OSPF capability transit

September 29, 2008 at 1:00 pm | Posted in OSPF, Routing | Leave a comment

OSPF area capability transit is enabled by default, allowing the OSPF Area Border Router to install better-cost routes to the backbone area through the transit area instead of the virtual links.

If you want to retain a traffic pattern through the virtual-link path, you can disable capability transit by entering the no capability transit command. If paths through the transit area are discovered, they are most likely to be more optimal paths, or at least equal to, the virtual-link path. To reenable capability transit, enter the capability transit command.

If you need to verify whether OSPF area capability transit is enabled for a specific routing process, enter the show ip ospf command.

DOC CD Navigation

  • Cisco IOS IP Routing Protocols Configuration Guide, Release 12.4
  • Part 5: OSPF
  • OSPF Area Transit Capability

Also we can look up in the Command Reference.

Weird behavior: Redistribution with Route-map from OSPF to RIP

August 13, 2008 at 11:17 am | Posted in Blogroll, OSPF, Routing | Leave a comment

It is observed that if we do OSPF to RIP redistribution (or EIGRP as well, even though I have not tested with EIGRP yet) without route-map, then we introduce a route-map, e.g. to filter routes, the route-map will only take place for OSPF routes that have been bounced, removed or newly learnt. We can bounce routes by resetting OSPF process (this change only impact routes learnt from neighbors, but not the connected routes) and/or bouncing the interface

Here’s the detailed observation
Topology:

R1 ——- R3 ——- R2

OSPF Area0  |   RIP

R1#sh ver | in IOS
Cisco IOS Software, 3700 Software (C3725-ADVENTERPRISEK9-M), Version 12.4(17a), RELEASE SOFTWARE (fc2)

R1#

interface Loopback71
ip address 77.1.1.1 255.255.255.0
!
interface Loopback72
ip address 77.1.2.1 255.255.255.0
!
interface Loopback73
ip address 77.1.3.1 255.255.255.0
!
interface Loopback77
ip address 77.77.77.1 255.255.255.0
ip ospf network point-to-point
!
interface Serial1/1
description Connection to R3
ip address 13.0.0.1 255.255.255.0
!
!
router ospf 1
log-adjacency-changes
area 1 range 77.0.0.0 255.0.0.0
network 13.0.0.1 0.0.0.0 area 0
network 77.1.0.0 0.0.255.255 area 1
network 77.77.77.1 0.0.0.0 area 77

R3#

!
interface Serial1/2
description Connection to R1
ip address 13.0.0.3 255.255.255.0
!
interface Serial1/3
description Connection to R2
ip address 23.0.0.3 255.255.255.0
serial restart-delay 0
!
router ospf 1
network 13.0.0.3 0.0.0.0 area 0
!
router rip
version 2
redistribute ospf 1 metric 1 route-map OSPF->RIP
passive-interface default
network 23.0.0.0
neighbor 23.0.0.2
no auto-summary
!
!
!
ip prefix-list SUMMARY seq 5 permit 77.0.0.0/8
ip prefix-list SUMMARY seq 10 deny 0.0.0.0/0 le 32
!
route-map OSPF->RIP permit 10
match ip address prefix-list SUMMARY
!
route-map OSPF->RIP deny 20

R2#

interface Serial1/1
description Connection to R3
ip address 23.0.0.2 255.255.255.0
!
router rip
version 2
passive-interface default
network 23.0.0.0
neighbor 23.0.0.3
no auto-summary

This configuration result in only summary route being received on R2, as expected.

R2#sh ip route rip
R    77.0.0.0/8 [120/1] via 23.0.0.3, 00:00:18, Serial1/1

R3 has a summary route 77.0.0.0 and a specific 77.77.77.0 (both are learnt from R1)

R3#sh clock
08:59:34.219 UTC Wed Aug 13 2008
R3#sh ip route ospf
77.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O IA    77.77.77.0/24 [110/65] via 13.0.0.1, 00:00:18, Serial1/2
O IA    77.0.0.0/8 [110/65] via 13.0.0.1, 00:16:07, Serial1/2

If we advertize OSPF to RIP without the route-map, we will see that the specific route is also shown up on R2 (almost immediately)

R3#sh clock
09:05:28.035 UTC Wed Aug 13 2008

R3(config)#router rip
R3(config-router)#no  redistribute ospf 1 metric 1 route-map OSPF->RIP
R3(config-router)#redistribute ospf 1 metric 1

R2#sh clock
09:05:43.919 UTC Wed Aug 13 2008
R2#sh ip route rip
77.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
R       77.77.77.0/24 [120/1] via 23.0.0.3, 00:00:01, Serial1/1
R       77.0.0.0/8 [120/1] via 23.0.0.3, 00:00:01, Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
R       13.0.0.0 [120/1] via 23.0.0.3, 00:00:01, Serial1/1

If we reapply the route-map, the specific route stay on !!!

