From: Scott Morris (swm@emanon.com)
Date: Fri Jun 10 2005 - 16:43:56 GMT-3
Except the order of your K values for EIGRP is incorrect then....
B, D, L, R & M.... (Big Dogs Like Red Meat)
I haven't ever had a need for mnemonics on the logging stuff, but I would
think that remembering them in order would be more helpful. *shrug*
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Drew
Whitaker
Sent: Friday, June 10, 2005 1:35 PM
To: ccielab@groupstudy.com
Subject: Re: mnemonics - eg for BGP Route selection
Here's a few that I teach my students:
BGP:
We - weight
Love - local preference
Algorithms - as-path
On - Origin
My - MED
Router - router-id
It doesn't cover all of them, but it does cover most of the main ones.
Also, for EIGRP:
Big - bandwidth
Daddy - Delay
Really - Reliability
Loves - Load
Me - MTU
And for logging:
Entry-level - Emergencies
Admins - Alerts
Create - critical
Errors - errors
When - warnings
Networks - notifications
Improperly - informational
Designed - debugging
On 6/9/05, Daniel Kutchin <daniel@kutchin.com> wrote:
> Tim and *,
>
> I'd like to know if you or anyone has any mnemonics he'd like to share
> with us.
>
> Especially, I'd like to know if you folks have any mnemonic for
> lerning the BGB Route selection algorithm below:
>
>
> Discard any route whose next hop is unreachable
> Prefer the route with the highest weight.
> Select the route with the highest local preference attribute.
> Prefer routes originated on this router.
> Prefer the route with the shortest AS_PATH.
> Prefer Interior to Exterior to Incomplete origin.
> Prefer those with the lowest MED value.
> Prefer routes with external rather than internal sources.
> Prefer the path through the closest IGP neighbor.
> Prefer the path with the lowest originating router ID.
>
> TIA,
>
>
> ---
>
> Dr. Daniel Kutchin
> Consultant Cisco(TM) Networks
> Heinrich-Pesch-Str. 55
> 41239 Moenchengladbach, Germany
> Tel. +49 173 5348189
> www.kutchin.com
>
>
>
> ----- Original Message -----
> From: "ccie2be" <ccie2be@nyc.rr.com>
> To: "Group Study" <ccielab@groupstudy.com>
> Sent: Tuesday, June 07, 2005 1:06 AM
> Subject: Re: STP- Port cost vs. Port-priority
>
>
> Bob,
>
> I also tend to give the benefit of a doubt to the double ccie if what
> I believe differs with what a double ccie.
>
> However, with the knowledge you now have regarding STP, I would think
> that you can verify any STP config for the scenario my comments applied
to.
>
> Here's the mnemonic I used to keep this crap straight.
>
> D U D
>
> C P I
>
> Where D = downstream and U = Upstream (which includes root)
>
> And, C = cost; P = port priority; and I = interface #
>
> So, what the table says is this:
>
> If you want to influence which ports are blocking or not by using
> cost, make change on Downstream switch.
>
> If you want to influence which ports are blocking or not by using port
> priority, make change on Upstream switch.
>
> Of course, you can't change the interface # but it's in there because
> it's the last tiebreaker when all else is equal. But, just the same,
> you need to know that it's the Downstream which uses interface # as the
tiebreaker.
>
> By knowing that fact, you can determine which port will go into
> forwarding mode next after a port failure.
>
> Bob, I think you're doing the right thing by experimenting with these
> variations. But, don't take my word for it or a double ccie or even a
> quad ccie.
>
> Only TRUST what the switch tells you empirically from your experiments.
>
> I read over your note quickly and didn't see any glaring
> mis-statements but at the moment I'm seeing double so don't go by that.
>
> I think that for you do this right, you need to do these experiments
> systematically.
>
> First, start by getting used to configuring STP to put ports in
> blocking and forwarding mode by changing these parameters, one at a time,
for all vlans.
>
> IOW, for your first experiment, see which ports are blocking and
> forwarding, by default and determining which STP rules are causing the
default result.
