Re: IGRP and RIP redistributions mutual

zillah2004 · ‎01-18-2006

I have got this scenario

RouterA is configured as shown below:

router igrp 100

network 197.135.20.0

network 197.135.24.0

network 197.135.27.0

redistribute rip

default-metric 10 100 255 1 1500

distance 140 0.0.0.0 255.255.255.255 9

access-list 9 permit 197.135.20.0

access-list 9 permit 197.135.24.0

access-list 9 permit 197.135.27.0

1- Are RIP and IGRP two way redistributions (It is obvious that we can redistribute RIP into IGRP but can we do vice versa ) ?

2- Does the command "distance 140 0.0.0.0,,,,,,," affect (change administrative distance) the redistributed RIP and the three networks addresses (197.135.20.0, 197.135.24.0, 197.135.27.0) as well, or it only change ?

3- Why has the wildcard been omitted with the standard ACL above ?

mheusinger · ‎01-18-2006

Hello,

A.1) You CAN redistribute practically any IP routing protocol into any other IP routing protocol. The "redistibute" command tells a routing process to take the routes inserted into the routing table by the specified IP routing protocol. So as an example

router eigrp 10

redistribute ospf 100

tells EIGRP to pick up the networks inserted into the routing table through OSPF process 100.

So we can redsitribute RIP into IGRP and/or IGRP into RIP. For each "direction" you will need one separate command each under the "router rip" and "router igrp"

A.2) From "IP Routing Protocol-Independent Commands" at

http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_command_reference_chapter09186a00800ca69c.html

we get:

In the following example, the router igrp global configuration command sets up IGRP routing in autonomous system number 109. The network router configuration commands specify IGRP routing on networks 192.168.7.0 and 172.16.0.0. The first distance router configuration command sets the default administrative distance to 255, which instructs the Cisco IOS software to ignore all routing updates from routers for which an explicit distance has not been set. The second distance command sets the administrative distance for all routers on the Class C network 192.168.7.0 to 90. The third distance command sets the administrative distance for the router with the address 172.16.1.3 to 120.

router igrp 109

network 192.168.7.0

network 172.16.0.0

distance 255

distance 90 192.168.7.0 0.0.0.255

distance 120 172.16.1.3 0.0.0.0

Hope this helps! Please rate all posts.

Regards, Martin

pkhatri · ‎01-18-2006

Hi,

Addressing your points above:

1. As Martin pointed out, there is no restriction on which protocols you can redistribute between. You can certainly redistribute IGRP into RIP.

2. The 'distance 140' will apply to all routes matching ACL 9 received via IGRP from all neighbors (since you have used 0.0.0.0 255.255.255.255 which applies to all neighbors). Since ACL 9 matches on only three addresses, the distance command will only apply to these three routes (with all prefix lengths that can apply to them - see my response to 3 below). Pls be aware that the use of an ACL with the distance command is quite different to the use of ACL with inbound/outbound access-lists. In this case, the ACL will look for prefixes received in IGRP updates that match 197.135.20.0, 197.135.24.0 and 197.135.27.0 regardless of their subnet masks (which is not an issue with a classless protocol like IGRP anyway).

Also note that this distance command will not affect any of the routes redistributed from RIP, since the routes that are redistributed from RIP will be present in the routing table as RIP routes. Since the originating protocol for these routes is RIP, any distance command you apply to the IGRP process will have no effect on these routes.

When you redistribute routes from protocol A into protocol B, they still appear in the routing table as being learned from protocol A.

3. A missing wildcard usually means it is a host route. However, as I indicated above, in the case of matching route prefixes, it will mean that for example, access-list 9 permit 197.135.20.0 will match any of:

197.135.20.0 255.255.255.127

197.135.20.0 255.255.255.63

197.135.20.0 255.255.255.31

197.135.20.0 255.255.255.15

197.135.20.0 255.255.255.7

197.135.20.0 255.255.255.3

197.135.20.0 255.255.255.1

197.135.20.0 255.255.255.0

Hope that explains it...

Pls remember to rate posts.

Paresh.

zillah2004 · ‎01-19-2006

((2. The 'distance 140' will apply to all routes matching ACL 9 received via IGRP from all neighbors (since you have used 0.0.0.0 255.255.255.255 which applies to all neighbors).))

In the scenario,,,the networks 197.135.20.0, 197.135.24.0 and 197.135.27.0 are not neighbor networks, because they are directly connected to my router,,,,why did you call them as neighbors ?

((197.135.20.0 255.255.255.127

197.135.20.0 255.255.255.63

197.135.20.0 255.255.255.31

197.135.20.0 255.255.255.15

197.135.20.0 255.255.255.7

197.135.20.0 255.255.255.3

197.135.20.0 255.255.255.1

197.135.20.0 255.255.255.0 ))

Did you mean 0.0.0.0 127 and 0.0.0.0.63-----etc ?

pkhatri · ‎01-19-2006

I said they were neighbor networks because the distance command would only be applied to these routes if received from other neighbors.

If you are not getting these routes in updates from your neighbors, then I agree, the config is useless...

Pls remember to rate posts.

Paresh.

zillah2004 · ‎01-19-2006

In this scenario, with these 3 network addresses, I have got two possibility, either they are directly connected or they are form neighbors.

They can not be form neighbors because they are configured under "network" command for IGRP,,,,Does that mean there is a contradiction in this scenario, between "network" command and "distnace" command and networks addresses ?

pkhatri · ‎01-19-2006

Why not ?

Consider this:

RTA --- RTB

The link IP on RTA is 192.168.1.1/24 and that on RTB is 192.168.1.2/24.

If they are running EIGRP between these links, they will both have:

router eigrp 10

network 192.168.1.0

Therefore, for both of them 192.168.1.0/24 is a route eligible to be advertised by EIGRP.

Does that make sense ?

Paresh.

zillah2004 · ‎01-19-2006

((Therefore, for both of them 192.168.1.0/24 is a route eligible to be advertised by EIGRP. ))

If I iusse ip route on both RTA and RTB,,,the network 192.168.1.0/24 will be marked as "C" directly connectd not D as "EIGRP"

zillah2004 · ‎01-21-2006

Another thing I forgot to mention ,,,why can I use the subnet mask as well the wild card mask with the configuration of EIGRP's distnace command ?,,,

I meant why does a router not complain when we used wildcard mask with distance command with EIGRP,,,,because Cisco's documentation refers to subnet mask not wild card mask.

pkhatri · ‎01-21-2006

Hi,

To answer your first question: yes, the route will appear as directly connected. However, that does not mean that the same route cannot be received in an EIGRP update from a neighbor. Remember that connected routes (with an AD of 0) will always take precedece over routes learned by any other means.

To your second question: it is true that the network statement fo EIGRP will accept both a subnet mask and a wildcard mask. The router is smart enough to recognise that you have specified a subnet mask and will convert it to a wildcard mask. It's there just to make life easier for you. Also note that the router will always display the wildcard mask with the network and not the subnet mask.

Pls do remember to rate posts.

Paresh.