From: Brian Dennis (bdennis@internetworkexpert.com)
Date: Wed Dec 03 2003 - 16:14:19 GMT-3
Did you see this part of my e-mail?
<Quote>
Since the two OSPF processes do not communicate with each other, the only
way to prefer a route from one process over another is to change the
administrative distance of the OSPF process itself.
</Quote>
You are trying to prefer a route based on the cost. This will not
have the desired effect. Change the administrative distance of the OSPF
process itself. In my example I changed the administrative distance of OSPF
to prefer one route over another as the router does not compare the cost
between processes.
Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpert.com
Toll Free: 877-224-8987
Direct: 775-745-6404 (Outside the US and Canada)
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
________________________________________
From: Varghese Thomas [mailto:vnthomas3@hotmail.com]
Sent: Wednesday, December 03, 2003 11:10 AM
To: Brian Dennis; ccielab@groupstudy.com
Subject: Re: Dual OSPF Issue
Hello Brian,
Thanks a lot for the valuable info; even after adding metric, it still does
not prefer 'preferred route.
BB1 - 192.168.1.0/24 R1 - 10.2.2.0/24 R2 - 172.16.1.0/24 BB2
Both BBs sending default-route E1 type which I have no control.
R1#sh run | be router
router ospf 64
log-adjacency-changes
network 192.168.1.0 0.0.0.255 area 0
!
router ospf 1
log-adjacency-changes
network 10.2.2.0 0.0.0.255 area 0
default-information originate metric 100
R2#sh run | be router
router ospf 64
log-adjacency-changes
network 172.16.1.0 0.0.0.255 area 0
!
router ospf 1
log-adjacency-changes
network 10.2.2.0 0.0.0.255 area 0
default-information originate metric 200
Event 1 - when both hubs sending default-route: R1 prefers default-route
learned by BB1
R1#sh ip os neighbor
Neighbor ID Pri State Dead Time Address Interface
172.16.1.1 1 FULL/DR 00:00:32 10.2.2.2
FastEthernet0/0
192.168.1.2 1 FULL/DR 00:00:31 192.168.1.2
FastEthernet0/1
R1#
R1#sip | in 0.0.0.0
Gateway of last resort is 192.168.1.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 2 subnets
O*E1 0.0.0.0/0 [110/11] via 192.168.1.2, 00:04:24, FastEthernet0/1
Event 2 - when BB1 stops sending default-route: R1 prefers default-route
learned by BB2 via R2
R1#sion
Neighbor ID Pri State Dead Time Address Interface
172.16.1.1 1 FULL/DR 00:00:35 10.2.2.2
FastEthernet0/0
R1#sip | in 0.0.0.0
Gateway of last resort is 10.2.2.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 2 subnets
O*E2 0.0.0.0/0 [110/200] via 10.2.2.2, 00:00:12, FastEthernet0/0
R1#
Event 3 - when BB1 re-sending default-route: R1 still prefers default-route
learned by BB2 via R2, even though it has higher metric and E2 type.
R1#sip | in 0.0.0.0
Gateway of last resort is 10.2.2.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 2 subnets
O*E2 0.0.0.0/0 [110/200] via 10.2.2.2, 00:02:42, FastEthernet0/0
R1#sh ip os da ex
R1#sh ip os da external
OSPF Router with ID (10.1.1.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 794
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 172.16.1.1
LS Seq Number: 80000004
Checksum: 0x63C5
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 200
Forward Address: 0.0.0.0
External Route Tag: 1
OSPF Router with ID (192.168.1.1) (Process ID 64)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 1025
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 192.168.1.2
LS Seq Number: 80000008
Checksum: 0x8A35
Length: 36
Network Mask: /0
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 1
Forward Address: 0.0.0.0
External Route Tag: 1
R1#
Thanks again for the support on this.
Tx n rd
----- Original Message -----
From: Brian Dennis
To: 'Varghese Thomas' ; ccielab@groupstudy.com
Sent: Tuesday, December 02, 2003 8:25 PM
Subject: RE: Dual OSPF Issue
Dual OSPF processes can be messy to say the least. When I was at
Cisco in 1996, I supported a large customer that ran dual OSPF processes in
a few locations. Needless to say their NOC had a hard time troubleshooting
OSPF problems in these locations and ended up calling me a lot ;-)
Since the two OSPF processes do not communicate with each other, the
only way to prefer a route from one process over another is to change the
administrative distance of the OSPF process itself. Back in the old days
;-), around IOS version 10.3, this was not an option ;-) Support for
comparing the administrative distance between OSPF processes was added in
IOS version 11.0.
