RIPv2 Broadcast updates
RIP version 1 always uses broadcasts. 255.255.255.255 That is expected behavior.
The updates aren't sent classless per se. They are sent without a
mask. The receiving side makes the assumption of the associated mask
based on the receiving interface. So RIPv1 can actually work in a
subnetted network assuming two things:
if we want to test this between R1 and R2 change the version of RIP and check the debug
R1# config t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router rip
R1(config-router)#version 1
R1(config-router)#exit
R1(config)#exit
R1#de
*Mar 2 21:29:31.232: %SYS-5-CONFIG_I: Configured from console by console
R1#deb ip rip
RIP protocol debugging is on
R1#
R1#
R1#
R1#
*Mar 2 21:29:37.016: RIP: sending v1 update to 255.255.255.255 via Loopback1 (1.1.1.1)
*Mar 2 21:29:37.020: RIP: build update entries
*Mar 2 21:29:37.020: subnet 1.1.0.0 metric 1
*Mar 2 21:29:37.024: subnet 1.1.2.0 metric 1
*Mar 2 21:29:37.024: subnet 1.1.3.0 metric 1
*Mar 2 21:29:37.024: network 2.0.0.0 metric 1
*Mar 2 21:29:37.028: network 3.0.0.0 metric 3
*Mar 2 21:29:37.032: network 4.0.0.0 metric 1
*Mar 2 21:29:37.032: network 12.0.0.0 metric 1
*Mar 2 21:29:37.036: network 14.0.0.0 metric 1
*Mar 2 21:29:37.036: network 23.0.0.0 metric 1
*Mar 2 21:29:37.040: network 34.0.0.0 metric 1
*Mar 2 21:29:37.040: network 172.16.0.0 metric 4
R1#
R1#
*Mar 2 21:29:37.336: RIP: ignored v2 packet from 14.1.1.2 (illegal version)
*Mar 2 21:29:37.456: RIP: sending v1 update to 255.255.255.255 via Serial0/0 (12.1.1.1)
*Mar 2 21:29:37.460: RIP: build update entries
*Mar 2 21:29:37.460: network 1.0.0.0 metric 1
*Mar 2 21:29:37.464: network 2.0.0.0 metric 1
*Mar 2 21:29:37.464: network 4.0.0.0 metric 1
*Mar 2 21:29:37.468: network 14.0.0.0 metric 1
*Mar 2 21:29:37.468: network 34.0.0.0 metric 1
*Mar 2 21:29:37.468: network 172.16.0.0 metric 4
R1#no deb ip rip
RIP protocol debugging is off
R1#
-===version 2
R1(config)#router rip
R1(config-router)#version 2
R1(config-router)#
*Mar 2 22:59:19.368: RIP: sending v2 update to 224.0.0.9 via Loopback10 (172.16.0.10)
*Mar 2 22:59:19.372: RIP: build update entries
*Mar 2 22:59:19.372: 1.1.0.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.376: 1.1.1.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.376: 1.1.2.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.380: 1.1.3.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.384: 2.2.4.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 2 22:59:19.384: 2.2.5.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 2 22:59:19.388: 2.2.6.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 2 22:59:19.388: 2.2.7.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 2 22:59:19.388: 3.3.8.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.388: 3.3.9.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.388: 3.3.10.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.388: 3.3.11.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.388: 4.4.12.0/24 via 0.0.0.0, metric 3, tag 0
*Mar 2 22:59:19.388: 4.4.13.0/24 via 0.0.0.0, metric 3, tag 0
*Mar 2 22:59:19.388: 4.4.14.0/24 via 0.0.0.0, metric 3, tag 0
*Mar 2 22:59:19.388: 4.4.15.0/24 via 0.0.0.0, metric 3, tag 0
*Mar 2 22:59:19.388: 12.1.1.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 2 22:59:19.388: 14.1.1.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.388: 23.1.1.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 2 22:59:19.388: 34.1.1.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 2 22:59:19.388: 172.16.0.20/32 via 0.0.0.0, metric 1, tag 0
*Mar 2 22:59:19.400: RIP: ignored v2 packet from 172.16.0.10 (sourced from one of our addresses)
R2#
*Mar 2 22:59:21.392: RIP: received packet with MD5 authentication
*Mar 2 22:59:21.396: RIP: received v2 update from 12.1.1.1 on Serial0/0
*Mar 2 22:59:21.400: 1.1.0.0/24 via 0.0.0.0 in 1 hops
*Mar 2 22:59:21.400: 1.1.1.0/24 via 0.0.0.0 in 1 hops
*Mar 2 22:59:21.404: 1.1.2.0/24 via 0.0.0.0 in 1 hops
*Mar 2 22:59:21.408: 1.1.3.0/24 via 0.0.0.0 in 1 hops
*Mar 2 22:59:21.408: 2.2.6.0/24 via 0.0.0.0 in 4 hops
*Mar 2 22:59:21.412: 4.4.12.0/24 via 0.0.0.0 in 2 hops
*Mar 2 22:59:21.412: 4.4.13.0/24 via 0.0.0.0 in 2 hops
*Mar 2 22:59:21.416: 4.4.14.0/24 via 0.0.0.0 in 2 hops
R2#
*Mar 2 22:59:21.420: 4.4.15.0/24 via 0.0.0.0 in 2 hops
*Mar 2 22:59:21.424: 14.1.1.0/24 via 0.0.0.0 in 1 hops
*Mar 2 22:59:21.424: 34.1.1.0/24 via 0.0.0.0 in 2 hops
*Mar 2 22:59:21.424: 172.16.0.10/32 via 0.0.0.0 in 4 hops
*Mar 2 22:59:21.424: 172.16.0.20/32 via 0.0.0.0 in 4 hops
R2#
R2#
Tuesday, 27 October 2015
RIPv2 source update validation
RIPv2 source update validation
R2(config)#router rip
R2(config-router)#no validate-update-source
RIP (and IGRP too) checks to see if the source of the update received is in the same subnet as that configured on the router's receiving interface.
