Re: Set metric +/-<metric> on route-map for EIGRP

I believe the behaviour is down to only being able to increase the composite
metric overall and not decrease it, decreasing a metric can lead lead to
routing loops which IOS protects against similar to how an offset list is
used.

The idea I guess is making a route more attractive then advertising out to its
peers could cause peers to prefer this path whilst the peer modifying the
route to a negative metric actually prefers the path via the same peer
preferring him and vice versa, or similar along those lines, I think this also
meets the EIGRP FC should Cisco have not seen it coming i.e If, for a
destination, a neighbor router advertises a distance that is strictly lower
than our feasible distance, then this neighbor lies on a loop free route to
this destination -irrelevant but that's my understanding

In your case the modified "less attractive" route is then advertised to EIGRP
peers, as you've seen but is seen as the genuine value in its own topology
table as advertised by upstream peers.

In an offset-list you effectively change the delay value to affect the
composite metric I think it's similar for your final solution but I would
calculate according to the EIGRP algorithm to be sure.

I hope that helps.

--
BR
Tony
Sent from my iPad
> On 7 Jan 2014, at 17:04, BALAKRISHNAN Balaji <Balaji.BALAKRISHNAN_at_swift.com>
wrote:
>
> Hi All,
>
> While using route-map in the eigrp distribute-list, when I was configuring
the metric, I stumble across a problemb&I wanted to offset the composite
metric by a value so  I used the command bset metric  +1000000b but it did
not have any impact.. Even if I use  bset metric  1000000b, it still did not
have any impact.. Then I kept increasing the metric value and at certain value
it start taking effect..  So,  I realized that  set metric command  will only
work when the new metric is higher than the existing composite metric for that
route and also  b+<metric>b  does not do any offset or add  to the current
composite metric.. Can anyone explain this behaviour ?  Is there any way to
implement the offset metric feature with route-map ?
>
> ## with No metric statement
> R1# sh route-map FTAG-BA2MSG
> route-map FTAG-BA2MSG, permit, sequence 10
>  Match clauses:
>    tag 193
>  Set clauses:
>  Policy routing matches: 0 packets, 0 bytes
>
>
> R2#sh ip eigrp topology 172.24.225.0  255.255.255.0
> EIGRP-IPv4 Topology Entry for AS(1)/ID(10.30.128.7) for 172.24.225.0/24
>  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1028864
>  Descriptor Blocks:
>  10.25.128.10 (GigabitEthernet2/3), from 10.25.128.10, Send flag is 0x0
>      Composite metric is (1028864/1028608), route is External
>      Vector metric:
>        Minimum bandwidth is 2500 Kbit
>        Total delay is 190 microseconds
>        Reliability is 255/255
>        Load is 3/255
>        Minimum MTU is 1500
>        Hop count is 5
>      External data:
>        Originating router is 10.30.192.3
>        AS number of route is 0
>        External protocol is Connected, external metric is 0
>        Administrator tag is 193 (0x000000C1)
>
>
> ## with metric statement set in R1
>
> R1#sh route-map FTAG-BA2MSG
> route-map FTAG-BA2MSG, permit, sequence 10
>  Match clauses:
>    tag 3
>  Set clauses:
>    metric 1000000      <-- metric set
>  Policy routing matches: 0 packets, 0 bytes
>
> R2#sh ip eigrp topology 172.24.225.0  255.255.255.0
> EIGRP-IPv4 Topology Entry for AS(1)/ID(10.30.128.7) for 172.24.225.0/24
>  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1028864
>  Descriptor Blocks:
>  10.25.128.10 (GigabitEthernet2/3), from 10.25.128.10, Send flag is 0x0
>      Composite metric is (1028864/1028608), route is External      <--    No
change in Composite metric in R2
>      Vector metric:
>        Minimum bandwidth is 2500 Kbit
>        Total delay is 190 microseconds
>        Reliability is 255/255
>        Load is 3/255
>        Minimum MTU is 1500
>        Hop count is 5
>      External data:
>        Originating router is 10.30.192.3
>        AS number of route is 0
>        External protocol is Connected, external metric is 0
>        Administrator tag is 193 (0x000000C1)
>
>
>
> ## with +metric statement set in R1
>
> R1#sh route-map FTAG-BA2MSG
> route-map FTAG-BA2MSG, permit, sequence 10
>  Match clauses:
>    tag 3
>  Set clauses:
>    metric +1000000  <-- + metric set
>  Policy routing matches: 0 packets, 0 bytes
>
>
>
> R2#sh ip eigrp topology 172.24.225.0  255.255.255.0
> EIGRP-IPv4 Topology Entry for AS(1)/ID(10.30.128.7) for 172.24.225.0/24
>  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1028864
>  Descriptor Blocks:
>  10.25.128.10 (GigabitEthernet2/3), from 10.25.128.10, Send flag is 0x0   o
still No change in the composite metric. Still backup route is preferred
>      Composite metric is (1028864/1028608), route is External  <--    No
change in Composite metric in R2
>      Vector metric:
>        Minimum bandwidth is 2500 Kbit
>        Total delay is 190 microseconds
>        Reliability is 255/255
>        Load is 3/255
>        Minimum MTU is 1500
>        Hop count is 5
>      External data:
>        Originating router is 10.30.192.3
>        AS number of route is 0
>        External protocol is Connected, external metric is 0
>        Administrator tag is 193 (0x000000C1)
>
>
>
> ## Increase the metric higher than the current composite metric for that
route
>
> R1#sh route-map FTAG-BA2MSG
>
> route-map FTAG-BA2MSG, permit, sequence 10  o   Set the metric value to
1050000
>  Match clauses:
>    tag 3
>  Set clauses:
>    metric 1050000     <--  metric value higher than the current composite
metric
>  Policy routing matches: 0 packets, 0 bytes
>
>
> R2#sh ip eigrp topology 172.24.225.0  255.255.255.0
> 10.25.128.10 (GigabitEthernet2/3), from 10.25.128.10, Send flag is 0x0
>      Composite metric is (268800256/268800000), route is External      <-
Change took effect
>      Vector metric:
>        Minimum bandwidth is 9 Kbit
>        Total delay is 10 microseconds
>        Reliability is 0/255
>        Load is 3/255
>        Minimum MTU is 241
>        Hop count is 5
>      External data:
>        Originating router is 10.30.192.3
>        AS number of route is 0
>        External protocol is Connected, external metric is 0
>        Administrator tag is 193 (0x000000C1)
>
>
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