[c-nsp] ISP LAN Design

[Todd, Douglas M.]

All:

I might add that on certain Cisco switches 4000's and 6500s CatOS at least there
is a nice command:

Usage: l2trace <src_mac_addr> <dest_mac_addr> [vlan] [detail]
       l2trace <src-ip-addr> <dest-ip-addr> [detail]
       (src-ip-addr, dest-ip-addr: IP alias or IP address)

Which helps with showing a switching path through your network.  

==DMT>



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>-----Original Message-----
>From: cisco-nsp-bounces at puck.nether.net 
>[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jon Lewis
>Sent: Wednesday, May 25, 2005 09:22
>To: cisco-nsp at puck.nether.net
>Subject: Re: [c-nsp] ISP LAN Design
>
>On Wed, 25 May 2005, Gert Doering wrote:
>
>> On Wed, May 25, 2005 at 01:06:54PM +0100, Mark Tohill wrote:
>> > Everybody claims layer 2 problems are easier to troubleshoot than 
>> > layer
>> > 3 problems.
>>
>> L2 problems are MUCH harder to troubleshoot than L3 problems.  L3 is 
>> either "there are all relevant routes" (traceroute will tell 
>you) or "not".
>>
>> L2 brings you loops, spanning-tree blocks, spanning-tree 
>oscillations, 
>> unwanted flooding of packets, and lots of other fun.
>
>And with L3, you see the hops, so you know where your packets 
>are going and and pretty easily see what path they're taking.  
>With L2, you have invisible L2 hops and won't realize packets 
>are taking a suboptimal path unless you look very carefully at 
>ports and their counters.
>
>----------------------------------------------------------------------
> Jon Lewis                   |  I route
> Senior Network Engineer     |  therefore you are
> Atlantic Net                |
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