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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
I've got a Class C (/24, subnet of 256 IPs) that I assign glue addresses for point-to-point links out of. Although all these little /30 subnets are in the same location, they are not guaranteed to be on the same router. So, the question is, how can I see which …
Posted on in Networking
Generally speaking, a route server is a network device that does not participate directly in routing, but carries an entire routing table that other devices may refer to. Often times, this is a router that carries the entire Internet BGP routing table (currently over 220,000 routes).
More commonly, a …
Posted on in Networking
Use Cisco ip helper-address deliberately: verify the default UDP broadcasts it forwards, keep DHCP working, and restrict only the protocols your topology does not need.
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
This is the full text rate limiting example that accompanies my Catalyst rate limiting post. This example was derived on a Cisco Catalyst 2960 and should be ready to copy and paste directly to your device.
mls qos
ip access-list extended ACL_SLAP
permit ip any any
class-map match-all CLASS_SLAP
match …Posted on in networking
If you need to limit the inbound bandwidth of a switch port on a Cisco Catalyst, the key is in the QoS configuration. Rather than going into an depth discussion of QoS and how it works, let's skip that (check out Wikipedia to get started with that) and jump into …
Posted on in Networking
When a Cisco switch or router reports a power problem, start by finding out whether the issue is input power, a failed supply, redundancy, PoE budget, or a sensor alarm. Those are related, but they are not the same failure.
For most Cisco IOS and IOS XE platforms, this is …
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 …
