From: Godswill Oletu (oletu@inbox.lv)
Date: Mon Jul 05 2004 - 18:39:41 GMT-3
My thinking is, if the route from one AS1 is redistributed into AS2, then you
could be able to load balance on both routes in AS2.
All EIGRP load balancing commands are AS specific and do not cut across ASs:
r6(config)#no router eigrp 100
r6(config)#router eigrp 100
r6(config-router)#variance ?
<1-128> Metric variance multiplier
r6(config-router)#maximum-paths ?
<1-6> Number of paths
As you can see both commands must be implemented within the same AS.
See my other post about this. I will try it in my home lab and inform you of
my findings.
Godswill Oletu
===========
In the future everything will Work
----- Original Message -----
From: MD
To: Godswill Oletu ; ccielab@groupstudy.com ; security@groupstudy.com
Sent: Monday, July 05, 2004 5:23 PM
Subject: Re: Modifying AD for EIGRP external routes
Thanks for your explaination. And I agree it may be a bad design which may
be causing poison-reverse as I had tried turning split-horizon 0n and Off with
no help and even using variance 128 with no help.
But I would still appreciate if somebody can share their experience and
answer my question without even considering this example.
---> Is load balancing possible for 2 routes learned from 2 AS's that the
router is participating in . Or if there is any known limitation or this being
a design feature to avoid traffic load balancing over 2 AS's in IOS?
thanks,
MD
Godswill Oletu <oletu@inbox.lv> wrote:
MD,
From you topological database below, though EIGRP (AS318) entries for
route
172.16.15.0/28 states that, the calculated metrics (FD/AD) =
(46738176/46226176), but the metric for that route was set to 4294967295,
from the line below taken from your output (Marked Output A):
Output A = "State is Passive, Query origin flag is 1, 0 Successor(s), FD
is
4294967295"
One can deduce from above that there is no Successor (0 Successor) route
to
172.16.15.0/28, thats NO ROUTE to that destination from EIGRP (AS318),..
Interestingly look at this line (Marked output B) from EIGRP (AS305):
Output B = "State is Passive, Query origin flag is 1, 1 Successor(s), FD
is
46738176",
Only 1 Successor, no Feasible Successor, so the route from EIGRP (AS318)
is
not being considered.
The only explaination to this, is from output A above take note of "FD is
4294967295" and I quote from page 249 of "ALL-IN-ONE CISCO CCIE LAB STUDY
GUIDE" by Stephen Hutnik & Michael Satterlee:
"POISON RESERVE
Split horizon is a scheme used by the router to avoid problems caused by
advertising routes back to the router from which they were learned. The
split horizon scheme omits routes learned from one neighbor in updates
sent
to that neighbor. Split horizon with poison reverse includes the routes
in
updates but sets the metric to 4294967295. When a router sees increases
in
routing metrics, it generally indicates a routing loop. The router then
sends poison reverse updates to remove the route and place it in
holddown."
This explains why the route only become available when you shutdown
serial2.
From one of your earlier post, you indicated that, you manipulated the
routes in order for their metrics to be same. This might be the source of
the whole problem, because you have mechanically made the routes to be
the
same in all respects and shapes, so the EIGRP process that sends routes 1
and sees another route 2, but it is a look-alike of route 1 in every
respect
might think that this is route 1 coming back to me again, this must be a
loop, I better do sometime to stop this loop, so its loop avoidance
mechanisms will kick-in to stop that loop (Agreed, for equal load
balancing
metrics have to be the same, but these are natural ocurring and
calculated
metrics arrived at by different values in the various parameters
considered - Some can throw more light on this and also correct me where
necessary).
Metrics do not have to be same to achive load balancing.
Your first goal should be to set both routes back to their natural
caculated
metrics, then compute appropriate variance value to use.
Otherwise, if you want to use the routes as they are now, since metric
(output A) is set to 4294967295 and the metric of output B is 46738176,
try
using a variance of 4294967295/46738176 = 91.8 = 93 (unexpected results
may
occur)
Godswill Oletu
===========
In the future everything will Work
----- Original Message -----
From: "MD"
To: ;
Sent: Monday, July 05, 2004 2:18 AM
Subject: Re: Modifying AD for EIGRP external routes
> FYI--Variance command did not help.