When a router running Routing Information Protocol (RIP) receives an update from a neighboring router, it checks whether the source of the update belongs to the same network or sub-network as the receiving interface. If they are the same, the routes are accepted for installing into the routing table. Otherwise, the update is dropped.
- Source of a RIP packet must be on the same subnet as the receiving interface
- Packet not coming from the same subnet will be ignored.
R2(config)#router rip
R2(config-router)#no validate-update-source
RIP (and IGRP too) checks to see if the source of the update received is in the same subnet as that configured on the router's receiving interface.
When a router running Routing Information Protocol (RIP) receives an update from a neighboring router, it checks whether the source of the update belongs to the same network or sub-network as the receiving interface. If they are the same, the routes are accepted for installing into the routing table. Otherwise, the update is dropped.
This situation is more common in dial-up environments when the ip unnumbered command is issued on one end and ip address negotiated
command is issued on the other end, which can result in different
subnet masks, although the addresses are actually assigned from the same
subnet. This can also occur when connecting across a firewall which
does not participate in routing but transparently forwards the updates
between the routers connected to its various interfaces belonging to
different subnets. This can also occur if RIP is used in Multiprotocol
Label Switching (MPLS) Virtual Private Network (VPN) environments over
multiple Generic Routing Encapsulation (GRE) tunnels belonging to
different Virtual Routing and Forwarding (VRF) tables on the router, and
the same addresses are used as tunnel endpoints for the different
tunnels.
Resolution:
If you issue the debug ip rip command, the error message starting with the text RIP: ignored v2 update from bad source or RIP: ignored v1 update from bad source is not displayed depending on the RIP version being used. This indicates that the source of the update is not on the same subnet as the receiving interface.
To resolve this problem, issue the no validate-update-source command under router configuration mode of RIP, which stops validating the source address and accepts the updates.
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#router rip
R2(config-router)#no validate-update-source
R2(config-router)#end
R2#
Make
sure that you issue this command with caution since it may hide a real
problem if the IP addresses on the routers are misconfigured. When using
RIP over GRE tunnels with VRFs in an MPLS VPN environment, use unique
endpoints as tunnel source and tunnel destination for different GRE
tunnels.
Monday, 26 October 2015
RIPv2 filtering with Administrative distance
RIPv2 filtering with AD
In this example we are filtering from R2 the subnet 2.2.5.0/24
R1(config)#access-list 5 permit 2.2.5.0 ?
A.B.C.D Wildcard bits
log Log matches against this entry
<cr>
R1(config)#access-list 5 permit 2.2.5.0 0.0.0.255 ?
log Log matches against this entry
<cr>
R1(config)#access-list 5 permit 2.2.5.0 0.0.0.255 log
R1(config)#router rip
R1(config-router)#dist
R1(config-router)#distance 255 0.0.0.0 255.255.255.255 ?