R3#sh clock
09:07:34.755 UTC Wed Aug 13 2008
R3#c
Enter configuration commands, one per line.  End with CNTL/Z.
R3(config)#router rip
R3(config-router)#redistribute ospf 1 metric 1 route-map OSPF->RIP
R3(config-router)#

R2#sh clock
09:09:29.383 UTC Wed Aug 13 2008
R2#sh ip route rip
77.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
R       77.77.77.0/24 [120/1] via 23.0.0.3, 00:00:22, Serial1/1
R       77.0.0.0/8 [120/1] via 23.0.0.3, 00:00:22, Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
R       13.0.0.0 [120/1] via 23.0.0.3, 00:00:22, Serial1/1
R2#sh clock
09:09:57.151 UTC Wed Aug 13 2008
R2#sh ip route rip
77.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
R       77.77.77.0/24 [120/1] via 23.0.0.3, 00:00:21, Serial1/1
R       77.0.0.0/8 [120/1] via 23.0.0.3, 00:00:21, Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
R       13.0.0.0 [120/1] via 23.0.0.3, 00:00:21, Serial1/1
R2#sh clock
09:11:36.359 UTC Wed Aug 13 2008
R2#sh ip route rip
77.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
R       77.77.77.0/24 [120/1] via 23.0.0.3, 00:00:11, Serial1/1
R       77.0.0.0/8 [120/1] via 23.0.0.3, 00:00:11, Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
R       13.0.0.0 [120/1] via 23.0.0.3, 00:00:11, Serial1/1


The specific route stays on until I bounce the route.

R1(config-if)#int lo77
R1(config-if)#shut
Aug 13 09:12:46.815: %LINK-5-CHANGED: Interface Loopback77, changed state to administratively down
Aug 13 09:12:47.819: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback77, changed state to down
R1(config-if)#no shut
R1(config-if)#
Aug 13 09:12:51.963: %LINK-3-UPDOWN: Interface Loopback77, changed state to up
Aug 13 09:12:52.963: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback77, changed state to up

R2#sh ip route rip
77.0.0.0/8 is subnetted, 1 subnets
R       77.0.0.0 [120/1] via 23.0.0.3, 00:00:09, Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
R       13.0.0.0 [120/1] via 23.0.0.3, 00:00:09, Serial1/1

Note that after I bounce the interface on R1, only the affected route (77.77.77.0/24 disapears from routing table on R2, as R3 does not sends it anymore). The 13.0.0.0/24 still stays on, (i.e. this unaffected route is not subject to the new route-map).

R3#sh ip route ospf
77.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O IA    77.77.77.0/24 [110/65] via 13.0.0.1, 00:05:49, Serial1/2
O IA    77.0.0.0/8 [110/65] via 13.0.0.1, 00:33:45, Serial1/2

R3#debug  ip rip
RIP protocol debugging is on
Aug 13 09:21:39.387: RIP: sending v2 update to 23.0.0.2 via Serial1/3 (23.0.0.3)
Aug 13 09:21:39.391: RIP: build update entries
Aug 13 09:21:39.391:    13.0.0.0/24 via 0.0.0.0, metric 1, tag 0
Aug 13 09:21:39.395:    77.0.0.0/8 via 0.0.0.0, metric 1, tag 0
Aug 13 09:21:39.395: RIP: Update contains 2 routes
Aug 13 09:21:39.399: RIP: Update queued
Aug 13 09:21:39.399: RIP: Update sent via Serial1/3

R2#sh clock
09:16:28.351 UTC Wed Aug 13 2008
R2#sh ip route rip
77.0.0.0/8 is subnetted, 1 subnets
R       77.0.0.0 [120/1] via 23.0.0.3, 00:00:23, Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
R       13.0.0.0 [120/1] via 23.0.0.3, 00:00:23, Serial1/1
R2#sh clock
09:16:45.031 UTC Wed Aug 13 2008
R2#sh ip route rip
77.0.0.0/8 is subnetted, 1 subnets
R       77.0.0.0 [120/1] via 23.0.0.3, 00:00:14, Serial1/1
13.0.0.0/24 is subnetted, 1 subnets
R       13.0.0.0 [120/1] via 23.0.0.3, 00:00:14, Serial1/1

If I remove the route-map and put it back in, we can see again that R3 continues to advertize all routes to RIP, NOT subject to the route-map

R3(config)#router rip
R3(config-router)#no redistribute ospf 1 metric 1 route-map OSPF->RIP
R3(config-router)#redistribute ospf 1 metric 1
R3(config-router)#redistribute ospf 1 metric 1 route-map OSPF->RIP

Aug 13 09:24:51.883: RIP: sending v2 update to 23.0.0.2 via Serial1/3 (23.0.0.3)
Aug 13 09:24:51.887: RIP: build update entries
Aug 13 09:24:51.887:    13.0.0.0/24 via 0.0.0.0, metric 1, tag 0
Aug 13 09:24:51.891:    77.0.0.0/8 via 0.0.0.0, metric 1, tag 0
Aug 13 09:24:51.891:    77.77.77.0/24 via 0.0.0.0, metric 1, tag 0
Aug 13 09:24:51.895: RIP: Update contains 3 routes
Aug 13 09:24:51.895: RIP: Update queued
Aug 13 09:24:51.899: RIP: Update sent via Serial1/3

If we clear OSPF process, we can see that only OSPF routes affected by the OSPF adjacency reset are subject to the route-map. The connected route (part of OSPF database), will still being advertized to RIP without being subject to the route-map.