>
> Then, manually change which switch is the root and looking at the same
> show commands. What changed? Does this change make sense based on
> how you understand the STP rules? IF so, now, decide which ports you
> want to be in blocking and forwarding mode and the order of which
> ports change mode in case of failure. Write this down on paper.
>
> IOW, as an experiment, let's say you decide you want the downstream
> switch's ports, fa0/x, fa0/y, and fa0/z to be forwarding blocking and
> blocking, respectively.
>
> And, if fa0/x fails, fa0/z should forward next and if both fa0/x and
> fa0/z fail, then fa0/y goes into forwarding mode.
>
> Now, config only the Upstream switch to achieve that result. Once
> that works, undo whatever config's you made and now config only the
> downstream to achieve that result.
>
> Once you're very comfortable with doing and verifying those types of
> config's, now config your various vlan load-balancing scenarios by
> changing those same parameters but on a per-vlan basis.
>
> Once you're good with those scenarios, you shouldn't have anything to
> be concerned about on the lab when it comes to STP.
>
> Remember, in the lab, there are only 2 3550's connected back to back.
> So, there are only so many potential STP scenarios they can throw at you.
>
> Of course, you also have to know how and when to use the various STP
> commands that lower STP convergence time. But, that's another topic.
>
> BTW, assuming you really want to understand STP, you should read the
> Kennedy and Clark classic book, LAN Switching especially the chapter on
STP.
>
> Make sure you know how STP elects the root bridge and then determines
> which ports are put in forwarding and blocking states.
>
> HTH, Tim
>
> _____
>
> From: Bob Nelson [mailto:nelsnjr@cox.net]
> Sent: Monday, June 06, 2005 4:06 PM
> To: ccie2be
> Subject: Re: STP- Port cost vs. Port-priority
>
> Tim:
>
> I labbed up each combination of settings as per your last reply. I
> have a
> 5-6 page report on the combinations, but thought I would shorten it
> here with text.
> Sorry, this may be a little long. If you have input, it would be most
> appreciated.
>
> Scenario: Configuring STP load sharing, with two 3550 switches and
> one designated the root for all vlans.
> The switches are connected together with two trunks on ports 23 and 24.
> The testing was done using the cost and port-priority parameters to
> determine what effect each had on the forwarding and block of the
> specified vlans.
>
> Results:
> 1. On the primary switch, no matter what the configuration, both
> ports 23 and 24 were always forwarding.
> The cost parameters and the port-priority parameters changed from
> their default STP values when using either cost command or
> port-priority configuration, however the ports remained in forwarding
> status.
>
> 2. Using the cost commands on the primary switch changed the costs
> parameters for STP, but did not
> cause a load balancing condition as the only port that was
> blocking was port 24 on the secondary switch for all vlans.
> Adding the cost commands to the secondary switch caused the load
> balancing conditions to become effective
> where vlans 3-6 were blocked on port 23 of the secondary switch,
> but were forwarded on port 24
> Vlans 8-10 were forwarded on port 23 but were blocked on port 24.
>
> 3. Using the port priority commands on the secondary switch changed
> the priority parameters for STP, but did not
> cause a load balancing condition as the only port that was
> blocking was port 24 on the secondary for all vlans.
> Adding the port priority commands on the primary switched caused
> the load balancing conditions to become effective
> where vlans 3-6 were blocked on port 23 of the secondary switch,
> but were forwarded on port 24
> Vlans 8-10 were forwarded on port 23 but were blocked on port 24.
>
> Conclusions:
> Configuring the switches for load balancing must be done using the
> port-priority commands on the primary (root) switch or the cost
> commands on the secondary (non-primary) switch to cause a load
> balancing condition between the switches.
>
> The commands need only be placed on a single switch, in the case of a
> two switch configuration lab scenario, to create the required load
> balancing condition. Putting cost commands on the primary or
> port-priority commands on the non-primary, would be an incorrect
> configuration, even though there was no effect. It is up to the test
> candidate to determine which method, cost or port-priority, to use
> depending on the language in the task. The answer may be given
> earlier in the switching scenario, where the root switch is to be
> designated for particular or all vlans. When in doubt ask the
> proctor.