<1-99> IP Standard access list number
<1300-1999> IP Standard expanded access list number
WORD Standard access-list name
<cr>
R1(config-router)#distance 255 0.0.0.0 255.255.255.255 5
R1(config-router)#do clear ip route *
R1(config-router)#
*Mar 2 00:57:26.809: %SEC-6-IPACCESSLOGNP: list 5 permitted 0 2.2.5.0 -> 0.0.0.0, 1 packet
R1(config-router)#do sh ip route 2.0.0.0
Routing entry for 2.0.0.0/24, 3 known subnets
Redistributing via rip
R 2.2.4.0 [120/1] via 12.1.1.2, 00:00:14, Serial0/0
R 2.2.6.0 [120/3] via 14.1.1.2, 00:00:18, Serial0/1
R 2.2.7.0 [120/1] via 12.1.1.2, 00:00:14, Serial0/0
R1(config-router)#
Another example
we have two paths to arrive to a destination in subnet 4.4.12.and 4.4.15 starting from R2 we wnat to make one path primary ,and filter the second one
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 23.1.1.2, 00:00:29, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
R 1.1.0.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
R 1.1.1.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
R 1.1.2.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
R 1.1.3.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
2.0.0.0/24 is subnetted, 4 subnets
C 2.2.4.0 is directly connected, Loopback0
C 2.2.5.0 is directly connected, Loopback1
C 2.2.6.0 is directly connected, Loopback2
C 2.2.7.0 is directly connected, Loopback3
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
R 3.3.9.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
R 3.3.10.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
R 3.3.11.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/2] via 23.1.1.2, 00:00:02, Serial0/1
[120/2] via 12.1.1.1, 00:00:11, Serial0/0
R 4.4.13.0 [120/2] via 12.1.1.1, 00:00:11, Serial0/0
R 4.4.14.0 [120/2] via 23.1.1.2, 00:00:02, Serial0/1
[120/2] via 12.1.1.1, 00:00:11, Serial0/0
R 4.4.15.0 [120/2] via 23.1.1.2, 00:00:02, Serial0/1
[120/2] via 12.1.1.1, 00:00:11, Serial0/0
23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial0/1
172.16.0.0/32 is subnetted, 2 subnets
C 172.16.0.20 is directly connected, Loopback20
C 172.16.0.10 is directly connected, Loopback10
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
R 14.1.1.0 [120/1] via 12.1.1.1, 00:00:13, Serial0/0
R2#config t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#acc
R2(config)#access-list 12 permit 4.4.12.0
R2(config)#access-
R2(config)#access-list 13 permit 4.4.15.0
R2(config)#router rip
R2(config-router)#distance 255 23.1.1.2 0.0.0.0 ?
<1-99> IP Standard access list number
<1300-1999> IP Standard expanded access list number
WORD Standard access-list name
<cr>
R2(config-router)#distance 255 23.1.1.2 0.0.0.0 12
R2(config-router)#distance 255 12.1.1.1 0.0.0.0 13
R2(config-router)#do clear ip route *
R2(config-router)#do sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 23.1.1.2, 00:00:09, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
R 1.1.0.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
R 1.1.1.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
R 1.1.2.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
R 1.1.3.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
2.0.0.0/24 is subnetted, 4 subnets
C 2.2.4.0 is directly connected, Loopback0
C 2.2.5.0 is directly connected, Loopback1
C 2.2.6.0 is directly connected, Loopback2
C 2.2.7.0 is directly connected, Loopback3
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
R 3.3.9.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
R 3.3.10.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
R 3.3.11.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/2] via 12.1.1.1, 00:00:12, Serial0/0
R 4.4.13.0 [120/2] via 12.1.1.1, 00:00:12, Serial0/0
R 4.4.14.0 [120/2] via 23.1.1.2, 00:00:12, Serial0/1
[120/2] via 12.1.1.1, 00:00:12, Serial0/0
R 4.4.15.0 [120/2] via 23.1.1.2, 00:00:12, Serial0/1
23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial0/1
172.16.0.0/32 is subnetted, 2 subnets
C 172.16.0.20 is directly connected, Loopback20
C 172.16.0.10 is directly connected, Loopback10
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
R 14.1.1.0 [120/1] via 12.1.1.1, 00:00:13, Serial0/0
R2(config-router)#
In this example we are filtering from R2 the subnet 2.2.5.0/24
R1(config)#access-list 5 permit 2.2.5.0 ?
A.B.C.D Wildcard bits
log Log matches against this entry
<cr>
R1(config)#access-list 5 permit 2.2.5.0 0.0.0.255 ?
log Log matches against this entry
<cr>
R1(config)#access-list 5 permit 2.2.5.0 0.0.0.255 log
R1(config)#router rip
R1(config-router)#dist
R1(config-router)#distance 255 0.0.0.0 255.255.255.255 ?
