From: Joseph D. Phillips (josephdphillips@fastmail.us)
Date: Tue Jul 06 2004 - 17:27:57 GMT-3
Well the advantage of using tags is that you don't need to specify which
networks are which in an access list.
Let's say there are two routing protocols: OSPF and RIPv2
Your statement under router ospf would be something like:
redist rip sub metric-ty 1 metric 50 route-map r2o
Your statement under router rip would look something like:
redist ospf (process no.) metric 2 ma in ex route-map o2r
The route maps would look like:
route-map r2o deny 10
match tag 110 <----stop routes with tag 110 from coming in
route-map r2o perm 20
set tag 120 <-------accept RIP routes and tag them as 120
route-map o2r deny 10
match tag 120 <-----stop routes with tag 120 from coming in
route-map perm 20
set tag 110 <-----accept OSPF routes and tag them as 110
The numbers used to assign tags are arbitrary, but I like to associate
them with administrative distance.
The purpose of the above route-maps is to prevent route feedback.
It seems to work rather well. I've had no problem with it.
----- Original message -----
From: "Rohan Grover" <rohang@cisco.com>
To: "'Joseph D. Phillips'" <josephdphillips@fastmail.us>, "'group
study'" <ccielab@groupstudy.com>
Date: Wed, 7 Jul 2004 00:35:02 +0530
Subject: RE: Redistribution Methodology
Hi Joseph,
Can you give an example of how the scenario described below could be
achieved with tags?
Thanks
Rohan
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Joseph D. Phillips
Sent: Wednesday, July 07, 2004 12:23 AM
To: group study
Subject: Redistribution Methodology
Start doing it with tags. There's a good chance you will be asked to do
that on the exam.
----- Original message -----
From: "Joe Rinehart" <jjrinehart@hotmail.com>
To: "'Group Study (E-mail)'" <ccielab@groupstudy.com>
Date: Tue, 6 Jul 2004 11:42:52 -0700
Subject: Redistribution Methodology
I have a question that has been bugging me for a little while and would
like to see what the overall opinion is on the subject.
When redistributing routing protocols (I am speaking here mainly of IGP
redistribution), I know that route feedback can be an issue,
especially where mutual redistribution is concerned. Something I have
been doing in those instances is putting in filters and route
maps to prevent that.
Here is the basic methodology, per protocol:
1. Create an access list with the routes to be filtered (i.e., those
already in that IGP that shouldnt be coming back in from
another source). This is a series of deny statements followed by a
permit any statement.
2. Create a route map calling that access list.
3. Configure the redistribute statement under the target IGP calling
that route map.
Here is an example below, you may recognize it from CPSV2: router eigrp
2003 redistribute ospf 1 route-map filter-eigrp
redistribute rip route-map filter-eigrp passive-interface default no
passive-interface Serial0/0.103105 network 175.10.16.0
0.0.0.255 network 175.10.120.0 0.0.0.255 default-metric 1544 100 254 1
1500 no auto-summary no eigrp log-neighbor-changes !
router ospf 1 log-adjacency-changes area 0 authentication
message-digest area 500 stub redistribute connected route-map
CONNECTED redistribute eigrp 2003 subnets route-map filter-ospf
redistribute rip subnets route-map filter-ospf network 10.1.1.0
0.0.0.255 area 500 network 192.168.1.0 0.0.0.255 area 100 network
192.168.2.0 0.0.0.255 area 0 ! router rip version 2
redistribute eigrp 2003 route-map filter-eigrp redistribute ospf 1
route-map filter-eigrp passive-interface default no
passive-interface Serial0/0.100 network 175.10.0.0 default-metric 5
no auto-summary
access-list 1 deny 175.10.1.0 0.0.0.255
access-list 1 deny 175.10.16.0 0.0.0.255
access-list 1 permit any
access-list 2 deny 175.10.0.0 0.0.63.255
access-list 2 permit any
access-list 3 deny 10.10.1.0 0.0.0.255
access-list 3 deny 10.10.2.0 0.0.0.255
access-list 3 deny 192.200.0.0 0.0.255.255
access-list 3 deny 192.168.0.0 0.0.31.255
access-list 3 permit any
dialer-list 1 protocol ip permit
route-map filter-ospf permit 10
match ip address 3
!
route-map filter-eigrp permit 10
match ip address 1
!
route-map filter-rip permit 10
match ip address 2
Here is my question. I KNOW that this approach works rather splendidly
and can take pretty much everything into account as a
template overall, but is this the kind of thing that can cost you points
on the exam? I know that the rules of thumb are if they
dont forbid something you are allowed to do it, and ultimately the other
test is if it works, but I also know there is a subjective
aspect as well.
Thoughts?
Joe Rinehart
AT&T
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