamic Host Configuration Protocol">DHCP</acronym> to assign IP addresses, name servers, etc. DHCP clients use network broadcasts to alert a DHCP server to their presence. Once a request for an address has been made, the …
Posted on in Networking
This isn't late breaking information, but there's an interesting post in the Cisco WAN, Routing and Switching Forum regarding a particular regular expression that, when used in conjunction with the show ip bgp regexp, results in a router crash. Here is the full command.
show ip bgp regexp (.*)(_\1 …Posted on in Networking
Let me start by saying this article is not about server load-balancing. That's a different topic, and I apologize if that's what you were looking for. That said, interface load-balancing is an interesting topic and one that comes up quite frequently.
A time will come when it becomes necessary to …
Posted on in Networking
On most networks, there is a subset of IP addresses assigned to "management" hosts. These hosts might be the workstations of network administrators or monitoring servers. One of the keys to network security is restricting who has access to the device. Generally, we think of access restriction in terms of …
Posted on in Networking
The last thing I want to do when some network administrator leaves my organization is change all the login passwords on the Cisco network devices. (For now, let's just assume the administrator in question didn't know the enable secret.) If you have relatively few machines, it's easy to setup username …
Posted on in Networking
If you followed my recent Cisco Catalyst rate-limiting post, you already know that policing traffic on a Cisco Catalyst switch requires a bit of thought. Mainly, you have to do a bit of calculating to determine the best bucket size for your application. The good news is that achieving the …
Posted on in Networking
If you work on a fairly spread out network (or have remote clients), you might be managing Cisco Catalyst switches that are far, far away. For a long time, I thought the only option was to have someone on site to pre-configure the switch just enough to get it on …
Posted on in Networking
Sending log messages from your Cisco network equipment to a centralized syslog server is a fairly normal activity. Most of the time, this setup works fine and there's no reason to do anything out of the ordinary. Occasionally though, you might need to run a debugging session over an extended …
Posted on in Networking
Ars Technica recently discussed the effect YouTube has had on the popularity of P2P networking. According to a study done by Ellacoya Networks, HTTP traffic has surpassed P2P protocols as the dominant form of Internet downloads for the first time in four years. Considering my recent discussion of the top …
Posted on in Networking
If you are using your Cisco Catalyst switches to
insert DHCP Option 82 information
and you are also using your Cisco routers as DHCP relay-agents (via ip helper-address),
you'll notice right away that your Option 82 enabled DHCP requests are not being
forwarded by your routers.
As a security measure …
Posted on in Networking
If you're interested in DHCP Option 82 in your Cisco Catalyst-based network, you'll be happy to know that the configuration can be summed up in 4 easy steps.
ip dhcp snooping. Although we're only turning this on to get …Posted on in Networking
How many times has this happened to you?
SLAP#write memory
startup-config file open failed (Device or resource busy)
If you work in an environment where multiple users have enable access on Cisco devices, you've probably seen it more than once. This particular error is caused when another user has …