<1-99> IP Standard access list number
<1300-1999> IP Standard expanded access list number
WORD Standard access-list name
<cr>
R1(config-router)#distance 255 0.0.0.0 255.255.255.255 5
R1(config-router)#do clear ip route *
R1(config-router)#
*Mar 2 00:57:26.809: %SEC-6-IPACCESSLOGNP: list 5 permitted 0 2.2.5.0 -> 0.0.0.0, 1 packet
R1(config-router)#do sh ip route 2.0.0.0
Routing entry for 2.0.0.0/24, 3 known subnets
Redistributing via rip
R 2.2.4.0 [120/1] via 12.1.1.2, 00:00:14, Serial0/0
R 2.2.6.0 [120/3] via 14.1.1.2, 00:00:18, Serial0/1
R 2.2.7.0 [120/1] via 12.1.1.2, 00:00:14, Serial0/0
R1(config-router)#
Another example
we have two paths to arrive to a destination in subnet 4.4.12.and 4.4.15 starting from R2 we wnat to make one path primary ,and filter the second one
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 23.1.1.2, 00:00:29, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
R 1.1.0.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
R 1.1.1.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
R 1.1.2.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
R 1.1.3.0 [120/1] via 12.1.1.1, 00:00:08, Serial0/0
2.0.0.0/24 is subnetted, 4 subnets
C 2.2.4.0 is directly connected, Loopback0
C 2.2.5.0 is directly connected, Loopback1
C 2.2.6.0 is directly connected, Loopback2
C 2.2.7.0 is directly connected, Loopback3
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
R 3.3.9.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
R 3.3.10.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
R 3.3.11.0 [120/1] via 23.1.1.2, 00:00:02, Serial0/1
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/2] via 23.1.1.2, 00:00:02, Serial0/1
[120/2] via 12.1.1.1, 00:00:11, Serial0/0
R 4.4.13.0 [120/2] via 12.1.1.1, 00:00:11, Serial0/0
R 4.4.14.0 [120/2] via 23.1.1.2, 00:00:02, Serial0/1
[120/2] via 12.1.1.1, 00:00:11, Serial0/0
R 4.4.15.0 [120/2] via 23.1.1.2, 00:00:02, Serial0/1
[120/2] via 12.1.1.1, 00:00:11, Serial0/0
23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial0/1
172.16.0.0/32 is subnetted, 2 subnets
C 172.16.0.20 is directly connected, Loopback20
C 172.16.0.10 is directly connected, Loopback10
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
R 14.1.1.0 [120/1] via 12.1.1.1, 00:00:13, Serial0/0
R2#config t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#acc
R2(config)#access-list 12 permit 4.4.12.0
R2(config)#access-
R2(config)#access-list 13 permit 4.4.15.0
R2(config)#router rip
R2(config-router)#distance 255 23.1.1.2 0.0.0.0 ?
<1-99> IP Standard access list number
<1300-1999> IP Standard expanded access list number
WORD Standard access-list name
<cr>
R2(config-router)#distance 255 23.1.1.2 0.0.0.0 12
R2(config-router)#distance 255 12.1.1.1 0.0.0.0 13
R2(config-router)#do clear ip route *
R2(config-router)#do sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 23.1.1.2, 00:00:09, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
R 1.1.0.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
R 1.1.1.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
R 1.1.2.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
R 1.1.3.0 [120/1] via 12.1.1.1, 00:00:09, Serial0/0
2.0.0.0/24 is subnetted, 4 subnets
C 2.2.4.0 is directly connected, Loopback0
C 2.2.5.0 is directly connected, Loopback1
C 2.2.6.0 is directly connected, Loopback2
C 2.2.7.0 is directly connected, Loopback3
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
R 3.3.9.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
R 3.3.10.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
R 3.3.11.0 [120/1] via 23.1.1.2, 00:00:12, Serial0/1
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/2] via 12.1.1.1, 00:00:12, Serial0/0
R 4.4.13.0 [120/2] via 12.1.1.1, 00:00:12, Serial0/0
R 4.4.14.0 [120/2] via 23.1.1.2, 00:00:12, Serial0/1
[120/2] via 12.1.1.1, 00:00:12, Serial0/0
R 4.4.15.0 [120/2] via 23.1.1.2, 00:00:12, Serial0/1
23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial0/1
172.16.0.0/32 is subnetted, 2 subnets
C 172.16.0.20 is directly connected, Loopback20
C 172.16.0.10 is directly connected, Loopback10
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
R 14.1.1.0 [120/1] via 12.1.1.1, 00:00:13, Serial0/0
R2(config-router)#
RIPv2 filtering with standard access-list
example
R1 and R2 We have applied in R1 an access-list to filter from route R2 a particular route 2.2.6.0 255.255.255.0
R1(config)#ip access-list standard NET226
R1(config-std-nacl)#5 deny 2.2.6.0 0.0.0.255
R1(config-std-nacl)#20 permit any
R1(config-std-nacl)#do sh run | s ip acc
ip access-list standard NET226
deny 2.0.0.0 0.0.0.255
permit any
R1(config t)#router rip
R1(config-router)#distribute-list NET226 in
R1(config-router)#do clear ip route *
