From: dwhitley@xxxxxxxxx
Date: Sun Jan 28 2001 - 17:26:31 GMT-3
Jeff Doyle, Routing TCP/IP volume 1 Chapter 13 route filtering.
I just read this chapter and he has a good explanation.
I haven't done the lab but in the setup it calls for MD5 authentication
between r1 and r2 using RIP version 2. And as for the administrative
distances because you are doing mutual redistribution routes will be learned
from 2 sources. For example R2 will get routes for R1's ethernet from OSPF
and use this route because of the default administrative distance of 110
even though the better route would be via the serial to R1 learned from RIP
distance 120. A route filter could be used be at the expense of losing
redundacy. So setting all default distances to 130 and then specifically
assigning a distance of 110 to the optimal routes using the access-lists
will allow optimal routing and if the primary goes away you still will have
a backup route after reconvergence with a higher admin distance.
The distance command in plain text is
distance 110 0.0.0.0 255.255.255.255 1
Assign a distance of 110 to routes from route source 0.0.0.0 255.255.255.255
that are permitted by access-list number 1
-----Original Message-----
From: Piperw222@aol.com
To: ccielab@groupstudy.com
Sent: 1/28/01 12:09 PM
Subject: CCIE BOOTCAMP LAB7 - ROUTING LOOPS
Hi everyone,
I have been working with lab 7 and I am trying to understand the
logic
of what is going on with some of the configs - in preventing the routing
loops via the redistribution gong on in both R6 and R2. can anyone
explain to
me the logic of the administrative distance and access-lists in the
following
configs as well as how this prevents routing loops from occurring... In
addition why is it that you need to have rip version2 between r2 and r6
is it
because of the requirement or is it needed for routing to work more
efficiently.
Thanks,
R6
router ospf 1
redistribute rip metric 100 subnets
network 10.100.1.6 0.0.0.0 area 0
network 10.6.1.1 0.0.0.0 area 6
distance 130
distance 110 0.0.0.0 255.255.255.255 1
!
router rip
timers basic 5 15 0 30
redistribute ospf 1 metric 2
passive-interface Ethernet0
passive-interface Serial0
network 10.0.0.0
distance 130
distance 120 10.65.1.2 0.0.0.0 2
!
no ip classless
no logging console
access-list 1 permit 10.3.0.0 0.0.255.255
access-list 1 permit 10.33.0.0 0.0.255.255
access-list 1 permit 10.101.0.0 0.0.255.255
access-list 1 permit 137.20.20.0 0.0.0.255
access-list 2 permit 10.51.0.0 0.0.255.255
access-list 2 permit 10.21.0.0 0.0.255.255
access-list 901 deny any any all any sap
access-list 901 deny any any all any rip
access-list 901 deny any any all any 457
access-list 901 permit any any all any all
!
R2
router ospf 1
redistribute rip metric 100 subnets
network 10.101.1.2 0.0.0.0 area 0
network 137.20.20.1 0.0.0.0 area 2
default-information originate metric 200 metric-type 1
distance 130
distance 110 0.0.0.0 255.255.255.255 1
!
router rip
version 2
timers basic 5 15 0 30
redistribute ospf 1 metric 2
passive-interface Ethernet0
passive-interface Serial0
network 10.0.0.0
distance 130
distance 120 10.21.1.2 0.0.0.0 2
!
no ip classless
ip route 0.0.0.0 0.0.0.0 137.20.20.2
no logging console
access-list 1 permit 10.33.0.0 0.0.255.255
access-list 1 permit 10.3.0.0 0.0.255.255
access-list 1 permit 10.6.0.0 0.0.255.255
access-list 1 permit 10.100.0.0 0.0.255.255
access-list 2 permit 10.51.0.0 0.0.255.255
access-list 2 permit 10.65.0.0 0.0.255.255
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