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ConfigureTerminal.com Networking Tips
Resources for the networking
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Important updates
By David Bombal
Email:
IMPORTANT UPDATE
This was planned for this month, but has been
delayed to June.
Because of the increased numbers of people
subscribing to the newsletters, we have decided that we will
need to upgrade our e-mail server delivery services. This will
enable us to provide a better and more reliable service to you.
Please look for an e-mail requesting you to confirm that you
want to continue to receive the newsletters.
NOTE: You
will not receive any more e-mails unless you confirm so keep a
lookout for the e-mail in the coming weeks.
To your success
David Bombal
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FREE GUI interface to Dynamips/Dynagen - GNS3
By David Bombal
Now, this is the way to run emulated Router & PIX Hardware! A
GUI front end to Dynamips/Dynagen. This really takes out the
pain of using Dynamips.
From the GNS3 team:
"GNS3 is a excellent complementary tool to real labs for
administrators of Cisco networks or people wanting to pass their
CCNA, CCNP, CCIP or CCIE certifications.
It can also be used to experiment features of Cisco IOS or to
check configurations that need to be deployed later on real
routers. This project is an open source product that may be used
on multiple platforms, including Windows, Linux, and MacOS X."
Video
Click on the video to see a demonstration on how to install and
configure this powerful product.
Screenshots:
For more information go to:
http://www.GNS3.net
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Connecting Switches in different domains-Don't be bitten by this one
By Kevin Whelan-
When you connect switches in different vtp
domains with a trunk you get an error message that the trunk
cannot be established. The port then comes up (but only as an up
interface though) and you think it is working ....
"show interface trunk" shows you that the trunk is not up.
you fix it with "switchport nonegotiate"
very handy tip
Another one - if you interconnect layer 3 switches with trunks,
a VLAN ACL examines the traffic even for traffic in the same
vlan if it originates from a distant switch - very confusing in
a mixed l2 l3 environment.
Caught me out at the weekend.
Kevin
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Richard's CCIE Cheat Sheets -
Rapid Spanning Tree
By
Richard Bannister
This is an extract from Richards CCIE Blog
(http://rbcciequest.wordpress.com).
Richard is now studying for his CCIE and he has created a
wonderful resource for anyone else
pursuing this. We will now be including
tips and tricks from Richard's blog to benefit
everyone. All the best with your studies
Richard!
Rapid Spanning Tree Protocol
(802.1w – now part of 802.1D-2004)
Overview
- 3 missed hello’s =
reaction (not max-age time)
- New states
- ‘Discarding’
(‘blocking’)
- Transitions
straight to ‘learning’ (no ‘listening’)
- Listening
isn’t needed because of active querying of
neighbours
- Portfast,
Uplinkfast, and Backbonefast standardized
- New backup DP
feature (same shared segment)
- TC’s are now
flooded by all switches via DP’s and RP’s
- Undefined 802.1d
bits used
- e.g. Hello
option equivalent to RLQ BPDU
Port Categorization
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Link type
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Description
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Configuration
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Point-to-point
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Switch to
switch.
Automatic when FDX + hello’s.
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spanning-tree
link-type point-to-point
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Shared
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Switch to hub
(are other switches reachable?)
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spanning-tree
link-type shared
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Edge
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Switch to
end-user device.
If BPDU is received fallback to normal STP rules.
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spanning-tree
portfast
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Port Roles:
Root
port
Closest port to root (based on best BPDU)
Designated port
Sends best BPDU onto
segment
Alternate port
Alternate path to root
(equivalent of uplinkfast)
Backup port
Backup DP (same switch &
same segment)
Note to self – Two
switches connected together
à one switch stops receiving hello’s
from the other
à how long does it take to move the
port into DP state?
à 3 x
Hello time (configured at root) + learning state forward delay
time (configured at root)
à Default = 21 secs
Configuration
To enable (should be on all switches if
possible):
spanning-tree mode rapid-pvst
Majority of commands the
same as Cisco PVST+
New BPDU Format
(type 2, version 2 – no legacy device support) –
‘Flags’ Byte
- Topology Change
- Proposal
- Port role
- First bit
- Port role
- Second bit
i.
00 = Unknown
ii.
01 =
Alternative/Backup
iii.
10 = Root
iv.
11 =
Designated
- Learning
- Forwarding
- Agreement
- Topology Change Ack
BPDU Handling
- BPDU sent every
hello by all switches
- Not just when
received/relayed
- BPDU ‘keepalives’
(x 3 miss) are used for backbonefast equivalent
- If a switch
receives an ‘I am the new root’ from a neighbour that
has lost its hello’s on RP and the local switch can
still see them on its RP it will tell the neighbour that
it can still see the root
- No election
- Forwarding
straight away for neighbour on previously blocked
interface
Great document on RSTP :
Rapid
Spanning Tree
(802.1w) and MST (802.1s) in Campus Networks
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