R1# sh run | s rou
router rip
version 2
offset-list 10 in 5 Serial0/0
network 1.0.0.0
network 12.0.0.0
network 14.0.0.0
distribute-list NET226 in
no auto-summary
R1(config-std-nacl)#do sh ip access
Standard IP access list 10
10 permit 172.16.0.10 (651 matches)
Standard IP access list NET226
5 deny 2.2.6.0, wildcard bits 0.0.0.255
20 permit any (484 matches)
R1(config)#do sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 14.1.1.2, 00:00:05, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
C 1.1.0.0 is directly connected, Loopback0
C 1.1.1.0 is directly connected, Loopback1
C 1.1.2.0 is directly connected, Loopback2
C 1.1.3.0 is directly connected, Loopback3
2.0.0.0/24 is subnetted, 3 subnets
R 2.2.4.0 [120/1] via 12.1.1.2, 00:00:05, Serial0/0
no presen 2.2.6.0[120/1] via 12.1.1.2-============
R 2.2.5.0 [120/1] via 12.1.1.2, 00:00:05, Serial0/0
R 2.2.7.0 [120/1] via 12.1.1.2, 00:00:06, Serial0/0
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/2] via 14.1.1.2, 00:00:06, Serial0/1
[120/2] via 12.1.1.2, 00:00:06, Serial0/0
R 3.3.9.0 [120/2] via 14.1.1.2, 00:00:01, Serial0/1
[120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.10.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.11.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
R 4.4.13.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
R 4.4.14.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
R 4.4.15.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
23.0.0.0/24 is subnetted, 1 subnets
R 23.1.1.0 [120/1] via 12.1.1.2, 00:00:09, Serial0/0
172.16.0.0/32 is subnetted, 2 subnets
R 172.16.0.20 [120/3] via 14.1.1.2, 00:00:01, Serial0/1
R 172.16.0.10 [120/3] via 14.1.1.2, 00:00:01, Serial0/1
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
C 14.1.1.0 is directly connected, Serial0/1
R1(config)#
R1 filters incoming update about net 2.2.6.0/24 from both R4 and R2, in other words it prevents route installation in its rip database regardless of the source of the incoming update.
------------------- NOTE -----------------------
The distribute-list is not a standalone filtering mechanism, the distribute-list command lets us to apply different filtering mechanisms to a routing process.
---------------- END NOTE -------------------
I can be more specific when using a distribute-list and filtering only the update coming in from a specific neighbor-->link-->interface. For example let's suppose that R1 must learn about network 2.2.6.0/24 only from R4 and not directly from the R2. here what can I do using the same ACL defined before:
R1(config)#router rip
R1(config-router)#no distribute-list NET226 in
R1(config-router)#do clear ip route *
R1(config-router)#do sh ip route 2.2.6.0 --everything restore to original
Routing entry for 2.2.6.0/24
Known via "rip", distance 120, metric 1
Redistributing via rip
Last update from 12.1.1.2 on Serial0/0, 00:00:02 ago
Routing Descriptor Blocks:
* 12.1.1.2, from 12.1.1.2, 00:00:02 ago, via Serial0/0
Route metric is 1, traffic share count is 1
R1(config-router)# ----we applied again the access-list but to interface
R1(config-router)#
R1(config-router)#distribute-list NET226 in serial 0/0
R1(config-router)#do clear ip route *
We have one path to 2.2.6.2 using R1-To R4, R3 and R2
R1(config-router)#do sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 14.1.1.2, 00:00:06, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
C 1.1.0.0 is directly connected, Loopback0
C 1.1.1.0 is directly connected, Loopback1
C 1.1.2.0 is directly connected, Loopback2
C 1.1.3.0 is directly connected, Loopback3
2.0.0.0/24 is subnetted, 4 subnets
R 2.2.4.0 [120/1] via 12.1.1.2, 00:00:00, Serial0/0
R 2.2.5.0 [120/1] via 12.1.1.2,
*Mar 2 00:09:56.394: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up 00:00:00, Serial0/0
R 2.2.6.0 [120/3] via 14.1.1.2, 00:00:07, Serial0/1
R 2.2.7.0 [120/1] via 12.1.1.2, 00:00:02, Serial0/0
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/2] via 14.1.1.2, 00:00:15, Serial0/1
[120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.9.0 [120/2] via 14.1.1.2, 00:00:15, Serial0/1
[120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.10.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.11.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
R 4.4.13.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
R 4.4.14.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
R 4.4.15.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
23.0.0.0/24 is subnetted, 1 subnets
R 23.1.1.0 [120/1] via 12.1.1.2, 00:00:09, Serial0/0
172.16.0.0/32 is subnetted, 2 subnets
R 172.16.0.20 [120/3] via 14.1.1.2, 00:00:15, Serial0/1
R 172.16.0.10 [120/3] via 14.1.1.2, 00:00:15, Serial0/1
