From: gladston@br.ibm.com
Date: Mon May 16 2005 - 13:22:11 GMT-3
Hi Sean,
Thanks for your time,
I was trying to do what you proposed, when this new variable comes up.
After configuring bandwidth on R2 (I did that when testing another
feaute), things changed.
Before it, just R5 had the command 'bandwidth 64'. R5 is the hub of this
multipoint net, where R1 and R2 are spokes. R1 and R5 are ASBR,
generanting external 55.55.55.0.
After adding 'bandwidth 64' on R2, CAT2 changed the preference to R1. If I
remove 'bandwidth 64' from R2, CAT2 preference goes back to R5:
Rack2CAT2#sir 55.55.55.0
Routing entry for 55.55.55.0/24
Known via "ospf 1", distance 110, metric 20, type extern 2, forward
metric 1563
Last update from 142.20.28.2 on Vlan20, 00:07:33 ago
Routing Descriptor Blocks:
* 142.20.28.2, from 142.20.1.1, 00:07:33 ago, via Vlan20
Route metric is 20, traffic share count is 1
Rack2CAT2#sh ip os database external 55.55.55.0
OSPF Router with ID (142.20.8.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 1606
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 55.55.55.0 (External Network Number )
Advertising Router: 142.20.1.1
LS Seq Number: 80000007
Checksum: 0x67E8
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Routing Bit Set on this LSA
LS age: 418
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 55.55.55.0 (External Network Number )
Advertising Router: 142.20.5.1
LS Seq Number: 8000000A
Checksum: 0x4504
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
On R2, the result of the same show ip route shows it is load-sharing:
Rack2R2#sir 55.55.55.0
Routing entry for 55.55.55.0/24
Known via "ospf 1", distance 110, metric 20, type extern 2, forward
metric 1562
Redistributing via isis
Advertised by isis metric 0 metric-type internal level-2
Last update from 142.20.125.1 on Serial0/0, 00:02:04 ago
Routing Descriptor Blocks:
* 142.20.125.5, from 142.20.5.1, 00:02:04 ago, via Serial0/0
Route metric is 20, traffic share count is 1
142.20.125.1, from 142.20.1.1, 00:02:04 ago, via Serial0/0
Route metric is 20, traffic share count is 1
Rack2R2#sh ip os database external 55.55.55.0
OSPF Router with ID (142.20.2.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 1712
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 55.55.55.0 (External Network Number )
Advertising Router: 142.20.1.1
LS Seq Number: 80000007
Checksum: 0x67E8
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Routing Bit Set on this LSA
LS age: 43
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 55.55.55.0 (External Network Number )
Advertising Router: 142.20.5.1
LS Seq Number: 8000000B
Checksum: 0x4305
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
It now chooses a router with RID smaller, so I am inclinated to believe it
is not the cause of the preference.
I don't know why CAT2, having two LSA with the same metric, chooses R5 if
R2 has no 'bandwidth 64' and chooses R1 if it has this command.
Cordially,
------------------------------------------------------------------
Alaerte Gladston Vidali
IBM Global Services - SO
Tel.55+11+2121-2879 Fax:55+11+2121-2449
"Sean C" <Upp_and_Upp@hotmail.com>
16/05/2005 10:18
To
Alaerte Gladston Vidali/Brazil/IBM@IBMBR
cc
Subject
Re: OSPF External Route - Choosing one ASBR
Hi Gladston,
Not sure if I know this one, but, assuming all else equal, perhaps the
router chooses the ASBR with the higher router ID. What happens if you
change R1's RID to 142.20.111.1 (assuming the ospf process is cleared, no
virtual-links need the old RID, etc...) - does Cat2 now use R1?
Just a guess....
----- Original Message -----
From: <gladston@br.ibm.com>
To: <ccielab@groupstudy.com>
Sent: Monday, May 16, 2005 8:46 AM
Subject: OSPF External Route - Choosing one ASBR
> R1 and R5 injects de same route, 55.55.55.0, on area 0
> Metric used on redistribution is the same, 20.
> Metric to ASBR R1 and R5, from CAT2, is the same, 65.
>
> CAT2 always choose R5. Are you aware of the reason?