>
> In addition to using the cost and port priority commands, I can
> accomplish the same result by setting one switch as the primary for
> vlans 3-6 and the other switch primary for vlans 8-10. In this
> instance, port 23 on both switches forwards vlans 3-6 and port 24 on
> both switches forwards vlans 8-10. Again the lab will dictate which
> of the three methods to use.
>
> Tim, if you want to see the interface configs and the show
> spanning-tree commands for this, let me know as I have them in a Word
> document. The reason I was so concerned about learning this is that I
> attended a CCIE lab prep class and the instructor gave the following
> result for this question of load balancing.
> I did not agree with him, but he told me I was wrong. Thanks to you,
> I believe I have the correct answer. He had 2 CCIEs already, so I
> gave him credit for the CCIEs.
>
> From my studies of this, I think this is incorrect.
> Configure VLANs 4, 12, and 57 to use F0/23 and VLANs 111,112, and 113
> to use F0/24.
>
> SW1
> Interface F0/23
> Spanning-tree vlan 4 port-priority 240
> Spanning-tree vlan 12 port-priority 240
> Spanning-tree vlan 57 port-priority 240 Interface F0/24
> Spanning-tree vlan 111 port-priority 0
> Spanning-tree vlan 112 port-priority 0
> Spanning-tree vlan 113 port-priority 0
>
> SW2
> Interface F0/23
> Spanning-tree vlan 4 port-priority 0
> Spanning-tree vlan 12 port-priority 0
> Spanning-tree vlan 57 port-priority 0 Interface F0/24
> Spanning-tree vlan 111 port-priority 240
> Spanning-tree vlan 112 port-priority 240
> Spanning-tree vlan 113 port-priority 240
>
>
> Thanks again!!
>
> Bob
> ----- Original Message -----
> From: "ccie2be" < <mailto:ccie2be@nyc.rr.com> ccie2be@nyc.rr.com>
> To: "'Bob Nelson'" < <mailto:nelsnjr@cox.net> nelsnjr@cox.net>
> Sent: Friday, June 03, 2005 2:01 PM
> Subject: RE: STP- Port cost vs. Port-priority
>
> > Bob,
> >
> > What I was describing isn't load-sharing. In my description, the
> > ports
> that
> > would be forwarding would be forwarding for all vlan's and the ports
> > that are blocking are blocking all vlans.
> >
> > However, what I described can very easily be adapted to vlan
> load-balancing
> > because the same rules apply.
> >
> > For example, instead of changing the port cost for all vlans, just
> > change
> it
> > for one or more vlans. Likewise, for port priority.
> >
> > Just remember, for priority (port or per-vlan) to have any affect,
> > it must be changed on the upstream switch and for cost to have any
> > effect, it must be changed on downstream switch.
> >
> > Here's why.
> >
> > The root switch will always have all it's port in forwarding mode.
> > But,
> the
> > downstream must use the STP decision tree to determine which ports
> > are designated and which are blocked. Also, the root or upstream
> > switch sends priority to the downstream switch but doesn't send
> > cost. Cost is always determined based on the incoming port, not the
outgoing port.
> >
> > Now, review my notes for the STP decision tree.
> >
> > -Cost is determined the same way for STP as it is for IGP's: Cost =
> > cost
> of
> > local int (going towards root) plus the cost of all int's pointing
> upstream
> > towards destination.
> > -If there are multiple trunks connecting the 2 Cat's & each trunk is
> allowed
> > to carry traffic for all vlan's (the default), STP will block at
> > least one interface. Assume Cat1 is the root bridge for vlan X.
> > Once Cat1 is set
> (or
> > elected) Root Bridge, Cat2 must decide which port is its root port
> > to
> Cat1.
> > 1. Cat2 will compare the cost of each trunk interface (by def,
> > they're all equal) 2. Cat2 will compare BID's from each trunk - of
> > course, they're equal.
> > 3. Cat2 will then compare the port priority for each link sent from
> > Cat1.