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
C 14.1.1.0 is directly connected, Serial0/1
R1(config-router)#
R1 will reach 2.2.6.2 in three hops
R1#sh ip route 2.2.6.0
Routing entry for 2.2.6.0/24
Known via "rip", distance 120, metric 3 -========
Redistributing via rip
Last update from 14.1.1.2 on Serial0/1, 00:00:12 ago
Routing Descriptor Blocks:
* 14.1.1.2, from 14.1.1.2, 00:00:12 ago, via Serial0/1
Route metric is 3, traffic share count is 1
R1#
R1 and R2 We have applied in R1 an access-list to filter from route R2 a particular route 2.2.6.0 255.255.255.0
R1(config)#ip access-list standard NET226
R1(config-std-nacl)#5 deny 2.2.6.0 0.0.0.255
R1(config-std-nacl)#20 permit any
R1(config-std-nacl)#do sh run | s ip acc
ip access-list standard NET226
deny 2.0.0.0 0.0.0.255
permit any
R1(config t)#router rip
R1(config-router)#distribute-list NET226 in
R1(config-router)#do clear ip route *
R1# sh run | s rou
router rip
version 2
offset-list 10 in 5 Serial0/0
network 1.0.0.0
network 12.0.0.0
network 14.0.0.0
distribute-list NET226 in
no auto-summary
R1(config-std-nacl)#do sh ip access
Standard IP access list 10
10 permit 172.16.0.10 (651 matches)
Standard IP access list NET226
5 deny 2.2.6.0, wildcard bits 0.0.0.255
20 permit any (484 matches)
R1(config)#do sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 14.1.1.2, 00:00:05, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
C 1.1.0.0 is directly connected, Loopback0
C 1.1.1.0 is directly connected, Loopback1
C 1.1.2.0 is directly connected, Loopback2
C 1.1.3.0 is directly connected, Loopback3
2.0.0.0/24 is subnetted, 3 subnets
R 2.2.4.0 [120/1] via 12.1.1.2, 00:00:05, Serial0/0
no presen 2.2.6.0[120/1] via 12.1.1.2-============
R 2.2.5.0 [120/1] via 12.1.1.2, 00:00:05, Serial0/0
R 2.2.7.0 [120/1] via 12.1.1.2, 00:00:06, Serial0/0
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/2] via 14.1.1.2, 00:00:06, Serial0/1
[120/2] via 12.1.1.2, 00:00:06, Serial0/0
R 3.3.9.0 [120/2] via 14.1.1.2, 00:00:01, Serial0/1
[120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.10.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.11.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
R 4.4.13.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
R 4.4.14.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
R 4.4.15.0 [120/1] via 14.1.1.2, 00:00:01, Serial0/1
23.0.0.0/24 is subnetted, 1 subnets
R 23.1.1.0 [120/1] via 12.1.1.2, 00:00:09, Serial0/0
172.16.0.0/32 is subnetted, 2 subnets
R 172.16.0.20 [120/3] via 14.1.1.2, 00:00:01, Serial0/1
R 172.16.0.10 [120/3] via 14.1.1.2, 00:00:01, Serial0/1
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
C 14.1.1.0 is directly connected, Serial0/1
R1(config)#
R1 filters incoming update about net 2.2.6.0/24 from both R4 and R2, in other words it prevents route installation in its rip database regardless of the source of the incoming update.
------------------- NOTE -----------------------
The distribute-list is not a standalone filtering mechanism, the distribute-list command lets us to apply different filtering mechanisms to a routing process.
---------------- END NOTE -------------------
I can be more specific when using a distribute-list and filtering only the update coming in from a specific neighbor-->link-->interface. For example let's suppose that R1 must learn about network 2.2.6.0/24 only from R4 and not directly from the R2. here what can I do using the same ACL defined before:
R1(config)#router rip
R1(config-router)#no distribute-list NET226 in
R1(config-router)#do clear ip route *
R1(config-router)#do sh ip route 2.2.6.0 --everything restore to original
Routing entry for 2.2.6.0/24
Known via "rip", distance 120, metric 1
Redistributing via rip
Last update from 12.1.1.2 on Serial0/0, 00:00:02 ago
Routing Descriptor Blocks:
* 12.1.1.2, from 12.1.1.2, 00:00:02 ago, via Serial0/0
Route metric is 1, traffic share count is 1
R1(config-router)# ----we applied again the access-list but to interface
R1(config-router)#
R1(config-router)#distribute-list NET226 in serial 0/0
R1(config-router)#do clear ip route *
We have one path to 2.2.6.2 using R1-To R4, R3 and R2
R1(config-router)#do sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
34.0.0.0/24 is subnetted, 1 subnets
R 34.1.1.0 [120/1] via 14.1.1.2, 00:00:06, Serial0/1
1.0.0.0/24 is subnetted, 4 subnets
C 1.1.0.0 is directly connected, Loopback0
C 1.1.1.0 is directly connected, Loopback1
C 1.1.2.0 is directly connected, Loopback2
C 1.1.3.0 is directly connected, Loopback3
2.0.0.0/24 is subnetted, 4 subnets
R 2.2.4.0 [120/1] via 12.1.1.2, 00:00:00, Serial0/0
R 2.2.5.0 [120/1] via 12.1.1.2,
*Mar 2 00:09:56.394: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up 00:00:00, Serial0/0
