From: Scott Morris (swm@emanon.com)
Date: Thu Mar 10 2005 - 22:29:06 GMT-3
Hehhehe... Never quite thought of it that way! :) there are reasons to
have multiple RIBs where you don't want to share. The biggest reason that
comes to mind is MPLS VPNs. Obviously out of scope for the R&S exam, but a
good example of keeping routing information and yet not sharing everything
with everyone!
HTH,
Scott
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Thursday, March 10, 2005 4:11 PM
To: 'Scott Morris'; 'marvin greenlee'; 'Group Study'
Subject: RE: IS-IS multi-area [bcc][faked-from][bayes]
Thanks, Scott.
See comments in-line.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Scott Morris
Sent: Thursday, March 10, 2005 2:36 PM
To: 'ccie2be'; 'marvin greenlee'; 'Group Study'
Subject: RE: IS-IS multi-area [bcc][faked-from][bayes]
To know whether you have to be in multiple areas at the same time, the big
thing leaping out in my mind would be if I were told to not have any Level-2
connections. And yet I'm told that there are multiple areas.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
In this above scenario, is this analogous to running eigrp in multiple AS's
but, unlike eigrp you're not allowed to redistribute?
And, therefore, you don't have full reachability?
And in determining whether to run one routing process or multiple processes,
I suppose would depend on whether every router was expected to have every
router or not.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If there can't be full reachability, why would anyone configure their
networks that way?
This kind of reminds me of the time when eigrp for appletalk and ipx were
running on the same set of routers along with ip. Is this a good analogy?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Just thoughts off the top of my head.
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Thursday, March 10, 2005 1:21 PM
To: 'marvin greenlee'; Group Study
Subject: RE: IS-IS multi-area [bcc][faked-from][bayes]
Hi Marvin,
I guess the problem I'm having with this is trying to imagine what the task
would say in the lab that would tell me, "To fulfill this task I need to use
multi-area."
Because I also know that "full reachability" is typically required and it
sounds like with each L1 area being independent of the other L1 areas, you
lose full reachability. But, I'm sure if that's true.
Is isis multi-area analogous to a eigrp router running with multiple AS's?
Routers in each of the different eigrp AS's won't know about the routes the
other has, but if I want I can redistribute between them.
I've read your post several times and some others on the topic, but it's
still not truly "clicking" in my head.
Thanks for trying to help me get this.
Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
marvin greenlee
Sent: Thursday, March 10, 2005 12:30 PM
To: 'ccie2be'; Group Study
Subject: RE: IS-IS multi-area [bcc][faked-from][bayes]
The system ID uniquely identifies the router in the topology.
***********
Multihoming vs. multiarea:
Multihoming runs both NETs under the same process, effectively merging the
areas together.
Router isis
Net 49.0001.1111.1111.1111.00
Net 49.0002.1111.1111.1111.00
Multiarea is configuring multiple IS-IS processes with tags.
Int Eth0
router isis A3253-02
Int Eth1
router isis A3253-01
Int Ser0
router isis BB
router isis BB
net 49.2222.0000.0000.0005.00
!
router isis A3253-01
net 49.0553.0001.0000.0000.0005.00
is-type level-1
!
router isis A3253-02
net 49.0553.0002.0000.0000.0005.00
is-type level-1
Reference - Cisco - IS-IS multi-area support
http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1830/products_fea
ture_guide09186a00800e9780.html#wp1034096
**********
Cisco Press - IS-IS Network Design Solutions Multihoming "...the devices
begin to exchange all their originally separate Level 1 databases, which are
then flooded to the other level 1 neighbors. This effectively merges the two
areas."
Multi-area
"Multi-area support allows a single router to participate in up to 29
independent Level 1 areas with one of them doubling as Level 2 if
necessary...
...Redistribution between processes is not allowed; however, external
routing sources can be redistributed into each area independently."
**********
Key points are how Level 1 and 2 are affected.
Multi-area
Max 1 Level 2
Level 1 processes independent
Cannot redistribute between processes
Can redistribute external routing sources into each area independently
Multihoming
Can have multiple Level 2
Level 1 databases merged
**********
Marvin Greenlee, CCIE#12237, CCSI# 30483 Network Learning Inc
marvin@ccbootcamp.com www.ccbootcamp.com (Cisco Training)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Thursday, March 10, 2005 9:17 AM
To: Group Study
Subject: IS-IS multi-area [bcc][faked-from][bayes]
Importance: Low
Hi guys,
I understand how to configure multiple areas by using tags like this:
!
router isis TEST-1
net 49.0001.0000.0000.0005.00
is-type level-1
!
router isis TEST-2
net 49.0002.0000.0000.0005.00
router isis TEST-3
net 49.0003.0000.0000.0005.00
But, what I can't figure out, is how to recognize a requirement for multiple
areas. How could tell that something
like the above is needed instead of something like this:
Router isis
net 49.0001.0000.0000.0001.00
net 49.0002.0000.0000.0001.00
net 49.0003.0000.0000.0001.00
BTW, why does the system ID portion of all areas have to be the same when
the area ID is different?
TIA, Tim
This archive was generated by hypermail 2.1.4 : Sun Apr 03 2005 - 17:56:44 GMT-3