> > 4. Last, Cat2 will use its own port's ID as the last tiebreaker
> >
> > -As a result of above process, if you have to config a particular
> > link to
> be
> > in forwarding mode & you can't config Cat2 to do this, then change
> > Port Priority on Cat1.
> > -If the change can only be made on Cat2, lower port cost on Cat2.
> > Notice that if you're restricted to modifying either port cost or
> > port priority, that restriction determines on which Cat you have to make
the change.
> > -Verify config with show spanning-tree [options].
> >
> > Please let me know if you find any discrepancies between what I say
> > and
> what
> > your experimenting shows.
> >
> > HTH, Tim
> >
> >
> >
> > -----Original Message-----
> > From: Bob Nelson [mailto:nelsnjr@cox.net]
> > Sent: Friday, June 03, 2005 4:44 PM
> > To: ccie2be
> > Subject: Re: STP- Port cost vs. Port-priority
> >
> > Tim:
> >
> > I have been researching this topic for some time, and I do not
> > necessarily understand your answer.
> > The usual case for this question seems to be the load sharing of
> > traffic between switches, where you are given the requirement that
> > vlan abc uses port one of the trunk and vlan xyz uses the other port
> > of the trunk.
> >
> > I have labbed this up with my 3550s and found no difference in the
> > functioning using port-priority or cost from either the root switch
> > or the secondary. Using vlans 3-6 and 8-10, I can make 3-6 prefer
> > trunk fa0/23 and 8-10 prefer trunk fa0/24 using either method. The
> > correct ports are
> blocked
> > in either case. This example is
> > directly out of the 3550 DOC CD.
> >
> > Cisco does make a distinction between the two methods:
> > You configure load sharing on trunk ports by using STP port
> > priorities or STP path costs.
> > For load sharing using STP port priorities, both
> > load-sharing
> links
> > must be connected to the same switch.
> > For load sharing using STP path costs, each load-sharing
> > link can
> be
> > connected to the same switch or to two different switches
> >
> > Tim, in taking your answer literally, I would believe it to mean
> > that I could use the priority command from the root to the
> > secondary, but I would have to use the cost to configure this from
> > the secondary to
> the
> > primary. However, it does not work, at least for me, to do this. Can
> > you elaborate on your answer a little more?
> >
> > Thanks,
> >
> > Bob
> > ----- Original Message -----
> > From: "ccie2be" < <mailto:ccie2be@nyc.rr.com> ccie2be@nyc.rr.com>
> > To: "'Sumit'" < <mailto:sumit.kumar@comcast.net>
> > sumit.kumar@comcast.net>;
> < <mailto:ccielab@groupstudy.com> ccielab@groupstudy.com>
> > Sent: Thursday, June 02, 2005 1:08 PM
> > Subject: RE: STP- Port cost vs. Port-priority
> >
> >
> > > Sumit,
> > >
> > > Which parameter you change depends on which switch you're making
> > > the
> > change.
> > >
> > > The port priority is sent by the upstream switch (root) to the
> downstream
> > > switch so changing this value on the downstream switch wouldn't do
> > > any
> > good.
> > >
> > > Likewise, changing cost on the upstream switch wouldn't affect the
> > selection
> > > of which port the downstream switch decides is the root port.
> > >
> > > Make sure you know this stuff. It's very important.
> > >
> > > HTH, Tim
> > >
> > >
> > > -----Original Message-----
> > > From: <mailto:nobody@groupstudy.com> nobody@groupstudy.com
> [mailto:nobody@groupstudy.com] On Behalf Of
> > > Sumit
> > > Sent: Thursday, June 02, 2005 3:27 PM
> > > To: <mailto:ccielab@groupstudy.com> ccielab@groupstudy.com
> > > Subject: STP- Port cost vs. Port-priority
> > >
> > > Mates,
> > >
> > > As I understand the "Spanning tree port cost " manipulation
> > > should be
> > able
> > > to make vlan traffic prefer a trunk port over another one.
> > > Is there any case we need to change "port-priority" unless
> > > changing
> port
> > > cost is restricted?
> > >
> > > thanks
> > > Sumit
> > >
> > > __________________________________________________________________
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