R 2.2.6.0 [120/3] via 14.1.1.2, 00:00:07, Serial0/1
R 2.2.7.0 [120/1] via 12.1.1.2, 00:00:02, Serial0/0
3.0.0.0/24 is subnetted, 4 subnets
R 3.3.8.0 [120/2] via 14.1.1.2, 00:00:15, Serial0/1
[120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.9.0 [120/2] via 14.1.1.2, 00:00:15, Serial0/1
[120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.10.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
R 3.3.11.0 [120/2] via 12.1.1.2, 00:00:09, Serial0/0
4.0.0.0/24 is subnetted, 4 subnets
R 4.4.12.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
R 4.4.13.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
R 4.4.14.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
R 4.4.15.0 [120/1] via 14.1.1.2, 00:00:15, Serial0/1
23.0.0.0/24 is subnetted, 1 subnets
R 23.1.1.0 [120/1] via 12.1.1.2, 00:00:09, Serial0/0
172.16.0.0/32 is subnetted, 2 subnets
R 172.16.0.20 [120/3] via 14.1.1.2, 00:00:15, Serial0/1
R 172.16.0.10 [120/3] via 14.1.1.2, 00:00:15, Serial0/1
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
14.0.0.0/24 is subnetted, 1 subnets
C 14.1.1.0 is directly connected, Serial0/1
R1(config-router)#
R1 will reach 2.2.6.2 in three hops
R1#sh ip route 2.2.6.0
Routing entry for 2.2.6.0/24
Known via "rip", distance 120, metric 3 -========
Redistributing via rip
Last update from 14.1.1.2 on Serial0/1, 00:00:12 ago
Routing Descriptor Blocks:
* 14.1.1.2, from 14.1.1.2, 00:00:12 ago, via Serial0/1
Route metric is 3, traffic share count is 1
R1#
RIPv2 filtering with Passive interface
RIP filtering with Passive interface
We can consider passive-interface an indirect form of filtering.
R1#sh run | s rou
router rip
version 2
offset-list 10 in 5 Serial0/0
network 1.0.0.0
network 12.0.0.0
no auto-summary
R1#config t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router rip
R1(config-router)#pass
R1(config-router)#passive-interface s0/0 -===condition 1
in this router we have
R1(config-router)#do sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES NVRAM administratively down down
Serial0/0 12.1.1.1 YES NVRAM up up
FastEthernet0/1 unassigned YES NVRAM administratively down down
Serial0/1 unassigned YES NVRAM administratively down down
Loopback0 1.1.0.1 YES NVRAM up up
Loopback1 1.1.1.1 YES NVRAM up up
Loopback2 1.1.2.1 YES NVRAM up up
Loopback3 1.1.3.1 YES NVRAM up up
before condition 1
R2#sh ip route 1.0.0.0
Routing entry for 1.0.0.0/24, 4 known subnets
Redistributing via rip
R 1.1.0.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
R 1.1.1.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
R 1.1.2.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
R 1.1.3.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
after condition 1 applied i a few minutes
R2#sh ip route 1.0.0.0
% Network not in table
R2#
if we run debup ip rip we will see that s0/0 is rx routes but not sending over the interface
after so time we will not see any route from R1 or any other interface behind it .
if we applied in R2
R1# sh ip route 2.0.0.0
Routing entry for 2.0.0.0/24, 4 known subnets
Redistributing via rip
R 2.2.4.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R 2.2.5.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R 2.2.6.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R 2.2.7.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R1# sh ip route 2.0.0.0
We can consider passive-interface an indirect form of filtering.
R1#sh run | s rou
router rip
version 2
offset-list 10 in 5 Serial0/0
network 1.0.0.0
network 12.0.0.0
no auto-summary
R1#config t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router rip
R1(config-router)#pass
R1(config-router)#passive-interface s0/0 -===condition 1
in this router we have
R1(config-router)#do sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES NVRAM administratively down down
Serial0/0 12.1.1.1 YES NVRAM up up
FastEthernet0/1 unassigned YES NVRAM administratively down down
Serial0/1 unassigned YES NVRAM administratively down down
Loopback0 1.1.0.1 YES NVRAM up up
Loopback1 1.1.1.1 YES NVRAM up up
Loopback2 1.1.2.1 YES NVRAM up up
Loopback3 1.1.3.1 YES NVRAM up up
before condition 1
R2#sh ip route 1.0.0.0
Routing entry for 1.0.0.0/24, 4 known subnets
Redistributing via rip
R 1.1.0.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
R 1.1.1.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
R 1.1.2.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
R 1.1.3.0 [120/1] via 12.1.1.1, 00:02:46, Serial0/0
after condition 1 applied i a few minutes
R2#sh ip route 1.0.0.0
% Network not in table
R2#
if we run debup ip rip we will see that s0/0 is rx routes but not sending over the interface
after so time we will not see any route from R1 or any other interface behind it .