> Rack2CAT2#sir 55.55.55.0
> Routing entry for 55.55.55.0/24
> Known via "ospf 1", distance 110, metric 20, type extern 2, forward
> metric 65
> Last update from 142.20.28.2 on Vlan20, 00:00:27 ago
> Routing Descriptor Blocks:
> * 142.20.28.2, from 142.20.5.1, 00:00:27 ago, via Vlan20
> Route metric is 20, traffic share count is 1
>
> Rack2CAT2#
> Rack2CAT2#sh ip os da ex
> Rack2CAT2#sh ip os da external 55.55.55.0
>
> OSPF Router with ID (142.20.8.1) (Process ID 1)
>
>
> Type-5 AS External Link States
>
> Routing Bit Set on this LSA
> LS age: 838
> Options: (No TOS-capability, DC)
> LS Type: AS External Link
> Link State ID: 55.55.55.0 (External Network Number )
> Advertising Router: 142.20.1.1
> LS Seq Number: 80000001
> Checksum: 0x73E2
> Length: 36
> Network Mask: /24
> Metric Type: 2 (Larger than any link state path)
> TOS: 0
> Metric: 20
> Forward Address: 0.0.0.0
> External Route Tag: 0
>
> Routing Bit Set on this LSA
> LS age: 43
> Options: (No TOS-capability, DC)
> LS Type: AS External Link
> Link State ID: 55.55.55.0 (External Network Number )
> Advertising Router: 142.20.5.1
> LS Seq Number: 80000001
> Checksum: 0x57FA
> Length: 36
> Network Mask: /24
> Metric Type: 2 (Larger than any link state path)
> TOS: 0
> Metric: 20
> Forward Address: 0.0.0.0
> External Route Tag: 0
>
> Rack2CAT2#
> Rack2CAT2#
> Rack2CAT2#sir 55.55.55.0
> Routing entry for 55.55.55.0/24
> Known via "ospf 1", distance 110, metric 20, type extern 2, forward
> metric 65
> Last update from 142.20.28.2 on Vlan20, 00:02:17 ago
> Routing Descriptor Blocks:
> * 142.20.28.2, from 142.20.5.1, 00:02:17 ago, via Vlan20
> Route metric is 20, traffic share count is 1
>
> Rack2CAT2#
> Rack2CAT2#sh ip os da external 55.55.55.0
>
> OSPF Router with ID (142.20.8.1) (Process ID 1)
>
>
> Type-5 AS External Link States
>
> Routing Bit Set on this LSA
> LS age: 940
> Options: (No TOS-capability, DC)
> LS Type: AS External Link
> Link State ID: 55.55.55.0 (External Network Number )
> Advertising Router: 142.20.1.1
> LS Seq Number: 80000001
> Checksum: 0x73E2
> Length: 36
> Network Mask: /24
> Metric Type: 2 (Larger than any link state path)
> TOS: 0
> Metric: 20
> Forward Address: 0.0.0.0
> External Route Tag: 0
>
> Routing Bit Set on this LSA
> LS age: 144
> Options: (No TOS-capability, DC)
> LS Type: AS External Link
> Link State ID: 55.55.55.0 (External Network Number )
> Advertising Router: 142.20.5.1
> LS Seq Number: 80000001
> Checksum: 0x57FA
> Length: 36
> Network Mask: /24
> Metric Type: 2 (Larger than any link state path)
> TOS: 0
> Metric: 20
> Forward Address: 0.0.0.0
> External Route Tag: 0
>
> Rack2CAT2#
> Rack2CAT2#sh ip os border-routers
>
> OSPF Process 1 internal Routing Table
>
> Codes: i - Intra-area route, I - Inter-area route
>
> i 142.20.2.1 [1] via 142.20.28.2, Vlan20, ABR/ASBR, Area 16, SPF 2
> I 142.20.4.1 [1065] via 142.20.28.2, Vlan20, ASBR, Area 16, SPF 2
> I 142.20.5.1 [65] via 142.20.28.2, Vlan20, ASBR, Area 16, SPF 2
> I 142.20.1.1 [65] via 142.20.28.2, Vlan20, ASBR, Area 16, SPF 2
> Rack2CAT2#
> Rack2CAT2#sir 142.20.1.1
> Routing entry for 142.20.1.1/32
> Known via "ospf 1", distance 110, metric 66, type inter area
> Last update from 142.20.28.2 on Vlan20, 00:22:19 ago
> Routing Descriptor Blocks:
> * 142.20.28.2, from 142.20.2.1, 00:22:19 ago, via Vlan20
> Route metric is 66, traffic share count is 1
>
> Rack2CAT2#sir 142.20.5.1
> Routing entry for 142.20.5.1/32
> Known via "ospf 1", distance 110, metric 66, type inter area
> Last update from 142.20.28.2 on Vlan20, 00:22:23 ago
> Routing Descriptor Blocks:
> * 142.20.28.2, from 142.20.2.1, 00:22:23 ago, via Vlan20
> Route metric is 66, traffic share count is 1
>
> Rack2CAT2#
>
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