>
> Let me explain the problem again. Router has 2 EIGRP processes 318 and
305. It is learning route 172.16.15.0 from both the AS with same
metric(46738176/4622617).
>
> AS318 from Serial 0(NBMA) and AS305 from Serial2(PtoP)
>
> Here is the EIGRP topological database--See the difference in FD of
both
routes but same metric. IOS for some reason is increasing the FD for one
route when it learns the same route from 2 EIGRP processes. Check
this--when
I shut down Serial2. see the change in FD. .
>
>
> EIGRP TOPOLOGICAL DATABASE WHEN BOTH S0 and S2 are UP.
>
> IP-EIGRP (AS 318): Topology entry for 172.16.15.0/28
> State is Passive, Query origin flag is 1, 0 Successor(s), FD is
4294967295
> Routing Descriptor Blocks:
> 172.16.123.1 (Serial0), from 172.16.123.1, Send flag is 0x0
> Composite metric is (46738176/46226176), Route is Internal
> Vector metric:
> Minimum bandwidth is 56 Kbit
> Total delay is 40000 microseconds
> Reliability is 255/255
> Load is 1/255
> Minimum MTU is 1500
> Hop count is 1
> IP-EIGRP (AS 305): Topology entry for 172.16.15.0/28
> State is Passive, Query origin flag is 1, 1 Successor(s), FD is
46738176
> Routing Descriptor Blocks:
> 172.16.35.2 (Serial2), from 172.16.35.2, Send flag is 0x0
> Composite metric is (46738176/46226176), Route is Internal
> Vector metric:
> Minimum bandwidth is 56 Kbit
> Total delay is 40000 microseconds
> Reliability is 255/255
> Load is 1/255
> Minimum MTU is 1500
>
> SH IP ROUTE-- shows only one route
>
> D 172.16.15.0/28 [90/46738176] via 172.16.35.2, 00:01:29, Serial2
>
> EIGRP TOPOLOGICAL DATABASE WHEN S2 is SHUT DOWN
>
> h ip eigrp topology 172.16.15.0 255.255.255.240
> IP-EIGRP (AS 318): Topology entry for 172.16.15.0/28
> State is Passive, Query origin flag is 1, 1 Successor(s), FD is
46738176
> Routing Descriptor Blocks:
> 172.16.123.1 (Serial0), from 172.16.123.1, Send flag is 0x0
> Composite metric is (46738176/46226176), Route is Internal
> Vector metric:
> Minimum bandwidth is 56 Kbit
> Total delay is 40000 microseconds
> Reliability is 255/255
> Load is 1/255
> Minimum MTU is 1500
> Hop count is 1
> % IP-EIGRP (AS 305): Route not in topology table
>
> SH IP ROUTE- again shows only one route
>
> D 172.16.15.0/28 [90/46738176] via 172.16.123.1, 00:00:07, Serial0
>
>
> This tells me there is something in the IOS that prevents load
balancing
for a particular route over 2 different AS( Irrespective of being
external
or internal and despite having same Metric). Please confirm if you also
think so , unless anybody has actually tried load balancing over 2 AS
???????????
>
>
>
> thanks,
> MD
>
>
>
> Godswill Oletu wrote:
> Set the AD of both routes to be the same. Check your EIGRP topological
> database to make sure that both routes are in the topological database,
> though it is only the best route that will be selected from the
topological
> database and installed in the routing table.
>
> Note the metric values of both routes in the EIGRP topological database
eg
> if:
> route 1 metric= 12313
> route 2 metric= 35262
> route 2 metric/route 1 metric = 2.86 = 3
>
> To setup unqual load balance across both route 1 and route 2:
> Under the EIGRP process, set variance = 3
>
> This will make EIGRP to install both routes into the routing table and
load
> balance across both routes. A simple traceroute command will confirm
the
> load balance.
>
> Godswill Oletu
> ===========
> 8,x$:0`0:$x,88,x$:0 In the future everything will Work
:$x,88,x$:0`0:$x,8
>
>
>
> ----- Original Message -----
> From: "MD"
> To: ;
> Sent: Sunday, July 04, 2004 10:36 PM
> Subject: RE: Modifying AD for EIGRP external routes
>
>
> > I tried using "distance eigrp 90 91 " command and it does maka the
> external AD to 91 but here is another problem now.