if we applied in R2
R1# sh ip route 2.0.0.0
Routing entry for 2.0.0.0/24, 4 known subnets
Redistributing via rip
R 2.2.4.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R 2.2.5.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R 2.2.6.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R 2.2.7.0/24 is possibly down,
routing via 12.1.1.2, Serial0/0
R1# sh ip route 2.0.0.0
RIPv2 Offset list example
RIPv2 - Manipulation of the Metric with Offset Lists
An offset-list is a filtering tool when used as an extrema ratio. By default an offset-list is a tool used to INCREASE the metric of a route. Of course, if we increase the metric so it reaches 16 hops or more the route will become inaccessible and then discarded/filtered. Note
offset-list keyword can invoke Standard-ACL (numbered or named)This tutorial shows how to manipulate the metric in RIPv2 with the help of offset lists. Offset Lists Lets take a lab of 2 routers and do some basic RIPv2 configuration:
The routing table of R1:
Two more loopback interfaces are added to R2. The routes have an administrative distance of 120 and a metric of "1", which basically is a hop count. This value has a range of 1 to 15.
R2#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#interface loopback 10
R2(config-if)#ip address 172.17.0.10 255.255.255.255
R2(config-if)#exit
R2(config)#interface loopback 20
R2(config-if)#ip address 172.17.0.20 255.255.255.255
R2(config-if)#end
R1#show ip route
Gateway of last resort is not set
172.17.0.0/32 is subnetted, 4 subnets
R 172.17.0.20 [120/1] via 192.168.100.2, 00:00:05, Serial1/0
R 172.17.0.10 [120/1] via 192.168.100.2, 00:00:05, Serial1/0
C 172.17.0.1 is directly connected, Loopback0
R 172.17.0.2 [120/1] via 192.168.100.2, 00:00:05, Serial1/0
192.168.100.0/30 is subnetted, 1 subnets
C 192.168.100.0 is directly connected, Serial1/0
The two new routes now appear in the routing table of router R1. The
metric of RIP routes can be manipulated with offset lists. For this to
work an accesslist has to be configured. The metric of 172.17.0.10 will
be increased by 5 on router R1 incoming on the interface S1/0, the
metric of 172.17.0.20 will be increased by 7 outgoing on router R2.
R1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#access-list 10 permit 172.17.0.10 0.0.0.0
R1(config)#router rip
R1(config-router)#offset-list 10 in 5 Serial 1/0
R1(config-router)#end
R2#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#access-list 20 permit 172.17.0.20 0.0.0.0
R2(config)#router rip
R2(config-router)#offset-list 20 out 7 Serial 1/0
R2(config-router)#end
R1#show ip route
Gateway of last resort is not set
172.17.0.0/32 is subnetted, 4 subnets
R 172.17.0.20 [120/8] via 192.168.100.2, 00:00:00, Serial1/0
R 172.17.0.10 [120/6] via 192.168.100.2, 00:00:00, Serial1/0
C 172.17.0.1 is directly connected, Loopback0
R 172.17.0.2 [120/1] via 192.168.100.2, 00:00:00, Serial1/0
192.168.100.0/30 is subnetted, 1 subnets
C 192.168.100.0 is directly connected, Serial1/0
offset-list
To add an offset to incoming and outgoing metrics to routes learned via Routing Information Protocol (RIP), use the offset-list command in router configuration mode. To remove an offset list, use the no form of this command.
offset-list {access-list-number | access-list-name} {in | out} offset [interface-type interface-number]
no offset-list {access-list-number | access-list-name} {in | out} offset [interface-type interface-number]
Syntax Description
Defaults
This command is disabled by default.
Command Modes
Router configuration
Command History
|
Release
|
Modification
|
|---|---|
10.0
|
This command was introduced.
|
10.3
|
The interface-type and interface-number arguments were added.
|
11.2
|
The access-list-name argument was added.
|
Usage Guidelines
The offset value is added to the routing
metric. An offset list with an interface type and interface number is
considered extended and takes precedence over an offset list that is not
extended. Therefore, if an entry passes the extended offset list and
the normal offset list, the offset of the extended offset list is added
to the metric.
Examples
In the following example, the router applies an offset of 10 to the delay component of a router only to access list 21:
offset-list 21 out 10
In the following example, the router applies an offset of 10 to routes learned from Ethernet interface 0:
offset-list 21 in 10 ethernet 0
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