From: Alexei Monastyrnyi (alexeim73@gmail.com)
Date: Fri Feb 13 2009 - 16:51:16 ARST
If I remember right "distance NNN" command is not a routing protocol
specific one, hence it affects the routes already installed in routing
table and doesn't really know which routing protocol installed them there.
A..
Hobbs wrote:
> I think I figured it out. This only works for directly connected
> neighbors. When I use the distance command for 2.2.2.2, nothing
> happens. It's still weird that it would affect LSAs that are not
> generated by the router though...I guess it applies the distance to
> all routes learned by that router.
>
> Another example:
>
> 192.168.61.0 is between R1 and R6.
> R4 learns this route through R5 right now and has a distance of 100:
>
> R4#sho ip route 192.168.61.0
> Routing entry for 192.168.61.0/24
> Known via "ospf 1", distance 100, metric 3, type inter area
> Last update from 192.168.45.5 on Serial1/0, 00:03:26 ago
> Routing Descriptor Blocks:
> * 192.168.45.5, from 5.5.5.5, 00:03:26 ago, via Serial1/0
> Route metric is 3, traffic share count is 1
>
> By manipulating cost I can have R4 choose the path through R3:
>
> R5(config)#int s1/0
> R5(config-if)#ip ospf cost 10
>
> Now the LSA that is actually used to build the route entry is from R2,
> and the distance command is not applied anymore (even though R2 ends
> up using R5 as transit/load balancing))
>
> R4#sho ip route 192.168.61.0
> Routing entry for 192.168.61.0/24
> Known via "ospf 1", distance 110, metric 4, type inter area
> Last update from 192.168.34.3 on Serial1/1, 00:01:10 ago
> Routing Descriptor Blocks:
> * 192.168.45.5, from 5.5.5.5, 00:01:11 ago, via Serial1/0
> Route metric is 4, traffic share count is 1
> 192.168.34.3, from 2.2.2.2, 00:01:11 ago, via Serial1/1
> Route metric is 4, traffic share count is 1
>
>
> Kind of interesting, it looks like OSPF uses one LSA to install the
> route, but if multiple paths exists, i will install both paths.
> However the distance command works on the LSA that was
> installed...maybe not the correct way to explain it, still a little
> fuzzy...
>
> On Wed, Feb 11, 2009 at 4:51 PM, Hobbs <deadheadblues@gmail.com> wrote:
>
>> Here you go:
>>
>> R4#sho ip route 1.1.1.1
>> Routing entry for 1.1.1.1/32
>> Known via "ospf 1", distance 100, metric 4, type inter area
>> Last update from 192.168.45.5 on Serial1/0, 00:00:08 ago
>> Routing Descriptor Blocks:
>> 192.168.45.5, from 5.5.5.5, 00:00:08 ago, via Serial1/0
>> Route metric is 4, traffic share count is 1
>> * 192.168.34.3, from 2.2.2.2, 00:00:08 ago, via Serial1/1
>> Route metric is 4, traffic share count is 1
>>
>> Here is a drawing of my topology
>> http://imagebin.ca/view/st0dcn6.html
>>
>> thanks,
>>
>> On Wed, Feb 11, 2009 at 4:38 PM, Brian McGahan
>> <bmcgahan@internetworkexpert.com> wrote:
>>
>>> Post the output of "show ip route 1.1.1.1".
>>>
>>> Brian McGahan, CCIE #8593 (R&S/SP/Security)
>>> bmcgahan@internetworkexpert.com
>>>
>>> Internetwork Expert, Inc.
>>> http://www.InternetworkExpert.com
>>> Toll Free: 877-224-8987 x 705
>>> Outside US: 775-826-4344 x 705
>>>
>>>
>>>
>>> Hobbs wrote:
>>>
>>> I have R4 as an internal router to Area 1.
>>> R2 and R5 are border routers generating a type-3 LSA for route 1.1.1.1
>>> into area 1.
>>> Instead of using cost, I would like to use distance (if possible) to
>>> alter path selection.
>>>
>>> R4 has two routes to 1.1.1.1
>>> :
>>>
>>> R4#sho ip route | sec 1.1.1.1
>>> O IA 1.1.1.1 [110/4] via 192.168.45.5, 00:01:10, Serial1/0
>>> [110/4] via 192.168.34.3, 00:01:10, Serial1/1
>>> R4#
>>>
>>> Here we see both type-3 LSAs, one each generated by R2 and R5:
>>>
>>> R4#sho ip osp database
>>>
>>> Summary Net Link States (Area 1)
>>>
>>> Link ID ADV Router Age Seq# Checksum
>>> 1.1.1.1 2.2.2.2 207 0x80000001 0x0033FB
>>> 1.1.1.1 5.5.5.5 170 0x80000002 0x00E040
>>>
>>>
>>> R4(config)#router ospf 1
>>> R4(config-router)#distance 100 5.5.5.5 0.0.0.0
>>>
>>> Both routes get changed:
>>>
>>> R4#sho ip route | sec 1.1.1.1
>>> O IA 1.1.1.1 [100/4] via 192.168.45.5, 00:00:03, Serial1/0
>>> [100/4] via 192.168.34.3, 00:00:03, Serial1/1
>>>
>>>
>>> Why does the command alter both routes AD if I specified wildcard mask
>>> of 0.0.0.0 ?
>>>
>>> I know that the ACL portion of the command works, to alter distance of
>>> specific routes, but it appears the router-id/mask has no impact in
>>> choosing between different ABR's.
>>>
>>> thank you,
>>>
>>>
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>
>
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