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jocke Posts

PVLAN Trunk-hack

Published October 29, 2010

Ever had the need to use PVLANs in conjunction with one or more trunks, but your Cisco-switch doesn’t support it? I did. And I found a solution. It works well, but if you need to trunk many PVLANs, then this is not the solution you’re looking for; get a 4500/6500 to play with instead.

I’ll be using my scenario as an example in this article, but you could use it for whatever other reasons you might have. At school we have a Cisco-lab, with 5 racks containing various Cisco-equipment. For a while now, there’s been situations where you’d really like a DHCP-server, TFTP-server, or similar, at hand. So, since we already had a VMware ESXi-server running in the lab, it was fairly easy to setup a dedicated lab-server. However, since this ESXi also had to be publicly available, and the lab-network shouldn’t be, we decided to use a trunk between the ESXi and our 3560G (sitting as a gateway between the lab, the servers, and the internet). Each VM is then assigned to their respective VLANs. All well so far.

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Cisco IOS Clock Sync (with NTP) and Summer Time/Daylight Saving Time

Published October 21, 2010

Tired of having a Cisco-device that always ends up with a wrong clock? I was.

The first thing you’ll need, is a proper NTP-server. You can either set up one locally (which syncs from a hardware-device ? like a GPS ? or from an external server), or you can choose one of the public available NTP-servers. I’ve chosen to use ?158.37.91.134? in this example.

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Add timestamp to ping

Published September 27, 2010

I’ve been in some situations where I’d like to add timestamp to pings. There could be loads of reasons as to why you’d like to do this, but I used it to check if there where specific times of the day that had higher latency on my internet-connection at home.

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Cisco IOS NAT Virtual Interface

Published September 24, 2010

Up until recently, I’ve had ADSL at home for some years. For the last year or so, I’ve used a Cisco 1812 as my router (the ISP-router was put into bridge-mode). A few weeks ago, when I got a 10/10Mbps fiber-connection, it suddenly became more relevant to host some services at home (why pay for web-hosting, when you can host it home, for free?). As a result of this, I stumbled upon a “problem” that annoyed me a bit; loopback-support – the ability to reach your services using your external IP, and hence applying port-forwards (this way you could use ssh externalip -p "some odd port number" regardless if you are home or not). This is quite useful if you move between different networks a lot (e.g. using a laptop – which was the case for me). This feature is known as tromboning, or hairpinning, and is something that often works on cheap routers you get from your ISP. So, why shouldn’t this work on a Cisco-device?

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