R3#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
R3#
Aug 13 09:31:25.135: RIP: sending v2 update to 23.0.0.2 via Serial1/3 (23.0.0.3)
Aug 13 09:31:25.139: RIP: build update entries
Aug 13 09:31:25.139:    13.0.0.0/24 via 0.0.0.0, metric 1, tag 0
Aug 13 09:31:25.143:    77.0.0.0/8 via 0.0.0.0, metric 1, tag 0

Now if we bounce the connected interface, we can see that it will be blocked by the route-map, and it will no longer be redistributed to RIP.

R3#c
Enter configuration commands, one per line.  End with CNTL/Z.
R3(config)#int serial1/2
R3(config-if)#shut
Aug 13 09:33:02.771: %OSPF-5-ADJCHG: Process 1, Nbr 13.0.0.1 on Serial1/2 from FULL to DOWN, Neighbor Down: Interface down or detached
Aug 13 09:33:04.735: %LINK-5-CHANGED: Interface Serial1/2, changed state to administratively down

R3(config-if)#no shut
R3#
Aug 13 09:34:11.847: RIP: sending v2 update to 23.0.0.2 via Serial1/3 (23.0.0.3)
Aug 13 09:34:11.851: RIP: build update entries
Aug 13 09:34:11.851:    77.0.0.0/8 via 0.0.0.0, metric 1, tag 0

R2#sh clock
09:34:50.047 UTC Wed Aug 13 2008
R2#sh ip route rip
R    77.0.0.0/8 [120/1] via 23.0.0.3, 00:00:13, Serial1/1

Redistribution note – Lab 11 Task 3.9

August 10, 2008 at 3:15 pm | Posted in Blogroll, EIGRP, OSPF, Routing | Leave a comment

If an interface is redistributed into OSPF, then if we redistribute from OSPF -> EIGRP, then the interface is not automatically redistributed into EIGRP. We have to manually redistribute the connected interface into EIGRP.

RSRack1R5#srsr
router eigrp 10

redistribute ospf 1 metric 1 1 1 1 1 route-map OSPF_TO_EIGRP

router ospf 1
redistribute connected subnets route-map CONNECTED_TO_OSPF
redistribute eigrp 10 subnets route-map EIGRP_TO_OSPF

In this config, the CONNECTED_TO_EIGRP is missing. As the result, R6 will not see R5 Loop0. The R2 also learns an sub-optimal route of R5 loopback via R3 OSPF route, instead of from R5 directly.

OSPF network types

May 6, 2007 at 11:35 pm | Posted in OSPF | 1 Comment

Point to point:

Hello and LSA are sent to 224.0.0.5. No DR/BDR is required.

Point to multipoint:

This network types must be statically defined. The router treat frame-relay multipoint network like many point-to-point links. No DR/BDR is elected. OSPF packets are multicast.

Broadcast:

Hellos are sent to 224.0.0.5
LSA are sent to 224.0.0.6. Only DR and BDR listen to this address.
NBMA:

Neighbors are statically defined. DR & BDR are elected based on priority (which should be configured manually), and other tie break parameters. DR/BDR should be the hub routers. All OSPF packets are unicast.

OSPF NSSA routes: O IA, O N1, O N2

May 6, 2007 at 10:03 pm | Posted in Blogroll, OSPF, Routing | Leave a comment

In addition to the Intra Area type (O), the following route types can exist in an NSSA router. 

 CE1#sh run

interface FastEthernet0
 ip address 50.50.50.10 255.255.255.0
 speed 10
 full-duplex
!
interface Serial0
 ip address 32.29.1.2 255.255.255.252
 clockrate 4000000

router ospf 100
 log-adjacency-changes
 area 1 nssa
 network 32.29.1.2 0.0.0.0 area 1
 network 50.50.50.0 0.0.0.255 area 1

CE1#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

S    200.200.200.0/24 is directly connected, Null0
     50.0.0.0/24 is subnetted, 1 subnets
C       50.50.50.0 is directly connected, FastEthernet0
     32.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C       32.34.1.1/32 is directly connected, Loopback0
O IA    32.29.1.12/30 [110/192] via 32.29.1.1, 00:04:48, Serial0
O IA    32.29.1.8/30 [110/128] via 32.29.1.1, 00:04:48, Serial0
C       32.29.1.0/30 is directly connected, Serial0
O N1 130.130.0.0/16 [110/84] via 32.29.1.1, 00:03:47, Serial0
     165.87.0.0/32 is subnetted, 3 subnets
O IA    165.87.1.3 [110/193] via 32.29.1.1, 00:04:49, Serial0
O IA    165.87.1.2 [110/129] via 32.29.1.1, 00:04:49, Serial0
O IA    165.87.1.1 [110/65] via 32.29.1.1, 00:04:49, Serial0
O N2 150.150.0.0/16 [110/20] via 50.50.50.150, 00:04:50, FastEthernet0
CE1#

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