From: OhioHondo (ohiohondo@columbus.rr.com)
Date: Fri Dec 20 2002 - 11:18:31 GMT-3
Hunt
The RIPv1 process on the sending router looks at the interface that it is
sending its update on. It looks at the subnet mask used and the classful
network of the interface. It looks at the IP routing table and builds it's
routing update to send with the following rules:
- if the routing table entry has the same classful network and the same
subnet mask, it becomes part of the update.
- if the routing table entry has the same classful network and a different
subnet mask, it is dropped and DOES NOT become part of the update.
- if it IS NOT of the same classful network, an update is created using the
natural mask of the classful network
Use "debug ip rip" to see what updates are sent.
If you want a router to send updates of routes that have the same classful
network but a different subnet mask than the interface that they are being
sent on, you must summarize those routes to have the same sunet mask as the
interface that they are being sent on.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Hunt Lee
Sent: Thursday, December 19, 2002 10:40 PM
To: 'ccielab@groupstudy.com'
Subject: What if EIGRP routes have different masks than RIP?
Guys,
I'm sure this question has been asked many times before, but can someone
kindly explain to me again? There are some /25 routes & /29 routes in EIGRP
that I need to redistribute into RIP v1. The serial frame relay link that
connects R1 with R4 has a /24 mask, and so as the Ethernet link that
connects R4 & R5. How can I inject /25 & /29 EIGRP routes into a classful
routing domain in a case such as this?
172.16.5.1 /25
---------------
|
R1
/ | \
/ | \
R2 R3 R4 --- R5
The entire Hub & Spoke network is EIGRP only, except R4 which is running
both EIGRP & RIPv1 (& mutual redistribution between the 2 protocols), & R5
is running RIPv1 only.
R1's Multipoint interface to R2 & 3 - 192.168.1.1 /29
R1's P-2-P interface to R4 - 192.168.2.1 /24
R2's FR interface - 192.168.1.2 /29
R3's FR interface - 192.168.1.3 /29
R4's FR interface to R1 - 192.168.2.2 /24
R4's Ethernet to R5 - 172.16.2.1 /24
R5's interface - 172.16.2.2 /24
From what I read from Cisco books, since the RIPv1 network in this e.g. is
/24, both routes 192.168.1.0/29 & 172.16.5.0/25 would need to be summarized
into a /24 (at R1) before R4 would be willing to pass these routes to R5.
However, on the moment, all I had at R1 is:-
interface Serial0/0.2 point-to-point
ip address 192.168.2.1 255.255.255.0
ip summary-address eigrp 65001 172.16.5.0 255.255.255.0 5
frame-relay interface-dlci 130
And you can see that R5 "somehow" managed to get the Frame-Relay route
(192.168.1.0/29) - into a /24, don't undersantd how.
R5#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter
area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 4 subnets
R 172.16.5.0 [120/5] via 172.16.2.1, 00:00:24, Ethernet0
R 172.16.6.0 [120/5] via 172.16.2.1, 00:00:24, Ethernet0
C 172.16.2.0 is directly connected, Ethernet0
R 172.16.3.0 [120/5] via 172.16.2.1, 00:00:24, Ethernet0
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, Dialer0
R 192.168.1.0/24 [120/5] via 172.16.2.1, 00:00:24, Ethernet0
R 192.168.2.0/24 [120/5] via 172.16.2.1, 00:00:24, Ethernet0
30.0.0.0/24 is subnetted, 1 subnets
C 30.3.3.0 is directly connected, Loopback0
R5#
Yet I can see it clearly that the Frame Relay routes were definitely a /29
R1#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter
area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
D 172.16.5.0/24 is a summary, 03:55:51, Null0
C 172.16.5.0/25 is directly connected, Loopback1
D 172.16.6.0/24 [90/20640000] via 192.168.1.2, 03:53:17, Serial0/0.1
D 172.16.2.0/24 [90/2195456] via 192.168.2.2, 03:54:30, Serial0/0.2
D 172.16.3.0/24 [90/20640000] via 192.168.1.3, 03:56:00, Serial0/0.1
192.168.1.0/29 is subnetted, 1 subnets
C 192.168.1.0 is directly connected, Serial0/0.1
C 192.168.2.0/24 is directly connected, Serial0/0.2
R1#
R4#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter
area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 4 subnets
D 172.16.5.0 [90/2297856] via 192.168.2.1, 03:56:59, Serial0
D 172.16.6.0 [90/21152000] via 192.168.2.1, 03:55:45, Serial0
C 172.16.2.0 is directly connected, Ethernet0
D 172.16.3.0 [90/21152000] via 192.168.2.1, 03:56:59, Serial0
192.168.1.0/29 is subnetted, 1 subnets
D 192.168.1.0 [90/21024000] via 192.168.2.1, 03:56:59, Serial0
C 192.168.2.0/24 is directly connected, Serial0
R4#
Thanks in advance,
Hunt
.
.
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