In this example, two routers (R3 & R5) are sending a default route
as an OSPF type-E2 to R4. R3 is sending the default with a cost of 30. R5
is sending the default with a cost of 25. Theoretically R4 should prefer
R5's default as it has the lower cost. But as we can see R4 is choosing the
route with the higher OSPF cost. This is happening because the two OSPF
processes are no communicating with each other. By increasing the
administrative distance of OSPF process 1 (default from R3), we will start
preferring the default learned from OSPF process 2 (default from R5).
Rack2R4#sho run | be router ospf
router ospf 1
router-id 150.1.4.4
network 10.34.34.4 0.0.0.0 area 0
!
router ospf 2
router-id 150.2.4.4
network 10.45.45.4 0.0.0.0 area 0
!
Rack2R4#show ip route ospf
O*E2 0.0.0.0/0 [110/30] via 10.34.34.3, 00:11:36, Ethernet0/0
Rack2R4#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Rack2R4(config)#router ospf 1
Rack2R4(config-router)#distance 115
Rack2R4(config-router)#^Z
Rack2R4#show ip route ospf
O*E2 0.0.0.0/0 [110/25] via 10.45.45.5, 00:00:03, Ethernet0/1
Rack2R4#
Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpertcom
Toll Free: 877-224-8987
Direct: 775-745-6404 (Outside the US and Canada)
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Varghese Thomas
Sent: Tuesday, December 02, 2003 9:13 AM
To: ccielab@groupstudy.com
Subject: Re: Dual OSPF Issue
Hello,
I forgot to add the folowing
1. Tried ospf distance ext 115
2. tried distance 90 192.168.1.2 0.0.0.0
----- Original Message -----
From: Varghese Thomas
To: ccielab@groupstudy.com
Sent: Tuesday, December 02, 2003 10:58 AM
Subject: Dual OSPF Issue
Hello,
Need help on a dual OSPF issue.
Setup is as follows:
BB1 - 192.168.1.0/24 R1 - 10.2.2.0/24 R2 - 172.16.1.0/24 BB2
Requirement:
1. R1 & R2 should only pass default-route learned from BB1 & BB2
respectively
2. If BB1 stops sending default-route, R1 should have default-route from
BB2
via R2; vice vesa.
3. When all are working, both BB1 is sending external default-route, type
1.
BB1 & R1 is running OS process 64, R1 & R2 is running OSPF process 1; R2 &
BB2
is ruuning OSPF process 64.
R1's Config:
router ospf 1
log-adjacency-changes
network 10.2.2.0 0.0.0.255 area 0
default-information originate
!
router ospf 64
log-adjacency-changes
network 192.168.1.0 0.0.0.255 area 0
R2's config:
router ospf 1
log-adjacency-changes
network 10.2.2.0 0.0.0.255 area 0
default-information originate
!
router ospf 64
log-adjacency-changes
network 172.16.1.0 0.0.0.255 area 0
R1's RT
R1#sip | in 0.0.0.0
Gateway of last resort is 10.2.2.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 1 subnets
O*E1 0.0.0.0/0 [110/11] via 192.168.1.2, 00:00:12, FastEthernet0/1
R2's RT:
R2#sh ip route | in 0.0.0.0
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 1 subnets
O*E1 0.0.0.0/0 [110/11] via 172.16.1.2, 00:10:49, FastEthernet0/0
However, if I bring down, r1-bb1 link or r2-bb2 link, and brings back,
things
are different.
R1' RT:
Gateway of last resort is 10.2.2.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 2 subnets
O*E2 0.0.0.0/0 [110/1] via 10.2.2.2, 00:00:26, FastEthernet0/0
R1 prefers E2 route than a E1 route:
If I make route-metric type to E1, it still prefers higher metric route:
R1#sip | in 0.0.0.0
Gateway of last resort is 10.2.2.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 2 subnets
O*E1 0.0.0.0/0 [110/20001] via 10.2.2.2, 00:14:54, FastEthernet0/0
R1' OSPF DB:
R1#sh ip os da ex 0.0.0.0
OSPF Router with ID (192.168.1.1) (Process ID 64)
Type-5 AS External Link States
LS age: 2703
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 12.12.12.51
LS Seq Number: 80000002
Checksum: 0x6179
Length: 36
Network Mask: /0
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 1
Forward Address: 0.0.0.0
External Route Tag: 1
Routing Bit Set on this LSA
LS age: 1216
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 192.168.1.2
LS Seq Number: 80000001
Checksum: 0x982E
Length: 36
Network Mask: /0
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 1
Forward Address: 0.0.0.0
External Route Tag: 1
OSPF Router with ID (10.1.1.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 978
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 172.16.1.1
LS Seq Number: 80000001
Checksum: 0x185C
Length: 36
Network Mask: /0
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 1
Forward Address: 0.0.0.0
External Route Tag: 1
Thanks in advance.
Tx n RD
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