Re: Common operational misconceptions

[Mathias Wolkert]

Autoneg. The old timers that don't trust it after a few decades of decent code. 
Or those that lock one side and expect the other to adjust to that. 

/Tias

15 feb 2012 kl. 21:47 skrev John Kristoff :

> Hi friends,
> 
> As some of you may know, I occasionally teach networking to college
> students and I frequently encounter misconceptions about some aspect
> of networking that can take a fair amount of effort to correct.
> 
> For instance, a topic that has come up on this list before is how the
> inappropriate use of classful terminology is rampant among students,
> books and often other teachers.  Furthermore, the terminology isn't even
> always used correctly in the original context of classful addressing.
> 
> I have a handful of common misconceptions that I'd put on a top 10 list,
> but I'd like to solicit from this community what it considers to be the
> most annoying and common operational misconceptions future operators
> often come at you with.
> 
> I'd prefer replies off-list and can summarize back to the list if
> there is interest.
> 
> John
> 

Re: Choice of address for IPv6 default gateway

[Mathias Wolkert]

Hi

On 1/25/12 23:53 , Owen DeLong wrote:
[...]
> Note, you can use RA for default gateway while still using static addressing.

Could you give me a little bit more on this?

It seems to me that most platforms stop listening to RAs once you give
them a static address.

Letting a host run slaac and then add a static address is not good
enough as the slaac address might be chosen for locally generated packets.

If it works with listening on RAs when running with statically
configured address, why HSRP/VRRP?

[...]>
> Owen
> 
> 

/Tias

Re: flow generating tool

[Mathias Wolkert]

Linux pktgen.
http://landley.net/kdocs/ols/2005/ols2005v2-pages-19-32.pdf

/Tias


On 9/26/11 12:07 , Naiden Dimitrov wrote:
> Hello,
>
>
>
> I need a tool that generates traffic flows from different source IP addresses 
> for network tests.
>
>
>
> Regards,
>
>
>
> Naiden Dimitrov
> Mobile: +359 885 906 155
> naiden.dimit...@maxtelecom.bg
> www.maxtelecom.bg
>
>
>
>
>

Re: Linux Router: TCP slow, UDP fast

[Mathias Wolkert]

I would turn off ethernet flow control. Maybe you already have.

It can be really mean on tcp's own flow control if the switch has an  
issue of some kind (load).


/Tias

15 feb 2009 kl. 10.24 skrev Chris :


Thanks, Karl, Allen and Nickola.
I failed-over to another router last night and briefly had full  
expected
throughput but this morning despite dropping providers and moving  
between
routers again for trial and error I still see _outbound_ TCP at  
about the

same 300 - 600kbps per session.

I eliminated conntract modules firstly, then iptables as a whole. I've
eliminated TSO and checksumming (which caused very sticky  
connections) on

the e1000 NIC.

The failover router has a slightly older kernel and was working before
Christmas so it's not most likely not kernel versions. I've also tried
removing FIB_TRIE as a stab in the dark with no success. And the  
failover

router connects using FE not GE so I've eliminated NICs and connection
speeds to a front-facing switch.

The only constant is the front-facing switch (it's negotiating  
perfectly at

FD though) so all I can think of is removing that from the equation.

It's definitely only _outbound_ TCP getting buffered though ! I've  
pushed

92Mbps on a FE link with UDP and uploaded at 16Mbps on a 16Mbps link.

Any last ideas appreciated before causing headaches removing  
switches would

be appreciated.

Thanks,

Chris

Re: Network diagram software

[Mathias Wolkert]

Thanks all for your input.
One thing that hits me is how different networks are documented.
Are there any best practice communicated (RFC/IETF)?

I like the idea of having one physical version showing cables and devices
(CDP/EDP/LLDP view pretty much) and one logical view showing IP subnets.
Many times I found *documented* networks where this is all combined making
it very unclear.
The hard part is to visually show what VLANs are active in each switch.

Thoughts?

/Tias

Network diagram software

[Mathias Wolkert]

I'd like to know what software people are using to document networks.
Visio is obvious but feels like a straight jacket to me.
I liked netviz but it seems owned by CA and unsupported nowadays.

What do you use?

/Tias