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Posted on in Networking
This is a bit of random oddness I stumbled upon this morning.
I was working on a Cisco Catalyst 2960 switch and
needed to know which MAC addresses the device had learned on a particular
interface. The usual way to do this is with the
show mac-address-table interface command. While …
Posted on in Networking
I've noticed a mysterious new protocol popping up in my protocol lists lately: 19101/TCP. Apparently, this TCP port is used by the Clubbox service. I 'm not fluent in Korean, so I can't really tell you what the site says, but I can tell you what it does!
Clubbox …
Posted on in Networking
What is Local <acronym title="Policy-Based Routing">PBR</acronym>?
Policy-based routing makes routing decisions based on factors other than normal routing protocols. For example, it might be necessary to forward all <acronym title="Session Initiation Protocol">SIP</acronym> packets via a more expensive low-latency link while all other traffic use …
Posted on in Networking
Today I was browsing through the Cisco NetPro Forums and came across someone that needed to track down which switch port a <acronym title="Media Access Control">MAC</acronym> address had been dynamically learned on.
I'd seen this sort of thing before in the Bridge MIB, so I assumed it …
Posted on in Networking
By default Point-to-Point Tunneling Protocol (PPTP) will now work properly through a Cisco Adaptive Security Appliance (ASA) firewall or it's forerunner the Cisco <acronym title="Private Internet EXchange">PIX</acronym>.
Prior to PIX software version 6.3, allowing PPTP to work through a PIX was a painful procedure involving static …
Posted on in Networking
The following are the Peer-to-Peer (P2P) protocols recognized by Cisco's NBAR Protocol Discovery.
If I've missed any, leave a comment below or use the Slaptijack Contact Form to update me.
Thanks!
Posted on in Networking
Occasionally you might need an Autonomous System Number (ASN) that is only used on your network. The need for these should be infrequent, but it does happen.
One thing that comes to mind is a customer that connects to your network in multiple locations. That customer needs an ASN for …
Posted on in Networking
You'll find that some network problems can only be solved by sticking a packet sniffer on the network and seeing what the packets are doing. In a switched environment, this will not work properly since each port is configured to only broadcast traffic destined for the MAC addresses it has …
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 …
