From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Tue Sep 20 2005 - 22:02:59 GMT-3
Sorry,
was just browsing and could not resist to chime in (without reviewing
all the thread).
I remember a similar topic, and the answer was... that the router does
not compare different protocol routes even if AD is the same.
There is like a default hierarchy where EIGRP is better than OSPF is
better than RIP... and even if you place the same AD for all, EIGRP will
win (given routes to same CIDR) no matter what its costs are.
sundar.palaniappan@verizon.com @ 20/09/2005 21:39 dixit:
> The question here is not what's the GENERIC process for route selection.
> Thing that was brought up is when TWO protocols have the same distance, how
> does a router decide which one to use or does it load balance. Your
> response doesn't address the subject.
>
> See the results for yourself below.
>
>
> R2#show run
> Building configuration...
>
> (output edited to retain context)
> !
> interface Loopback0
> ip address 2.2.2.2 255.255.255.255
> !
> interface Loopback1
> ip address 11.11.11.11 255.255.255.255
> !
> interface Ethernet0
> ip address 10.110.110.2 255.255.255.0
> !
> router eigrp 100
> network 2.0.0.0
> network 10.0.0.0
> no auto-summary
> !
> router ospf 1
> log-adjacency-changes
> network 2.2.2.2 0.0.0.0 area 1
> network 10.0.0.0 0.255.255.255 area 0
> network 11.0.0.0 0.255.255.255 area 1
>
>
>
> R3#show run
> Building configuration...
> !
> interface Ethernet0
> ip address 10.110.110.3 255.255.255.0
> !
> router eigrp 100
> network 10.0.0.0
> no auto-summary
> !
> router ospf 1
> log-adjacency-changes
> network 10.0.0.0 0.255.255.255 area 0
> distance 90 11.11.11.11 0.0.0.0 1
> !
> access-list 1 permit any
>
>
>
> R3#show ip eigrp nei
> IP-EIGRP neighbors for process 100
> H Address Interface Hold Uptime SRTT RTO Q Seq
> Type
> (sec) (ms) Cnt Num
> 0 10.110.110.2 Et0 10 01:34:39 959 5000 0 9
> R3#show ip ospf nei
>
> Neighbor ID Pri State Dead Time Address Interface
> 11.11.11.11 1 FULL/DR 00:00:37 10.110.110.2 Ethernet0
> R3#show ip route
> Codes: C - connected, S - static, I - IGRP, 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, E - EGP
> 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
>
> 2.0.0.0/32 is subnetted, 1 subnets
> D 2.2.2.2 [90/409600] via 10.110.110.2, 00:00:01, Ethernet0
> 10.0.0.0/24 is subnetted, 1 subnets
> C 10.110.110.0 is directly connected, Ethernet0
> 11.0.0.0/32 is subnetted, 1 subnets
> O IA 11.11.11.11 [90/11] via 10.110.110.2, 00:00:01, Ethernet0
>
> HTH,
> Sundar Palaniappan
> CCIE #14532
>
>
>
>
>
> "mani poopal"
> <mani_ccie@yahoo. To: Sundar X. Palaniappan/EMPL/PA/Verizon@VZNotes,
> com> "Dan Espino" <drespino@gmail.com>
> Sent by: cc: ccielab@groupstudy.com, nobody@groupstudy.com,
> nobody@groupstudy rosybird@gmail.com
> .com Subject: Re: Administrative distance tie
>
>
> 09/20/2005 07:10
> PM
> Please respond to
> "mani poopal"
>
>
>
>
>
>
> Guys,
>
> Simple rule in Cisco, if a route is learned by more than one routing
> protocols or same routing protocols, selection in the routing table is
> based on:
> 1. Longest prefix
> 2. Lowest AD(administrative distance)
> 3. If same AD(same routing protocols), Lowest Metric(for rip hop count,
> ospf cost etc)
> 4. If Metric also same, then all routing protocols support equal cost path
> load balancing
> 5. When metrics are different and if you want to do load balancing, it is
> called unequal cost path load balancing, only cisco's protocol(igrp and
> eigrp) support this feature by variance command.
>
> hope this helps for beginers
>
>
> Mani
>
> sundar.palaniappan@verizon.com wrote:
> Comparing metric of two different protocols would be like comparing apples
> and oranges.
>
> I believe, the protocol that owns the native administrative distance wins.
> Let's say, a router learns NET X via RIP & OSPF and you lower the distance
> to 110 for the RIP route, router will install the OSPF route in the routing
> table and not the RIP route.
>
> I don't have any documented explanation for the behavior. But, it makes
> sense the IOS prefers the native admin distance over the modified one when
> both are same.
>
> HTH,
> Sundar Palaniappan
> CCIE #14532
>
>
>
> "Dan Espino"
> om> cc:
> Sent by: Subject: Re: Administrative distance tie
> nobody@groupstudy
> .com
>
>
> 09/20/2005 05:10
> PM
> Please respond to
> "Dan Espino"
>
>
>
>
>
>
> OK, rip had a hop count to 3 and ospf has a cost of 10.
> Now who wins
>
>
> On 9/20/05, rosy bird wrote:
>
>>i guess...here is where metric comes into picture...
>>
>>On 9/21/05, Dan Espino wrote:
>>
>>>If 2 protocols have the same AD (because one was adjusted), and the
>
> same
>
>>>prefix length, how does the router determine which to choose?
>>>
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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