[TriLUG] DHCP Problems and a Network Tap

[Matt Pusateri]

Here’s a cheaper alternative to the HP switch: http://www.roc-noc.com/mikrotik/routerboard/RB260GS.html

Matt P.

On Feb 17, 2014, at 1:12 AM, Pinkham <steve.pinkham at gmail.com> wrote:

> Running tcpdump on the router should give you what you need, modulo any
> hardware problems. Just dump to a file and analyze with wireshark on
> your laptop, if that's what you're comfortable with.
> 
> Otherwise, the 750 series Mikrotik routers are about the cheapest way to
> do port mirroring(~$45 for 100Mb, ~$60 for 1Gb) and you get a device
> that's also useful for other things.  Similarly, picking up a 8 port
> smart managed switch like the HP 1810-8g or Cisco SG200-08 for about
> $100 gives you another toy you might find useful in the future as well
> as solving your current problem.
> 
> On 2/16/14, 6:49 PM, Sean Alexandre wrote:
>> I'm still debugging a sporadic DHCP problem. I've got a Debian firewall
>> attached to my Time Warner cable modem (bridge mode). Sometimes it can complete
>> the DHCP handshake and get an IP address. Other times it can't.
>> 
>> I've got a laptop that can always get one.
>> 
>> I've used wireshark to look at details, and have configured the firewall to
>> give the same DHCPDISCOVER request as the laptop. Everything's identical,
>> including MAC address, but I still don't get an DHCPOFFER back.
>> 
>> I want to put a network tap (or hub) on the connection coming from the firewall
>> so I can see the actual traffic. Anybody know where I could get one? Ideally
>> I'd like to find one locally or build one.  (I've already checked Intrex.)
>> 
>> I found these instructions, and may end up trying this:
>> http://www.instructables.com/id/Make-a-Passive-Network-Tap/?ALLSTEPS
>> 
>> Anybody got a hub they want to get rid of (or router with a tap port)?
>> 
>> Or, any other suggetions?
>> 
> 
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