> >
> > My objective was to test load balance 2 routes learned by internal
EIGRP
> and external EIGRP by making the AD and metric same for both routes.
After
> using the above command , I was able to make metric and AD same but now
I
> see that router is not doing load balancing between 2 routes which have
same
> metric and AD but instead prefer the internal Eigrp route.
> >
> > As a workaround , I even tried getting the external route as internal
> route via different AS No. but then again the same problem. Router
would
not
> do load balancing even though the metrics and AD are same because it is
> learning routes from 2 different AS's.
> >
> > So my question is- Can you achieve load balancing for a particular
route
> learned from 2 different AS's and make the router shows both routes in
the
> routing table.
> >
> >
> >
> > thanks,
> > MD
> >
> >
> > Matt Hill wrote:
> > Can you try running EIGRP in different ASes, with different ADs and
> > doing redistribution?
> >
> > Matt
> >
> > --
> > Matt Hill
> > Network Engineering
> > Alcatel Australia Pty Ltd
> > 180-188 Burnley St
> > Richmond, Vic
> > 3121
> >
> > v: +61 3 8687 5739
> > f: +61 3 8414 3115
> > e: matt.hill@aapt.com.au
> > u: http://www.alcatel.com.au
> > m: ask and you may receive
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> > ccievision@yahoo.com
> > Sent: Monday, 5 July 2004 4:17 AM
> > To: ccielab@groupstudy.com; security@groupstudy.com
> > Subject: Re: Modifying AD for EIGRP external routes
> >
> > Thanks everyone for your input.
> >
> > I will try changing the AD for all EIGRP routes and then modify AD
again
> > at downstream routers to see if I can achieve my objective.
> >
> > Any other suggestions would also be appreciated.
> >
> > thanks,
> > MD
> > Richard Gallagher wrote:
> > It is possible to change the distance for external routes, but you
> > cannot
> > change it for specific prefixes:
> >
> >
http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_command_
> > reference_chapter09186a00801a807f.html#wp1075239
> >
> > router(config-router)#distance eigrp 90 ?
> > <1-255> Distance for external routes
> >
> > router(config-router)#distance eigrp 90 171 ?
> >
> >
> > HTH, Rich
> >
> > ----- Original Message -----
> > From: "MD"
> > To: ;
> > Sent: Sunday, July 04, 2004 10:56 AM
> > Subject: Modifying AD for EIGRP external routes
> >
> >
> > > Has anybody tested reducing the AD of external EIGRP routes from
170
> > to
> > some other value (say 91).
> > >
> > > I have tried the distance command under EIGRP but it changes the
> > distance
> > only for internal eigrp routes and not external eigrp routes.
> > >
> > > Here is the relevant configs...
> > >
> > >
> > > router eigrp 318
> > > redistribute eigrp 300 route-map 300to318
> > > offset-list 99 in 20 Serial0
> > > network 172.16.123.0 0.0.0.31
> > > neighbor 172.16.123.1 Serial0
> > > neighbor 172.16.123.4 Serial0
> > > distance 91 172.16.123.1 0.0.0.0 98
> > > distance 91 172.16.123.4 0.0.0.0 97
> > > no auto-summary
> > > !
> > >
> > > access-list 97 permit 10.2.4.0 0.0.3.255
> > > access-list 98 permit 172.16.15.0 0.0.0.15
> > >
> > >
> > > SH IP ROUTE
> > >
> > > D EX 172.16.15.0/28 [170/46738176] via 172.16.123.1, 00:00:07,
Serial0
> > > D 10.2.4.0/22 [91/46251776] via 172.16.123.4, 00:25:30, Serial0
> > >
> > >
> > > FYI-- 172.16.123.1 is sending external EIGRP routes and
172.16.123.4
> > is
> > sending internal EIGRP routes and I am trying to make both these
routee
> > to
> > show up with AD 91 in the routing table.
> > >
> > >
> > > thanks,
> > >
> > > MD
> > >
> > >
> > >
> > >
> > >
> > > ---------------------------------
> > > Do you Yahoo!?
> > > Yahoo! Mail - 50x more storage than other providers!
> > >
> > >
> >
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