From: Li Guoyi (Guoyi.Li@scs.com.sg)
Date: Wed Jan 31 2007 - 02:42:42 ART
Right. In most cases, we don't need to adjust AD. I feel router is smart
enough to do the redistribution correctly. Do you have some good
examples on the scenarios where multiple redistribution points cause
routing loops? Like between EIGRP and OSPF, or OSPF and BGP
Another thing is, let us say, the routing loop does happen after the
redistribution at multiple points , it may take long time (I am not sure
how long, maybe a few minutes) to be detected. The symbol may be routes
come and go, and come and go,etc . In this case, by checking the routing
table, we may have wrong impression that redistribution is working fine,
as the routes are there. So how can we ensure the redistribution is ok?
Is there a systematic approach to do redistribution in the lab?
-----Original Message-----
From: Scott Morris [mailto:swm@emanon.com]
Sent: Wednesday, January 31, 2007 10:00 AM
To: Li Guoyi; 'Filyurin, Yan'; ccielab@groupstudy.com
Subject: RE: Multiple route redistribution points
During practice, you take the extra steps... Until you can anticipate
what's going to happen. (think like the router does)
As for mutual redistribution on the same router, it often poses no
problem.
Most protocols (other than RIP) notice the difference of internal vs.
external routes. Other times, the AD may already be in the direction
you want it to be, so nothing needs to be done.
Don't count on this though! Especially in the lab. Things are seem TOO
EASY are often areas where points are lost!
But watching what happens to your routing table(s) is really the way to
go.
Even in the lab, doing "debug ip routing" isn't a bad thing as long as
you are used to seeing the output and therefore know what it is you are
looking at!
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
JNCIE #153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPexpert VP - Curriculum Development
IPexpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Li Guoyi
Sent: Tuesday, January 30, 2007 8:11 PM
To: Scott Morris; Filyurin, Yan; ccielab@groupstudy.com
Subject: RE: Multiple route redistribution points
Hi Scott,
I am a bit confused by mutual redistribution also.
Are there any rules for multiple route redistribution points? Is it
always necessary to adjust AD? In the workbook solutions, sometimes no
loop prevention measures (like ajusting AD) are taken at all. How do we
know when the prevention measures are necessary? In addition, there are
many combinations of mutual redistribution, like Rip and OSPF, OSPF and
Eigrp, OSPF and BGP, etc. Will the rules apply to all the combinations?
Or as you said, we need to perform the step by step redistribution
during lab exam? It will take long time to finish redistrition portion
this way.
Please advise.
Thanks,
Li
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Scott Morris
Sent: Tuesday, January 30, 2007 3:48 AM
To: 'Filyurin, Yan'; ccielab@groupstudy.com
Subject: RE: Multiple route redistribution points
As opposed to their being a "best way" (which there rarely is anything
that fits all circumstances), the best thing you can do is sit and plan,
configure and watch what occurs at each point.
A good way with this involves both TCL script for pinging (every IP
address of your network should be listed) and debugs...
Before doing any redistribution it is simple to predict what things you
can or cannot ping from any one location. Before doing any
redistribution, enable "debug ip routing". Assuming you have stable
protocols to begin with, when you do your first redistribution, you
should see a predictable influx of routes and be able to know what
things can or cannot be pinged from any location. (gaps here may answer
your redistribute connected
question)
As you add more and more redistribution points, each time, repeat the
process. Again, you'll be able to watch the routes move (from the
debug) and test things with pings to make sure what you are getting
lines up with what you thought should be happening.
This process, while very tedious, is the best way to get a true grasp
about what your router is (or is not) thinking during the redistribution
processes. The ability to think it through and predict what will happen
will help you figure out what will happen in any situation that you
happen to run across. Also, using route tags may be a more efficient
way of allowing/not allowing routes in different places.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
JNCIE #153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPexpert VP - Curriculum Development
IPexpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Filyurin, Yan
Sent: Monday, January 29, 2007 2:03 PM
To: ccielab@groupstudy.com
Subject: Multiple route redistribution points
Hello Group Study. I have a possible set of questions regarding route
redistribution. Let's say I have 4 routers A, B, C and D, all
interconnected and running the same routing protocol. For example OSPF.
Routers A and B connect to the same RIP domain and routers C and D
connect to say EIGRP domain. Mutual redistribution needs to be done
between all IGP protocols.
The first task that needs to be done is that since there are multiple
redistribution points, all I have to do is through the use of route tags
control so that routes from one routing protocol don't redistributed
back into it. That is pretty straightforward.
What becomes interesting is when it is a good idea to use distance
command.
For example if routers A and B are acting as redistribution points into
RIP and RIP has higher distance than OSPF, then router B or router A
will have RIP routes from RIP domain and OSPF E1 or E2 routes that got
redistributed.
So it would see logical to set distance of RIP to be 109 for example.
And if I do that suddenly OSPF routes from C and D not to mention routes
that came from EIGRP domain have a similar problem. On A an B they
become preferred through RIP. Similar problems could exist with EIGRP,
but at least with EIGRP it is easier since it does differentiate between
external and internal
Since RIPv2 does not distinguish between internal and external routes, I
guess I could do something, assuming I can't summarize and need complete
redundancy. I can set distance command to selectively choose which
routes get what distance and from what sources, but that takes access
lists and I have to do it both redistribution point routers. Is there
anything else I can do to make the whole thing easier and does any of
this sound right?
Also is it always a good idea when doing mutual redistribution to
redistribute connected routes into all IGP protocols, that haven't been
redistributed previously or were not part of the network statement?
Yan
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